1 TASMAN FOLD BELT SYSTEM IN VICTORIA
This file contains all but one of the tables for TFBSV Special Publication (the missing one is a corel
file). Do not reformat the justifications as different justification is used in different columns.
Column width is 87 mm
Table 1.1 Comparison of recent timescales for the Palaeozoic
Period
CARBONIFEROUS
Epoch
Early
Late
DEVONIAN
Middle
Early
Pridoli
Stage
Visean
Tournaisian
Famennian
Frasnian
Givetian
Eifelian
Emsian
Pragian
Lochkovian
Ma1
343
354
364.5
369.5
377.5
384
399.5
404.5
408–412
414
417
420–421
421
425
429
432
434
443
454.5
459
467
471
477
481
484.5
490
Ma2
363
367
377
381
386
(394)
(401)
409
411
Ma3
391
400
412
417
419
Ma4
362
376.5
382.5
387.5
394
409.5
413.5
418
419
424
Ma5
Ma6
343
354
364.5
369.5
377.5
384
400
418
419
Ludfordian
Gorstian
424
423
SILURIAN
Homerian
Wenlock
Sheinwoodian
430
428
428
Telychian
Llandov
Aeronian
Rhuddanian
439
443
441
441
Bolindian
Late
Eastonian
Gisbornian
458
459
Darriwilian
ORDOMiddle
Yapeenian
VICIAN
Castlemainian
477
Chewtonian
Early
Bendigonian
(492)
(483)
Lancefieldian/
510
495
513
490
490
Warendian
Datsonian
491
491
491
Payntonian
492
Late
Iverian
496
Idamean
497
(516)
505
497
Mindyallan
498
CAMBRIAN
Boomerangian
500
Undillan
503
Middle
Late Temple- 506
tonian/ Floran
Early Temple- 508
554
518
508
tonian/Ordian
“Toyonian”
528.5
560
522
510
510
“Botomian”
525
519
519
Early
“Atdabanian”
530
522
522
“Tommotian”
534
531
531
Nemakit–
545
570
545
544
544
Daldynian
The dates apply to the base of the box. Dates in brackets are inferred from the information given in the respective paper.
Ages are from 1Young & Laurie (1996); 2Harland et al. (1990); 3Tucker & McKerrow (1995); 4for Ordovician and Lower
Silurian: Tucker et al. (1990), for Upper Silurian and Devonian: Tucker et al. (1998); 5from revisions to the Cambrian
summarised by Bowring & Erwin (1998) based on geochronology in Landing et al. (1998) and Davidek et al. (1998);
6timescale used in this volume.
Ludlow
Table 1.2 Radiometric ages of Early Devonian cauldron rocks and the Early Devonian timescale.
A: Timescale used in this volume; B: timescale from Tucker et al. (1998). 1: Tambo Crossing Tonalite, ring pluton of the
Mount Elizabeth Cauldron Complex, K/Ar, Richards and Singleton, 1981; 2: ring dyke of the Dartella Cauldron, U/Pb,
VandenBerg et al., 1998; 3: Besford Ignimbrite, U/Pb, VandenBerg et al., 1998; 4: Jemba Ignimbrite, Rb/Sr, Brooks &
Leggo, 1972.
Table 1.3 Metallic mineralisation styles
Style
Metals
present1
Tectonics
Transporting
fluid
Host
Controls
Timin
Orogenic gold
Au, Sb, Ag,
Pb, Cu, Hg
Convergent to
post-convergent
Metamorphic
± magmatic
± meteoric
Lower Palaeozoic turbidites (slate
belt); Cambrian tholeiites; granites
Epige
Magmatic–
Hydrothermal
Sn, Mo, W,
Cu, Au, F, Bi,
Ni, platinum
group elements, U
(kaolinite)
Cu, Zn, Ag,
Au, Pb, Fe,
Mn (barite,
pyrophyllite)
Rift; post-collision
extension; crustal
scale extension
arrays between
major strike-slip
faults
Rift; post-collision
extension
Magmatic
± meteoric
Plutons and adjacent country rocks3, 4
(Sub)greenschist metamorphism; convergent structures;
rocks with favourable rheology
and chemistry
Magma chemistry4
?magmatic
± connate
± meteoric
Cambrian submarine tholeiites and
calc-alkaline volcanics; Upper Silurian
and Lower Devonian submarine volcanic/sedimentary sequences
Submarine deposition; major
growth faults
Pb, Zn, Ag,
Cu, Fe, Mn
(barite)
Fe, Cu, Au
Rift
Upper Silurian and Lower Devonian
carbonates
Diagenetic permeability; major
growth faults
Lower Devonian volcanic/sedimentary
sequences
Au, Sb, Ag,
Pb, Zn, Cu, F
(barite, pyrophyllite)
Rift; caldera; postcollision extension
Major growth faults; reactive
carbonates; impermeable ‘trap’
lithologies
Extensional structures
Epige
Other
Epigenetic
?magmatic
± connate
± meteoric
?magmatic
± connate
± meteoric
Meteoric
± magmatic
Synge
mecha
ed) to
seaflo
feeder
Epige
Red-bed copper
Cu, U, V, Ag
Extensional to
convergent
Redox and pH boundaries;
anticlines/domes; underlying
Cambrian tholeiitic volcanics
Epige
Seafloor
volcanicassociated
Carbonate
hosted
Metasomatic
replacement
Rift
Connate
Au
Post-orogenic
River
1 Many deposits do not have the complete suite of metals and minerals listed
2 See Figure 2.44
3 See Figure 4.4
4 See Figure 4.3
Placer gold
Cambrian calc-alkaline volcanics;
Lower Devonian rift volcanics and
surrounding rift structures (± coeval
dykes); Lower and Upper Devonian
cauldron rocks and surrounding structures
Upper Devonian fluvial sequences
Upper Devonian fluvial sequences
Table 2.1 Distribution of Cambrian igneous rocks
Unit
Association
Truro Volcanics
Within-plate
MORB
Ultramafic
Zone
Associated fault
Glenelg
numerous faults
Glenelg
numerous faults
minor secondary nickel
Calc-alkaline
Glenelg
numerous faults
subeconomic seafloor volcanic-associated, epigenetic and
porphyry deposits
Dimboola Igneous
Complex
Magdala Volcanics
Tholeiite–boninite
Glenelg
numerous faults
Tholeiite–boninite
Stawell
Moyston Fault
Pitfield Volcanics
Heathcote Volcanics
Tholeiite–boninite
Tholeiite–boninite
Stawell
Bendigo
Jamieson and Licola Volcanics
Calc-alkaline
Melbourne
(Selwyn Block)
Lickhole Volcanics
Dookie Igneous
Complex
Thiele Igneous
Complex
Tholeiite–boninite
Tholeiite–boninite
Tabberabbera
Tabberabbera
Avoca Fault
Mount
William
Fault
unknown—
separated
by
Thomas Fault from
overlying sedimentary rocks
Governor Fault
Governor Fault
Ultramafic
Tabberabbera
Governor Fault
Hummocks, Williamson Road and
other serpentinites
Mount Stavely Volcanic Complex
basalt–
Table 2.2 Outcropping serpentinite bodies
Hummocks
Serpentinite
Serpentine, talc and magnetite pseudomorphing a
coarse cumulate texture, with original igneous minerals
including olivine, orthopyroxene and chrome spinel
(Turner et al., 1993). CSIRO (in Costelloe, 1994) considered that cobalt-bearing pentlandite was formed from
nickel liberated from silicates during serpentinisation
or metamorphism–deformation. Pyrite–chalcopyrite–
ankerite veins in the sheared serpentinite are clearly
related to deformation (Cowan in Rickards, 1991).
Mineralisation
subeconomic seafloor volcanic-associated deposits
subeconomic seafloor volcanic-associated deposits
subeconomic seafloor volcanic-associated and epigenetic
deposits
subeconomic seafloor volcanic-associated deposits
Synge
(e.g. s
Epige
Synge
3 TASMAN FOLD BELT SYSTEM IN VICTORIA
Serpentinised, cumulate-textured peridotite with
phlogopite, kaersutite, abundant apatite as well as
serpentinised olivine and clinopyroxene, chromite and
chrome spinel.
Brecciated, web-textured serpentinite of chrysotile(?)
and chromite with abundant replacement quartz, opaline silica and fine magnetite (Buckland, 1986).
Steep Bank
Rivulet bodies
Williamsons
Road
Serpentinite
Thiele
Igneous
Complex
Intrusions include peridotites and dunites that have
been variably serpentinised, clinopyroxenite, orthopyroxenite, and rodingite. The ultramafic rocks consist of
bastite (rarely with orthopyroxene cores), with or without pseudomorphs after olivine, and minor amounts of
magnetite ± chromite. Some rocks show cumulate layering and alignment of elongate olivine grains. Several
massive chromite bodies occur within the ultramafics. A
single outcrop of completely serpentinised mafic volcanic rock shows a volcanic texture (Duddy, 1974) and
a pillow-like body with a probable chilled margin (Andrews, 1988).
Table 2.3 Within-plate basalt–MORB association
Truro Volcanics
Drill holes
Dergholm–
Wando area
VIMP 2 intersected coarse leucogabbro or mafic diorite
regionally metamorphosed to upper greenschist to lower
amphibolite facies. It has a MORB composition similar to
Late Proterozoic rift tholeiites of W. Tasmania (Maher et
al., 1997a).
Two holes drilled by MIM: YANS1 intersected altered
picritic lava and YANS2 intersected serpentinised olivinerich cumulates derived from the picritic lava (Maher et
al., 1997a). They are high-T, low-Ti lavas identical to rift
tholeiites of W. Tasmania (Maher et al., 1997a).
Dykes or sills of coarse equigranular metagabbro and
metadiorite commonly have massive cores and foliated
margins (Anderson & Gray, 1994). In Nolans Creek there
are outcrops of plagioclase-phyric andesite and tourmaline-bearing chert (Rossiter, 1989) as well as carbonate
altered rocks of probable volcanic origin. Near Dergholm a
metabasalt lava in the Glenelg River is fine-grained with
a variolitic texture and phenocrysts of plagioclase. Similar
metabasalt crops out west of the Hummocks (Morand et
al., in prep.).
Table 2.4 Rocks of the tholeiite–boninite association
Knonagel Igneous Complex
Sparsely drilled from near Moyston northward to Dimboola. At the Frying pan prospect near Moyston a single drillhole intersected mafic–
ultramafic originally glassy lava of low-Ti, high-Mg boninitic composition with large phenocrysts and glomerocrysts of low-Ca pyroxene,
occasional olivine phenocrysts and small chromite grains. Phenocrysts are altered to serpentine and bastite and the groundmass to albite,
chlorite, calcite, talc, tremolite–actinolite and quartz, which may be a weak hydrothermal overprint. Small blebs of more felsic rock are
present. They consist of occasional orthopyroxene phenocrysts in a vesicular groundmass of clinopyroxene and plagioclase. At Wartook
numerous drillholes intersected a variety of rock types including: high-Mg boninitic and tholeiitic volcanics, some showing quench textures
and others with vesicles; associated andesitic–dacitic volcaniclastics and a range of mafic and ultramafic porphyritic intrusions, some with
cumulate layering, and dolerite–diorite–monzogranite granophyres (Stewart, 1993). All have greenschist metamorphic assemblages typical
of sea-floor alteration. Farther N near Dimboola numerous drillholes have intersected high-Mg, low-Ti tholeiitic–boninitic volcanics, volcaniclastics and cumulate gabbros that have variably developed greenschist assemblage. Some blueish secondary amphiboles have been reported.
Stawell Zone
Magdala
Volcanics
Pitfield Volcanics
Dominant lithology is tholeiitic basalt lava (Watchorn & Wilson, 1989) with igneous textures, flow horizons, flow-top
breccias, pillow layers, minor interflow sedimentary rocks in the Stawell mine. Flows appear to range up to 50 m thick.
Intercalated are much thinner, often infaulted, bands of pyritic, dark grey carbonaceous sedimentary rocks, volcanogenic
sandstone. Compositions range from pyroxene-rich ultramafic to porphyritic plagioclase tholeiite to spherulitic rhyolitic
lava (MacGeehan, 1982). Volcanogenic sedimentary rocks overlying the lavas at Stawell consist of sulphide-rich
schist, chert, mafic tuff, chloritic and carbonaceous schist intercalated with thin pillowed basalt flows. On the crest of the
Moray Antiform are quartz–magnetite rocks which may represent strongly deformed sedimentary rocks.
Altered glassy to porphyritic lavas and high-level intrusions of tholeiitic basaltic composition, and rare ultramafic cumulates. Some interflow sedimentary rocks and hyaloclastite occur, and gabbro (probably from sills or dykes), rare peridotite cumulates. Most samples are strongly schistose and have greenschist assemblages (Ramsay et al., 1996; Taylor et al.,
1999).
Heathcote Volcanics
Mount
William
Metabasalt
Lazy Bar
Andesite
Sheoak Gully
Boninite
>2.5 km (N segment), >1.6 km (S segment) of basalt and dolerite flows and sills, with minor interbedded basalt-derived
sandstone, black shale (Fig. 2.2b), chert, chert breccia, mudstone and mass-flow deposits. Entirely tholeiitic in the southern segment. Basalt is mostly massive but pillow basalt and vesicles occur sporadically (Fig. 2.2a). The uppermost sill at
Romsey displays well-developed cooling columns (Edwards et al., 1998a).
Massive andesitic lava with intercalated graded andesitic sandstone. A laminated tuff with flattened lenticles indicates
explosive, probably subaerial activity (Edwards et al., 1998a).
Boninitic lava, mainly massive but with minor pillow lava, intercalated with boninitic hyaloclastite breccia and sandstone beds. A flow banded, partially quench fragmented and perlitic rhyolite lava with stretched vesicles occurs in type
section (Edwards et al., 1998a).
Waratah Bay
Mostly massive basalt, some undeformed pillow lava (Fig. 2.3). Interbedded strongly deformed sediment packages include volcanogenic sandstone, black and red mudstone, shale and chert (Lindner, 1953; VandenBerg et al., in prep.).
Metamorphic grade is of sub-greenschist grade (prehnite-pumpellyite facies) with granular augite and albitised plagioclase set in a serpentinised groundmass (Crawford, 1982).
Gabbro (Fig. 2.4) with a complex metamorphic history. Completely altered rock contains pyroxene with hornblende overgrowths indicating amphibolite-grade metamorphism, significantly higher than the adjacent basalt (Crawford, 1988);
local mylonitisation shows that they are in fault contact, although they are probably derived from similar tholeiitic parent magmas (Crawford, 1988). Includes sheared serpentinised peridotite and talc-chlorite rocks. Osmium–iridium alloys
from the serpentinite occur in Cainozoic placers up to 40 km away. Similar deposits are associated with Tasmanian
Cambrian ophiolites (Brown, 1989).
Maitland
Beach Volcanics
Corduroy
Creek Gabbro
Dookie Igneous Complex
Basalts are tholeiitic flows that appear to lie between two successions of similar sedimentary rocks. Sedimentary rocks comprise mainly
chert and quartz–albite beds, probably volcanic ash (Christie, 1978), with rare detrital quartz grains and sponge spicules. Also present are
black shale, siltstone, sandstone and conglomerate with fragments of basalt and gabbro. A thick sill of gabbro occurs in the ‘lower’, southern belt of sedimentary rocks.
Lickhole Volcanic Group
Eagles Peak
Basalt
Malcolm Creek
Hyaloclastite
Sheepyard Flat
Boninite
Mountain Chief
Andesite
1.5–2 km of pillowed and massive aphyric tholeiitic basalt with minor amounts of interflow and interpillow cherty
sedimentary rocks, intruded by comagmatic gabbro and dolerite sills and dykes.
~750 m of 5–10 m thick beds of hyaloclastite with occasional beds of pebbly grit and volcaniclastic sandstone—
hyaloclasts contain phenocrysts of fresh augite, sparse chloritised olivine and albitised plagioclase, and the volcaniclastics contain clasts of boninite, serpentinite and porphyritic andesite.
1–1.5 km of ultramafic boninitic lava (Fig. 2.5) and volcanic breccia with remarkable textural variations and rare
interbeds of finer volcaniclastics and with two thin flows of tholeiitic basalt flows.
100-250 m of andesitic breccia, minor volcaniclastic sediment (incl. hyaloclastite) and thin autobrecciated mafic boninite lava.
Table 2.5 Seafloor tholeiitic volcanic-associated deposits
Magdala
Volcanics
Heathcote
Volcanics
Dookie
Igneous
Complex
The stratabound Mount Ararat copper deposit occurs within a NW-trending sequence of quartz–actinolite, quartz–biotite
and graphitic schists, interpreted to be metamorphosed mafic to intermediate lava, sedimentary rocks and black shale
(Cochrane, 1982). Sulphide mineralisation occurs as disseminated pyrrhotite, pyrite and low-grade chalcopyrite in the
metavolcanic rocks surrounding richer layers of banded and massive pyrrhotite, chalcopyrite, sphalerite and minor pyrite
(Fig. 2.8; Cochrane, 1982). Mineralisation is parallel with a penetrative S2 fabric developed during thrusting (Cayley, 1988).
Geological setting, metamorphic and structural constraints suggest an exhalative origin (Cochrane, 1982).
Concordant banded pyrrhotite occurs in similar rocks at the Magdala deposit, Stawell. Pyrrhotite has light sulphur (δ34S = –
15‰; Gulson et al., 1990b) of probable exhalative origin (Watchorn & Wilson, 1988).
Interflow sedimentary rocks at the Lake Cooper quarry have high gold (average 65 ppb). The mineral assemblage and trace
and rare earth element pattern of the sedimentary rocks are compatible with an exhalative volcanogenic origin (Bierlein et
al., 1998b). Similar rocks at Mount Camel contain pyrite, pyrrhotite and minor chalcopyrite (Cochrane, 1982).
At Dookie stratiform banded barite–sulphide horizons and pyritic black shale occur in chert overlying gabbro and basalt
(Tickell, 1989). Basalt is altered and contains quartz–sulphide–chlorite  carbonate veins (Wilkie & Brookes, 1997). Banded
pyrrhotite–rhodonite horizons occur in chert in the Tatong volcanic sequence (Wilkie & Brookes, 1997). In both areas mineral assemblages have been modified by contact metamorphism by Upper Devonian granites. Despite elevated base and precious metal values in regolith, drill intersections show weak mineralisation. Prominent iron and manganese oxide gossans
have been investigated as iron resources.
Table 2.6 Cambrian volcanics—Grampians–Stavely Zone
Mount Stavely Volcanics—Mount Stavely belt
Buckland (1986); Crawford et al., (1996)
Porphyritic tonalite
Lalkaldarno
Tonalite
Dacitic volcaniclastic sandstone with some laminated
Towanway
chert, sandstone and siltstone.
Tuff
Nanapundah
Tuff
Fairview
Andesitic
Breccia
Narrapumelap Road Dacite Member dacite lava
with plagioclase and quartz phenocrysts.
Andesitic volcaniclastic sandstone, massive, variably
sorted; partly laminated.
Andesitic matrix-supported breccia, and andesite and
basalt lava. Clasts display cooling rinds.
Glenronald Shale Member is a layer of pyritic cherty
black shale and volcaniclastic sandstone.
Mount Stavely Volcanics—Mount Dryden belt
Crawford et al. (1996)
Andesitic–dacitic lavas usually have some phenocrysts
(1) Lavas
(2) Volcanic
breccias
of feldspar, pyroxene, some hornblende (Fig. 2.9). Rhyodacitic—rhyolitic lavas have conspicuous quartz phenocrysts, basaltic lavas have calcic plagioclase, occasionally olivine. Some more uniformly holocrystalline
rocks are probably sills. Vesicles are sometimes present.
Lavas form flow packages 200 m thick with intercalated volcaniclastic packages 100 m thick. Columnar
joints present in places.
Generally monomictic andesitic to rhyodacitic breccia
(Fig. 2.9) often difficult to distinguish from the coherent
lavas. Angular clasts 0.5 m in size are set in a
groundmass of crystal-rich sand-sized debris.
5 TASMAN FOLD BELT SYSTEM IN VICTORIA
(3) Volcanic
sandstones
Intrusion
near
McMurtrie
Hill
Range from crystal-rich andesitic to rhyodacitic sandstone to rarer siliceous siltstone. Much is comprised of
thin graded beds of crystal debris (quartz, plagioclase,
pyroxene, hornblende). Chloritic groundmass occasionally has spherulitic textures. Some coarser beds contain
small pyroxene-bearing lava clasts.
Large dioritic–gabbroic intrusion contains augite phenocrysts with reaction rims of hornblende and partial
replacement by actinolite, albitic plagioclase laths
largely replaced by epidote, chloritised orthopyroxene.
Groundmass consists largely of intergrown quartz and
plagioclase, occasionally with minor hornblende.
Mount Stavely Volcanics?—Black Ranges
Altered and metamorphosed volcanic rocks including basalt, andesite,
dacite, rhyodacite of calc-alkaline character, commonly strongly cleaved.
Some rocks have vesicles (McArthur, 1990).
Table 2.7 Cambrian volcanics in the Mount Useful Fault Zone
Group
Licola
Volcanics
Jamieson
Volcanics
Rock unit
Distribution
Lithology
Whisky Knob Rhyolite
Cobbs Spur
Andesite
Breccia
Tobacco Creek Andesite
Handford Creek Fm
Hardwicke Creek
Rhyolite
Lakelands Flat Andesite Breccia
Wrens Flat Andesite
Mitchells Andesite
Breccia
Brissces Hut Andesite
Fullarton Spur and
Whisky Knob windows
Porphyritic rhyolite lava intercalated with minor rhyolitic,
crystal-rich volcaniclastic sedimentary rock.
Licola, Fullarton Spur
and
Whisky Knob windows
Monomictic–polymictic volcanic breccia (Fig. 2.10) with occasional olistoliths of shallow marine limestone intercalated
with crystal-rich volcaniclastic sandstone and shale.
Hornblende andesite, pyroxene andesite and hornblende +
pyroxene andesite (Fig. 2.10).
Jamieson
Window
River
Volcaniclastic sandstone, shale and conglomerate
Rhyolite lava intercalated with rhyolitic hyaloclastite breccia,
dacitic and andesitic lava and volcaniclastic sedimentary rock
Polymictic andesite breccia with minor pyroxene andesite lava
and volcaniclastic sedimentary rock
Porphyritic pyroxene andesite lava and pillow lava
Monomictic andesite breccia and amygdaloidal andesite
Porphyritic pyroxene andesite lava
Table 2.8 Mount Stavely Volcanics—isotopic ages
Rock unit
Towanway Tuff
Min’l
Method
Age (2SD)
Reference
zr
U/Pb
495 ± 5
501 ± 91
500 ± 2
1
1
2
Lalkaldarno
bi
Ar/Ar
Tonalite
Samples are all from type localities.
References: 1: Stuart-Smith & Black, 1999; 2: Foster et al., 1998.
1 Age is from detrital zircons that set a maximum age limit
Table 2.9 Mineralisation in the Mount Stavely Volcanic Complex
Victor 2 (or Wickliffe) prospect
Base metal mineralisation is in a silica–pyrite and sericite–chloritealtered sequence of volcanic sandstone and hyaloclastite breccia in the
Towanway Tuff (Donaghy, 1994). Pyrite–chalcopyrite–sphalerite ± galena
occur disseminated and as stringers associated primarily with sericite–
chlorite alteration. Minor fracture-controlled sphalerite is associated with
pervasive silica–pyrite alteration and with remobilised dolomite alteration and veining. Metal distribution was controlled by lithology with
copper grades highest in breccia and volcanic sandstone, and zinc ± lead
grades highest in volcanic siltstone and dacite (Donaghy, 1994).
Sulphur isotope studies indicate that the simplest sulphur source model
for the silica–pyrite and sericite–chlorite–pyrite mineralisation is mixing
between magmatic or deep sulphur and sea-water sulphate. A syngenetic
model is proposed whereby circulating seawater, leaching the volcanic
pile, was accompanied by low-temperature silica–pyrite alteration and
zinc–lead mineralisation. Waxing of the system accompanied by an input
of magmatic fluids led to an increase in copper grades and sericite–
chlorite alteration. Much later, burial metamorphism or deformation
remobilised zinc and gold along faults within epigenetic carbonate veins.
Subsequent brittle deformation sheared the top off the mineralising alteration system and juxtaposed unaltered Glenthompson Sandstone
against altered Towanway Tuff (Donaghy, 1994).
McRaes prospect
This VHMS zinc–copper–gold mineralisation occurs in a sequence of
originally glassy dacitic–rhyolitic lavas. These are brecciated in places
and are intercalated with minor volcanogenic sedimentary rocks. Several
styles of alteration occur. Intense hydrothermal phyllic (sericite–quartz–
pyrite) alteration is most common, with less intense propylitic (chlorite–
epidote) alteration also present. A weak quartz–albite ± sericite ± chlorite
± epidote alteration is present (Crawford, 1994). Early laminated–
massive pyrite hosting disseminated chalcopyrite and sphalerite is crosscut by sulphide and sulphide-bearing quartz–calcite veinlets (Radojkovic,
1996). A variably developed overprinting foliation is related to the growth
of regional-scale thrust faults in the Early Cambrian (Cayley & Taylor,
1997).
Thursdays gossan (or Victor 1) prospect
This is the best-studied porphyry-style deposit. Intermediate–mafic subvolcanic, high-K, I–type stocks contain disseminated and stockwork copper mineralisation (Crawford et al., 1996; Buckland, 1986). Low-grade
chalcopyrite occurs over large intervals (e.g. 229 m @ 0.22% Cu), with
minor molybdenite and trace gold. All but the youngest more mafic stocks
are mineralised (Hovarth, 1995). The best Cu grades occur in intensely
fractured rock and shear zones. Weak to pervasive sericitic, propylitic,
silicic, argillic and advanced argillic alteration is widespread, covering
3 km2 (Spencer, 1996). Fluid inclusions suggest a complex hydrothermal
history with porphyry-type mineralisation overprinted by epithermal
mineralisation (Hovarth, 1995; Spencer, 1996). High-grade supergene
chalcocite is developed at the base of an acid-leached cap (e.g. 15 m
@ 1.8% Cu). Acid leaching is typically 20–40 m deep but up to 150 m deep
in areas of intermediate argillic alteration.
Table 2.10 Mineralisation in the Jamieson and Licola volcanics
Hill 800 VHMS gold–copper prospect
The prospect is in interbedded andesite lava, breccia and volcanogenic
sedimentary rocks of the Mitchells Andesite Breccia. Very fine disseminated gold mineralisation occurs in strongly altered silica–paragonitic
(Na-rich) sericite–pyrite schist (Fig 2.12; Cherry, 1998). Chalcopyrite vein
mineralisation associated with muscovitic (K-rich) sericite alteration was
interpreted as a footwall stringer zone to the gold mineralisation (Cherry,
1998). The deposit lies within an E–W striking sequence of the Jamieson
Volcanics and dips moderately S. Away from the deposit, metamorphic
assemblages are lower greenschist facies in both the footwall and hanging
wall andesitic lavas. A syngenetic origin has been proposed whereby goldrich hydrothermal fluids, driven by a local intrusion, percolated up
through clastic rocks and were possibly confined by an impervious dacite
cap. Favourable physical and chemical conditions in certain clastic horizons resulted in metal deposition (Cherry, 1998). The prospect has been
likened to VHMS mineralisation in the Mount Read Volcanics (Turner,
1996).
Whisky Knob
The Bluff prospect lies at the sheared contact between felsic volcanogenic sedimentary rocks of the Whisky Knob Rhyolite and a sequence of
cherty black shale and volcanogenic sedimentary rocks (D. Cherry, pers.
comm., 1999), almost certainly Howqua Chert. The NW-trending, subvertical shear zone is host to disseminated pyrite and weak copper and
gold mineralisation. Late-stage quartz veining is unrelated to mineralisation and cross-cuts it. The copper–gold mineralisation may be associated
with a series of strong magnetic anomalies along the shear zone (D. Cherry, pers. comm., 1999).
At Mike’s Bluff, south of Whisky Knob, weak, possibly shear-hosted
disseminated copper and zinc mineralisation occurs within a well defined
zone of strong sericite and carbonate-altered felsic sedimentary rocks (D.
Cherry, pers. comm., 1999).
Violet Hill prospect
7 TASMAN FOLD BELT SYSTEM IN VICTORIA
At this prospect, in the Fullarton Spur Window, weak lead–zinc–arsenic 
gold mineralisation occurs in a 30 m wide zone of laminated sulphidic
quartz, probably of multiple crack-seal origin. The quartz veins lie on the
Thomas Fault between Cobbs Spur Andesite Breccia and Murderers Hill
Siltstone and may be thrust-related (D. Cherry, pers. comm., 1999).
Rhyolite Creek prospect
This gold–silver prospect lies in a zone of pervasive argillic alteration
across the sheared contact between rhyolitic volcanics and epiclastics in
the Hardwicke Creek Rhyolite (Hendrickx, 1993; VandenBerg et al.,
1995). Two styles of gold mineralisation occur: (1) epithermal quartz
microveining and pervasive silicification are associated with later pyrophyllite, pyrite, graphite and secondary jarosite development; and (2) a
siliceous massive sulphide lens in breccia within volcaniclastic sedimentary rocks (Raetz & Parrington, 1988). The genesis of the gold mineralisation has been likened to other pyrite–pyrophyllite-rich epithermal gold
systems deposited from sulphur-rich high-temperature, acidic and probably magmatic-derived fluids (Raetz & Parrington, 1988; Hendrickx, 1993).
Recent studies suggest that the mineralisation may be related to two
major northwest-trending fault lines (Perseverance, 1998).
Table 2.11 Sedimentary rocks of the Delamerian Fold Belt
Moralana
Supergroup
Nargoon
Group
Sandstone turbidites interbedded with mudstone predominate. Graded bedding occurs in a thick unit of metagreywacke (Wells, 1956; Gibson & Nihill, 1992). Arenites
include quartz sandstone, quartz-wacke, micaceous sandstone and quartz–feldspar-lithic greywacke. Lithic clasts
include chert and low-grade schist; plagioclase and Kfeldspar are common detrital minerals along with muscovite, zircon and tourmaline. Rare mafic volcaniclastic
sandstones have clasts of basalt and plagioclase. Much
sandstone is poorly sorted. Minor granule conglomerate
contains rounded chert and basalt pebbles. Graphitic
slates of mostly quartz and muscovite in places have
abundant pyrite/pyrrhotite; some black slate is dolomitic.
A thin marble in Nolans Creek has a fine tectonic foliation.
South of Dergholm, metabasalt lava in the Glenelg River
is fine-grained with a variolitic texture and phenocrysts of
plagioclase. Numerous metagabbro dykes/sills commonly
have massive cores and foliated margins (Anderson &
Gray, 1994). Metadiorite dykes also occur in this area.
Nolans Creek shows outcrops of plagioclase-phyric andesite and tourmaline-bearing chert (Rossiter, 1989) and
carbonate altered rocks of probable volcanic origin.
Black Ranges and Yarramyljup Creek area: sedimentary rocks are dominated by sandstone and mudstone
(turbidites), also black slate and chert.
Glenthompson Sandstone: generally thin-bedded turbiditic sandstone, greywacke and mudstone. Sandstone
comprises quartz, large detrital muscovite, biotite, lithic
fragments, occasional K-feldspar, plagioclase, rare pyroxene and zircon grains. Matrix is quartzofeldspathic silt
and clay typically altered to chlorite (Bartrop, 1983,
Stone, 1989). Lithic fragments include mudstone, granite,
chert, occasional regional metamorphic rocks. Close to the
Mount Stavely Belt, contains rare calcareous mudstone
and conglomerate bands with rounded andesite clasts
(Buckland, 1986). Sandstone is texturally immature,
classifies as sublitharenite (Folk, 1980). Simple, repetitive
Tace beds are common.
Table 2.12 St Arnaud Group—units and lithology
Pyrenees
Formation
Beaufort
Formation
Very sandy unit (sandstone/mudstone ratio ~3:1), most
sandstones are Tae sequences 5 cm to 2.5 m thick (avge
~0.5 m; Fig. 2.13A); occasional amalgamated units 4 m.
Most are sheet-like, with a few channellised beds. Thin
carbonaceous mudstone occurs in places.
Fine-grained quartz sandstone is subordinate to dark grey
siltstone and black to blue graphitic shale. Sandstone beds
range from a few millimetres to 1 m, averaging ~30 cm.
Sandstones are mostly Ta. Thick beds are channellised.
Siltstones are spotted with siderite and other carbonates,
form packages up to 5 m thick with primary structures
masked by cleavage. Bioturbation is absent. The presence
of thick, massive carbonaceous and pyritic mudstones
capable of reducing ore fluids that caused gold segregation
give it the highest concentration of orogenic gold deposits
in the group (Cayley & McDonald, 1995; Krokowski de
Vickerod et al., 1997). Pyrrhotite in these beds may be
Warrak
Formation
responsible for linear magnetic trends up to 20 nT
(Whitehead, 1995).
Predominantly thin-bedded sandstone and mudstone with
a sandstone/mudstone ratio of 0.5:1–2:1 and sandstone
bed thickness mostly <30 cm. Black shale is minor, bioturbation absent. Lithofacies (1) is sand-dominated packages of thicker turbidite beds, mostly of Tbc with occasional Tabc; (2) is regularly bedded fine thin-bedded Tce.
(1) and (2) form interlayered packages 20–50 m thick.
Less common are coarser Tabc sandstones up to 1 m thick,
sometimes with rip-up siltstone clasts, often channellised,
sometimes with strongly erosive bases. Sporadic (3) consists of dark carbonaceous mudstone up to 15 m thick.
Sandstones contain carbonate concretions preserved in
contact aureoles (Fig. 2.13B).
A lithic granulestone NE of Great Western contains
rounded polycrystalline quartz and altered mafic
pebbles.
Table 2.13 Cambrian sedimentary rocks of the Heathcote Fault Zone and Waratah Bay
Goldie
Chert
Knowsley
East
Shale
Bear Gully
Chert Bed
190–290 m of chert and siliceous siltstone. Outcrops extensively in the S segment of the Heathcote Fault Zone
(Fig. 2.15) but may also be present as a fault slice at Ladys Pass north of Heathcote (Edwards et al., 1998).
Heathcote: spectacular basal upward-thinning package of
graded sandstone beds composed of pyroxene crystals
with minor feldspar overlain by black shale with thick
beds of polymictic conglomerate at higher levels containing clasts of black shale, chert, jasper and mafic lava in a
sandstone matrix.
S segment: 200–500 m of black shale with interbeds of
graded volcanogenic sandstone (Fig. 2.16), occasional thin
felsic ash beds (= Monegeetta Shale of VandenBerg, 1992).
Pale grey chert bed with fine internal lamination partly
disrupted by soft-sediment and brittle early deformation,
and apparently by burrowing (Figs 2.17 & 2.7). Capped by
scattering of well-rounded pebbles that include vein
quartz and quartz-veined chert (Merry, 1987).
Table 2.14 Radiometric ages of Glenelg Zone rocks
Group/
Supergroup
Mount
Stavely
Volcanics
Moralana
Supergroup
Bringalbert
Gabbro (G440)
Duchembegarra
Granite (G405)
Dergholm Granite
(G424)
Ferres Creek
Tonalite (G423)
St Elmos
Granodiorite
(G422)
Kalingur Tonalite
(G441)
Rock type
Min’l
Meth.
Towanway Tuff
zr
U/Pb
Narrapumelap
Road Dacite Member
Lalkaldarno
Porphyry
metapelite
slate
slate
slate
slate
metagabbro
zr
U/Pb
hb
Ar/Ar 500 ± 2
10
TR
TR
TR
TR
TR
zr
K/Ar
K/Ar
K/Ar
K/Ar
K/Ar
U/Pb
572 ± 9
558 ± 6
556 ± 6
553 ± 9
551 ± 6
524 ± 9
5
5
5
5
5
8
mafic tonalite
zr
U/Pb
404 ± 6
8
granite
granite
bi
K/Ar
K/Ar
F-T
F-T
K/Ar
diorite
sph
F-T
453 ± 6
443 ± 7
484 ± 24
452 ± 22
488 ± 5
479 ± 6
428 ± 18
3
3
4
4
5
5
4
Dergholm
granite
bi,
plag
sph
granodiorite
bi
K/Ar
482 ± 9
1, 2
3 km NE of Wando Vale
tonalite
bi
K/Ar
476 ± 6
3
Wando Vale
granodiorite
tonalite gneiss
sph
zr
F-T
U/Pb
470 ± 28
504 ± 8
4
8
Wando Vale
DDH VIMP11, Corona
Age
(2SD)
Ref.
Location
501 ± 9
7, 11
4.5 km W of Wickliffe
495 ± 5
7, 11
Comments
Youngest clastic grains in
volcaniclastic sandstone.
Hopkins R., 5 km SSW of Dacite within Towanway
Wickliffe
Tuff.
7.5 km ENE of Glenthompson
Steep Bank Rivulet
Probably geologically meaningless mixed ages between
the detrital mica ages and
new growth in the Delamerian Orogeny.
DDH VIMP 2
Syn-depositional dyke or
sill?
DDH VIMP1
8 km NNW of Dergholm
Baileys Rocks Reserve
Caupaul, NE of Dergholm
9 TASMAN FOLD BELT SYSTEM IN VICTORIA
granodiorite
bi
K/Ar
401 ± 5
3
8 km NNE of Coleraine
Hassalls Creek
Granodiorite
(G409)
granodiorite
bi
K/Ar
410 ± 4
2
8 km NNE of Coleraine
granodiorite
sph
F-T
granite
zr
U/Pb
4
4
4
11
8 km NNE of Coleraine
Bushy Creek
Granodiorite
(G395)
405 ± 21
410 ± 18
412 ± 21
489 ± 7
granite
bi
Ar/Ar 500 ± 2
10
14 km SW of Wickliffe
granodiorite
bi
Ar/Ar 499 ± 2
10
17 km WSW of Wickliffe
Loftus Creek
Granodiorite (G422)
Kout Norien Granodiorite (G410)
granodiorite
zr
U/Pb
484 ± 7
12
Loftus Creek
granodiorite
bi
mus
zr
K/Ar
K/Ar
U/Pb
466 ± 6
487 ± 6
~ 590
3
3
8
2 km NE of Harrow
mus
bi
bi
mus
bi
bi
K/Ar
K/Ar
K/Ar
K/Ar
K/Ar
K/Ar
497 ± 4
490 ± 4
501 ± 4
493 ± 5
491 ± 6
490 ± 6
9
9
9
9
5
5
DDH VIMP12
DDH VIMP 12
DDH VIMP13
DDH VIMP13
Glenelg River Chetwynd
Wando River
TR
bi
bi
Mus
K/Ar
Ar/Ar
Ar/Ar
K/Ar
485 ± 8
490 ± 6
485 ± 5
495 ± 5
5
6
6
5
Wando River
Wando
Glenelg River
Schofield Creek
mus
K/Ar
biotite gneiss
biotite schist
Glenelg River
Metamorphic
Complex
schist
gneiss
schist
schist
schist?
pegmatite: postkinematic
pegmatite: late
post- kinematic
Possible resetting during the
Devonian.
Bushy Creek
DDH VIMP12
Appears to be the age of
detrital zircons in the rock.
Age of high grade
Metamorphism.
491 ± 5
5
Yarramyljup Creek
480 ± 5
5
mus
K/Ar 488 ± 5
5
Yarramyljup Ck Bridge
pegmatite: D2 demus
K/Ar 493 ± 6
5
Yarramyljup Creek
formation
491 ± 5
5
pegmatite: from
mus
K/Ar 504 ± 5
5
Yarramyljup Creek
sheared lens
498 ± 6
5
Abbreviations: bi biotite, F-T fission track, hb hornblende, mus muscovite, plag plagioclase, sph sphene, TR total rock, zr zircon.
Sources: 1: Bowen, 1975; 2: McKenzie et al., 1984; 3: Richards & Singleton, 1981; 4: Gleadow & Lovering, 1978; 5: Turner
et al., 1993; 6: Turner et al., 1996; 7: Stuart-Smith & Black, 1999; 8: Fanning, in Maher et al., 1997a; 9: Webb, in Maher et
al., 1997a; 10: Foster et al., 1998; 11: Stuart-Smith & Black, 1999; 12: C.M. Fanning unpublished data.
Table 2.15 Timing constraints on the Delamerian Orogeny in Victoria.
Stratigraphic constraints
Glenelg
Zone
Grampians–
Stavely Zone
Radiometric constraints
Youngest deformed
rocks
Oldest overlying rocks
Metamorphic
micas
Syntectonic
intrusions
Post-tectonic
intrusions
Moralana Supergroup,
probably Early Cambrian (545–510 Ma?—
deformed in phase 1
and 2)
Mount Stavely Volcanics (500 Ma—deformed
in phase 2)
Silurian?
Grampians Gp (440–
420 Ma?)
500–485 Ma
510–490 Ma
490–470 Ma
Silurian?
Grampians Gp (440–
420 Ma?)
500 Ma
Summary: Deformation age based mainly on radiometric determinations. Phases 1 and 2 span 510–490 Ma in Glenelg
Zone; phase 2 spans a short time interval around 500 Ma in Grampians–Stavely zones.
Table 2.16 Lower Ordovician clastic units
Castlemaine Group
Thick sequence of turbidites consisting of sandstone and mudstone with minor granule conglomerate and black shale. Thick sandstones are
mostly Ta (Fig. 2.22A), with scoured bases, rip-up clasts, flame and load cast structures and minor T bc (Fig. 2.23) or Tace sequences. Grains
are mostly of clear plutonic quartz; polycrystalline metamorphic and vein quartz grains also common. Minor K-feldspar, lithic fragments of
sedimentary and metamorphic quartz-rich sandstone and micaceous mudstone, occasionally showing a crenulation cleavage. Sandstone is
texturally immature; some are quartz-wackes ( 15% matrix). Mudstone and minor black shale form packages metres to tens of metres
thick with Tde and Tbcde beds. Mudstone is typically massive whereas black shale is well laminated, rich in graptolites, often also in phyllocarid crustaceans and conodonts. Granule conglomerate is similar to those in Angry Hill Sandstone. Chert dominates in thick intervals of
hemipelagic deposits on Mornington Peninsula (Figs 2.22B,C).
Romsey Subgroup (see Fig. 2.14)—VandenBerg (1992)
Angry Hill
Sandstone
Bryo Gully
Shale
Split Hill
Sandstone
Stauro Gully
Shale
Lano Gully
Sandstone
~790 m, predominantly sandstone, thick-bedded Ta, or thick to medium-bedded Tbc (Fig. 2.24), commonly with interbedded siltstone. Black siliceous shale is conspicuous in the lower part. Contains at least two units of banded granule/pebble
conglomerate. Some are lithic with plentiful chert and shale clasts; others are solely of quartz, with vein quartz by far the
most abundant, minor detrital feldspar, muscovite, biotite, rare garnet, yellow tourmaline (dravite), rutile, microcline.
~240 m in type section; basal 60 m thick black siliceous shale overlain by ~60 m of soft, mostly thin-bedded siltstone, followed by ~40 m of black siliceous shale and some siltstone.
Upper unit, 15 m of thick to medium-bedded sandstone and siltstone; middle unit, 31 m of predominantly black siliceous
shale; basal unit, 16 m of thick-bedded sandstone and siltstone. Sandstone is turbiditic, similar to sandstone of the Lano
Gully Sandstone.
20–35 m, consists exclusively of black siliceous shale, often with visible pyrite.
280–180 m, thick-bedded quartz-rich but somewhat lithic sandstone (lithic quartz-wacke), somewhat micaceous, lesser
siltstone/shaly siltstone; no siliceous shale. Most sandstone beds are thick Ta with very thin Tb, silty Tc. Some have waterescape structures (Fig. 2.24), amalgamation. Lithic component is mostly regional metamorphic rocks, including crenulated
mica schist, vein quartz, chert, plagioclase feldspar.
Pinnak Sandstone—VandenBerg et al. (1992, 1996, 1998); Orth et al. (1995); Hendrickx et al. (1996); Simpson et al. (1996,
1997); Willman et al. (1999a); Fergusson and Tye (1999)
Thicker sandstone (>50 cm) is massive to graded, poorly sorted, medium to coarse, some with scattered granule sized particles in the base
(Simpson et al., 1996). Thinner sandstone is finer, normally graded, planar and cross laminated. Sandstone is dominantly quartzwacke but
ranges from greywacke to protoquartzite. Quartz grains are angular to subrounded, variable recrystallisation obscures grain provenance.
Feldspar (dominantly plagioclase) and muscovite are common accessories, rare lithics, no mafic minerals. Mudstone is yellow, grey or, in
rare instances, black, generally consist of alternating quartz-rich and clay-rich beds 0.2–5 cm thick in packages 5 m thick, beds grade from
quartz-rich silt to clay.
Sandstone-dominated packages consist of the thicker coarser beds, with sandstone/mudstone ratios generally 2:1. In mudstone-dominated
packages, mudstone/sandstone ratio is 4:1, sandstone beds are <50 cm thick, have locally well-developed cross lamination or grading; mudstone is mostly planar laminated. Flaser bedding is locally developed. In packages with sandstone/mudstone ratios about 2:1, beds are variable in thickness and internal structure.
Table 2.17 Facies associations in the Ordovician rocks—wide form
Facies
*)
Bed types and sedimentary structures
1 Amalgamated sandstone
B2
2 Thick-bedded sandstone or sand dominant
C
3 Massive sandstone–
granulestone
A
4 Mixed sandstone–
mudstone
C &
D
Multiple, amalgamated, thick beds, generally massive, variously graded. Ta makes up all or most of
the beds. Minimum sand/mud ratio is 6:1. Beds are up to several metres thick, facies intervals range
from several to tens of metres. Scouring and channelling at the base of beds, and mudstone intraclasts are relatively common.
Thick turbidites and minor intercalated mudstone, with sand/mud ratio of 3.5:1 to 6:1. T a or Ta(c)e
divisions dominant, up to several metres thick, facies intervals up to several tens of metres thick.
Some channelling is discernible. Is frequently in association with facies 1, forming thick sandstone
bodies. Sometimes thin intervals of 2 occur within facies 5. Slumped and redeposited layers are common in facies 2, less so in 4, particularly in the Adaminaby Group.
Well-sorted massive sandstone to granulestone. Beds are up to several metres thick, in packages tens
of metres thick, show strong thickness variation and scoured bases. Some show laminar/tabular cross
lamination (Fig. 2.25). Most commonly associated with facies 1 and 2.
Regularly interbedded thin sandstone and mudstone with sand/mud ratio of 0.5:1 to 3.5:1 (Figs 2.23,
2.29, 2.30, 2.31). Beds are tens of centimetres to centimetres thick, facies intervals up to tens of metres. Ta divisions still prominent but Tb, Tc, T(d)e, Tcde common.
Sand/mud ratio <0.5:1, with intervals of mudstone up to tens of metres thick. Mudstone is massive to
laminated, contains intercalations of thinly bedded siltstone or fine sandstone. Ripple drift lamination or starved ripples common, Tc(d)e common in the siltstone/sandstone interbeds, Interbeds of
facies 2 and 4 sandstone may also occur.
Generally pure black shale with laminae ~1 mm thick, in beds ranging from a few millimetres to
several metres, rarely tens of metres (Figs 2.32, 2.33). Most commonly associated with facies 5 and 4,
in places with 7. Regional compositional variation occurs: in the Castlemaine Group and Mount
Easton Shale, black shales contain a significant pelitic component whereas in the Adaminaby and
Bendoc groups, black shales are highly siliceous with silica contents as high as 85–90% (e.g. Morand,
1990). Such siliceous shales often show stylolites.
Laminated, banded and massive chert in beds ranging from a few millimetres to occasionally tens of
centimetres thick (Fig. 2.22C). Black when fresh, weathered outcrops are grey to brown to nearwhite. Associated with most other facies but most commonly with the black shale facies.
5 Mudstone
(-dominant)
6 Black shale
G
7 Chert
G
*) Facies types of Walker & Mutti (1973).
Table 2.17 Facies associations in the Ordovician rocks —narrow form
Facies
*)
Bed types and sedimentary structures
1 Amalgamated
sandstone
B2
2 Thick-bedded
sandstone or
sand -dominant
C
Multiple, amalgamated, thick beds, generally massive, variously graded. Ta makes
up all or most of the beds. Minimum
sand/mud ratio is 6:1. Beds are up to several metres thick, facies intervals range
from several to tens of metres. Scouring
and channelling at the base of beds, and
mudstone intraclasts are relatively common.
Thick turbidites and minor intercalated
mudstone, with sand/mud ratio of 3.5:1 to
6:1. Ta or Ta(c)e divisions dominant, up to
several metres thick, facies intervals up to
several tens of metres thick. Some channelling is discernible. Is frequently in
11 TASMAN FOLD BELT SYSTEM IN VICTORIA
3 Massive
sandstone–
granulestone
A
4 Mixed
sandstone–
mudstone
C&
D
association with facies 1, forming thick
sandstone bodies. Sometimes thin intervals of 2 occur within facies 5. Slumped
and redeposited layers are common in
facies 2, less so in 4, particularly in the
Adaminaby Group.
Well-sorted massive sandstone to granulestone. Beds are up to several metres
thick, in packages tens of metres thick,
show strong thickness variation and
scoured bases. Some show laminar/tabular
cross lamination (Fig. 2.25). Most commonly associated with facies 1 and 2.
Regularly interbedded thin sandstone and
mudstone with sand/mud ratio of 0.5:1 to
3.5:1 (Figs 2.23, 2.29, 2.30, 2.31). Beds are
tens of centimetres to centimetres thick,
facies intervals up to tens of metres. Ta
divisions still prominent but Tb, Tc, T(d)e,
Tcde common.
Sand/mud ratio <0.5:1, with intervals of
mudstone up to tens of metres thick. Mudstone is massive to laminated, contains
intercalations of thinly bedded siltstone or
fine sandstone. Ripple drift lamination or
starved ripples common, Tc(d)e common in
5 Mudstone
(-dominant)
6 Black shale
G
7 Chert
G
the siltstone/sandstone interbeds, Interbeds of facies 2 and 4 sandstone may also
occur.
Generally pure black shale with laminae
~1 mm thick, in beds ranging from a few
millimetres to several metres, rarely tens
of metres (Figs 2.32, 2.33). Most commonly
associated with facies 5 and 4, in places
with 7. Regional compositional variation
occurs: in the Castlemaine Group and
Mount Easton Shale, black shales contain
a significant pelitic component whereas in
the Adaminaby and Bendoc groups, black
shales are highly siliceous with silica
contents as high as 85–90% (e.g. Morand,
1990). Such siliceous shales often show
stylolites.
Laminated, banded and massive chert in
beds ranging from a few millimetres to
occasionally tens of centimetres thick (Fig.
2.22C). Black when fresh, weathered outcrops are grey to brown to near-white.
Associated with most other facies but most
commonly with the black shale facies.
*) Facies types of Walker & Mutti (1973).
Table 2.18 Sunbury Group—units and lithology
Darraweit
Guim
Mudstone
Bolinda
Shale
Riddell
Sandstone
Up to 20 m of massive black calcareous mudstone with
poorly developed bedding parting and with over 40% of
finely disseminated primary carbonate, overlain by 25 m
of well-bedded fine shaly siltstone that shows tightly
contorted bedding interpreted as slump folds.
500 m of regularly interbedded thin-bedded shale, massive siltstone and sandstone. Pelites are quite coarse and
quartz-rich. Lamination in the shale is due to slight differences in grain size and degree of sorting. Sandstone
beds are fine to medium-grained, quite well-sorted, and
display plane-parallel and/or ripple-drift lamination.
>800 m of turbiditic sandstone, siltstone, black shale, rare
fine conglomerate (Fig. 2.34), very coarse sandstone.
Sandstone beds show various types of Bouma intervals.
Coarsest deposits are granule and uncommon pebble
conglomerate—pebbly mudstone is rare. Associated sandstone may show traction structures such as tabular and
trough cross bedding and large amplitude ripples.
Table 2.19 Bendoc Group—units and lithology
Akuna
Mudstone
In the type section, lower 150 m of laminated mudstone is
followed by 30 m of siliceous siltstone, overlain by siltstone with thin sandstone laminae, some of which are
New
Country
Sandstone
Warbisco
Shale
Sunlight
Creek
Formation
lenticular. In Mountain Creek, consists of thin- to thickbedded laminated siltstone with some thin rippled sandstone, occasional thick quartz sandstone. Sporadic mottling and bioturbation.
Characterised by pale to dark grey sandstone, often
somewhat lithic, with low but prominent detrital mica
content; interbedded mudstone is often deep black, varies
from richly micaceous to non-micaceous. Shale is a minor
component. Bed thickness in sandstone ranges from thin
to very thick (>1 m), probably amalgamated units (Fig.
2.35).
Consists almost entirely of black pyritic siliceous shale
(Fig. 2.33) with minor quartzitic sandstone which is up to
~2 m thick. The shale is composed almost entirely of
quartz, disseminated pyrite and carbonaceous material
and displays a characteristic well-developed bedding
fissility. Graptolites are abundant (VandenBerg et al.,
1992).
Rhythmically alternating thin beds of dark siltstone and
pale fine sandstone—hence the characteristic 'stripy'
appearance (Fig. 2.31). Mudstone is massive to bioturbated, occurs with thin-bedded chert. Thick-bedded/lenticular
quartzitic sandstone occurs in many places. In some areas
mudstone is more siliceous and sandstone more abundant.
Table 2.20 Kiandra Group—units and lithology
Main lithology is chert, black cherty slate, and mafic arenite with grains
of juvenile crystals of plagioclase, clinopyroxene and hornblende, intercalated in a succession of black and grey mudstone and fine to mediumgrained quartz sandstone and siltstone.
Thinly interbedded, finely fractured grey and white chert,
Banksia
grey to black mudstone, siliceous mudstone, poorly sorted
Chert
medium-grained quartz sandstone. Individual chert packMember
ages are 30 m thick,
Mafic arenite forms massive graded beds interbedded
Brumby
with mudstone. Arenite is mainly well-sorted, contains
Mafic
intraclasts of mudstone. Grains include angular plagioArenite
clase, clinopyroxene, hornblende; rock fragments include
Member
basalt and chloritised volcanics(?). Relict glass shards,
pumice shreds and accretionary lapilli are locally preserved. Quartz is rare.
Mostly quartz sandstone, siltstone, feldspathic (arkosic)
Southern
greywacke. Quartz-rich sedimentary rocks are indistinbelt
guishable from Pinnak Sandstone, but chert and mafic
arenite beds are intercalated (Willman et al., 1999a)
Table 2.21. Timing constraints on the Benambran Orogeny in Victoria.
Stratigraphic constraints
Radiometric constraints
Youngest deformed rocks
Oldest overlying rocks
Metamorphic micas
Whitelaw
Terrane
Gisbornian (Upper Ord)
Sunbury Group at Lancefield (~456 Ma)
Silurian or Devonian
Kerrie Congl. (430–
390 Ma)
460–450, 440 and
425–420 Ma in Stawell and Bendigo
zones
Benambra
Terrane
Late Llandov. (Early Sil)
Yalmy Gp (~430 Ma); also
Late Ord. Bendoc Gp
(~440 Ma)*
Late Silurian Mitta
Mitta Rhyolite and
Thorkidaan Volc.
(425–420 Ma)
450445 Mallacoota
Zone; 440–430 Ma in
Tabberabbera Zone
Syntectonic
intrusions
Post-tectonic
intrusions
410–400 Ma
435–425 Ma
425–415 Ma
Summary: Main deformation 455–440 Ma in Whitelaw Terrane (based on radiometric determinations),
440–425 Ma in most of Benambra Terrane (based on stratigraphic and radiometric constraints). *Locally
in the Benambra Terrane Lower Silurian rocks are unconformable on Upper Ordovician rocks.
Table 2.22 Moornambool Metamorphic Complex: metamorphic zones and their prograde minerals.
Protolith
Biotite zone
Garnet zone
Shale
biotite, chlorite, muscovite, quartz
Mafic
volcanics
chlorite, actinolite,
epidote, albite,
sphene
biotite, muscovite,
quartz, garnet, Kfeldspar
Hornblende, garnet, plagioclase, sphene
13 TASMAN FOLD BELT SYSTEM IN VICTORIA
Table 2.23 Moornambool Metamorphic Complex—units and lithology
Good Morning Bill
Schist
Lexington
Schist
Deenicull
Schist
Rhymney
Schist
Carrolls
Amphibolite
Schist with amphibolite-grade assemblages of quartz–
muscovite–biotite–(garnet). Strong schistosity is a transposition fabric formed by isoclinal folding of an earlier
fabric along which are thin quartz veins segmented into
thin augen. Occasionally deformed asymmetric augen of
K-feldspar also occur. Quartz grains show undulose
extinction and lobate to serrate boundaries. Biotite in
mica domains is largely overgrown by muscovite. Euhedral almandine is mostly confined to micaceous layers,
overgrowing micas.
Predominantly quartz and biotite with variable amounts
of graphite, muscovite, cordierite, actinolite, epidote and
sillimanite (Roder, 1977). Banding of pelitic and psammitic domains may be relict bedding but is transposed
along the schistosity. Layering and subparallel thin
quartz veins are tightly folded around steeply plunging
ptygmatic folds with associated well-developed crenulation cleavage. In places with mylonitic fabric.
Includes a variety of rocks, with mafic schist dominated
by tremolite and more felsic schist dominated by chlorite.
Predominant mineral assemblage is chlorite–biotite–
quartz–albite+muscovite+graphite
(+aluminosilicate
spots), with tremolite in place of chlorite in more mafic
schist. Chlorite occurs in irregular amorphous patches
with micas. Albite may be detrital. Pelitic rocks east of
the Magdala Antiform (“Eastern Schist” of Watchorn &
Wilson, 1989) are laminated psammites with interbedded
carbonaceous and chloritic schist. The assemblage is
quartz–actinolite–chlorite–muscovite–albite.
Schist consists of thin graded beds of metaquartzite and
pelitic layers of quartz, sericite, biotite, and 50% of
graphitic material, commonly with pyrrhotite and pyrite.
Graphite is concentrated along cleavage planes (Roder,
1977). Some rocks contain amphibole.
Generally amphibolite-grade polydeformed schist and
mylonite (Fig. 2.38). Textures and assemblages are variable, with plagioclase–hornblende–tremolite?–garnet–
epidote typical. Amphiboles (actinolite/actinolitic hornblende and tremolite) predominate (Roder, 1977) with, in
contact aureoles, minor pyroxene (diopside; McKnight,
1994) and discontinuous veins of quartz and calcite parallel to S1. Epidote is locally abundant. Schist in the
hanging wall of the Mount Ararat Fault contains amphibole together with quartz, epidote, plagioclase, clinopyroxene, andradite to grossular garnet, sphene, cummingtonite, anthophyllite, zoisite and calcite in a rock whose
texture varies from foliated and layered to massive,
rarely with deformed infilled amygdales. A narrow belt of
quartz–magnetite rock on the W flank of the Mt Ararat
range with minor garnet, plagioclase and grunerite may
represent metamorphosed quartz–hematite or quartz–
olivine–magnetite protolith (Deer et al., 1992). Locally,
micas occur as retrograde products after hornblende.
Deformation after high-grade metamorphism is indicated
by shear planes that truncate hornblende/epidote domains, and overprinting of porphyroblasts of deformed
hornblende and hornblende/quartz aggregates by a
transposition schistosity defined by aligned quartz–
muscovite and hornblende ribbons. Euhedral almandine–
grossular garnet porphyroblasts overgrow hornblende
and appear to overgrow the main transposition fabrics,
indicating a late genesis.
Table 2.24. Omeo Metamorphic Complex: metamorphic zones and their prograde minerals.
Protolith
Cordierite zone
Sillimanite–
muscovite zone
Andalusite–
K-feldspar zone
Sillimanite–
K-feldspar zone
Migmatite zone
Shale
biotite, muscovite,
cordierite, albite, andalusite, staurolite,
quartz
quartz, muscovite,
biotite
biotite, muscovite,
cordierite, sillimanite, quartz, albite
biotite, cordierite,
andalusite, K-feldspar,
quartz, plagioclase
quartz, muscovite,
biotite
quartz, biotite,
K-feldspar, plagioclase
biotite, cordierite,
sillimanite,
K-feldspar, quartz,
garnet, plagioclase
quartz, biotite,
K-feldspar, plagioclase
biotite, cordierite,
sillimanite,
K-feldspar, spinel,
garnet, plagioclase
quartz, biotite,
K-feldspar, plagioclase
quartz, epidote, actinolite-hornblende,
sphene, plagioclase
quartz, plagioclase,
diopside, hornblende, sphene
quartz, plagioclase,
diopside, hornblende,
sphene
quartz, plagioclase,
diopside, hornblende,
sphene
Sandstone
Calcsilicate
Table 2.25 Kuark Metamorphic Complex: metamorphic zones and their minerals.
Protolith
Andalusite–
cordierite zone
K-feldspar–sillimanite
zone
Shale
biotite, muscovite,
andalusite, cordierite, albite, quartz
quartz, biotite,
muscovite
biotite, sillimanite, Kfeldspar, quartz, cordierite,
plagioclase (muscovite)
quartz, biotite, K-feldspar,
plagioclase
Sandstone
Table 2.26 Hydrothermal alteration, isotopes and fluid inclusions
Hydrothermal alteration
Veins of quartz and discolouration of host rocks are the most obvious products of hydrothermal fluid passage and alteration (Bierlein et al., 1998a);
others are carbonates, chlorite, sericite, biotite, albite, barite, pyrite, arsenopyrite, galena, chalcopyrite, sphalerite, pyrrhotite, tetrahedrite and gold
(Gao & Kwak, 1997). Paragenesis is fairly uniform (e.g. Fig. 2.51). Carbonates were precipitated over a long period whereas deposition of chlorite,
muscovite, sulphides (except pyrite) and gold was more rapid. Host rock
chemistry strongly reflects the effects of hydrothermal alteration (Fig.
2.52). At deposit-scale, alteration assemblages vary little downdip and
along strike of fluid conduits, implying relatively isothermal conditions for
vein emplacement and metasomatism; away from fluid conduits zonation is
marked (e.g. Li, 1998). At zone scale, ambient temperature, hence crustal
level, controlled what mica and iron-sulphide species was formed (Fig.
2.45).
Quartz vein oxygen isotopes
Compositions are broadly homogeneous at both local and regional scales
(Fig. 2.48; Gray et al., 1991a; Wilson & Golding, 1988) and are different
from host rocks. They point to a fluid-dominated system along the fluid
conduit, uniform 18O of the fluids, and essentially isothermal conditions
(McCuaig & Kerrich, 1998), consistent with fluid derivation and emplacement during regional metamorphism. Vein quartz in aureoles of posttectonic granites has significantly lighter oxygen isotopes, showing that
granites post-date the homogenising event. In the Stawell and Bendigo
zones, 18O values increase in progressively younger host rocks, reflecting
fluid–host rock 18O exchange. As a consequence, there are marked steps in
18O values across major reverse faults (Gray et al., 1991a).
Ore fluid hydrogen isotopes
Compositions in the Bendigo Zone are fairly uniform (D = –64 to –47‰;
Changkakoti et al., 1996). These values, and calculated 18O values (assuming 325  25C) overlap both the magmatic and metamorphic fluid fields
but lie predominantly within the metamorphic fluid field (Fig. 2.50).
Sulphur isotopes
Compositions are fairly uniform with 34S values ranging from –1 to 10‰
(Gulson et al., 1988). They are lighter than in diagenetic pyrite, which
approaches values for seawater sulphate (Gulson et al., 1988). Derivation is
therefore either from magmatic–hydrothermal fluids or from dissolution
and/or removal of sulphur from magmatic sulphides in Cambrian boninite.
The former is unlikely, given the time lag between gold emplacement and
magmatism.
Radiogenic lead isotopes
Compositions of hydrothermal sulphides in the Stawell and Bendigo zones
are fairly uniform (Fig. 2.49) pointing to transport of metals by a largescale hydrothermal system. Compositions which deviate from this broadly
follow the 400 Ma isochron, dating lead emplacement (Bierlein &
McNaughton, 1998). Lead is only partly derived from host rocks (Gulson et
al., 1988; Gulson et al., 1990a, b; Bierlein & McNaughton, 1998). Other
sources are contentious (e.g. Gulson et al., 1988, 1990b suggested a mixed
crust–mantle and Bierlein & McNaughton, 1998 a crustal source). Inferences on the source of ore fluids and gold based on the provenance of lead
may be misleading. Victorian orogenic gold ore fluids mostly have low
salinities and temperatures, hence low solubility of lead. Hydrothermal
lead is unlikely to reflect the source of ore fluids and gold (Phillips &
Hughes, 1996). At the Magdala deposit, Stawell, where gold and lead were
probably transported as chloride complexes in high-temperature ore fluids,
lead isotope values deviate from other orogenic gold values and approach a
‘mantle source’ signature (Gulson et al., 1990b).
Fluid inclusions
Fluid inclusions in Bendigo Zone mineralised quartz veins indicate trapping pressures and temperatures around 0.15–0.2 GPa and 300–350C
(Changkakoti et al., 1996; Cox et al., 1991b). Inclusions can be grouped into
three main categories:
1.
H2O–CO2 inclusions (two- or three-phase);
2.
CO2-rich inclusions with variable amounts of CH4, C2H6 and N2 and
small amounts of H2O; and
3.
H2O (two-phase) aqueous inclusions.
15 TASMAN FOLD BELT SYSTEM IN VICTORIA
Type (1) have a salinity between 2–4 wt.% NaCl equivalent, while type (3)
have salinities between 3.0–10.1 wt.% NaCl equivalent. Fluids in types (2)
and (3) represent trapping of immiscible phases exsolved from an original
liquid represented by type (1).
Gayle—in Table 2.27 below please reduce Column 1 in width and show text vertically
Table 2.27 Grampians Group—units and lithology
Mount
Wartook
Sandstone
Difficult
Moora-Moora
Sandstone
Serra
Sandstone
Subgroup
Silverband
Formation
Red Man
Major Mitchell
Sandstone
Bluff
Kalymna Falls
Sandstone
Murray Hill
Sandstone
Watgania Gap
Sandstone
Subgroup
Gariwerd
Sandstone
Thermopylae
Conglomerate
250 m of generally thick-bedded quartz to quartzo-feldspathic sandstone with minor mica and mostly
thin interbedded siltstone. Beds are sheet-like, laminated, cross bedded and rarely trough cross bedded
(Fig. 2.54A). Occasional basal pebbly sandstone is generally cross bedded scattered sub-angular vein
quartz pebbles. Bioturbated in parts with abundant Skolithos.
Daahl Sandstone Member: 10-20 m of clean quartz sandstone with large-scale aeolian dune cross
bedding (Fig. 2.54D).
200-500 m of generally thin-bedded sandstone with minor micaceous mudstone; coarser and more
feldspathic and muddy in the N. Lamination is planar or low-angle cross bedding. There are rippled
surfaces, rip-up mud clasts and beds rich in Skolithos and other trace fossils.
350-500 m, overall upward-fining with many upward-fining cycles (George, 1994). Two lithofacies:
(1) Lower pebbly lithofacies of very coarse pebbly quartz sandstone with some feldspar and abundant
lag horizons or scattered pebbles of rounded to sub-angular vein quartz. Beds laminated, (trough)
cross bedded (Fig. 2.54A) (Jenkin, 1989; George, 1994).
(2) Upper finer sandstone with horizons rich in trace fossils, less feldspathic and with rare quartz
pebbles. Bedding generally thinner, with planar or low-angle swaley cross bedding (Fig. 2.54C),
abundant Skolithos horizons (Fig. 2.54B), rare ripple surfaces.
Teddy Bear Conglomerate Member: 4–15 m of polymictic conglomerate with clasts of cleaved mudstone, vein quartz, cleaved and veined quartz sandstone. Planar lamination and trough cross bedding.
750 m of mudstone, mostly thinly laminated red, micaceous, with some interbeds of planar laminated
or cross bedded micaceous quartz sandstone. Some contain rip-up mudstone clasts. Rare thin beds of
coarse quartz sandstone are laterally discontinuous. Occasional rhombs of 2º carbonate present, surfaces with symmetrical ripples common; polygonal desiccation cracks (Fig. 2.55A), raindrop imprints,
small burrows and trace fossils are present (Jenkin, 1989). Upper part contains the only body fossil
assemblage of the group, with some fossils indicating an Upper Silurian (Ludlow) age (Young &
Turner, in press).
Glen Hills Sandstone Member: 350 m of stacked packages each capped by thin red mudstone. Packages are upward-fining and -thinning. Sandstone is purplish quartz sandstone with abundant large
mica flakes, minor feldspar, show planar, tabular and trough cross lamination, mudstone pellets.
Wannon Sandstone Member: 30 m of pale micaceous quartz sandstone, predominantly planar laminated, occasionally cross bedded, minor thin micaceous siltstone.
300–450 m thick, shows considerable lateral variation. Mostly reddish yellow somewhat micaceous
quartz sandstone with minor feldspar; haematitic silt matrix; thinner micaceous siltstone. Sandstone
generally planar and cross laminated. Trace fossils, particularly Skolithos, abundant in some horizons.
450 m of mostly quartz sandstone, abundant thin laminated purple micaceous siltstone. Generally
planar-laminated, occasionally cross bedded. Minor thin-bedded coarse sandstone, some with vein
quartz pebble lags.
300 m. Generally coarse quartzo-feldspathic sandstone with planar, tabular and trough cross bedding.
Abundant widespread vein quartz pebble lag horizons. Occasional rounded, sand sized, pale yellow
grains may be the thorium-rich mineral monazite.
Pohlner Conglomerate Member: 2 m of polymictic conglomerate only observed in the N. Poorly
sorted with clasts of pebbly sandstone, vein quartz, rarer siltstone, chert, mafic and felsic volcanics
(Fig. 2.55B). Gold in the unit may be a placer deposit or associated with alteration.
200 m of thin beds of laminated siltstone interbedded with thicker massive, planar-laminated or
trough cross bedded, coarse quartzo-feldspathic sandstone. Reddish laminated to cross bedded, partly
micaceous quartzo-feldspathic sandstone in hinge of the Pohlner Anticline.
300 m of thinly interbedded coarse quartzo-feldspathic sandstone and micaceous siltstone. In the N it
consists of thickly cross bedded, medium to coarse, somewhat pebbly, quartzo-feldspathic sandstone.
300 m of polymictic, poorly sorted conglomerate with clasts of vein quartz and veined quartz sandstone
in a matrix of pebbly coarse, slightly feldspathic sandstone.
Table 2.28 Rocklands Volcanics—stratigraphy and distribution
Name
Barangaroo
Ignimbrite
Toolondo
Volcaniclastics
Distrib’n
Lithology
S
S
Rhyolite and mafic dykes.
40 – > 90 m of flow-banded, locally autobrecciated aphyric rhyolite.
Consists almost entirely of vitric material
with 1–2% of small quartz and plagioclase
phenocrysts. Transition from basal pyroclastic textures into flow banded, lava-like
textures in the main body of the unit (Fig.
2.56A).
Feldspar-phyric lava.
Breccia, non-welded feldspar-phyric, pumice-rich ignimbrite, bedded volcaniclastics
of pumice and crystal-rich layers alternating with layers rich in accretionary lapilli—with pyroclastic surge-style cross bed-
N, 115 km2
S
N, sporadic
Glendinning
Ignimbrite
S, >180 km2
Yat Nat
Ignimbrite
N, small
area
Mooralla
Ignimbrite
Gatum
Ignimbrite
Nigretta
Ignimbrite
N, S;
patchy
S, 135 km2
S, 270 km2
S
S, 520 km2
N, S
N
ding.
Mostly undifferentiated, dark brown,
pumice and vitric-rich, densely welded,
passing up and laterally into a rheomorphic flow banded rock. <5% of small
quartz and feldspar phenocrysts. Widespread rheomorphism to produce lava-like
flow banding (Fig. 2.56B).
Pumice-rich and lithic-poor, <10% quartz
and orthoclase phenocrysts in a densely
welded matrix.
Quartz-feldspar-phyric lava.
>20 m of vitric-rich ignimbrite; up to 10%
of plagioclase and rare orthoclase phenocrysts. Strongly attenuated rheomorphic
fiamme foliation.
10–30 m single flow unit, similar to the
Nigretta Ignimbrite but finer grained, no
lithic fragments, up to 15% total phenocrysts. Conspicuous pink fiamme foliation
with locally developed rheomorphic flow
foliation
Volcanic sandstone/conglomerate.
>60 m, moderately crystal-rich (20–25%
quartz, pink orthoclase, rarer plagioclase).
Dense welding and conspicuous fiamme
foliation near base; remainder devitrified
and recrystallised, with semi-continuous
rheomorphic flow foliation. Small lithics of
quartz sandstone and metavolcanics. Thin
immature volcanic sandstone intercalated.
Quartz latite.
Non-volcanic conglomerate.
Table 2.29 Kerrie Conglomerate
The conglomerate is remarkably uniform, massive to crudely bedded
(Fig. 2.57). Sorting is moderate, with clasts ranging from pebble to boulder size. Clasts are generally well-rounded and almost all sedimentderived, consisting of quartzite, sandstone, chert, gritstone and some
vein quartz. The range of lithologies is consistent with derivation from
the Castlemaine Group. Interbedded fine-grained unit of thin-bedded
siltstone and lesser fine sandstone shows a variety of sedimentary structures including small-scale bedding truncations, cross bedding, softsediment deformation, one example of hummocky cross-stratification
suggesting reworking by storm waves.
Table 2.30 Yalmy Group—units and lithology
Tongaro
Formation
(Bolger,
1982)
Towanga
Sandstone
(Orth et al.,
1995; Allen,
1987)
Sandstone packages range from very thick-bedded massive quartzite (Fig. 2.59D) to more commonly interbedded
thick to thin-bedded sandstone and siltstone. Most display
Bouma sequences. Siltstone packages consist of siltstone
with very thin beds of quartzitic sandstone. Conglomerate is dominated by tectonically stretched quartzite with
minor green-grey chert, similar in many respects to the
Seldom Seen Formation conglomerate.
Most of the limestone lenses are very pure massive (Fig.
2.60B) to planar-bedded carbonates, some have stylobreccia (Fig. 2.60C). Some are rich in macrofossils, most are
unfossiliferous. Contacts with surrounding sedimentary
rocks are often obscured but one has a sharp basal contact
with underlying siltstone which is finely banded and not
calcareous. The top of this body is separated by a thin
scree-covered interval from quartzitic turbidites. The
carbonate has not mixed with the host rocks.
Mostly thick-bedded quartz sandstone interbedded with
minor laminated mudstone. Beds are massive, most have
thin graded tops of planar-laminated or cross bedded
siltstone. Sandstone consists of >95% quartz grains with a
minor clast content of chert, quartz siltstone and altered
intermediate to mafic volcanics. Siltstone lithofacies
comprises thin-bedded siltstone and fine quartz sandstone. Thin but persistent conglomerate beds occur at
several horizons (Fig. 2.61B). Rough Creek Conglomerate Member is massive to weakly bedded pebble conglomerate with local quartz sandstone with thin pebble
layers. Pebbles are mostly of white–grey chert, less abundant quartz sandstone, mudstone, green feldspathic rock,
vein quartz. Some chert pebbles containing Upper Ordovician, probably Gisbornian, conodonts were derived from
the Bendoc Group.
17 TASMAN FOLD BELT SYSTEM IN VICTORIA
Seldom
Seen
Formation
(Orth et al.,
1995)
Sy3
(VandenBerg et al.,
1992)
Sy2
(VandenBerg et al.,
1992)
Sy1
(VandenBerg et al.,
1992),
Bedded sandstone packages consist of quartzarenite,
occasionally with some mica, and litharenite with composition similar to the conglomerate. Sorting is very good
except in the coarsest beds. Beds show planar lamination,
cross lamination, amalgamated bedding, occasional climbing ripples, festoon cross bedding. Very minor mudstone is
locally interbedded. Intercalated in the bedded sandstone
facies are thick units of breccia/conglomerate and very
coarse sandstone that lack bedding but show a range of
sedimentary structures that indicate deposition by
slumps, e.g. sedimentary dykes, sedimentary breccia with
blocks of bedded sandstone in conglomerate matrix, softsediment deformation. Truncated relationships between
the two lithofacies (Fig. 2.61A) are probably due to channel erosion. Clasts are mostly angular chert and black
shale that often show strong flattening along the cleavage, and rounded vein quartz and quartzite. Matrix is
chert,
quartz,
less
common
feldspar
and
mafic/intermediate intrusive rock. Sandstone consists of
mostly plutonic and vein quartz and grains of chert and
siltstone.
Thick packages of quartzitic sandstone are interbedded
with mudstone (Fig. 2.59C), with thick basal package of
thick-bedded sandstone. Sandstone shows amalgamated
bedding, plane parallel and small-scale cross lamination
and commonly structureless basal intervals. Mudstone is
similar to Sy2.
Dominated by mudstone, generally well bedded and laminated and with minor massive intervals, with packages
up to tens of metres thick of quartzitic sandstone of Sy3
type. Laminae consist of alternating silt and clay layers.
70 m of massive to laminated quartzose sandstone with
minor thin-bedded sandstone and mudstone overlain by
~400 m of thick to very thick-bedded sandstone with
grains ranging up to granule size (Figs 2.59A,B). Often
shows subtle but persistent horizontal size banding; less
common dish structures and small water escape pipes;
occasional large-scale cross bedding. Small pockets of
pebble conglomerate occur at the base of some beds.
Sandstone is predominantly quartzarenite but some are
litharenite with a large proportion of lithic grains that are
mostly sedimentary but include mafic igneous rock, probably andesite. Quartz is mostly granitic but feldspar and
detrital micas are very minor.
Table 2.31 Enano Group—units and lithology
Gibsons
Folly
Formation
(youngest)
Cowombat
Siltstone
Mostly grey siltstone with thin felsic volcaniclastic turbidites, also non-volcanic quartz sandstone and siltstone.
Intercalated are numerous stratiform lenses of variably
altered andesitic to dacitic volcanics. Irregularly shaped
outcrops of dacite and andesite around the Wilga Prospect are host to massive Wilga and Currawong VHMS
lenses. Rocks are fine-grained with 10–20% plagioclase
phenocrysts, rare or no quartz phenocrysts. Rhyolite is
moderately to strongly porphyritic in quartz, K-feldspar,
plagioclase and biotite. Minor rhyolitic volcaniclastics are
present. Dacite is massive with phenocrysts of quartz and
plagioclase. Andesite and basalt (Bumble Creek Andesite
of VandenBerg et al., 1984b). form the bulk of the sequence NE of the Mt Misery Trail, comprises green, fine
amygdaloidal andesite lava typically porphyritic in plagioclase or plagioclase and pyroxene.
Mostly grey, black and green massive to finely banded
siltstone interbedded with subordinate sandstone. Conglomerate occurs as occasional thin bands, with the
Mount Walterson Conglomerate Member at Bindi
large enough to deserve member status. Like other conglomerates, it consists of conglomerate and coarse pebbly
sandstone with clasts of quartz sandstone, chert, siltstone, rhyolite and limestone. It is at least 350 m thick
(Allen, 1987; Willman et al., 1999a). Other minor phases
include sandstone with various mixtures of volcanic and
basement-derived material, and grey or black siltstone
interbedded with abundant calcareous felsic volcanic
sandstone turbidite beds.
Large and small limestone bodies occur in all the outcrops. Larger ones have member status—the Old Hut
Limestone Member at Marble Gully, and the McCarty
and Claire Creek–Stony Creek lenses along Limestone
Thorkidaan
Volcanics
Creek—but others along Limestone Creek and at
Cowombat and Native Dog plains are unnamed. Most are
densely recrystallised bedded to massive limestone, often
with a strong tectonic foliation and prominent dissolution
features. Most appear sharply bounded, but good outcrops, e.g. Stony Creek, show a marginal phase of limestone breccia with angular blocks of pure limestone in a
mudstone matrix (Fig. 2.63A). Lower and upper lenses in
Claire Creek are separated by such breccia. In a few
places, thin to thick beds of limestone are interbedded
with siltstone and sandstone. Low in the upper lens at
Claire Creek is a band of limestone with large bipyramidal quartz crystals (Fig. 2.63B).
Svt3–Svt5 consist mostly of sedimentary rocks. Svt3 is
rhyolitic volcaniclastic sandstone with a basal conglomerate of rounded cobbles mostly of quartzite, possibly from
the underlying Towanga Sandstone (Fig. 2.64A). Svt4 is a
thin-bedded to laminated vitric-rich felsic ash. Svt5 comprises felsic volcanic breccia, pebbly sandstone and minor
siltstone. Svt6–Svt10 are all rhyolitic lavas of various
kinds although Svt7 also includes some dacite. Svt2 and
Svt11–Svt13 are similar but more porphyritic and largely intrusive (Figs 2.64B,C). Svt2 includes dacite. Copperhead Volcaniclastic Member comprises polymict
rhyolite breccia, sandstone, siltstone, minor conglomerate
with clasts mainly of lava fragments, some of pumiceous
debris. Blue Shirt Rhyolite Member is flow-banded
rhyolite intruding Towanga Sandstone. Rhyolite breccias
have mudstone matrix and are either debris flows or
peperitic breccias marginal to a shallow intrusion. Sapper Nose Rhyolite Member consists of fine-grained
weakly porphyritic rhyolite lava recognised on the basis
of its high potassium response.
Table 2.32 Wombat Creek Graben—units and lithology
limestone
bodies
Gibbo
River Fm
Toaks
Creek
Congl.
Undowah
Siltstone
Mitta Mitta
Rhyolite
Most show a very monotonous lithology, with 5–
10 cm thick pure carbonate beds separated by pelitic
laminae. They are planar bedded, usually bioclastic,
ranging from grainstone to packstone. Contact relationships with surrounding sedimentary rocks are
often not exposed but the 'Lower Mitta' lens is overlain by bedded conglomerate that contains no limestone pebbles.
400 m of grey-green to buff coloured well bedded
siltstone and calcareous siltstone; lesser interbedded
massive lithic sandstones with volcanic and quartz
pebbles and a high volcanic sand component display
TBC turbidite sequences. These sandstones overlie
closed-framework conglomerate consisting mostly of
quartzite clasts.
1400 m; conglomerate is massive to crudely bedded
with framework ranging from closed to very slightly
open. Pebbly sandstone makes up a much smaller
proportion of the rock, and sandstone is a minor
component. Clasts are generally very well-rounded
and change upwards from a heterogeneous assemblage including quartzite, sandstone, black chert,
abundant rhyolite lava and quartz–feldspar porphyry
and rhyodacite (Fig. 2.66C) and rare andesite and
granite clasts, to a much less diverse range with
quartzite and sandstone predominating. The sandstone clasts are identical to Pinnak Sandstone, and
the quartzite is similar to quartzites in the Bendoc
Group and Tongaro Formation. Some of the conglomerates in the Gibbo River area consist entirely of
limestone clasts.
150–200 m; basal breccia is a mixture of rhyolite lava
and feldspar and quartz crystal fragments, generally
well bedded (Fig. 2.66A), show planar lamination,
medium scale low angle and small-scale higher-angle
cross bedding, scour and fill, load casts. Feeding trails
of Helminthoida present (Fig. 2.66B). Elsewhere the
basal siltstone is dark grey, thinly laminated, with
abundant burrows. The bulk consists of massive
siltstone that changes upward from olive green to
dark purplish red; near the top are occasional bands
of conglomerate. At the southern end of the belt,
several limestone lenses occur, with thin turbiditic
fine sandstone and siltstone and limestone turbidites.
Lava is aphanitic to porphyritic, massive, autobrecciated, flow banded and with lithophysae. Perlitic
texture occurs in some flow-banded outcrops. Relatively common hyaloclastite forms pods up to 50 m
across, has highly angular unrotated clasts in dark,
19 TASMAN FOLD BELT SYSTEM IN VICTORIA
very fine silicic matrix. Locally shows jigsaw fit texture, clasts commonly show small lobate protrusions.
Volcaniclastics occur in two bands, consist of conglomerate and pebbly sandstone, show normal grading, cross bedding, small syndepositional (softsediment) faults. Clasts in one band show welldeveloped perlitic fractures, and in the other occur
together which abundant feldspar–quartz porphyry
clasts. Pumice lapilli in some beds show plastic deformation.
Table 2.33 Barmouth Group—units and lithology
Nobby Road
Sandstone
Koomberar
Formation
Pale yellow, strongly cleaved sandstone and siltstone
with composition varying from quartzose to arkosic,
with interbedded thin feldspathic granule conglomerate. Characteristic rare grains of very clear quartz,
probably derived from rhyolite. In the upper part, sedimentary micas become a small but prominent component.
Sandstone and conglomerate show graded bedding
where cleavage is weak. Clasts are mainly of porphyritic andesite lava with lesser sandstone, supported by a
matrix of very coarse sand and granule-sized lithic
fragments (mainly andesite) and medium to coarse
plagioclase feldspar sand grains. Rhyolite and rhyolitic
volcaniclastics contain clasts with bipyramidal and
embayed quartz grains in an originally glassy groundmass.
Table 2.34 Sardine Conglomerate and Wibenduck Limestone
Wibenduck
Limestone
(VandenBerg
et al., 1992)
Sardine
Conglom.
(VandenBerg
et al., 1992)
Three main framework components: terrigenous, bioclastic and micritic intraclastic (Taylor, 1984). The terrigenous component comprises fine to coarse sand grains,
mostly of quartz, and some of chert, and occasional subrounded sandstone pebbles. The bioclastic component is
dominated by large crinoid fragments, together with
complete or broken solitary rugose corals, bryozoans,
gastropods, algae, brachiopods, bivalves, possibly trilobites, and rare ostracods. The micritic component consists of a mixture of intraclasts, peloids and ooids.
Poorly to moderately sorted pebble to cobble conglomerate with a predominantly closed framework (Fig. 2.68).
Crudely bedded, beds mostly 0.5–1 m thick. Matrix is a
poorly sorted mixture of sand, small pebbles and silt.
Most clasts are micaceous sandstone (Pinnak Sandstone), with less quartzite, reef quartz, chert, black shale
and slate, and occasional fine-grained hornfels and rhyolite clasts. Minor volcanogenic sandstone.
Table 2.35 Mineralisation at the Wilga–Currawong prospects
Structure
The dominant structures are D2, characterised by tight to isoclinal NE-trending folds with NW-dipping axial planes. F2 structures are
overprinted by steep NNW to NNE-trending brittle faults and upright open folds (Fig. 2.69). D1 and D2 structures are ascribed to the Bindian Orogeny whereas D3 structures are ascribed to the Tabberabberan Orogeny (Allen & Barr, 1990). The Wilga deposit is a single lens
underlain by an F2 basal shear zone in an attenuated F2 fold hinge (Allen & Barr, 1990). The basal shear and D3 faulting are believed to
have displaced the chalcopyrite stringer zone from the base of the Wilga mineralisation to the Wilga South prospect (Fig 2.69). The Currawong deposit consists of two mineralised lenses dissected by sub-vertical D3 faults (Bodon & Valenta, 1995).
Mineralisation and alteration
Two styles of mineralisation occur: (1) banded pyrite–sphalerite–chalcopyrite massive sulphide consisting of pyrite and sphalerite-rich
bands containing blebs of chalcopyrite and minor galena (Fig. 2.70); and (2) pyrite–chalcopyrite-rich stringer mineralisation occurs as
irregular veins and patches in strongly cleaved rocks that show intense chlorite and chlorite–quartz alteration. Both styles of mineralisation occur in a pyrite–quartz–sericite alteration zone (Allen & Barr, 1990). An important difference between the Currawong and Wilga
deposits is the presence of gold, minor arsenopyrite and pyrrhotite at Currawong which is associated with lead–zinc and stringer ores (Bodon & Valenta, 1995).
Table 2.36 Timing constraints on the Bindian Orogeny in the Benambra Terrane
Stratigraphic constraints
Youngest deformed rocks
Radiometric constraints
Oldest overlying rocks
Metamorphic
mica ages
Syntectonic intrusion ages
Post-tectonic
intrusion ages
Late Silurian Enano
and Wombat Creek
groups (418 Ma)
Early Devonian Snowy
River Volcanics (415–400
Ma)
415–405 Ma (in
fault zones)
420–405 Ma
415–395 Ma
Summary: major deformation at about 418–410 Ma, based on stratigraphic and radiometric constraints.
The younger ages of syntectonic granites can be interpreted in two ways. Either the effects of the orogeny
lasted until about 405 Ma or the region remained above the closure temperature for the isotopic methods
used and therefore the younger ages represent a cooling age.
Table 2.37 Mount Tambo Group—units and lithology
Shanahan
Sandstone
Blackfellows
Flat
Conglomerate
Berrawan
Conglomerate
Sediment composition variable: some of the coarsest
beds have a high volcanic component and appear to be
reworked ignimbrites, whilst micaceous mediumgrained sandstone appears to have come from a granitic
and/or metamorphic terrain. In upper part, graded
bedding and planar lamination are common, and softsediment deformation is visible.
Basal Old Mill Ignimbrite Member is 35–250 m of
homogeneous densely welded coarse quartz ignimbrite
and reworked volcaniclastic sandstone (Fig. 2.72).
Conglomerate and sandstone with rare interbedded
tuff; siltstone increases upwards. Pebbles are wellrounded throughout. Lithic feldspathic sandstone,
gritstone and pebbly gritstone are characteristic, contain a mixture of volcanic and non-volcanic quartz,
volcanic rock fragments (mostly rhyolite lava, also
andesite), Pinnak Sandstone rock fragments. Some
contain fragments of vitric ignimbrite. Thin pyroclastic
intervals occur in the upper 700 m.
Basal vitric ignimbrite: 130–250 m of flows of cleaved
massive originally glassy rock with quartz phenocrysts
interbedded with conglomerate.
Mostly massive/crudely bedded conglomerate; well
stratified conglomerate is rare. Clasts in the lower
member comprise cobbles/boulders of granite, sandstone, quartzite, chert, gneiss, schist, locally black slate
presumably derived from Bendoc Group. Upper member has clasts mostly of quartzite and minor vein
quartz, and rare biotite schist. Sandstone shows a
greater compositional range, includes pebbles of rhyolite and flow banded dacite or andesite that are absent
from the coarser conglomerate.
Moonip Sandstone Member consists of poorly sorted
red lithic sandstone and minor siltstone, commonly
with lag deposits of rounded pebbles, and lenses of
massive sandy conglomerate with pebbles of quartzite,
vein quartz and slate. Bedding is laterally continuous,
includes massive sandstone, sandstone with planar and
small scale cross lamination, finely banded siltstone.
Table 2.38 Wentworth Group—units and lithology
Tabberabbera
Formation
Wild Horse
Formation
Kilgower Member: two sandy units are separated by
a unit of siltstone. Arenites are quartz sandstone,
arkose, lithic sandstone, and have minor interbedded
calcareous sandstone, mudstone and limestone. The
siltstone unit is calcareous in part. McCaw (1983)
estimated a total thickness of perhaps 1500 m.
Roaring Mag Member: up to 1000 m of mainly siltstone with minor silty sandstone and calcareous siltstone.
Dead Bull Member: lenticular unit of siltstone,
calcareous siltstone, claystone and muddy limestone
with very little outcrop.
Conglomerate is massive, poorly sorted, thick-bedded.
Sandstone in the middle part shows lenticular bedding
and erosional bases. Bed thickness and grain size
decrease upward. Clasts are largely from Pinnak
Sandstone, with minor chert and black shale from
Bendoc Group. Lithic sandstone contains minor metamorphic quartz, K-feldspar, large mica flakes, all
consistent with derivation from the Omeo Metamorphic Complex. However, there are no clasts of either
metamorphic or granitic rocks in the conglomerates.
In the north, arkoses occur that consist entirely of
granitic quartz and feldspar.
Table 2.39 Errinundra Group—units, lithology and mineralisation
21 TASMAN FOLD BELT SYSTEM IN VICTORIA
Boulder
Flat
Limestone
Bungywarr
Formation
~350 m of micritic and biomicritic limestone, silty carbonaceous micrite, calcareous to almost pure black shale,
minor dolomite; interbedded recrystallised sparry limestone. Shale has many small-scale slump structures.
Some outcrops show stylobrecciation. Dolomites are minor
(10%) but occur throughout. A locally discordant but persistent barite-rich zone near the base shows variable, subeconomic base metal mineralisation.
Blackwatch Volcaniclastic Member: ~350 m thick,
with a high proportion of volcanic material, both primary
and reworked. Volcaniclastics form the main component,
consist grain-supported sandstone and pebble conglomerate, vary from quartzarenite to litharenite and feldspathic
litharenite. Main framework components are quartz,
feldspar and rhyodacitic rock fragments (van Tatenhove,
1984). Interbedded ignimbrite-like rocks are unwelded,
show pumice fragments flattened along slaty cleavage.
Some ignimbrites have nodular devitrification texture,
with nodules developed around undeformed pumice fragments. Rhyolitic lava in Pine Creek is surrounded by
hyaloclastite (Fig. 2.73). Southeast of the main belt of
Bungywarr Formation is an isolated belt of strongly foliated brecciated felsic lava.
Bola Sandstone Member: >200 m of siltstone, shale,
(sub)litharenite, feldspathic arenite and quartzarenite,
with minor lenses of ignimbrite, limestone, carbonaceous
shale, dark red micaceous sandstone. Quartz-rich sandstone and minor gritstone occur near the top. Sublitharenite and litharenite consist of quartz, feldspar,
sedimentary and felsic volcanic fragments (15–25%).
Siltstone is much richer in volcanic fragments. Localised
granule conglomerate has a closed framework of volcanic,
sedimentary and metamorphic rocks fragments, finer
quartz (65–35%), otherwise similar to litharenite. Generally well-sorted, high textural maturity, show graded
bedding and channel-type cut-and-fill structures (van
Tatenhove, 1984; Byrne, 1983; VandenBerg et al., 1992).
A band of limestone about 30 m thick within the member
is black and micritic, similar to the Boulder Flat Limestone, is overlain by about 5 m of calcareous slate, followed by a felsic volcanic after an outcrop gap of about
20 m.
Mineralisation
Stratabound lead–zinc–silver mineralisation generally occurs near the
base of the Boulder Flat Limestone. It consists of argentiferous galena
and sphalerite in dolomitic limestone and chert or within lenses and veins
of barite (Cochrane, 1982, van Tatenhove, 1984). Minor occurrences of
vein-style and breccia-fill lead–zinc mineralisation. The widespread presence of barite suggests a syngenetic volcanic exhalative origin (Cochrane,
1982) with vein-style lead–zinc attributed to remobilisation during deformation.
.
Gayle, the following table needs to be cut up into page-size slabs, just make sure that breaks are immediately above a grey cell.
Table 2.40 Snowy River Volcanics—units and lithology. Subgroups and formations are arranged in
approximate stratigraphic order, with youngest at top.
Little River Subgroup
This is the most widespread and most diverse subgroup of the Snowy River Volcanics subgroup (Orth et al., 1995; VandenBerg et al., 1996;
additional information from Bull & Cas, 1991). Encompasses a very varied suite of juvenile pyroclastics and lavas, and their epiclastic derivatives, together with minor sedolithic sedimentary rocks (Orth et al., 1995; VandenBerg et al., 1996). A regional low-angle unconformity
separates it from all the older subgroups. It is the youngest of the Snowy River Volcanics subgroups and in many places passes conformably
into the overlying Buchan Group. The Moonkan and McRaes ignimbrites are included because they overlie the unconformity that marks
the base of the subgroup, but on compositional grounds they could also be placed in the Tara Range Subgroup.
Scattered flows near the top of the group in the SE of the Buchan Rift, generally only tens of m thick, maximum 180 m.
Moores Ford
Lava flows of mostly andesite but include high-silica trachyte and basalt. Massive grey to dark green-black porphyritic
Andesite
andesite lava is most common. Basalt lavas are grey and have olivine, generally show elongate silica-filled amygdales. At
New Guinea, a black trachyte has well-developed columnar jointing. Andesite at Lucas Point contains a hyaloclastite
breccia.
Thickens from 60 m W of Buchan to 250 m only 4 km farther S; in the "Amberley Dome" > 300 m thick. Flows of vitricJellung
rich feldspar ignimbrite, generally fine, grey-green to blue-green weathering to purple-pink, with dark grey or pink pumIgnimbrite
ice and with welding ranging from moderate to dense.
Up to 200 m thick. Vitric ignimbrite, purple to yellow, resembling fine-grained sandstone; 8% phenocrysts (5% feldFrying Pan
spar, quartz small and rare; minor hornblende), some pumice. Lithic clasts include rhyolite lava, red feldspar and quartz
Creek
ignimbrite, sedimentary rock clasts.
Ignimbrite
Raymond
Falls Lava
The most widespread rhyolite lava in the rift, 200–250 m thick at W-Tree. Rhyolitic to rhyodacitic lava and minor quartzfeldspar porphyry; originally generally very glassy with rarely up to 10% phenocrysts. Lava textures are porphyritic,
spherulitic, massive, flow banded and autobrecciated. The Raymond Creek–Rodger River body contains minor lenses of
fluvial sedimentary rocks.
McRaes
Ignimbrite
Boorabal
Andesite
Milky Creek
Ignimbrite
Boundary
Creek
Conglom.
Wulgulmerang Tuff
Rankin Road
Ignimbrite
Fairy
Sandstone
Holloways
Formation
Stonehenge
Ignimbrite
Gillingall
Ignimbrite
Carson
Creek
Ignimbrite
Detarka
Ignimbrite
Dandan
Andesite
Bally Hooley
Ignimbrite
Mount Tabby
Formation
Moonkan
Ignimbrite
100–120-m thick. Distinctive quartz ignimbrite with abundant large quartz phenocrysts in a bright red matrix. Welded
outcrops show well-developed eutaxitic foliation; non-welded outcrops resemble breccia. Lithic clasts include fragments of
jasperoidal silica, silicified volcanic clasts, minor fine sandstone, trachyte and very minor microgranite. The ignimbrite is
overlain by a thin sequence of epiclastic rocks.
Maximum 150 m thick. Andesite lava, lenses of basalt lava, breccia with minor intercalated sedimentary rocks. Andesite
contains two types of pyroxene and shows layering and prominent jointing. Basalt has vesicles filled with carbonate and
silica; flows show some vague columnar jointing.
Pink–purple ignimbrite, densely welded, vitric-rich, with green pumice fragments, red to pink volcanic and sedimentary
lithic clasts.
Up to 100 m thick. Pebble and cobble conglomerate, pebbly sandstone, sandstone and minor red siltstone, red to purple
and occasionally white, closed to open framework. Well-rounded pebbles and cobbles are largely derived from the Gelantipy Ignimbrite. Bedding is crudely developed, with an overall upward fining. Sedimentary structures include diffuse
bedding in coarser units, gradational boundaries between sandstone and siltstone, and small scours and channels.
~200 m thick in Little River, considerably thinner S-wards. Tuff-rich, yellow to white, occasionally red or green, showing
an upward change from ignimbrite and coarse sandstone and pebbly sandstone, to fine vitric-rich sandstone. Tuff predominates higher in the sequence and some may be primary. Lenses of different ignimbrites also occur high in the formation. A basal conglomerate, gritstone and pebbly sandstone varies from poorly sorted with some large-scale cross
bedding, to well-sorted conglomerate and crystal and lithic clast-rich sandstone. Becomes better bedded and sorted upwards with medium-grained sandstone, laminated fine sandstone and siltstone, all with a high proportion of glass
shards. Some thin beds consist entirely of flattened tube pumice fragments. Tuff is well bedded, with even to lens-like
and cross bedded layers, some rich in accretionary lapilli. Thin ignimbrite is common near the base of the formation.
Feldspar ignimbrite, non-welded bluish green with a variable but generally low phenocryst content in a fine vitriclastic
matrix.
Very widely distributed in the S part of the rift and includes a great variety of lithofacies. Very variable thickness: 550 m
at The Basin decreasing to 100–200 m on E flank of the Murrindal Synclinorium, ~200 m south of Gillingall, very thin
and discontinuous farther east Mudstone facies: dominated by turbiditic sandstone and mudstone, in places black and
pyritic (with sphalerite and high Ag) in the south, and by interbedded fine sandstone and laminated siltstone in the
north. In Spring Creek, calcareous siltstone with a freshwater assemblage of molluscs, arthropods and fish remains
occurs.
Sandstone facies: tabular sandstone, minor breccia and mudstone with less abundant pebbly sandstone and occasional
conglomerate. Often interbedded with thin feldspathic and vitric ignimbrite, tuff and occasional lava flows. It is the most
widespread association of the Fairy Sandstone.
Mass-flow breccia and conglomerate, associated with other sedimentary rocks, make up large portions of the formation north of W-Tree, and are scattered throughout the formation elsewhere. They are open to nearly closedframework breccia, diffusely bedded pebbly sandstone, coarse sandstone and pumiceous breccia, with clasts mostly of
ignimbrite and rhyolite lava, and occasionally andesite lava.
Pyroclastic tuff and lapilli facies: widespread but does not outcrop well. Best exposure shows interbedded low angle
cross bedded tuff and accretionary lapilli-bearing tuff (Fig. 2.81A) and, higher up, large low angle dune features in tuff,
and mantling lapilli beds with abundant pumice in a vitric matrix, indicating primary pyroclastic deposition. A thick
band of shaly yellow to white fine air-fall tuff occurs east of Timbarra.
Ignimbrites occur interbedded with the other facies, are generally thinly bedded and not welded, and of diverse composition.
Mostly known from drill intersections. Consists entirely of volcaniclastic rocks and mudstone (Bull, 1993; Bull & Cas,
1991). Predominance of massive to graded very coarse sandstone to microbreccia, together with sandy turbidites, slurry
sandstone, and closed and open-framework volcanic breccia ranging from a few centimetres to metres thick. Sandstones
consist of feldspar, with lithic fragments becoming more abundant as grain size increases. Flattened pumice fragments
are relatively abundant. Intervals of crudely bedded, poorly sorted pebble to cobble breccia with a closed to moderately
open framework also occur.
Key unit in understanding the stratigraphy and correlation in the W flank of the Buchan Rift (VandenBerg et al., 1996).
In the N is at least 300 m thick and lies on Yellow Waterholes Ignimbrite, but from there south it becomes a thin band
overlying progressively older units, until ultimately it overlies the Johnson Mudstone. At Buchan South it is a finegrained, very vitric feldspar ignimbrite, usually with well-developed eutaxitic foliation. Farther south the rock is moderately phenocrystic but has much the same ratio of crystal components and is not welded but has a well-developed eutaxitic foliation. The southern extension is a distinctive band of "massive vitriclastic sandstone facies" 15–24 m thick in
four diamond drill holes (Bull, 1993; VandenBerg et al., 1996) with similar composition to the northern outcrops but
clearly not primary pyroclastics. Beds are massive but some show a crude planar stratification; have reverse or normally
graded basal zones and normally graded tops. Thickness of individual units is 2–15 m; thicker units are probably amalgamated. The best preserved pumice fragments show uncollapsed vesicles.
Up to 150 m thick. Vitric-rich feldspar–quartz ignimbrite, red to pink (occasionally green), 15% of phenocrysts, Q:F is 1:2.
Rare volcanic lithic clasts.
Up to 600 m thick. Feldspar ignimbrite, green (rarely red), moderately phenocrystic, usually welded, with some interbedded breccia and fine tuff. Altered ferromagnesian minerals include hornblende, pyroxene and minor biotite. Minor sedimentary rocks include crystal-and-ash arkosic sandstone with diffuse bedding and deeply weathered open-framework
breccia showing plastic deformation.
Up to 120 m thick, appears to be stratigraphic equivalent of the Carson Creek Ignimbrite. Vitric-rich ignimbrite, finegrained dark green to red, with hornblende and some biotite forming the ferromagnesian minerals. In the north the Q:F
ratio is about 1:2 but in the south feldspar dominates. Pumice fragments in places give the rock a well-developed eutaxitic foliation.
Restricted to two lenses near The Basin lying directly on bedrock. Northern lens is 40 m thick, southern one as much as
300 m thick, of hornblende andesite lava and autobreccia containing both hornblende and pyroxene.
Up to 500 m thick. Granular to ash-like ignimbrite with abundant feldspar phenocrysts (mostly plagioclase) and few
quartz crystals, and with altered pyroxene as the mafic phase. Crystal content is 5–45%.
Lens up to 600 m thick within the Moonkan Ignimbrite. Four flows of feldspar ignimbrite, crystal-poor and lithic-rich,
range from non-welded to at least partially welded with a moderate phenocryst content including altered biotite, and
showing a eutaxitic foliation. Two lenses of grey-green vesicular basalt lava occur in the formation. A lens of fluvial sedimentary rock dominated by coarse, cross bedded and laminated volcaniclastic sandstone, overlies the lower basalt lava.
An open-framework breccia occurs above the lowest feldspar ignimbrite in Rodger River and farther south directly above
Moonkan Ignimbrite. It contains clasts of angular to subrounded rhyolite lava, sandstone, black quartz-feldspar ignimbrite and siliceous fine volcanic material. Large quartz and feldspar crystals and minor pumice are present in the fine
green groundmass.
At least 600 m thick, thinning to the S and W. Generally very coarse, with crystal content ranging from 10–50%, prominent large biotite flakes. Much is densely welded, with prominent eutaxitic foliation. Lithic clasts include sediment,
rhyolite lava, quartz-feldspar porphyry and ignimbrite, less common mafic volcanic clasts. Intercalated sediment lenses
are coarse sandstone, gritstone, open-framework breccia and tuff.
23 TASMAN FOLD BELT SYSTEM IN VICTORIA
Gelantipy
Ignimbrite
Sykes Tuff
~850 m in Little River, ~1300 m in Boundary Ck area, thins S-ward to 40 m near W-Tree—is the most extensive formation in the Buchan Rift. Numerous flows of pumiceous ignimbrite, with minor breccia and sediment lenses. Flows are
thick in the north (Fig. 2.81B) but become thinner and more numerous near the top of the formation and southward. The
degree of welding parallels this trend, with rocks in the north welded to densely welded whereas those in the south are
non-welded or partially welded. The ignimbrite is a quartz ignimbrite, black, weathered to grey, green and yellow, with
abundant (30%) green or pink flattened pumice fragments. Total crystal content is 10–25%. Lithic clasts vary in abundance and composition from place to place, showing that there were different sources for different flows.
260–300 m. Consists of breccia or conglomerate overlain by fine tuff. Conglomerates are poorly sorted with open to closed
framework. The breccia often contains large blocks and has interbedded pebbly and volcaniclastic sandstone. Clasts
include flow banded rhyolite lava, ignimbrite, quartzite and granite. Green to yellow tuff and minor breccia are wellbedded and cross bedded, with beds truncated or wedging out. Low-angle cross beds and accretionary lapilli are abundant.
Tulloch Ard Ignimbrite, Devils Den Conglomerate, Trendale Formation
Three formations not included in any subgroup (Orth et al., 1995)
Up to 900 m thick in Bengal Graben but thins S-ward to about 200 m, very thin over Meadow Creek Fault Zone. Many
Tulloch Ard
flow units of very vitric quartz–feldspar ignimbrite with a high concentration of shale lithic clasts (Fig. 2.80). GroundIgnimbrite
mass is grey-green, originally glassy and densely welded. Biotite is the only mafic mineral. Lithic clasts are mainly black
(Orth et al.,
shale and quartzite, although locally they include granite, granite breccia, ignimbrite, rhyolite lava and chert. Dark red
1995)
to dark green pumice fragments give a pronounced eutaxitic foliation.
200 to 500 m thick. Main lithology in the central Butcher's Creek area is massive open to closed-framework conglomerDevils Den
ate but elsewhere sandstone and siltstone predominate. Conglomerate is massive with only crude bedding and channel
Conglom.
features displayed. Clasts of Ordovician and Silurian bedrock make up 60–90% of the conglomerate, with the remainder
(Orth et al.,
being rhyolite lava and ignimbrite—milky quartz and granite are rare. Clasts are up to boulder size, sorting is poor to
1995)
moderate, rounding increases upwards. When matrix is present it is composed of volcaniclastic sandstone and rare mudstone.
Associated fine sedimentary rocks vary laterally and vertically. They include thin laminated sandstone and shale beds
and volcaniclastic sandstone and siltstone, with siltstone predominant higher in the sequence. In the west a basal breccia
fines rapidly upwards to gritstone, diffusely graded sandstone, trough cross-bedded sandstone and siltstone. In place of a
true matrix, a pseudomatrix is developed by compression of lithic clasts.
~200 m thick. Main lithology is quartz ignimbrite composed of many flow units. Phenocryst content varies from extremeTrendale
ly high to very low. Pumice fragments are ubiquitous and define a eutaxitic foliation. Near the top are minor lenses of
Formation
sandstone, tuff and breccia. They include low angle cross bedded and thinly bedded tuff, with pumice-rich interbeds, and
(Orth et al.,
coarse, well bedded volcaniclastic sandstone with flame structures. An open-framework poorly sorted volcaniclastic brec1995)
cia forms the top.
Mount Dawson Subgroup
Characterised by feldspar and feldspar–quartz ignimbrites (Q:F ratios 1:10–1:5) with distinctive red pumice (Orth et al., 1995)
North of Mt Elephant the entire subgroup is feldspathic ignimbrite with intercalated volcaniclastic sediment and tuff. In
Undifferentithe Half Moon Gully area, a 250 m thick lens of sandstone, siltstone and conglomerate lies between Doyle Gully and
ated
Bimmarn ignimbrite, and along strike is a breccia and sandstone lens with fragments of autobrecciated rhyolite lava.
Other minor phases include lenses of volcaniclastic breccia, sandstone and tuff. In the south, the widespread ignimbrites
recognised farther north lose their character and are difficult to trace.
330 m of vitric-rich ignimbrite with large quartz crystals and orange euhedral feldspar, up to 15% of pumice, some
Lookout Top
green and red volcanic lithics.
Ignimbrite
Plumb Gully
Ignimbrite
Bimmarn
Ignimbrite
Doyle Gully
Ignimbrite
Doonarlik
Ignimbrite
Dead Cattle
Gully
Ignimbrite
Woolshed
Creek
Ignimbrite
100 m of feldspar–quartz ignimbrite, dark, vitric, welded, 15–20% feldspar and 5% quartz, abundant glassy pumice.
Small lenses of breccia and sandstone with siltstone occur near the base and the top.
50 m of feldspar ignimbrite with vitric pumice and white euhedral feldspar phenocrysts (15-20%) and very minor visible
quartz in a black vitric matrix dotted with dark originally glassy volcanic fragments. Where thinnest it contains abundant lithic clasts.
~ 200 m of feldspar ignimbrite with a coarse, open-framework breccia (slate, quartzite, more abundant volcanic fragments in volcanic matrix). It is a red or pale green granular to originally glassy ignimbrite with minor visible quartz, and
contains distinctive angular, green volcanic clasts.
~ 130 m of distinctive feldspar ignimbrite with white to light green feldspar crystals (16% plagioclase, 10% K-feldspar),
no quartz, and abundant pumice, and, in a dark, welded groundmass. Pyroxene (10%) is the mafic mineral. Rare volcanic lithic clasts.
700 m of relatively vitric ignimbrite, dark grey to black, mostly welded. 20–30% feldspar (K-feldspar, less abundant
plagioclase), 2% small angular quartz, 20% pumice. Red volcanic and green lithic clasts increase in abundance southward, include lava, ignimbrite, cherty fragments, minor sedimentary rock clasts.
150 m of feldspar–quartz ignimbrite, granular (up to 30% feldspar phenocrysts, 2 mm long, 6% quartz, 1% biotite) with
abundant pumice. Lithic clasts rare, small, include red vitric fragments, shale and porphyritic quartz-feldspar ignimbrite
clasts.
Berrmarr Subgroup
Only the S portion has been mapped so its full extent is not known (Orth et al., 1995).
More than 600 m thick. Quartz ignimbrite, variably welded, black to purple, relatively crystal-rich and often coarsely granuBlack
lar. Mafic minerals are prominent biotite and minor hornblende. In addition to ubiquitous cognate lava blebs, lithic clasts
Mountain
are abundant and varied, dominated by volcanic fragments including intermediate and felsic lava, welded ignimbrite and
Ignimbrite
fine tuff.
At least 300 m thick. Composed of a jumble of variously sized clasts ranging from highly angular blocks, some reaching
Ballantyne
house size (Fig. 2.79B), to well-rounded pebbles in open-framework arrangement. Large blocks on the eastern margin are
Megacomposed of ignimbrite and rhyolite lava, but the largest is a coherent slab of fossiliferous Cowombat Siltstone in excess of
breccia
1 km long on the western margin at Blue Hill (see Allen, 1991). Smaller blocks also include these lithologies along with
granite, hornfels, bedrock sandstone and tuff. A poorly consolidated coarse pebbly sandstone forms the matrix between the
blocks. Does not extend as far S as Black Mountain as shown in Orth et al. (1993)—these outcrops belong to Deddick Lava.
Marroo Subgroup
In most places it forms the lowest part of the Snowy River Volcanics in the central portion of the Buchan Rift but in the northwest it overlies Wombargo Subgroup, in the southwest around Gillingall it overlies Windarra Formation and in the northeast it overlies and is partly
intruded by Deddick Lava (Orth et al., 1995).
Thickens from 170 m in the W to at least 200 m in Forest Ck. Quartz–feldspar ignimbrite, grey-green, medium-grained
Glen Shiel
crystal-rich with a bimodal quartz phenocryst population. K-feldspar is three times more abundant than plagioclase.
Ignimbrite
Opaques are abundant and include subhedral magnetite. Euhedral hornblende and biotite are present. Lithic clasts include
Currie
Creek
Ignimbrite
Black
Satin
Ignimbrite
Statham
Ignimbrite
intergrown feldspar, opaques and ferromagnesian mineral fragments, and fine-grained mafic to intermediate lava fragments.
At least 600-700 m thick. Quartz ignimbrite (Q:F ~ 1:2), green to grey, granular, coarse with a moderate to high crystal
content. Ferromagnesian minerals are biotite and minor hornblende. Welding ranges from moderate to strong.
At least 500 m thick, lies directly on Ordovician bedrock. Quartz ignimbrite, coarse brown to dark green, with moderate
phenocryst content and a strongly welded vitriclastic matrix. K-feldspar is up to four times more common than plagioclase.
Intergrown feldspar aggregates are also common. Mafic minerals are hornblende and biotite. Lithic clasts include abundant
green volcanics (non-welded ignimbrite and quartz-feldspar lava fragments) and some siliceous, red lithic clasts.
1600–1700 m near Mt Statham but thins rapidly to S. Characterised by large quartz and feldspar phenocrysts and red
pumice. Volcanic lithic clasts are common. Composed of many flows of dark grey and dark purple quartz ignimbrite, mostly
strongly welded. Minor biotite and hornblende make up the mafic minerals. Small pumice fragments are ubiquitous; some
rocks have large red pumice fragments. In addition to usual suite of lithic clasts, upper flows have distinctive fragments
containing very large quartz, zoned feldspar, altered hornblende, and clasts of intergrown feldspar and ferromagnesian
minerals, resembling a subvolcanic intrusive unit near Mt Seldom Seen. Minor lenses of feldspar ignimbrite and lenses of
breccia and finer grained rock, and thin andesite lava.
Tara Range Subgroup
Wairewa Graben (VandenBerg et al., 1996)
Consists mostly of mass-flow sedimentary rocks with minor pyroclastics. The most common and characteristic rock
Hospital Creek
type is thick-bedded, poorly sorted coarse red volcanolithic sandstone with mostly closed framework of rounded to
Sandstone
Tomato Creek
Ignimbrite
Northern part of
Wairewa Graben
highly angular quartz and feldspar crystal fragments, less abundant volcanolithics including rhyolite, andesite and
basalt lava, minor Ordovician sedimentary rocks. Lithic fragments include rhyolite, andesite and basalt lava, tube
pumice and volcanic glass, and Ordovician rocks. Matrix shows a coarse vitriclastic texture with non-aligned shards.
Sediments closely resemble ignimbrites in N part of graben.
From a few m to a hundred m or more thick. Mostly ignimbrite, with minor interbedded volcanic breccia and conglomerate, and silty vitric-rich sedimentary rocks and crystal-rich sandstone. Ignimbrite is coarse to very coarse red
quartz ignimbrite with a high crystal content, with biotite and/or hornblende. Welding ranges from none to dense. In
several places, the basal few tens of metres are rheomorphic. Pumice lapilli (airfall?) deposits are associated with the
ignimbrites.
Thick succession of mainly red quartz ignimbrite with minor quartz-feldspar ignimbrite, minor pyroclastic and epiclastic rocks. One thinly bedded crystal-rich sandstone contains a hyaloclastite breccia but other rocks are of fluvial
type.
Outflow units (VandenBerg et al., 1996; additional information from Orth et al., 1993, 1995)
Yellow
Waterholes
Ignimbrite
Fluke Knob
Ignimbrite
Member 3: dominated by densely welded very vitric-rich quartz ignimbrite with well-developed eutaxitic foliation.
Member 2: sequence of generally crudely bedded feldspathic sandstone with open to closed-framework and variable
sorting, and some with lithic and flattened pumice fragments. Contain very little quartz; some appear densely welded.
Member 1: red vitric quartz ignimbrite, eutaxitic to non-welded. Shows strong lateral variation, with some stratigraphic sections dominated by quartz ignimbrite but others showing relatively thin ignimbrite flows interbedded
with crystal-rich sandstone. Includes pyroclastics such as pumice fall deposits.
Thickness ranges from 650 m at the N end and 350 m near Fluke Knob, to ~80 m midway along the belt. Medium to
very coarse red quartz ignimbrite and a variety of volcaniclastics. The ignimbrite has a moderate to high phenocryst
content with welding ranging from dense to none. Sedimentary rocks are mostly pyroclastics but with a small proportion of epiclastics (Fig. 2.78). Pyroclastics include poorly sorted massive vitric tuffs associated with crystal-rich
mass-flow sedimentary rocks with abundant volcanic lithics (probably mudflows); well-bedded pumiceous tuffs; and
finely banded tuff with graded laminae.
Ninnie Subgroup
Only occurs in the southern end of the Buchan Rift and is best developed around Mount Nowa Nowa. It comprises three formations: Kanni
Ignimbrite, Boggy Creek Sandstone and Nowa Nowa Conglomerate (VandenBerg et al., 1996).
~150 m thick. Consists of volcanolithic conglomerate, sandstone and siltstone with a high proportion of grains and clasts of
Nowa
lava, mostly of rhyolite, and some of andesite. Well bedded, often graded, show sedimentary structures such as small scale
Nowa
rills and flames (load casts) at the base of sandstones, and intricate folding and bedding disruptions and faults which are
Conglom.
clearly of mass-flow origin. Framework usually closed, sorting is moderate. Rounding is poor, and some grains are hyaloclasts. Finer-grained rocks include vitriclastic pumiceous sandstone.
Thickens drastically from ~60 m on eastern slopes of Mt Nowa Nowa, to probably hundreds of metres in the Boggy Creek
Boggy
gorge. A range of volcanic rock types but dominated by mass flows of crystal-vitric ‘sandstone’ with a moderate to high
Creek
Sandstone crystal content and a very high feldspar/quartz ratio. Much of this ‘sandstone’ is interpreted as juvenile volcanic mass flows,
some of which are subaerial ignimbrites and others subaqueous turbidites. There are also interbedded andesitic or dacitic
lavas.
Turbidites are generally well bedded, have a closed framework, show graded bedding from fine conglomerate to sand, with
beds ranging from tens of metres to millimetres thick. Load casts and cross bedding are present. Some beds consist of hyaloclasts indicative of submarine eruption. Bedding may be discontinuous and disrupted indicating soft-sediment deformation. Pumice fragments are generally absent. The degree of grain rounding is similar in the turbidites and ignimbrites.
Ignimbrites form thicker units and show cooling columns, and welding is developed to a variable degree. Many, however,
show little or no welding and poor sorting, and may be subaerial (ignimbrite) or subaqueous. They have a moderate to very
high phenocryst content and are medium-grained.
~ 80–200 m of feldspar ignimbrite, moderate to very high phenocryst content but very low in quartz Lithic fragments inKanni
clude densely welded ignimbrite, rhyolite lava, feldspar porphyry, basalt and occasional bedrock. Small flat streaky pumice
Ignimbrite
lenticles occur, and welding varies from none to moderate. Clastic rocks are a minor component and include pumice lapilli
beds and thick-bedded ashy crystal sandstone, well-sorted, medium to coarse banded volcaniclastic sandstone, and volcanolithic conglomerate dominated by lava clasts, including hyaloclasts.
Timbarra Subgroup
Interfingers with Tara Range Subgroup in the S; near Gillingall, a lens of Statham Ignimbrite is intercalated at about the middle of the
subgroup (Orth et al., 1995; VandenBerg et al., 1996). Additional information from Bull & Cas (1991).
Up to 120 m thick. Small bodies of originally glassy massive, flow banded and autobrecciated rhyolite. Flank breccia is
Dinner Hill
unusual in that it includes clasts of ignimbrite and shale as well as the usual rhyolite. In between lava pods are pockets of
Gap Lava
mudstone and conglomerate, channel-bedded sandstone and gritstone.
Gordon Ck Quartz–feldspar ignimbrite, coarse, massively welded, red to purple, >100 m thick. Crystal content 20–40%, of quartz 5
mm, more abundant feldspar 3 mm, rare altered biotite. Lithics include felsic lava and ignimbrite, some sedimentary
Ignimbrite
clasts. Red vitric pumice is prominent.
Feldspar ignimbrite, pink, pumiceous, vitric, 250 m. Scattered feldspar, some quartz, ubiquitous small pumice fragments.
Dicks Ck
Abundant lithic clasts include mafic lava, feldspar- and quartz-feldspar ignimbrite, shale.
Ignimbrite
25 TASMAN FOLD BELT SYSTEM IN VICTORIA
Davidsons
Lane
Formation
Scorpion
Creek
Sandstone
Johnson
Mudstone
Windarra
Formation
Wilkinson
Creek
Conglom.
~ 750 m thick, exposure is generally poor to non-existent. The best outcrops consist of massive Pinnak sandstone-derived
sedolithic pebble and boulder conglomerate with a closed framework of moderately to well-rounded clasts 1 m of sandstone
in a sandy matrix of similar material. Volcanolithic conglomerate appears to be less common, possibly because of their
weathered and soft nature. Along Davidsons Lane, the upper part consists of soft arkosic volcaniclastic sandstone and fine
conglomerate with closed to very open framework and variable clast roundness, as well as a thin flow-banded rhyolite lava
flow (or sill) and minor tuff. The southernmost outcrop consists of thinly bedded volcaniclastic conglomerate and sandstone
with horizontal and low-angle cross lamination.
Conglomerates have open to closed framework with a mudstone or medium to fine sandstone matrix. Clast types includes
various Pinnak Sandstone lithologies and (Bendoc Group?) black shale, minor granite, and volcanics (rhyolite lava and
ignimbrite, hornblende-bearing quartz-latite lava, basalt).
Thin flows and lenses of basalt lava southeast of Mount Johnson are associated with basalt breccia and one has quenchbrecciated margins (Bull, 1993). A thin welded ignimbrite occurs north of the main Windarra Road and along Mt Victoria
Road. However, most of the ignimbrite-like rocks south of the Windarra Road appear to be non-welded and many may be
‘cold’ mass-flow deposits.
Sequence of distinctive green, red and buff interbedded sandstone and siltstone with tuff beds at the base. Overlying moderately sorted volcaniclastic litharenite is interbedded with thin siltstone beds containing occasional mica flakes. A 2-m
thick quartz-bearing ignimbrite occurs in the Scorpion Creek section.
~400–500 m thick at Mount Johnson, ~150 m at Fluke Knob. A range of rock types but mudstone tends to dominate in drill
core and good outcrops. Characterised by turbiditic mudstone and turbiditic sandstone (Fig. 2.77B), showing some reworking by bottom currents. Sequence is predominantly of volcanic origin. Litharenite and feldspathic litharenite, the most
common sandstone types, contain rounded mafic volcanic lava fragments as well as felsic lava and ignimbrite clasts. Pumice
is present in some of the sandstone, becoming more prevalent in the mass-flow deposits. Drill core from Fluke's Knob contains brachiopod and bivalve fragments, diagnostic of submarine sedimentation. Vitric and volcaniclastic sandstone increase upward, together with pumice-rich and pumice-poor mass-flow deposits. At its top along Mount Johnson Ridge is a
thick, massive pumiceous and lithic-rich vitriclastic sandstone which resembles non-welded ignimbrite, with non-aligned
elongate tube pumice fragments. Outcrop farther south is very poor, with plentiful float of crystal-rich, generally well-sorted
sandstone and ashy (vitric) mudstone, with occasional poorly sorted volcanolithic and sedolithic (derived from Pinnak Sandstone) conglomerate. Immediately south of Quire Road, a flow of densely welded vitric-rich feldspar ignimbrite is interbedded with the sedimentary rocks. Drill core shows a greater diversity of sedimentary rocks dominated by sandstone and fine
conglomerate (graded volcaniclastic sandstone facies, composite-bedded facies and heterolithic volcanic breccia facies with
intervals of mudstone facies (Bull, 1993).
Two lava bodies low occur in the formation near the intersection of Wattle Hill Road and Mollys Plain Road. The lower, ca
60 m above the base of the formation, is an evenly fine non-vesicular metabasalt(?) flow about 50 m thick. A much thicker,
strongly lenticular originally glassy rhyolite lava 80 m higher up shows well-developed flow banding. The close juxtaposition
of the two may not be coincidental, and may point to a nearby small eruption centre.
Maximum 660–700 m thick. Conglomerate and breccia predominate in the basal portions of the formation. They form the
entire sequence west and south of Mt Johnson where they are generally composed of Ordovician bedrock clasts and minor
volcanic fragments although locally granite and hornfels clasts are present. At Windarra the base is an open framework
conglomerate with volcanic clasts, as well as hornblende needles and sedimentary bedrock fragments. Thin conglomerate
composed almost entirely of bedrock clasts, including hornfels, is interbedded with volcaniclastic sandstone higher up.
Large blocks of Pinnak Sandstone and quartz-feldspar ignimbrite occur among the conglomerate in Timbarra River south
of Windarra. Rounded clasts of reworked volcanics (quartz-feldspar porphyry, ignimbrite, feldspathic lava) occur in all the
conglomerates, breccias and sandstones. In Buchan River, east of Gillingall, dark siltstone with planar and cross laminations, ripples and slump features is intercalated within coarse sandstone and conglomerate. In the southwest, float consists mostly of micaceous sandstone derived from Pinnak Sandstone, and quartz-feldspar ignimbrite clasts but also tuff
with accretionary lapilli. At Fluke Knob, drill core includes massive to graded bedded volcaniclastic sandstone facies and
some composite-bedded facies overlain by very thick mudstone not seen in outcrop (Bull, 1993). These southern tongues of
Windarra Formation underlie the Fluke Knob Ignimbrite.
Quartz-latite lava occurs at the base of the thick sequences east of Wilkinson Creek. It is interbedded with lenses of
tholeiitic basalt and overlain by conglomerate with quartz-latite lava fragments or by volcanic breccia and feldspathic ignimbrite. Small pods of spherulitic rhyolite lava occur near the top of the formation east of Gillingall, overlying a varied
sequence of conglomerate, sandstone and minor siltstone. Lenses of vitric feldspar ignimbrite with prominent eutaxitic
foliation occur throughout the thicker portions of the formation, and as a widespread unit which grades laterally into a
mass-flow deposit.
At least 500 m thick. Poorly bedded, closed-framework sedolithic conglomerate is the major lithology; interbedded with
breccia (Fig. 2.77A) and pebbly coarse to medium-grained well bedded sandstone and gritstone. Shows normally graded
bedding, scour and fill lenses and sharp bed bases. Most of the sandstone is litharenite, with up to 55% quartz, mostly plutonic quartz but some metamorphic and vein quartz. Fine-grained material is rare. Quartzite and sandstone make up 95%
of the pebbles. The remainder include clasts of black, green and grey shale, chert and rare biotite-rich Nunniong Granodiorite. Clasts range from well-rounded to angular.
Wombargo Subgroup
Total thickness ca 3000 m, of which about 10% is lava. Consists of three unnamed sedimentary units separated by two volcanic units
(Orth et al., 1995)
Sedimentary rocks include clast-supported conglomerate, bedded pebbly sandstone interbedded with massive sandstone, less abundant
fine well bedded sandstone, some showing scours infilled with coarse lag material. Volcanic pebbles absent at the base but lava and ignimbrite clasts increase upwards, and sandstone also shows an upward increase in volcanogenic material, with the uppermost unit including
common tuff layers.
Volcanics: Lowest unit is pink crystal-rich coarse quartz ignimbrite with quartzite and rhyolitic lava lithic clasts and small pumice fragments. Second unit is composite, with two black quartz ignimbrites separated by a pumiceous ignimbrite. Quartz ignimbrites are very
coarse and phenocryst-rich with a black to grey welded groundmass. Both hornblende and biotite are present. Pumiceous ignimbrite is very
vitric, and has abundant pumice, usually as fiamme.
Avonmore Subgroup
Only occurs at Bindi (Figs 2.183, 2.207) and in the Quindalup Syncline west of Ensay North, 30 km W of the W margin of the Buchan
Rift (Willman et al., 1999a). In addition to formations listed below includes a substantial sill of feldspar–hornblende porphyry and a very
small lens of originally glassy rhyolite lava. Subgroup has a maximum total thickness of ~700 m but this is very variable (Fig. 2.82) and the
sequence clearly overlies a mountainous landscape. All formations are present in the Bindi Syncline but only the Attunga Paringa Fm and
Quindalup Ignimbrite are present in the Quindalup Syncline.
Patchy distribution, up to 40 m thick. Includes crudely bedded pale grey coarse feldspathic and lithic sandstone, conglomerRoadsend
ate with chert and vein quartz pebbles and with pebbles of Quindalup Ignimbrite, granule conglomerate and coarse, mediFormation
um and fine sandstone with compositions ranging from pure vein quartz to mainly volcanogenic and with black shale clasts,
and thinly bedded siltstone. Some outcrops show medium scale tabular cross bedding.
Quindalup
Ignimbrite
Tin Pot
Ignimbrite
Carriage
Range
Ignimbrite
Attunga
Paringa
Formation
Strongly lenticular, up to 650 m thick. A number of relatively thin ignimbrite flows of salmon-pink quartz ignimbrite, often
with prominent quartz phenocrysts and very similar to Tara Range Subgroup rocks in the Buchan Rift. They show considerable variation in phenocryst and pumice content, grain size and degree of welding. Biotite is present but rare. Interbedded
with these are minor thin fluvial rocks.
Strongly lenticular, up to 120 m thick. A number of ignimbrite flows with variable phenocryst content, with the most distinctive having a very high feldspar phenocryst content (quartz/feldspar ratio 1:10). Welding is well developed. Accessory
lithics include Pinnak Sandstone rocks, muscovite schist and andesite or basalt lava.
Strongly lenticular valley-filling flows up to ~80 m thick. Quartz ignimbrite with variable phenocryst content. The coarsest
flows have very high phenocryst content, very large quartz phenocrysts and a very high content of cognate lithic fragments
that give the rock a clastic appearance. Biotite is rare, accessory lithics consist of Pinnak Sandstone rocks. Ignimbrites are
well lithified but non-welded.
Strongly lenticular, up to 320 m thick. Breccia, conglomerate, sandstone and pebbly sandstone generally with poor bedding
and poor to fair sorting. Rounding is very variable, generally very good in the conglomerate. Basal conglomerates are generally of the same rock type as the substrate and include granitic, rhyolitic and sedolithic (slate and quartzite) types. A hornfels breccia near Ensay North, by contrast, appears far from its source—it occurs in the midst of widespread granite. It is
overlain by well-sorted and rounded cobble conglomerate and pebbly coarse sandstone with clasts of granite, migmatite,
chert, sandstone and slate.
Table 2.41 Buchan Group—units and lithology
Murrindal
Limestone
Taravale
Marlstone
Buchan
Caves
Limestone
The Rocky Camp Limestone Member outcrops over a very small area near Murrindal. All outcrops are mound-like or
lenticular, reflecting original carbonate mounds. Lithology is varied, includes pale carbonate mudstone, wackestone, packstone and minor grainstone, all thickly bedded to massive. Has abundant corals, stromatoporoids, crinoids, algae, less
common brachiopods, large plates of Receptaculites. Minor patches of tabular stromatoporoids with interstitial carbonate
mudstone and some branching corals are found in growth positions (Wallace, 1982). In places stromatoporoids bind wackestone. The Rocky Camp Limestone is currently quarried for production of quicklime, flux, stock feed, paper manufacture
and agricultural purposes (McHaffie & Buckley, 1995a).
The generally well-bedded McLarty Limestone Member forms most of the outcrop area of the formation with a maximum thickness of 190 m. Basal part is poorly fossiliferous carbonate mudstone with occasional marly interbeds and some
thin, richly fossiliferous packstone (Wallace, 1982). Fossils include brachiopods, nautiloids, Thamnopora, favositids, stromatoporoids, scattered rugose corals. Alongside the Rocky Camp Limestone Member it is a grainstone rich in crinoid ossicles
but farther away it grades into packstone and wackestone.
Murrindal Synclinorium: basal beds are impure limestone rich in the brachiopod Protochonetes australis, passing up into
siltstone with sparse nodular limestone. Most limestone is extremely fine-grained and appears to be strongly calcified siltstone. Nodules were formed during diagenesis and have been greatly enhanced by compaction and cleavage formation (Fig.
2.85). Rare detrital limestone has abundant shelly fossils. In the tongue below the Murrindal Limestone, the upper part is
thinly bedded calcilutite with bands of packstone. The upper sequence in the south is muddier. Shelly fossils are moderately
common, faunas are more diverse than in the Buchan Caves Limestone. In some beds, fossil fragments are subangular to
rounded, indicating considerable transport (Teichert & Talent, 1958).
A sandstone interval high in the formation at Bindi forms a broad channel in which sandstone beds are interbedded with
marlstone. Some beds show tabular cross bedding, others show soft-sediment folds (Willman et al., 1999a). The sandstone is
feldspathic litharenite and lithic arkose, a mixture of quartz, feldspar, rock fragments, transported bioclastic material
(Wall, in Willman et al., 1999a). Both metamorphic and volcanic quartz and rock fragments (mostly rhyolite) are present.
Dominantly mid grey to black and occasionally red limestone and dolomite, densely recrystallised, generally well bedded
(mostly stylobedded; Fig. 2.86A), commonly referred to as ‘marble’. Basal 10–25 m are dolomitic and unfossiliferous, giving
way to normal calcitic carbonates with patchy dolomitisation and abundant fossils. In the Murrindal Synclinorium it is
generally upward-fining, with calcarenite dominant in the lower two-thirds and calcilutite in the remainder. In the Murrindal Synclinorium it consists of skeletal or often peloidal grainstone to wackestone (Wallace, 1982) and at Bindi it comprises biomicrite wackestone and packstone, and biosparite, pelsparite and oosparite grainstone (Brownlaw, 1991). Fragments of ostracods, brachiopods, corals, algal limestone, fish bones, bivalves, conodonts and a few gastropods make up the
bioclastic component, with algal pisoliths locally common (Fig. 2.86B). The calcarenite is generally poorly fossiliferous, but
locally beds are rich in brachiopod shells. Faunal diversity is low, with a single species, Spinella buchanensis, dominating.
The calcarenite has the greatest potential for industrial use, being relatively free of components other than carbonate
(McHaffie & Buckley, 1995a).
There are two volcaniclastic horizons low in the formation. One, on the western margin of the Murrindal Synclinorium,
is a 1-m thick non-welded pyroclastic flow about 5–10 m above the basal dolomites and mapped over 10 km (Orth et al.,
1995). The other, Amberley Park Volcaniclastic Member, about 150 m above the base of the formation, consists of 15 m
of volcanic (mostly andesitic, Fig. 2.86C) and Ordovician-derived material and rare carbonate bands. Includes graded beds,
ripples, slump structures, massive beds with an open framework that are probably slump deposits. The most likely source is
a large andesite volcano of which the neck is preserved in Whiskey Creek, north of Mount McLeod, 16–20 km north of the
andesitic clastics (VandenBerg et al., 1996).
Basal Spring Creek Member in the Murrindal Synclinorium is composed of reworked volcaniclastics, in places with
carbonate cement, with thin interbedded pyroclastics in a few places. Dolomite and limestone beds become more abundant
upwards. The basal portion shows a range of lithologies and sedimentary structures that indicate a variety of marginal
marine environments (Orth, 1982). These include coarse sandstone and gritstone with high-energy depositional structures
passing up into lagoonal laminated mudstone and nodular limestone. In the East Buchan area sequences are very thin
reworked volcaniclastics. In the southeast, juvenile volcanogenic mass-flow conglomerate and sandstone are overlain by
bedded well-sorted volcanogenic sandstone and minor conglomerate and, in places, banded cherty sedimentary rocks underlying limestone. In the western limb of the synclinorium, placer deposits and small-scale dune bedding indicate a shoreface
environment. Near Buchan South, volcaniclastics and thin ignimbrites are overlain by basalt. In the New Guinea area, a
thin lens of well bedded feldspathic and quartz sandstone appears to wedge out in the north and south against intrusive
rocks of the Snowy River Volcanics. In the Gillingall area, the member consists of conglomeratic sandstone with intercalations of vitric ash-rich sandstone and quartz sandstone and, in places, black shale.
Table 2.42 Buchan Rift-mineralisation styles and occurrences
Occurrence
Commodity
Formation and host rock
Carbonate-hosted
Back Creek
Hume Park
Pyramids
Henham’s
Pb, Zn, Ag
Pb, Zn, Ag
Pb, Zn, Ag
Pb, Zn, Ag
Buchan Caves Limestone—dolostone
Buchan Caves Limestone—brecciated dolostone
Buchan Caves Limestone—dolostone
Buchan Caves Limestone—dolostone
27 TASMAN FOLD BELT SYSTEM IN VICTORIA
Spring Creek
Cu, Pb
Neils Creek
Cu, Pb, Zn
McRaes
Fe
Cocks
Fe
Gilbert Road
Fe
Syngenetic base metal
Shaws Gully
Zn, Pb
New Guinea
Pb
Hacket Creek
Pb, Zn
Running Creek
Mn, Fe
Jacksons Crossing
Mn
Blue Bullock Creek
Pb, Zn
Flukes Knob
Pb, Zn
Good Hope
Ag, Pb, Ba, Fe
Iron Mask
Fe, Mn, Ba
Kanni Creek
Ba, Fe
Epigenetic vein-style
Glen Shiel
Ag
W-Tree Creek
Au
Pyramid Mountain
Au, Ag
Halls Peninsula
Cu, Au, Ag
Glen Shiel
Ba
Bally Hooley
Ba
Tulloch Ard Road
Ba
Scorpion Creek
Cu, Au, Ag
Tara Crown (Armistice)
Au, Pb, Ag
Monarch (of Tara)
Au
Dominion
Cu
Metasomatic replacement mineralisation
Two Mile
Fe
Five Mile
Fe
Six Mile
Fe
Seven Mile
Fe
Buchan Caves Limestone—dolostone
Buchan Caves Limestone—dolostone
Buchan Caves Limestone—McRaes limonite horizon
Buchan Caves Limestone—McRaes limonite horizon
Buchan Caves Limestone—McRaes limonite horizon
Fairy Sandstone—tuff, shale, breccia
Spring Creek Member—volcaniclastics
Fairy Sandstone—pyritic black shale
Fairy Sandstone—volcaniclastics
Fairy Sandstone—volcaniclastics
Spring Creek Mbr—tuff, volcaniclastics, shale
Johnson Mudstone—black shale, chert, volcaniclastics
Holloways Formation, Fairy Sandstone—volcaniclastics
Spring Ck Mbr/Fairy Sandstone?—volcaniclastics
Rankin Road Ignimbrite—volcaniclastics, minor vein-style
Gelantipy and Glen Shiel ignimbrites—laminated quartz veins
Raymond Falls Lava, Fairy Sandstone—fault breccia
Undiff. Snowy River Volcanics—breccia zone and massive quartz
Bally Hooley Ignimbrite—quartz stockwork
Gelantipy Ignimbrite—massive vein
Bally Hooley Ignimbrite—quartz veins, disseminated
Detarka Ignimbrite—veins
Windarra Formation—quartz vein
Jellung Ignimbrite—quartz veins & stockwork
Quartz–feldspar porphyry—quartz veins and stockwork
Undiff. ignimbrite & volcaniclastics—veins, quartz veins, disseminated
Boggy Creek Sandstone—massive
Tomato Ck Ignimbr., Silurian? limestone—massive, vein, disseminated
Kanni Ignimbrite—massive
Kanni Ignimbrite—massive, vein
Table 2.43 Mineralisation in the Deddick region
Deddick silver-lead field
The field covers over 80 argentiferous galena veins. Recorded production
is small (20 t of lead ore in 1898) but mine development suggests true
production was much higher. Veins are massive argentiferous galena
with accessory barite, sphalerite and pyrite, and have thin sericitic and
silica alteration envelopes. They occupy NW-trending fractures in the
Amboyne Granodiorite (G71). This trend is parallel to the Turnback
Fault which bounds the field in the NE, and sympathetic with the Buchan Rift. Nearby porphyritic dykes coeval with the Snowy River Volcanics
(Orth et al., 1995) contain disseminated galena.
Accommodation Creek
Accommodation Creek has a long history of intermittent mining, with
total recorded production of 3676 t of copper ore (Cochrane, 1982). Thin,
high-grade (1.2–4.0% Cu) chalcopyrite-bearing quartz veins with accessory barite and calcite lie in NW-trending faults in Yalmy Group hornfels
(Orth et al., 1995) along an arcuate magnetic dyke which marks a Mount
Gelantipy Cauldron ring fracture.
Table 2.44 Mount Burrowa Cauldron Complex—units and lithology
Ring dyke
Jemba
Ignimbrite
Cudgewa
Porphyritic rhyolite, coarse, dull to bright pink, and discontinuous rhyolite bands, up to 5 km long and 400 m
wide; large pink K-feldspar phenocrysts and bipyramidal
quartz, smaller green plagioclase and biotite in very fine
pink groundmass.
Base is dark bluish grey to almost black quartz-feldspar
ignimbrite with some biotite, with about 30% of phenocrysts in a densely welded matrix and a well defined eutaxitic foliation. Tourmaline is a ubiquitous accessory
mineral, together with magnetite and rare grains of
fluorite.
Passes abruptly upwards into pink to pale brown quartz
ignimbrite that constitutes the bulk of the unit. It is
coarse, crystal-rich with coarsely recrystallised matrix
and few small lithic fragments of Ordovician rocks and
granite.
Ignimbrites range from vitric-rich to moderately phenocryst-rich, are mostly fine to medium-grained. The most
Falls
Volcanics
widespread flow has a perlitic groundmass but is welded.
Tuffs are no more than a few metres thick and consist of
thin beds of fine tuff alternating with thicker beds of
coarser, poorly sorted crystal- and lithic-rich detritus.
Accretionary lapilli are abundant. Red-bed sedimentary
rocks comprise graded feldspathic sandstone beds interbedded with red shale that show plastic deformation.
Table 2.45 Dartella Volcanics—units and lithology
Ring dyke
Sheevers
Spur
Ignimbrite
Larsen
Creek
Ignimbrite
Murtagh
Creek
Ignimbrite
Dart River
Volcanic
Breccia
Tabor
Volcanics
Very coarse quartz–feldspar porphyry, generally bipyramidal quartz and euhedral feldspar in an originally glassy
groundmass. Size and composition of the phenocrysts
matches very well with those of the Murtagh Creek Ignimbrite. Unusual is the occurrence of Murtagh Creek
Ignimbrite pyroclastics in several places in the ring dyke.
Green feldspar–pyroxene ignimbrite with moderate to
high phenocryst content (30–40%), low in quartz (Q:F
1:10). Pyroxene is prominent, generally chloritised. Pumice is minor. Lithic fragments include Wallaby Granite,
quartzite and foliated Pinnak Sandstone rocks, porphyry
and basalt.
Basal part is pinkish–cream coloured ignimbrite, commonly with good eutaxitic foliation (Fig. 2.89), sometimes
with rheomorphic flow banding. Elsewhere it is a dark
greenish grey quartz to quartz–feldspar to vitric feldspar
ignimbrite with phenocryst 30–10%, quartz:feldspar ratios
from 1:1 to 1:10. Ferromagnesians are biotite and occasionally pyroxene and/or hornblende. Lithic fragments
include Wallaby Granite, schist, quartzite, sandstone,
slate, rhyolite, porphyry. Minor andesitic lavas and (hyalo)clastics, and volcanic sandstone and conglomerate
consisting of roughly rounded grains of andesite.
Quartz ignimbrite, red, very coarse, generally with a very
high crystal content and a very high quartz/feldspar phenocryst ratio and minor biotite. In W it has abundant
Pinnak Sandstone lithics (both lower and upper
greenschist facies), including large coherent blocks; and
cognate lithics of porphyritic lava with internal flow layering. Pumice is rare, strongly flattened. Some have much
lower phenocryst content and less quartz; some consist of
phenocryst-rich feldspar–pyroxene ignimbrite. A single
tuff, probably an air-fall deposit, occurs. A thin conglomerate with material derived from outside the cauldron is
intercalated with the ignimbrite and is the only fluvial
material.
Western outcrops: thin, fine-grained volcaniclastic sandstone, probably an airfall deposit. Farther east: mixture of
sedimentary breccia and conglomerate with clasts in
places entirely of Pinnak Sandstone but elsewhere with a
mixture of sedimentary and volcanic clasts (probably
Tabor Volcanics); with a matrix rich in volcanic quartz.
Outcrops now inundated contained clasts over 20 m long,
but present exposures show clasts up to 2 m. A few outcrops show large clasts of (probably Silurian) limestone
whose source is unknown; one outcrop consists of andesitic clastics. The matrix also contains grains of feldspar
porphyry and of basalt with trachytic flow texture.
Most outcrops are dark crystal-rich vitric ignimbrite with
eutaxitic foliation. Abundant Pinnak Sandstone lithics at
the base; small rhyolite lithics near the top. Small areas of
more mafic rocks include dark green, altered quartz phyric dacite breccia gradational with flow banded andesite
with a chilled margin.
Table 2.46 Mount Elizabeth Cauldron Complex—depositional units and lithology
Sedimentary rocks
Undifferentiated
One outcrop flanking a small pod of quench-fragmented
lava consists of graded beds of graded volcaniclastics with
abundant clasts of lava, locally ripped up sediment and
pumice; bedding shows syn-sedimentary brittle deformation. Graded sandstone–mudstone beds show turbidite
features. In the other, graded beds of breccia, pebbly
sandstone and well-bedded sandstone occur at the margins of a pod of lava but there may not be any genetic
association. Another lens is intercalated within the Fainting Range Ignimbrite and consist of poorly sorted coarse
sandstone grading up into well-sorted and diffusely bedded fine sandstone.
Quartz ignimbrite in the thin ring dyke around the
northern margin of the cauldron has a slightly lower
crystal content than the Slater Ignimbrite and lacks biotite.
29 TASMAN FOLD BELT SYSTEM IN VICTORIA
Slater
Ignimbrite
Fainting
Range
Ignimbrite
Quartz ignimbrite, densely welded, red with some biotite,
generally uniformly crystal-rich and very coarse, with
grain size decreasing to the north and west of the cauldron, where the crystal content is low. Commonly shows
pronounced eutaxitic foliation. There are no lithic fragments.
Most flows are densely welded black pumiceous vitric-rich
feldspar ignimbrite with 10% feldspar phenocrysts, mostly plagioclase, rare quartz. Pumice fragments usually
small, define eutaxitic foliation. Minor lithics include
Pinnak Sandstone, feldspathic ignimbrite, Slater Ignimbrite, rhyolitic lava, mafic volcanic, rare granitic fragments. Marginal breccia with a high proportion of Ordovician fragments is interpreted as cauldron wall debris
slumped into the cauldron during eruption. Rare crystalrich tuff of restricted extent.
Table 2.47 White Monkey Volcanics—units and lithology
Douglas
Ignimbrite
Bass Camp
Ignimbrite
Minchin
Ignimbrite
Bowen
Track Ignimbrite
Mackiesons
Spur Tuff
Feldspar ignimbrite, brown, fine-grained, moderately
vitric with abundant red pumice.
Quartz–feldspar ignimbrite, very coarse, crystal-rich,
red with distinctive red pumice and partly quartz-filled
cavities, probably gas accumulation spaces formed
during cooling.
Vitric ignimbrite, small quartz and feldspar phenocrysts in green-grey or red fine matrix. Abundant lithic
clasts include ignimbrite, originally glassy lava, and
sediment mainly from the Yalmy Group.
Quartz–feldspar ignimbrite, coarse, abundant white
feldspar and large quartz set in a welded black originally glassy groundmass. Aggregates of interlocking feldspar crystals are common. Minor small felsic lava or
sedimentary lithics, occasional pumice fragments. Biotite, altered hornblende, magnetite and ilmenite are
accessories.
Vitric ash, fine, welded (Fig. 2.92), black–grey, with thin
elongate slivers of limonite that may be attenuated
pumice fragments. Densely welded groundmass shows
flowage of shards around minor small phenocrysts.
Some layers have up to 10% large quartz and feldspar
phenocrysts. In places the formation includes ignimbrite and sediment below the more characteristic ash.
Table 2.48 Minor volcanic deposits—units and lithology
Besford
Ignimbrite
Eight Mile
Loop Rhyolite
Tongio Munjie
Volcanics
Pipeline
Volcanics
Yeerung River
Volcanics
Quartz–biotite ignimbrite, remarkably homogeneous,
very coarse, red, very high phenocryst content (~50%)
and a high quartz:feldspar ratio (1:2 or more), cognate
pyroclasts of lava, a few lithic fragments of sandstone
and shale or siltstone.
Generally massive but in places shows flow banding.
The sheet appears to have been faulted into two distinct parts by at least one reverse fault that has displaced the base by approximately 100 m.
Lithic-rich ignimbrite, interpreted to be the basal
layer, resembles breccia with abundant large fragments of both country rock and volcanics. Lithic assemblage is remarkably varied, including muscovite
schist, granite, angular quartz, rhyolitic lava and
probable ignimbrite, and altered basalt or andesite.
Lithic-poor phase: cream-coloured ignimbrite with
mostly quartz, few K-feldspar phenocrysts, altered
ferromagnesians, muscovite. Pumiceous ignimbrite
is similar but has large fragments of uncompressed
tube pumice.
Lithic quartz ignimbrite: welded coarse ignimbrite,
crystals of quartz + feldspar (20-50%), lithic grains
(20%) in a fine foliated matrix (30-60%), flattened
pumice. Lithics are mostly sandstone and shale. Matrix shows well-developed welding texture.
Quartz–feldspar porphyry forms a body separating
two ignimbrite outcrops and consists of bipyramidal
quartz phenocrysts up to 5 mm across in a fine sericitised matrix.
Outcrop along Yeerung River is composed of lithic
clasts (mostly rhyolite lava) along with grains of
quartz and calcite. Phenocrysts in the lava clasts
show undulose extinction in quartz, and kinking and
bent twin planes in plagioclase. Calcite has grown in
pressure shadows on quartz and plagioclase, and
between clasts. Quartzite clasts are generally rounded and contain biotite flakes and angular quartz
grains.
Pebbles derived from the volcanics include hyaloclastite, ignimbrite, flow-banded rhyolite and jasper-like
vein material with sulphide mineralisation.
Table 2.49 Silurian to Lower Devonian sequence at Heathcote
Mount Ida
Formation
McIvor
Sandstone
Dargile
Formation
Wapentake
Formation
Costerfield
Siltstone
Undifferentiated part of the formation consists of thin
graded sandstone–siltstone turbidite beds. Beds have
sharp bases and rippled tops, and are interbedded with
bioturbated, laminated mudstone and minor thick coarse
sandstone with irregular pebbly bases. Minor matrixsupported lithic conglomerate beds have irregular bases.
Cornella Member: thin turbidites often with sedimentary features destroyed by vertical burrowing. Large
mud-dominated slumps occur throughout, consist of
sandstone rip-up clasts in a slump-folded mudstone
matrix.
Dealba Member: thick beds of pale grey sandstone,
minor coarse and pebbly sandstone and impersistent
conglomerate. Beds show tabular and trough cross bedding, herringbone cross bedding, cut and fill structures.
Conglomerate bands contain abundant crinoid ossicles
and minor Skolithos.
Stoddart Member: diverse, thinly interbedded laminated mudstone, minor sandstone and conglomerate.
Mostly massive to thick-bedded well-sorted quartzite,
minor pebbly sandstone and conglomerate. The basal
Hylands Member is relatively monotonous thin-bedded
turbidite and bioturbated siltstone unit. Sandstone beds
commonly have rippled tops reworked into swaley laminations; true hummocky cross stratification also occurs
(VandenBerg & Gray, 1992). Large-scale nested channels are well exposed in the type section (Fig. 2.94).
~1900 m of weakly laminated to thinly bedded mudstone
with minor thin beds of sandstone with rippled tops, and
minor conglomerate beds. Common small-scale troughtype cross bedding. Conglomerate, most prevalent towards the base, is poorly sorted, grain-supported, oligomictic, with rounded lithic clasts of quartzite.
1500–1750 m upward-coarsening sequence of thick to
thin-bedded turbiditic sandstone and siltstone (Fig.
3.42). Sandstone beds are rarely graded, have sharp flat
bases, a few have rippled tops, some with swaley cross
stratification. Large channel structures are locally preserved. Mudstone accounts for about 30% but is generally weathered out.
>600 m of monotonous burrowed mudstone with upwards increase in thin sandstone beds, commonly rippled. Burrows may contain carbonate and pyrite cubes.
‘Illaenus Band’ high in the formation is a slump-folded
siltstone with small sandy pockets, clay pellets, oxidised
pyritic nodules and abundant coprolites and shelly fossils (Öpik, 1953).
Table 2.50 Silurian sequence of Darraweit Guim–Kilmore–Keilor
Kilmore
Siltstone
Chintin
Formation
Heterogeneous; dominantly thin-bedded bioturbated
siltstone and very thin sandstone commonly with asymmetric ripple marks. Interbedded at irregular intervals
are packages of turbidite sandstone 10–20 m thick, and a
variety of diamictites. Occasional very broad channels
contain sandstone with planar lamination and swaley and
tabular cross lamination. Diamictites up to tens of metres
thick include slump-folded siltstone interbedded with
apparently undisturbed siltstone, and low-angle bedding
discontinuities which are glide planes.
75–170 m of very dark grey to green diamictite alternating with packages of well-bedded sandstone and siltstone.
Some pebble conglomerate is grain-supported. Diamictites
have few or no pebbles, have chaotic soft-sediment folding;
some show smaller-scale bedding discontinuities (sedimentary boudinage, step faults, disrupted bedding). Bedded packages show large-scale bedding discontinuities
interpreted as slide planes. Some banding is primary (e.g.
bedding-parallel bioturbation) but much is discontinuous
pseudo-bedding resulting from plastic stretching. In addition to pebble types present in the Springfield Sandstone
are pebbles of crystalline limestone, bedded bioturbated
31 TASMAN FOLD BELT SYSTEM IN VICTORIA
Springfield
Sandstone
Deep
Creek
Siltstone
limestone and of tabulate coral colonies.
Thick sandstone beds often in packages tens of metres
thick (Fig. 2.96A) show a full suite of Bouma sequences
and amalgamation, and load casts, ball-and-pillow structures and flute casts (Fig. 2.96D). Some contain abundant
rip-up clasts. Thin sandstone beds are usually rippled and
show small-scale cross bedding. Siltstone varies from
massive to finely banded to bioturbated. Well-sorted
quartzarenites form bands 10 m thick, are generally
massive with traces of tabular cross bedding. Sandstone is
mostly quartzose but occasional beds are rich in metabasalt grains.
Lintons Creek and Stockdale conglomerate members and Calton Hill Sandstone Member are tens of
metres thick and contain both coarse traction deposits
(conglomerate, sandstone; Fig. 2.96B) and mass-flow
deposits (diamictites, Fig. 2.96C). Beds are often markedly lenticular although the members are continuous for
tens of kilometres and have low responses on radiometric
images against the higher background of the remainder
(Fig. 2.95). Pebbles are well-rounded, of mostly resistant
rock types (quartzite, sandstone, chert) but include originally glassy porphyritic rhyolite, very rare biotite schist.
Diamictites have similar pebbles and small to large rip-up
clasts with soft-sediment folds, in a matrix consisting of
mixed sandstone and mudstone. In the Calton Hill Member, conglomerate and diamictite form minor constituents.
Basal 140 m with significant thick-bedded turbiditic sandstone; remaining 800 m siltstone, commonly bioturbated,
generally 5–10 cm thick beds separated by thin to very
thin sandstone beds with ripple-drift and occasionally
plane-parallel lamination, commonly with rippled tops.
Thick sandstone beds are rare. High up is a single discontinuous composite band of coarse rocks probably >10 m
thick, with bedded conglomerate ± sandstone, sparsely
pebbly diamictite. Formation is strongly radiogenic in K
and Th (Fig. 2.95).
Table 2.51. Siluro-Devonian sequence of northwestern Melbourne Zone
Waranga
Formation
Puckapunyal
Formation
Broadford
Formation
>750 m, upward-fining; basal portion of thinly interbedded sandstone turbidites and burrowed claystone.
Sandstone beds often have irregular conglomeratic or
pebbly bases with flame structures and large rip-up
clasts, convolute lamination. Upper portion is dominated by thick beds of strongly burrowed claystone interbedded with thin rippled sandstone. Sandstone bed
bases are highly irregular with load casts and burrowing.
Upward-fining sequence of thin- to thick-bedded turbidites—quartz and quartz–lithic arenites, with irregular
bases and rip-up clasts; rippled tops commonly show
swaley cross-stratification. Finer rocks often show
slump structures, convolute laminations, minor lithic
clasts. Claystone is often burrowed.
Associations of massive sandstone and conglomerate,
and interbedded turbidites, form several upward-fining
and -thinning sequences and are characterised by basal
conglomerate grading up into massive sandstone overlain by classical turbidites. Conglomerates consist of
diamictic granulestone, polymictic pebble–boulder
conglomerate, pebbly sandstone. Overlying sandstones
are thick-bedded quartz and quartz–lithic arenites;
ripples and load structures common. Interbedded turbidites, in packages that become thicker and more
frequent towards the top, are thin- to thick-bedded,
often burrowed.
Table 2.52 Lower Devonian rocks of the Kinglake–Lilydale region
Cave Hill
Sandstone
Lilydale
Limestone
Lens
~60 m of fairly thick-bedded fine quartzite, minor interbedded mudstone, some thick beds of pebbly sandstone
with well-rounded pebbles of quartz and quartzite. Pebbly
beds contain moulds of spiriferid brachiopods (VandenBerg, 1971).
Lens 220–280 m thick and ~1.5 km long of variably dolomitised well-bedded pale grey and orange-pink limestone.
Wall and Webb (1994) recognised it comprises 1–6 m thick
upward-shallowing cycles (Fig. 2.98), most with wellwashed bioclastic peloidal grainstone at the base, containing thin layers of coarse bioclastic rudstone, and rarely
Humevale
Siltstone
overlain by oolitic grainstone. Some cycles begin with
bioclastic peloidal packstone (Wall et al., 1995). These
basal beds were deposited in clear, shallow, high energy,
well oxygenated waters, and contain a diverse and abundant fauna dominated by stromatoporoids (15 genera,
mostly dome-shaped; Webby et al., 1993), tabulate corals
(15 species; Hill & Jell, 1970), gastropods (24 species;
Tassell, 1980) and crinoids. Codiacean and dasycladacean
green algae are also common. Upper parts of cycles consists of orange-pink fenestrate peloidal wackestone and
laminated or massive lime-mudstone (usually finely dolomitic), containing abundant bioturbation and scouring,
and rare wave ripples, mudcracks and tepees. Quartz silt
(probably aeolian) is common in these orange-pink cycle
tops. The massive dolomudstones contain nodules up to
several centimetres across, representing calcite/dolomite
pseudomorphs after gypsum/anhydrite. The cycle tops
were deposited in an intertidal/supratidal environment
under a probably subarid climate. With an average CaCO3
content of 78% it has been an important source of limestone for the production of lime and for agricultural and
construction purposes (McHaffie & Buckley, 1995a).
Mainly thin-bedded siltstone (Fig. 2.97B), lamination
mostly continuous although burrowing is ubiquitous at
some levels. Thin sandstone commonly shows undisturbed
rippled tops, which in thicker beds overlie planar laminated sandstone, but in some areas beds show swaley (Fig.
2.97C) and uncommon hummocky cross lamination. The
upper part of the formation near Lilydale contains numerous coquina beds.
Table 2.53 Stratigraphy and correlation of the Jordan River Group
Age
Emsian
Devonian
Lower
Lochkov
Upper
Pridoli
Ludlow
Wenlock
Lower
Llandovery
Silurian
Mount Easton F Z
Mount Useful F Z
Wilson Creek Shale
Coopers Creek Limestone
Eildon Sandstone
Boola Formation
Whitelaw Siltstone
Sinclair Valley Sandstone
Bullung Siltstone
McAdam Sandstone
unnamed siltstone
unnamed siltstone
no equivalent
Wurutwun Formation(?)
no equivalent
Wurutwun Formation(?)
Murderers Hill Siltstone
Snake-Edwards Sandstone Member
Murderers Hill Siltstone
Serpentine Creek Sandstone
Donnellys Creek Siltstone
Lazarini Siltstone
Table 2.54 Jordan River Group—units and lithology
Wurutwun
Formation
Wilson
Creek
Shale
100–180 m of mostly siltstone with minor coarse lithic
clastics, shale, chert. Coarse rocks are very impersistent.
Siltstone is similar in all respects to Murderers Hill
Siltstone except for abundant small and large-scale softsediment deformation. Sandstone consists of subangular
quartz, volcanic grains, grains of sandstone in varying
proportions, includes discontinuous granulestone that is
a mixture of carbonate fossil fragments, quartz, chert,
basalt, minor feldspar. Occasional thick breccia/conglomerate with mudstone matrix contains clasts
2 m across, of lithic sandstone and granulestone, chert,
siltstone, basalt, limestone (Carey & Sandy, 1975).
Strong plastic deformation in many clasts of sandstone,
gritstone and siltstone shows that they were unlithified
when deposited. Harrison (1993) recorded black chert
beds persisting along strike for tens of metres, and black
siltstone making up the top few metres of the formation.
Limestone occurs as sharply bounded pods tens of
metres across with bedding discordant with the surrounding sedimentary rocks (Murray, 1878). The Deep
Creek body is least altered, with predominant lithology
of fossiliferous grainstone with a diverse biota mostly of
corals and crinoids (Fig. 2.99B). Lime mudstone is not
abundant, and a large proportion of the rock is cement.
(Sandy, 1975).
Monotonous thick-bedded black pyritic shale with
strongly bioturbated black siltstone at both base and top.
At Jacob's Creek near Erica, interbedded black shale and
limestone represents interfingering of the Wilson Creek
Shale and the Coopers Creek Limestone. At Seymour,
packages of shale alternate with thin siltstone beds (Fig.
2.100) that increase in frequency towards the top where
33 TASMAN FOLD BELT SYSTEM IN VICTORIA
Eildon
Sandstone
Coopers
Creek
Limestone
Boola
Formation
Murderers
Hill
Siltstone
Whitelaw
Siltstone
Sinclair V.
Sandstone
Bullung
Siltstone
McAdam
Sandstone
Serpentine
Creek
Sandstone
Donnellys
Creek
Siltstone
Lazarini
Siltstone
they occur together with sandstone (Edwards et al.,
1998). The shale is commonly pyritic, variably burrowed,
and in places forms chaotic slumps. A single limestone
lens at Coopers Creek is surrounded by the shale.
>500 m of medium to very thick-bedded turbiditic sandstone and interbedded siltstone; includes several
slumped beds, one of which contains limestone boulders
with tabulate coral heads (VandenBerg, 1975).
Base consists of limestone beds interbedded with graded
well-sorted pure chert conglomerate (Fig. 2.101A), overlain by a lower well-bedded limestone facies of various
biomicrites and sparites with several important features
in common that indicate they are resedimented (Rehfisch & Webb, 1993). Organic debris is an important
component, many show grading, geopetal structures are
random. Breccia (Fig. 2.101B) is poorly sorted, has open
to closed framework, clasts are identical to the micrites
and sparites. Upper massive limestone facies consists
largely of massive stromatoporoid–coral wackestone
with random orientation of bedding/geopetals in different clasts. Quarries at Tyers River and Coopers Creek
are for lime, cement and paper manufacture (McHaffie &
Buckley, 1995a).
Siltstone, similar in all respect to that of the Whitelaw
Siltstone, is intercalated with great variety of coarse
clastics. At Coopers Creek these include lithic sandstone/granulestone with abundant fragments of Cambrian metabasalt and chert (Fig. 2.99A), and Devonian
recrystallised limestone, interbedded with units of
slump-folded mudstone. Lithic components are characteristic in all outcrops. Sizeable lenses of limestone are
apparently hosted by lithic sandstone and granule conglomerate. North of Coopers Creek, includes strongly
lenticular very coarse clast-supported conglomerate with
mostly resistant clasts (quartzite, vein quartz, chert). In
westernmost outcrops only very thin beds of mafic lithic
sandstone remain (VandenBerg, 1975).
Thin to thick-bedded finely laminated siltstone/silty
shale with occasional fine sandstone (VandenBerg et al.,
1995). Snake-Edwards Sandstone Member consists
of ~220 m of well-bedded and banded siltstone with
interbedded thin quartz/lithic sandstone, occasional
thick beds of black shale. Sandstone shows depositional
banding of a few millimetres thick but usually no systematic grading.
600–1000 m of finely banded siltstone similar to the
Donnellys Creek Siltstone, with occasional burrows,
minor very thin sandstone, and rare thick-bedded sandstone (VandenBerg, 1975).
300 m of thick-bedded fine sandstone and interbedded
banded siltstone and thin sandstone and rare thin black
shale (VandenBerg, 1975).
~600 m of finely banded, structureless or burrowed
siltstone with rare thick sandstone, massive siltstone
with abundant shell grit at top (VandenBerg, 1975). The
banding is identical to that in the Donnellys Creek Siltstone. Sandstone beds show sedimentary structures
characteristic of turbidites.
>500 m of poorly sorted medium to thick-bedded dark
sandstone, banded siltstone, rare shale (VandenBerg,
1975). Sandstone shows similar features to Serpentine
Creek Sandstone.
Generally medium and thick-bedded sandstone (Fig.
3.46A), in some cases forming amalgamated units tens of
metres thick and occasionally with granule-sized basal
layers and abundant mud intraclasts, and siltstone
(VandenBerg et al., 1995). Detrital muscovite, although
minor, is prominent. Turbidites show a suite of Bouma
sequences and well-developed normal grading. Interbedded siltstone forms packages from a few metres to 200 m
thick and is finely banded (Fig. 2.102B), as in Donnellys
Creek Siltstone, or bioturbated, as in Lazarini Siltstone.
~450 m of monotonous, thick-bedded siltstone, uniformly
finely banded (VandenBerg et al., 1995). Fine parallel
banding in the siltstone consists of 1–2 mm thick parallel laminae of pale grey coarse silt that are persistent
but slightly crinkled, interbedded with somewhat thicker
beds of dark grey fine silt and clay. Coarser laminae are
richer in quartz and show no internal structure. Discrete
sandstone beds are extremely rare.
~625 m of grey siltstone with bedding in the form of
colour banding; abundant dark bioturbation blebs (Van-
denBerg et al., 1995; Fig. 2.102A). Generally shows no
grain size change across the beds, so that primary features disappear on weathering. The lowest portion contains interbedded thin fine quartz sandstone beds up to
several centimetres thick, spaced in the order of a metre
or so apart
Table 2.55 Walhalla Group—units and lithology
Montys Hut
Fm
Norton
Gully
Sandstone
Yeringberg
Formation
Dark brown, laminated to thickly bedded with planar
and laterally continuous beds. Siltstone predominates
but in places it is rhythmically interbedded with laminae
and thin beds of very fine to fine sandstone, most of
which have ripples and cross bedding.
Sandstone-dominated packages may range from tens to
hundreds of metres thick, are interbedded with intervals
of thin-bedded siltstone and packages of sandstone and
siltstone. Conglomerate and diamictite are associated
with some sandstone packages. Sandstone in the sandstone-dominated packages is generally poorly sorted
quartzwacke, forming thick beds, interbedded with minor thinly bedded sandstone, siltstone and shale (Figs
2.103A, B). Some beds have pebbly bases, many show
normal grading above bases that are smooth to irregular
and erosional, or have load casts. Many have Bouma
sequences. Laminated siltstone packages are of similar
thickness, consist of finely laminated siltstone (Fig.
2.103C), with thin interbedded sandstone commonly
showing fine cross laminations. Siltstone lamination
tends to be perfectly smooth, in contrast to the crinkly
lamination typical of Jordan River Group siltstone.
At least five conglomerate beds occur at Eildon and
east of Bonnie Doon but none in the Walhalla area. They
have closed framework of well-rounded pebbles of
quartzite, vein quartz, sandstone, occasionally granite
and limestone. Diamictites have a very open framework
with similar pebbles in a siltstone/sandstone matrix
(Fig. 2.103D), often with deformed clasts of siltstone.
Small to moderate-sized (tens of metres) bodies of pure,
often richly fossiliferous recrystallised limestone (“Loyola limestone” of Talent, 1965b) occur together with
conglomerate and sandstone east of Bonnie Doon.
Basal portion of thick-bedded mudstone, usually very
richly fossiliferous and with occasional slump folds, and
massive, thick-bedded calcareous siltstone is followed by
fairly thick-bedded turbiditic sandstone and some shale,
with occasional pebbly sandstone beds containing quartz
and quartzite pebbles (VandenBerg, 1971, 1988).
Table 2.56 Cathedral Group—units and lithology
Unnamed
upper unit
Koala
Creek
Formation
>1500 m mostly finely laminated dark brown–green siltstone and claystone. Sedimentary structures in the subordinate thin to thick-bedded sandstone (greywacke and
litharenite) include massive bedding, planar lamination,
tabular cross bedding and wrinkle and ripple marks
(Ryan, 1992).
Red and green sandstone ranges from litharenite to
quartzarenite, is strongly lenticular because of channelling especially in thicker units, shows sedimentary structures including massive bedding, planar lamination, tabular and trough cross bedding, wave-rippled tops, occasional desiccation cracks (Fig. 2.104B). Sandstone contains
occasional basalt grains, accessory feldspar (Ryan, 1992).
Sandstone in the Koala Creek area shows similar features
although basal sandstone contains up to 30% feldspar
(Osborne, 1997) and occurs in smaller amounts in the
upper part of the formation. Above the basal sandstone is
a 700-m interval of green siltstone and sandstone with
desiccation cracks. Upper 1200 m is dominated by red
sandstone with abundant rip-up clasts in lower massive
portions and planar-laminated upper portions. Rippled
and wrinkled tops common, raindrop impressions occur.
Desiccation cracks very common in interbedded red mudstone (Osborne, 1997).
Table 2.57 Waratah Bay area—Devonian units and lithology
Liptrap
Formation
~3200 m of thin-bedded quartz-rich siltstone and sandstone with minor thick-bedded sandstone and gritstone
(Fig. 3.50), and rare diamictite which contains chert and
limestone pebbles (O’Connor, 1978). Most of the sandstone
35 TASMAN FOLD BELT SYSTEM IN VICTORIA
Bell Point
Limestone
Waratah
Limestone
shows various combinations of Bouma sequences, but a
few beds show signs of reworking in their upper portions.
Limestone pebbles which are abundant in the diamictites
all suggest derivation from the Waratah Limestone (Singleton, 1967).
Basal calcareous pyritic siltstone with coquina beds of
gastropods, overlain by about 70 m of dark, thinly stylobedded calcareous siltstone, limestone, dolomitic limestone (Fig. 2.105B) with corals and brachiopods, including
occasional stromatoporoid rudstone (Sandiford, 1978). The
lower part is composed of cycles (average 65 cm thick)
with bases of laminated calcareous mudstone and gastropod-bivalve coquinas, and tops of thicker pale grey peloidal wackestone and packstone (Spencer, 1995). Gastropods include both juveniles and adults and are dominated
by two species. Large polygonal mudcracks occur on the
upper surface of many cycles. The middle part comprises
fenestrate cycles with a basal 1–1.5 m thick unit of interbedded grey lime-mudstone/wackestone and black silty
recessive lime-mudstone, overlain by 0.5–0.6 m of thicker
pale grey wackestone/packstone containing numerous
vertical tubular fenestrae infilled with coarse calcite spar;
they are probably root moulds or burrows (Read, 1973).
The sparse faunal assemblage in the basal part of each
cycle is dominated by solitary rugose corals and brachiopods (Spencer, 1995). In the upper part, the fenestrate
cycles gradually merge upward into stromatoporoid cycles
2–3 m thick, each comprising a basal thin-bedded peloidal
wackestone, mudstone and calcareous siltstone grading
up into thicker pale grey wackestone, packstone and
grainstone packed with large broken and abraded fossil
fragments. Lower portions of cycles are dominated by
gastropods, brachiopods, ostracods and tabulate and solitary rugose corals whereas upper parts contain a more
diverse and abundant coral/stromatoporoid fauna (Spencer, 1995).
Kiln Member: ~64 m of massive to thinly stylobedded
mainly pelletal–echinoderm packstone and grainstone,
with skeletal grainstone in the upper portion. The uppermost 30 m has numerous solution cavities which contain
quartz–mica siltstone, some of them cross laminated, and
dark carbonate-rich siltstone identical to the lowermost
Bell Point Limestone (Sandiford, 1978). Some horizons
contain a higher faunal diversity, with green algae, bryozoans, solitary rugose corals and small stromatoporoid
colonies (Spencer, 1995).
Walkerville Member: A basal granule conglomerate,
composed largely of chert clasts, is overlain by 11 m of
thinly stylobedded sandy limestones and dolomites containing abundant silicified tabulate corals, brachiopods,
nautiloids and gastropods. Basal bed fills solution cavities
in Digger Island Marlstone (Sandiford, 1978; Fig. 2.105A).
Table 2.58. Timing constraints on the Tabberabberan Orogeny in Victoria.
Stratigraphic constraints
Radiometric constraints
Youngest deformed
rocks
Early or Middle Devonian Cathedral
Group (~385 Ma)
Early Devonian
Wentworth Group
(415–400 Ma)
Oldest overlying
Metamorphic mica
Syntectonic
Post-tectonic
rocks
ages
intrusion ages
intrusion ages
Whitelaw
Late Devonian
390–380 Ma (Mel375–350 Ma
Terrane
caldera volcanics
bourne Zone)
(370–355 Ma)
Benambra
Frasnian (Late
385 Ma
385 Ma
Terrane
Devonian) Lewis
(Kancoona Fault)
(Mudgeegonga
Farm Conglom.
Granite)
(370 Ma)
Summary: Well constrained by stratigraphic and radiometric constraints to the interval between 385 and 380
Ma. Final but much weaker deformation straddles the age of the Woods Point Dyke Swarm (~376 Ma) and may have
extended to about 370 Ma.
Table 2.59 Middle Devonian orogenic gold deposits (Bendigo Zone and western part of Melbourne
Zone)
Table 2.59 Middle Devonian orogenic gold deposits (Bendigo Zone and western part of Melbourne
Zone)
Structural architecture and timing
Deposits in the Melbourne Zone occupy brittle faults and stockworks in
fold crests (Gao & Kwak, 1995). Mineralised faults are associated with N–
S compression (e.g. Nagambie mine, Bailieston deposit, Rushworth goldfield—See fig. 3.43). Controls on mineralisation in the Bendigo Zone are
less well understood, although reactivation of Benambran faults appears
to be important. Veins are thin (mostly <20 cm), occupy faults and fracture stockworks. Brittle deformation reflects shallow crustal levels (Fig.
2.45). Evidence of episodic brittle–ductile deformation is rare (e.g. few
veins are laminated) but hydraulic fracturing points to fluid pressures
exceeding lithostatic pressure. Under these conditions, heterogeneities in
rocks are critical to gold segregation. Mineralisation mostly occurs in
dykes and thick sandstone beds showing brittle deformation (e.g. Bailieston, Golden Mountain), and in permeable clastic rocks. Host rock permeability and ‘fluid choking’ are considered important in forming disseminated mineralisation (Kwak & Roberts, 1996).
Hydrothermal alteration
Alteration envelopes are thinner and less complex than in older deposits
and are characterised by abundant carbonate and sulphide; sericite and
chlorite are rare (Gao & Kwak, 1997). Paragenesis is fairly uniform (Fig.
3.53). Carbonates (siderite, ankerite, dolomite, ferromagnesite), chlorite,
sericite, pyrite, arsenopyrite, gold, stibnite and less common chalcostibnite are important alteration products. Metasomatism is similar to older
deposits (Fig. 3.54).
High antimony content points to the lower end of the temperature zonation model of Nesbitt et al. (1989)—consistent with lower ore fluid trapping temperatures measured by Changkakoti et al. (1996). The Jamieson
mercury deposit in the Melbourne Zone may represent the lowtemperature end-member of Nesbitt et al. (1989).
Stable isotopes
Uniform hydrogen and oxygen isotope values in ore fluids in deposits in
the Melbourne and Bendigo zones point to an evolved meteoric water
origin. Sulphur isotope values are consistent with sulphur leaching from
country rocks by convecting meteoric hydrothermal fluids.
In both zones, values of D in fluid inclusions are distinctly lower in
quartz associated with stibnite (–100 to –70‰) than associated with gold
(–64 to –47‰; Changkakoti et al., 1996). Measured D and calculated 18O
values (at 200  50C) suggest an evolved meteoric water origin for antimony-bearing ore fluids in both the Bendigo and Melbourne zones (Fig.
2.50).
Changkakoti et al. (1996) attributed the wide range of 34S values of
stibnite (Bendigo Zone –4.9 to 1.2‰; Melbourne Zone –1.0 to 11.2‰) to
multiple sources of sulphur. Convecting meteoric hydrothermal fluids
leaching sulphur from heterogeneous country rocks could account for this
range. Limited analysis of diagenetic pyrite in the Melbourne Zone shows
34S values <12‰, compatible with the high-range end of stibnite values.
Sulphur in stibnite in the Bendigo Zone is relatively lighter, broadly
compatible with values for abundant older hydrothermal pyrite and
points to leaching of older hydrothermal sulphides.
Fluid inclusions
Fluid inclusions in Middle Devonian quartz paragenetically associated
with stibnite in the Bendigo and Melbourne zones have fairly uniform
homogenisation temperatures, around 200  50C, and low salinities
(Changkakoti et al., 1996; Fig. 2.50). Temperatures are distinctly lower
than in older quartz–gold veins (the same three broad categories of inclusions are recognised). Trapping pressures of these inclusions are approximately 1.4 kb and H2O–CO2 ratios are highly variable, probably indicating effervescing fluid, removing the need for pressure corrections
(Changkakoti et al., 1996).
Gayle, it would be nice if this table could fit in a single column, or perhaps slightly wider but still with
normal text fitting alongside it. Column 1 could be narrowed by running the text vertically.
Table 2.60 Radiometric ages of Upper Devonian cauldron complexes
Cauldron
Unit
Acheron
Snobs Creek Volcanics
Cerberean Volcanics
Sample
Age (Ma)
Minl
Method
Ref.
GA838
367 ± 22
TR
Rb/Sr
2
GA877
367 ± 22
TR
Rb/Sr
2
GA216
365 ± 90
TR
Rb/Sr
2
GA841
340
344
365
362
364
358
362
Bi
K/Ar
2
Bi
K/Ar
2
Bi
K/Ar
2
Bi
K/Ar
2
Bi
K/Ar
2
GA840
365 ± 6
367 ± 6
359 ± 15
Bi
K/Ar
2
GA919
361 ± 13
Bi
K/Ar
3
GA842
GA843
GA867
GA868
Rubicon Rhyolite
37 TASMAN FOLD BELT SYSTEM IN VICTORIA
Cerberean
Lake Mountain Ignimbrite
GA216
353
Bi
K/Ar
1
Donna Buang Ignimbrite
GA875
367 ± 6
Bi
K/Ar
2
GA876
367 ± 6
Bi
K/Ar
2
GA916
Bi
K/Ar
3
Bi
K/Ar
3
GA917
366 ± 13
368 ± 13
371 ± 13
Toole-be-wong Granodiorite
GA918
371 ± 13
Bi
K/Ar
3
Cerberean Volcanics
GA213
345
Bi
K/Ar
1
GA213
365 ± 90
Bi
Rb/Sr
2
GA213
365 ± 90
TR
Rb/Sr
2
GA214
365 ± 90
TR
Rb/Sr
2
GA837
345
Bi
K/Ar
2
GA839
346
Bi
K/Ar
2
GA217
348
Bi
K/Ar
1
Rubicon Ignimbrite
Lake
Ignimbrite
Dandenong
Mountain
355
Bi
Rb/Sr
2
GA217
359 ± 15
TR
Rb/Sr
2
GA214
353
Bi
K/Ar
1
GA215
351
Bi
K/Ar
1
Cerberean Ring Dyke
GA878
358 ± 10
Bi
K/Ar
3
Ferny Creek Rhyodacite
GA123
376 ± 6
Bi
K/Ar
1
GA909
370 ± 13
Bi
K/Ar
GA910
372 ± 13
Bi
K/Ar
3
GA911
370 ± 13
Bi
K/Ar
3
GA337
348 ± 8
Bi
K/Ar
3
GA835
362 ± 4
Bi
K/Ar
2
GA881
368
TR
Rb/Sr
2
Ranges
Wabonga
GA217
Tolmie Igneous Complex
423846- 5930103
Tolmie Igneous Complex
400724 -5872385
Ryans Creek Ignimbrite
1: Evernden & Richards, 1962; 2: McDougall et al., 1966; 3: Richards & Singleton, 1981.
TR Total Rock, Bi Biotite
Table 2.61 Marysville Igneous Complex—stratigraphy, distribution, lithology
Subgroup
Formation
Intrusive rocks
Acheron
Cerberean
Donna Buang
Rhyodacite
Distribution,
max. thickness
(m)
Lithology
Acheron
Hornblende porphyry dykes: large phenocrysts of plagioclase and aggregates
of green hornblende, rarer embayed quartz and biotite in a part glassy
groundmass. Hornblende has replaced enstatite.
Quartz–enstatite–biotite porphyry dykes: quartz, feldspar, biotite and enstatite (see Box 11—Pyroxene nomenclature) phenocrysts with occasional large
pink almandine and rare cordierite. Fine groundmass indicates rapid
chilling, shows flow banding.
Radial and ring dykes of granodiorite and granite porphyry
Varies from light to dark grey according to degree of crystallisation. Phenocrysts of plagioclase, biotite, enstatite, rare quartz and K-feldspar. Forms
single cooling unit.
Probably lava, large unbroken phenocrysts of plagioclase, small quartz,
aggregates of secondary biotite in a fine devitrified groundmass. Flowbanded.
Remarkably uniform, porphyritic, abundant phenocrysts of quartz, plagioclase, biotite, minor enstatite, almandine, rare orthoclase, very rare cordierite in a fine groundmass. Lithic fragments of underlying rocks occur at all
levels.
Light bluish-grey, porphyritic. Basal lenticulites overlain by a quartzofeldspathic mixture showing a gradual upward increases in grainsize, biotite, almandine and plagioclase abundances. Cordierite shows no overall
trend.
Lower ignimbrite is dark vitric-rich rhyolite with a eutaxitic texture, recrystallised. Upper ignimbrite is dark rhyodacite with abundant phenocrysts and
accidental lithics. Both are partly rheomorphic and contain andesite lithics.
Also includes felsic lava, tuff, volcanic breccia, sporadic porphyritic andesite,
sporadic diamictites with andesite and bedrock lithics, lenticular welded
felsic ignimbrite.
Acheron
Cerberean
Acheron—1000
Ythan Creek
Rhyodacite
Acheron—thin,
limited outcrop
Lake Mountain
Rhyodacite
Cerberean—900
Acheron—500?
Rubicon Rhyolite
Cerberean—390
Acheron—300
Robleys Spur
Volcanics
Cerberean—150
Acheron—200
Torbreck Range
Andesite
Cerberean—360
Blue Range
Formation
Cerberean—120
Snobs Creek
Volcanics
Cerberean—285
Wightmans Hill
Conglom.
Cerberean—30
Taggerty
Numerous lava flows ranging from andesite almost to basalt, intercalated
with volcanogenic sandstone and conglomerate. Lava is fine-grained, grey,
some vesicular with secondary minerals including zeolites, zoisite, chlorite,
and carbonate. The sedimentary rocks are very common and variable.
Thin-bedded siltstone and fine sandstone, lenticular and discontinuous.
Much of sandstone is quartz-rich but volcanogenic sandstone is also abundant, especially towards the top.
Pale ignimbrite with flattened pumice, occasional phenocrysts of quartz and
feldspar in densely welded/recrystallised groundmass, shows upward increase in biotite phenocrysts, upper part not welded.
Mainly rounded pebbles of quartz sandstone, locally grades to a well-sorted
sandstone. In some areas metamorphosed to hornfels.
Table 2.62 Mount Dandenong Volcanics—units and lithology
Ferny Creek
Rhyodacite
Kalorama
Rhyodacite
Mount Evelyn Rhyodacite
Coldstream
Rhyolite
Chilled glassy base shows traces of eutaxitic foliation
parallel to the sediment band below, but remainder is
completely recrystallised. Composition is virtually
identical to the Donna Buang Rhyodacite with similar
upward textural changes, becoming increasingly crystalline and phenocryst-rich. Shows slight drop in silica
content towards the top.
Lenticulite at base overlain by recrystallised dark vitric-rich ignimbrite with large phenocrysts of quartz,
feldspar, occasional almandine garnet. Overlain by thin
band of volcanogenic sediments.
Phenocryst-rich sequence shows upward gradation from
dominantly quartz to more abundant oligoclase and
orthoclase and some almandine at higher levels, and
plagioclase predominating at the top. Lithic fragments
are of bedrock and Coldstream Rhyolite. Overlain by
thin band of volcanogenic sediments.
Partly massive, partly finely flow banded and autobrecciated rhyolite lava. Dark greenish to bluish grey, with
occasional phenocrysts of andesine in a cryptocrystalline matrix of oligoclase and orthoclase, chloritised
biotite, little quartz. Shows increased vesicularity upwards.
Table 2.63 Wabonga Cauldron—eruptive history
Phase 2
significant collapse
block faulting and erosion
major collapse
Phase 1
localised lava eruption
tilting and erosion
limited collapse
Phase 3
pre-subsidence
Molyullah Ignimbrite
Toombullup Ignimbrite
Ryans Creek Ignimbrite
Cobbler Rhyolite
Hollands Creek Ignimbrite
Lewis Farm Conglomerate
Table 2.64 Volcanics of the Tolmie Igneous Complex
Molyullah
Ignimbrite
Toombullup
Ignimbrite
Ryans Creek
Ignimbrite
Cobbler
Rhyolite
Hollands
Creek
Ignimbrite
Lewis Farm
>200 m of densely welded ignimbrite
>700 m of recrystallised rhyolitic/rhyodacitic ignimbrite with biotite and garnet, in places enstatite.
Coarse, abundant phenocrysts of quartz, feldspar,
biotite, garnet. Schlieren of granodiorite porphyry
occur.
At least 450 m (Maher et al., 1997b) of rhyolitic
quartz ignimbrite, cordierite and garnet phenocrysts,
densely welded/recrystallised (Birch, 1978). Shows
upward zonation from a chilled dark base, to eutaxitic
and partly microcrystalline, to recrystallised. Folding
of flow bands, and rotation and deformation of biotite
and other phenocrysts, may indicate rheomorphic flow
in part (Brown, 1961).
Rhyolitic lava with garnet phenocrysts, and lava
breccia that is probably resedimented.
At least 300 m (Gaul, 1982 cites a maximum of about
200 m) of rhyolitic to rhyodacitic quartz ignimbrite
rich in large phenocrysts and moderately to densely
welded.
Upward-fining sequence of quartzose conglomerate
39 TASMAN FOLD BELT SYSTEM IN VICTORIA
Conglomerate
and interbedded sandstone consisting entirely of
basement clasts. Conglomerate is thick-bedded and
shows channel structures. From its distribution Gaul
(1982) inferred four distinct palaeovalleys, all flowing
to the northeast.
Table 2.65 Proposed correlation scheme and rock relations for the Howitt Province and Wabonga
Cauldron
****Table now done in Corel.
Table 2.66 Delatite Group—distribution and lithology
Formation
and
distribution
Lithology
Moroka Glen
Formation
Freestone Creek Anticline: rapid lateral variation,
with impersistent intercalated basalt flows. Some
sections dominated by boulder conglomerate, others
by sandstone. Massive boulder conglomerate forms
large lenses filling valleys in the underlying bedrock
and grade up into pebble conglomerate, then into
pebbly sandstone and stacked packages of thickbedded massive sandstone. Elsewhere the sequence is
mainly sandstone with uncommon red mudstone
(Buckley, 1982). Localised basal shale-clast breccia
has scoured base into underlying Silurian. Angular to
subrounded clasts are from Cobbannah Group.
Wellington River: ~180 m, upward-fining (Winter,
1984; O’Halloran, 1996). Basal breccia is of locally
derived Warbisco Shale and angular quartz; rhyolite
pebble abundance increases upwards. Breccia fines
upward into coarse sandstone, finely laminated siltstone and mudstone. A conglomerate with basalt
pebbles near the top is overlain by finely laminated
mudstone and thinly bedded graded sandstone. In
places bedding is disrupted close to intrusive rhyolite
bodies that have irregular peperitic contacts (O'Halloran, 1996).
Burgoyne Gap: sandstone, pebbly sandstone, minor
pebble and cobble conglomerate, grey mudstone
(O'Halloran, 1996). Many beds grade from pebble/cobble conglomerate to sandstone/pebbly sandstone. Sandstones are quartz-rich sublitharenites
with no obvious felsic volcanic material.
Mount Arbuckle: basal part is mudstone and fine
sandstone; massive and laminated mudstone units up
to 2 m thick have intercalated grey structureless
tabular beds up to 30 cm of fine sandstone and siltstone.
>1000 m mainly of red siltstone with 10–20% interbedded sandstone. Basal lithic sandstone ~300 m
thick shows overall upward coarsening and thickening (McNamara, 1982; O’Halloran & Cas, 1995).
Lower part is identical to the sandstone/mudstone of
the Callemondah Conglomerate. Local mottled red
mudstone (palaeosols?), rare mud cracks. Above the
lithic sandstone is a unit of pebbly litharenite and
sublitharenite, lithic sandstone, red mudstone and
minor buff/green mudstone (O’Halloran & Cas, 1995).
Upper part is of usually massive red siltstone, occasionally with crude bedding.
80 m of polymictic conglomerate of angular/rounded
pebbles of vein quartz, chert, siltstone, sandstone and
quartzite, intraclasts of red mudstone. Framework
closed to open, with a matrix of sandstone (sedolithic
litharenite). Crude imbrication, indicates flow to the
southeast. Red lithic sandstone/mudstone facies,
interbedded on scales of tens of centimetres to <1 cm,
comprises a significant proportion of the unit. Sandstones show parallel to wavy discontinuous bedding
with cross lamination. Thicker sandstone beds with
scoured bases and trough and tabular cross bedding
appear near the top and form channel shaped bodies
within massive to laminated red mudstone
(McNamara, 1982; O’Halloran & Cas, 1995).
Southern
Synclinoria
Kevington
Creek
Formation
Mansfield
Basin, Jamieson Syncline
Callemondah
Conglomerate
Mansfield
Basin, Jamieson Syncline
Table 2.67 Wellington Volcanics—distribution and lithology
Formation
Lithology
Southern synclinoria
Undifferentiated
Typical
phenocryst
assemblages
are
euhedral/fragmented quartz (65-75%), K-feldspar (20–30%)
and minor plagioclase with a vitric groundmass.
Metasedimentary lithic fragments are also variably
preserved.
Mount Sunday: Thick flows of densely welded, vitricrich, coarsely porphyritic rhyolitic ignimbrite with
abundant sedimentary lithic fragments at their bases;
underlain by open-framework pebbly debris flows (VandenBerg et al., 1976).
Mount Skene Creek area: quartz-phyric rhyolite
lava, often flow banded, is common (VandenBerg et al.,
1976).
Wellington River: Thin tuff underlain by two cooling
units, 160 and 40 m thick, of crystal-poor, densely welded/rheomorphic pumiceous quartz ignimbrites (Winter,
1984) The same features occur in the Burgoyne Gap
area (Vogel, 1991). Cooling columns are well-developed
in some areas.
Burgoyne Gap: A thin biotite-rich rhyolitic ignimbrite
is overlain by ignimbrites similar to those at Wellington
River. The top is a distinctive sedimentary facies of
thin-bedded coarse sandstone derived from the ignimbrite, and red mudstone. Numerous thin unwelded
units are intercalated within thicker more massive,
columnar jointed units (O'Halloran, 1996).
Glenmaggie Weir: Ignimbrite contains abundant
angular fragments of densely welded ignimbrite (O'Halloran, 1996). A thin interval of volcanolithic channellised sandstone/pebbly sandstone fines upwards. A
boulder conglomerate near Glenmaggie Weir contains
boulders of densely welded ignimbrite and is closely
associated with breccia with clasts of densely welded
ignimbrite.
Freestone Creek: A lower ignimbrite package ~105 m
thick is separated by a strongly lenticular sedimentary
unit 90 m thick from an upper volcanic package 60 m
thick. Buckley (1982) counted 4 main ignimbrite units,
each of them composite, with individual flows as thin as
7 m recognisable; one has overlying tuff with base-surge
features. All are quartz ignimbrites with moderate–
high phenocryst content and no mafic minerals. Intercalated volcanogenic sediment package has a lower interval of laminated mudstone and thin graded sandstone
(O'Halloran, 1996—Fig. 2.116), overlain by fluvial sandstone and red mudstone (Buckley, 1982). Conglomerate
contains metasedimentary and ignimbrite clasts, and
slumped units. Topmost package of mudstone has thin,
semi-continuous laminae of sand-sized, fragmented
volcanic quartz and K-feldspar crystals, and devitrified
felsic volcanic lithic grains (O'Halloran, 1996). Red
mudstone is locally important.
Mitchell River Gorge and the lower reaches of Cobbannah Creek: outcrops are of spherulitic rhyolite with
chalcedonic geodes (Howitt, 1877). The easternmost
outcrops at Mount Taylor and Mount Alfred lying
directly on the Mount Taylor Granite (G132), are of
coarse, moderately phenocrystic quartz ignimbrite with
biotite, almandine garnet and cordierite (Reeves, 1985).
Northwestern margin of the Macalister Synclinorium
Howitt Spur
Formation
Bindaree
Formation
1: Brown siltstone unit: ~400 m of relatively uniform
siltstone and thin sandstone similar in all respects to
the green mudstone unit of the Bindaree Formation
(O’Halloran & Gaul, 1997), with a rhyodacite unit
<50 m thick near the top.
2: Pebbly sandstone unit: <150 m of upward-fining
pebble/cobble conglomerate/pebbly sandstone, minor
mudstone. Conglomerate is thin, lens-shaped, with
sharp erosional base. Laminated green mudstone and
siltstone are interbedded. Sandstones are channellised
bodies interbedded with minor mudstone. Mudstone is
red to grey and generally massive (O’Halloran & Gaul,
1997).
1: Black shale unit: <50 m thick black shale and green
laminated mudstone; black shale contains freshwater
fossil fish (Long & Werdelin, 1986) and plants and
contains pyrite and gas expansion structures (Long,
1980).
2: Green mudstone unit: 50–400 m thick, laterally
equivalent to the boulder conglomerate unit, comprises
laminated green mudstone interbedded with thin sandstone and siltstone with sedimentary structures indicat-
41 TASMAN FOLD BELT SYSTEM IN VICTORIA
Refrigerator
Gap Dacite
ing deposition in short-lived moderate to low flow regime levels. The rocks have a large proportion of angular, fine, volcanic quartz.
3: Boulder conglomerate unit ~350 m thick. Most
distinctive is an association of massive pebble/cobble
conglomerate. <95% of clasts are felsic rhyolitic lava
and ignimbrite identical to Tolmie Igneous Complex
rocks; remainder are local basement rocks and minor
basaltic material. Includes lenses of volcaniclastic sandstone. Imbrication indicates sediment dispersal towards
the
southeast.
Channellised
pebbly
sandstone/conglomerate within the boulder conglomerate
unit have a higher proportion of vein quartz. Laminated/massive fissile mudstone and fine sandstone are
sparsely interbedded.
Thin tabular flows of massive lava and occasional hyaloclastite, with a 20-m thick unit of black laminated
shale intercalated (Gaul, 1995; O’Halloran & Gaul,
1997).
Mansfield Basin
Highton
Volcanics
3: Ignimbrite unit: 120 m (<80 m) welded garnetbearing rhyolitic ignimbrite with prominent fiamme
(McNamara, 1982).
2: Clastic unit: more persistent, 20 m of polymictic
volcanolithic conglomerate and volcanolithic and andesitic sandstone (McNamara, 1982). Conglomerate is
massive, has a large proportion of trachytic and rhyolitic volcanic clasts. Interbedded volcanic sandstone has
euhedral grains of volcanic quartz, K-feldspar, biotite,
minor recycled sedimentary grains and a distinctive
population of fine-grained, microlitic mafic grains
(O’Halloran & Cas, 1995).
1: Lava unit: restricted lenticular (10–20 m) lower unit
of andesite lava, flow breccia and andesitic volcaniclastics.
Table 2.68 Mansfield Group—distribution and lithology
Snowy
Plains
Formation
Mount
Kent
Conglom.
Main facies are broad channellised sandstone bodies
enveloped within red/purple/green mudstone (McNamara, 1982; O’Halloran, 1996; O’Halloran & Gaul, 1997;
Figs 2.117, 2.118). Buff, red and purple sandstone has
erosive and occasionally pebbly bases. Sandstones are are
litharenites with with ~70% quartz. Lithics are mostly
metasedimentary although felsic volcanic detritus is also
present. Trace amounts of plagioclase and blue tourmaline are common in sandstone (O'Halloran, 1996). Provenance is mostly lower Palaeozoic metasedimentary and
granitic bedrock; felsic volcanic detritus is generally less
than for underlying successions. Red mudstone lithofacies locally comprises more than 75%. Very thin
calclitharenite beds consist of quartz, plagioclase, fine
mudstone grains and micritic calcite. Occasional mud
cracks, asymmetrical linear to arcuate ripples.
South Blue Range: 120–340 m of coarse sandstone and
massive channellised cobble conglomerate grading laterally into pebbly sandstone, and upwards through pebbly
sandstone into cross bedded sandstone (McNamara,
1982). Cobble conglomerate is intercalated with pebbly
sandstone and minor mudstone. Clasts are mostly
quartzite/quartzose sandstone; minor rhyolite, dacite,
andesite, chert, jasper, slate and (intraclastic) siltstone.
Pebbly arenites are quartz-rich, contain variable
amounts of outsized, well-rounded quartz and metasedimentary pebbles (O’Halloran & Cas, 1995). Above the
basal conglomerate is a more continuous quartz sandstone unit (O’Halloran & Cas, 1995) with quartz pebble
sandstone, purple sandstone and siltstone with occasional tabular cross bedding.
Southern Synclinoria: 1: Thick-bedded red/purple
conglomerate interbedded with pebbly, partly feldspathic
sandstone and mudstone (O’Halloran, 1996; O’Halloran
& Gaul, 1997). Conglomerate and overlying pebbly sandstone lithofacies have clasts of sandstone, quartzite,
quartz, red mudstone, occasional rhyolite, and near Mt
McDonald rhyolite, rhyodacite, minor dacite. Matrix
includes of felsic volcanic detritus and bedrock fragments. Minor red mudstone lithofacies.
2: Pebbly sandstone and channellised sandstone lithofacies locally dominant, have same clast composition as
conglomerate, also includes mudstone and dark grey
slate/shale fragments (from the Mount Easton Shale and
Garvey Gully Formation) and rhyolitic clasts (from the
Wellington Volcanics). Pebbly sandstone units often
grade up into sandstone with quartz (plutonic and volcanic), metasedimentary, and devitrified rhyolitic lithics,
trace tourmaline. In the Freestone Creek Anticline,
sandstone contains rhyolitic matrix material that is
progressively replaced upwards by bedrock lithics (O'Halloran, 1996).
3: Red mudstone lithofacies envelops channel-form sandstone units.
Table 2.69 Combyingbar Formation stratigraphy
Combienbar and Buldah synclines
Unit 3
gradational
on Unit 2
Unit 2
gradational
on Unit 1
Unit 1
400 m (Buldah) and >300 m (Combienbar) of crumbly
massive red mudstone, rippled siltstone and subordinate
thin sandstone (2.281B). Sandstone is generally thin (<1
m), well-sorted, fine-grained and planar laminated to
tabular cross bedded. Soft-sediment slumping and water
escape structures occur in fine sandstone.
>400 m of thin-bedded red sandstone and red mudstone.
Sandstone occurs as single beds separated by thicker
intervals of mudstone as stacked successions at least 2–
3 m thick. Sandstone is mainly massive to diffusely planar
laminated; also includes tabular cross bedded and graded
beds with rippled tops.
Includes the Mount Puggaree Conglomerate Member;
thickly bedded pebbly sandstone, sandstone, mudstone. At
Combienbar it mainly occurs along the SE margin where
it is at least 100 m thick. The northern apex of the Combienbar Syncline consists of thickly bedded sandstone. At
Buldah, it occurs along the W and S boundaries and is
450 m thick. Locally the base consists of red mudstone and
sandstone (Twyerould, 1984).
Where the Mount Puggaree Conglomerate Member is
missing or thin, Unit 1 is dominated by pebbly sandstone
passing up into purple–red sandstone, generally with little
mudstone. Broad, shallow channels contain basal lag
gravels and mud chips. Mudstone abundance and thickness increase upwards. Pebbles are of Ordovician rock
types and vein quartz.
Genoa River
6
5
4
3
2
1
Upward-fining cycles of interbedded massive mudstone
and sandstone similar to unit 2. Sandstone commonly
with scoured bases and channel geometry. Broad, shallow
channels occur within stacked sandstone sequences.
Unit of stacked, mainly lens-shaped beds. Mudstone rare
and very thin (Fig. 2.119A). Most sandstone beds are
laterally discontinuous, some are pebbly.
Basal 15 m red massive mudstone is overlain by stacked
thin-bedded sandstone with slightly scoured bases (Fig.
2.119A). Sandstone package fines upward and at the top of
unit 4 is a second interval of massive mudstone.
Characterised by pebbly sandstone/sandstone bands 3 m
thick in stacks to 15 m thick, and green–red mudstone to
5 m thick. Channel-form pebbly sandstone has scoured
bases, lens-shaped beds, contains mainly Ordovicianderived pebbles.
Upward-fining packages of single and stacked beds of
sandstone and red mudstone. Coarsens upwards, includes
graded beds of coarse sandstone. Sandstone is generally
well-sorted and has relatively abundant feldspar and
muscovite.
Thin pebbly sandstone and minor conglomerate overlain
by a stacked succession of thin, fine- to medium-grained
sandstone beds with lens-shaped geometry.
Table 2.70 Timing constraints on the Kanimblan Orogeny in Victoria.
Stratigraphic constraints
Youngest deformed rocks
Oldest overlying rocks
Radiometric constraints
Metamorphic
mica ages
Syntectonic intrusion ages
Post-tectonic
intrusion ages
Late Devonian to Early
Early Permian Urana For360–340 Ma in
340–325 Ma in
Carboniferous Mansfield
mation (Ovens Graben)
New South Wales
New South
Group and Combyingbar
(300–270 Ma)
Wales
Formation (~360 Ma)
Summary: Deformation at about 360–340 Ma, poorly constrained in Victoria to younger than 360 Ma on stratigraphic
grounds.
43 TASMAN FOLD BELT SYSTEM IN VICTORIA
Table 3.1 Structural subdivisions of the Tasman Fold Belt System in Victoria
Fold Belt
Delamerian
Lachlan
Terrane
Zones
Glenelg
Grampians–Stavely
Moyston Fault
Whitelaw
Stawell
Bendigo
Melbourne
Governor Fault (Baragwanath
Transform prior to Middle Devonian)
Benambra
Tabberabbera
Omeo
Deddick
Kuark
Mallacoota
Note: Major boundary faults are shown in italics.
Table 3.2 Glenelg Zone—characters of geophysical subzones
Name
(Fig. 3.2)
Geophysical character
Magnetic
Nolans
Subzone
Glenelg River
Metamorphic
Complex
Cogumbul
Domain
Ozenkadnook
Subzone
Generally low, but with rare
highly magnetic layers
Mostly weakly or nonmagnetic,
one moderately magnetic domain.
Moderately magnetic; includes
reversely magnetised units
Nonmagnetic, distinctive moderately to strongly magnetic layers; mostly high background
from magnetic rocks at depth.
Nonmagnetic with distinctive
moderately to strongly magnetic
layers
Upson
Subzone
Gravity
Moderate to high
Very high, especially in S, moderate in
N
High
High to very high
Moderate to high
Table 3.3 Structures in the Glenelg River Metamorphic Complex
D1 S1 is locally preserved in F2 crenulation hinges (Anderson & Gray,
D2
1994) or as a fine lamination in amphibolite (see Fig 2.21) or schist
(Kemp, 1995). F1 microfolds are rarely preserved in schist and
amphibolite. In migmatite and schist in the Harrow area, leucosomes have segregated along the S1 schistosity (Kemp, 1995).
As the biotite isograd is approached from the W, progressive overprinting of the second cleavage, S2 on S1 is accompanied by tight to
isoclinal F2 folds plunging to NW (Gibson & Nihill, 1992). S2 becomes dominant in the biotite and higher zones with S 1 commonly
transposed and obliterated by it. In pelitic and amphibolitic schist
S2 is a finely differentiated schistosity. F2 folds are upright and
verge SW (Gibson & Nihill, 1992) and appear to be co-axial with
F1. Zones of extreme D2 deformation have intrafolial folds, boudinage and a strong stretching lineation parallel to F2. In the Wando
Vale area several I-type tonalites and granodiorites contain the S2
foliation, which is strongest along their margins, and a down-dip
stretching lineation. Plutons were not emplaced during D2 (contra
Gibson & Nihill, 1992; Anderson & Gray, 1994) because schist
enclaves at the southern margin of the Wando Tonalite (G421)
display S2, hence the tonalite is post-D2 and the strong granite
foliation, though parallel to S2, must be younger. In the Wando
Vale area several high-strain zones developed on the limbs of F2
folds indicate SW transport, as do local S–C fabrics in the tonalites
(Gibson & Nihill, 1992).
In the Glenelg River between Dergholm and Burke Bridge S2 has a
similar character to that in the Wando Vale area, with strong
development in pelitic schist and amphibolite, and a weaker presence in the I-type Ferres Creek Tonalite (G423; Ferguson, 1993),
but the dominant strike is NE, at right angles to that to the immediate south. F2 axes plunge moderately NE (Ferguson, 1993). A
major fault that must separate this zone from the area to the S
must also strike NE, cutting across the regional structural grain of
the complex.
In the Harrow–Balmoral area S2 is the main fabric in both
metasediments and those S-type granites that carry a fabric
D3
D4
D5
(Kemp, 1995). Foliation in S-type granite in Chetwynd River and
Pigeon Ponds Creek also appears to be S2, as it has the same orientation as S2 in adjacent areas. Along Glenelg River, S1 layering is
folded into tight F2 folds. Layers of leucosome and pegmatite veins
parallel to S1 display ptygmatic F2 profiles. Parallel to F2 is a
strong rodding defining L2, which becomes the dominant structure
in many outcrops (Gibson & Nihill, 1992; Kemp, 1995). Transposition of S1 into S2 and boudinage along this transposed foliation are
common (Fig. 2.20A).
Several shear zones are parallel to S2 and have NE over SW shear
sense (Gibson & Nihill, 1992). In the E of the complex at Yarramyljup Creek, the Woodland Shear Zone, about 1 m wide, cuts
sillimanite-bearing schist, but within the shear zone is fine-grained
tremolite schist, presumably from an ultramafic protolith. The
shear zone trends NNW, parallel to the strike of adjacent schist,
and is subvertical It is probably a D2 structure. S–C fabrics indicate dextral strike-slip movement with but later kink folds overprinting it. The presence of ultramafic rock in the shear zone suggests a large displacement.
D3 has formed close to tight mesoscale folds in rocks of biotite
grade and higher. In the Wando Vale area a weak S3 crenulation
schistosity is axial planar to F3 folds in pelites and some amphibolites; quartzose and calc-silicate rocks have no axial planar fabric
(Anderson & Gray, 1994). F3 axes are usually parallel to F2 (Anderson & Gray, 1994), although local departure from this is seen in
type 2 fold interference patterns in Corea Creek. Complex relationships between pegmatite intrusion and deformation are also
evident in Corea Creek (Fig. 3.4B). Migmatites commonly show
complicated fold interference patterns, partly due to the extremely
plastic nature of these partially molten rocks (Fig. 3.4C).
Along Glenelg River between Dergholm and Burke Bridge and east
of Harrow, F3 folds are open to close, plunging at moderate to low
angles to the N and NW (Ferguson, 1993; Kemp, 1995), typically
with no axial planar fabric. Mesoscopic F3 folds range from outcrop
scale to map scale. North-trending folds in Robson Creek appear to
be of the same generation. F3 has a similar orientation throughout
the complex, even in the Burke Bridge area where S2 has an
anomalous strike. This indicates that the fault that bounds the
zone of NE-striking S2 here pre-dates D3. D3 has left little imprint
on granites that were intruded during D2, although the S2 granite
foliation shows rare close folds (Fig. 3.4D) that are probably F3.
D4 has only affected the northeastern part of the complex, producing close to open crenulations in S2 or S3, with no axial planar
fabric (Kemp & Gray, 1999). F4 axes plunge at low angles, mainly
to the north (Kemp, 1995).
D5 has affected much of the complex, producing steep open folds
(labelled F4 by Anderson & Gray, 1994 and Ferguson, 1993). The
axial planes strikes NE but have no associated fabric. Mesoscopic
folds are either gentle, curved structures or kink folds (Anderson &
Gray, 1994; Kemp, 1995). Some late syntectonic granites in the
Harrow area have F5 folds outlined by micaceous schlieren (Kemp
& Gray, 1999). F5 has also imparted broad map-scale folds, as at
Wando Vale (Anderson & Gray, 1994). This latest deformation
resulted from NW–SE compression, at a high angle to the previous
shortening events.
Table 3.4 Grampians–Stavely Zone—summary of geophysical subzones (Fig. 3.2)
Name
Geophysical character
Interpreted
rock types
Structure
Tectonic setting
Generally simply deformed, low-grade,
single cleavage although locally schistose
and of higher grade.
Late sinistral movement on some faults.
Weakly deformed and
metamorphosed in
outcrop. Fault intercalation of various volcanic and sedimentary
rocks. Late extensional(?) faults
Weakly deformed and
metamorphosed, fault
intercalation of various
volcanic and sedimentary rocks.
Ocean floor (mafic) and
overlying sedimentary rocks
plus later syn-orogenic (intermediate to felsic) and
post-collisional(?) volcanics.
Magnetic
Gravity
Miga
Subzone
Low, with weakly to moderately
magnetic zones
Moderate to
high; increases
to W and S
Intermediate, mafic and
felsic volcanics, black
slate and quartz-rich
turbidites. Typically
greenschist metamorphic
grade.
Dimboola
Subzone
Abundant
strongly magnetic units, particularly in the
north under
cover
Low flanked
by two highs
Linga
Subzone
Low, with weakly to moderately
magnetic zones
Moderate to
high
Predominantly quartzrich turbidites and intermediate volcanics in
outcrop. Poorly known
Dimboola Igneous Complex increases in extent to
N.
No drillhole control. Interpreted as predominantly quartz-rich turbidites and intermediate
volcanics.
Largely syn-/late orogenic
rocks derived from early
pulses of Delamerian Orogeny. Dimboola Igneous Complex of uncertain origin,
possibly accreted island
arc/forearc
Largely syn-/late orogenic
rocks derived from early
pulses of Delamerian Orogeny.
45 TASMAN FOLD BELT SYSTEM IN VICTORIA
Table 3.5 Major faults in the Delamerian Fold Belt in Victoria
Yarramyljup
Fault
Hummocks
Fault
Escondida
Fault
The fault is the eastern limit of the Glenelg River Metamorphic Complex. First recognised by Gibson and Nihill (1992), it separates amphibolite facies schists from
slates. A mylonite zone on the W side is several hundred
metres wide. Magnetic and gravity data show it to extend as far N as the Escondida Fault beneath the Murray Basin. To the S it appears to extend onto the marine
continental shelf. The fault is probably steeply dipping
as foliations either side are steep. A strongly transposed
mylonitic S2 fabric in schists along Yarramyljup Creek
(Gibson & Nihill, 1992) may be part of a high-strain zone
related to the fault, in which case a syn-D2 age is indicated. A dip-slip component of movement is likely, bringing high-grade rocks up on the west side, but the juxtaposition of high against low-grade rocks could have resulted from major strike-slip. It continues under cover
well into NW Victoria. Gibson and Nihill (1992) suggested that the Yarramyljup Fault was continuous with the
Lanterman Fault Zone in Antarctica, which adds at least
another 500 km of strike length to the fault. The Grampians Group appears to cover the fault, constraining
movement to before the Ordovician(?)–Silurian.
Separates low-grade rocks from biotite zone and higher
grades. The boundary, through the Hummocks Serpentinite, is recognised as a convex-east break in the gravity
as far south as the continental break of slope. North of
the Hummocks it is stitched by the Dergholm Granite
and other granites of the Padthaway Ridge.
Separates the Miga and Dimboola subzones. Interpreted
from geophysics under cover sequences in the north
(Moore, 1996a) and mapped in the Grampians region
(Cayley & Taylor, 1996), where an easterly dip was
interpreted. The fault trends approximately 335 and
can be traced for about 400 km, obliquely truncating
more N-trending structures in zones farther west, including the Yarramyljup Fault and Glenisla Fault System NE of the Black Range. Movement sense is difficult
to determine, but large scale dip-slip or strike-slip displacements may have occurred. Absence of associated
faulting in the Grampians Group suggests the fault is a
Delamerian structure. The southerly extent is difficult to
determine. A major, apparently west-dipping fault occurs near Chatsworth SW of Mt Stavely, between
greenschist facies rocks on the west from low-grade Mt
Stavely Volcanic Complex and Glenthompson Sandstone
on the east (Stuart-Smith & Black, 1999). This is intruded by the Late Cambrian Bushy Creek Granodiorite,
thus constraining its movement to Late Cambrian. It
may link into the Escondida Fault.
Table 3.6 Examples of fault duplication in the Grampians thrust-and-fold belt
In the Mount Stapylton region (northern Grampians) the Thermopylae
Fault ramps through the Murray Hill Sandstone to duplicate that formation and part of the overlying Kalymna Falls Sandstone south of Flat
Rock. The distinctive radiometric signature of the thorium-rich Murray
Hill Sandstone mirrors the duplication.
The Salamis Fault and the structurally higher Plataea Fault are widespread faults, both occurring at the contact between relatively incompetent
redbed mudstone and overlying massive sandstone. The Salamis Fault
ramps through a considerable thickness of sandstone and mudstone just
east of Halls Gap, resulting in an apparent repeat of this succession farther
S in the Mount William Range. North of Halls Gap in the N limb of the
Wartook Syncline, the Salamis Fault lies subparallel to bedding and the
extra package seen farther S is absent.
The Leuctra Fault lies variously within or at the boundary between the
Silverband Formation and the overlying Serra Sandstone. A splay is well
exposed at Cool Chamber in the Wonderland Range. Just to the S, part of
the hanging wall sequence, including the distinctive Wannon Sandstone
Member, becomes locally duplicated across a possible lateral ramp near
Dellys Dell.
A three-dimensional outcrop west of Mount Rosea shows the Granicus and
Mantinea faults branching and enclosing a large thrust sheet of duplicated sandstone which extends N into the Mount Difficult Range. Outcrops of
the branch triple-points here and at Mount Difficult are the best examples
of lateral ramp faults and thrust triple-points in the Grampians.
Faults in the Victoria Range separate imbricated packages of redbed
mudstone and quartz sandstone and in the light of structures seen in the
main ranges, these can be interpreted as imbricated Silverband Formation
and Mount Difficult Subgroup, with the Trebbia, Trasimene and Cannae
faults as best examples.
Table 3.7 Key evidence for the Marathon Fault
The fault and underlying bedrock are exposed in the SE (Spencer-Jones,
1965). In the Behncke quarry near Dunkeld, Grampians Group is
faulted over cleaved kaolinised Cambrian bedrock. The basal part of the
Grampians thrust stack (well over 1 km) is missing here, apparently truncated against this fault. Gentle veeing of the fault trace across the topography suggests that it dips about 20 W, sub-parallel to bedding.
Polydeformed schist occurs in dam spoil just E of the Mount Dundas
Range (Deeker, 1992). East-dipping beds in the range apparently truncate
against this bedrock and therefore cannot be continuous with the Victoria
Range sequence (contra Selwyn & Ulrich, 1867; Spencer-Jones, 1965).
Drillholes near Wartook have intersected Cambrian rocks in an area close
to the axis of the south-plunging Asses Ears Anticline, with Silverband
Formation exposed immediately to the S. Without a fault immediately east
of the drilled area, drillholes should have intersected very thick Red Man
Bluff Subgroup. Clearly a fault occurs between the drilled area and outcropping Grampians Group. Either this is steep, with a large vertical displacement and a highly sinuous trace, or it is a low-angle structure, underlying the Grampians Group and responsible for truncation of at least half
the group’s thickness.
In the Black Range, Cambrian bedrock is exposed along the southern
margin of the range and completely surrounds Mount Bepcha. The Grampians Group in this region dips consistently west (with minor folds) and
overlies exposed Cambrian bedrock with a sub-horizontal contact that
locally becomes elevated over a strike ridge of metavolcanics. It can be
demonstrated here that the Grampians Group here does not continue to
any depth, in spite of its consistent regional W dip. A near-horizontal fault
is therefore required to explain this outcrop pattern.
Preliminary modelling of gravity data by P.A. McDonald suggests that
the thickness of the Grampians Group is unlikely to exceed 1.5 km, even in
the vicinity of Halls Gap and beneath the Mount William and Serra Ranges. Modelling assumed an average density of 2.8 x 10 kg3/m3 for basement
and an average density of 2.6 x 10 kg3/m3 for Grampians Group. The depth
estimate is significantly less than would be expected if the full thickness of
deformed Grampians Group was present.
Table 3.8 Comparison of structural subdivisions in the southern Lachlan Fold Belt
Terranes
Victorian
zones in this
publication
Whitelaw
Stawell
Bendigo
Melbourne
Tabberabbera
Omeo
Deddick
Benambra
Kuark
Mallacoota
Equivalent New South Wales
zones (after Glen, 1992;
italics = Scheibner & Basden,
1996)
Main subdivisions of the
south of the Lachlan Fold
Belt (Gray, 1997, after
Glen, 1992)
Western Lachlan Fold Belt
Main subdivisions of
the South Lachlan
Fold Belt (Glen &
Walshe, 1999)
Southwestern Belt
Tabberabbera and Howqua
Wagga–Omeo
Canberra–Buchan
Snowy Plains
Hill End–Cooma
Kuark
Capertee–Mallacoota
Mallacoota–South Coast
Central Lachlan Fold Belt
Western Belt
Central Belt
Eastern Belt
Eastern Lachlan Fold Belt
Table 3.9 Characteristics of orogenic gold mineral domains1
Ballarat
Controls and timing: Main mineralisation was synkinematic spanning
folding through to late-tectonic faulting. While tectonism was chiefly
driven by the Benambran Orogeny—characterised by E–W compression,
late strike-slip movements along mineralised faults under N–S compression may reflect reactivation related to the Bindian Orogeny. Ar/Ar data
show episodic mineralisation at 440 Ma and between 420–400 Ma. Deposits mostly occur in greenschist facies rocks with structures of transitional brittle–ductile behaviour, are concentrated in the hanging walls of
large high-angle reverse faults, implying these acted as plumbing systems for gold-bearing fluids (Cox et al., 1991b). Ore fluid trapping temperatures decrease from W to E from 300C to 270C. Remobilisation of
orogenic gold during Early and Late Devonian magmatism was unimportant.
1
After Hughes et al. (1997).
47 TASMAN FOLD BELT SYSTEM IN VICTORIA
Key minerals: Veins have very low sulphide, on average <2%, and a
pyrite–arsenopyrite association. Only minor base metal sulphides are
present—predominantly galena, sphalerite and chalcopyrite, as well as
rare pyrrhotite. Trace antimony, where present, occurs as lead–copper–
antimony sulphosalts rather than stibnite. Silver minerals are absent
and the silver content of is gold low (average 4%).
Stawell–Ararat
Controls and timing: Main mineralisation lies in the hanging wall of
the E-dipping Pleasant Creek Fault, a major structure which links to the
NW with the Moyston Fault. Mineralisation occupies ductile–brittle
reverse shear zones related to back-thrusts like the Stawell Fault, and
are traced N and S away from Stawell. Mineralisation was localised due
to competent behaviour of Magdala Volcanics during deformation. The
structural style and mineral assemblage of many of the deposits point to
high emplacement temperatures consistent with late exhumation of the
mid-crustal Moornambool Metamorphic Complex along the Moyston
Fault. Main gold emplacement, dated at Magdala–Stawell at 440 Ma,
occurred in the waning phases of regional deformation. Remobilisation of
gold after 400 Ma was relatively unimportant.
Key minerals: Mostly similar to pyrite–arsenopyrite in the Ballarat
domain but is sulphide-rich close to Magdala Volcanics. Assemblages
contain pyrrhotite–stilpnomelane–biotite in addition to pyrite–
arsenopyrite–chalcopyrite.
Landsborough–Percydale
Controls and timing: At a regional scale mineralisation is concentrated
in the hanging walls of major reverse faults, while locally main mineralisation occupies brittle–ductile reverse faults and related extensional
arrays. Quartz–gold veins emplaced along younger faults (e.g. conjugate
NE and ESE faults, and horizontal faults) are less important. Fluid
inclusion and isotope studies show carbonic ore fluids of moderate temperature and low salinity. Mineralisation is concentrated in carbonaceous/pyritic beds in the Beaufort Formation which appear to have acted
as chemical traps. Magmatism post-dates main gold emplacement.
Key minerals: Deposits adjacent the Landsborough and Percydale
faults contain high silver and significant galena in addition to pyrite and
arsenopyrite. Sulphide content is locally <25%. Silver content of gold is
commonly <10% and up to 50%.
Costerfield
Controls and timing: Mineralisation is generally associated with Tabberabberan group 3 folds and faults which trend E–W indicating N–S
compression. Ore fluids have low formation temperatures (200  50C)
implying emplacement at shallow levels. Dykes and thick sandstone beds
which have deformed in brittle fashion, and permeable clastic units, are
preferentially mineralised. While widespread in the Melbourne Zone,
only eight deposits are known in the Bendigo Zone.
Key minerals: Characterised by minor to massive stibnite, with a few
percent pyrite–arsenopyrite, and trace chalcopyrite, galena, sphalerite,
berthierite and pyrrhotite. Gold occurs as native gold and aurostibite.
Woods Point
Controls and timing: Folding is more intense and metamorphic grades
higher than elsewhere in the Melbourne Zone, and mineral assemblages
and ore fluid temperatures are similar to Ballarat domain deposits.
Deposits have roughly the same distribution as the Woods Point Dyke
Swarm. Mineralisation was controlled by reverse faults with a strike-slip
component following the main Tabberabberan Orogeny. Mineralisation is
dated at 372  2 Ma, slightly younger than Woods Point Dyke Swarm
dykes.
Key minerals: Sulphide-poor, simple pyrite–arsenopyrite type as in the
Ballarat domain; gold is slightly more silver-rich (12–20%).
Chiltern
Controls and timing: In the N, main goldfields lie within a 25-km wide
corridor alongside the Kancoona–Kiewa faults. Most mineralised faults
trend NNW or N. Preliminary studies suggest that mineralisation followed the Benambran Orogeny and may be related to Bindian dextral
strike-slip fault reactivation. Main mineralisation is offset by Middle
Devonian strike-slip faults. The timing of mineralisation is better constrained in the S. At Haunted Stream mineralised faults resemble a
Riedel shear system related to dextral transport along the Haunted
Stream Fault (Willman et al., 1999a). The Haunted Stream Fault is
considered to be a late splay off the Kiewa Fault, probably by reactivated
strike slip late in the Early Devonian.
Key minerals: Simple arsenopyrite–pyrite assemblage as in the Ballarat domain; gold mostly contains <5% silver.
Bethanga
Controls and timing: Principal orogenic gold deposits form a narrow
corridor in Omeo Metamorphic Complex. The bulk of mineralisation was
formed late in the Early Devonian when SW movement of the High
Plains Subzone caused reactivation of major faults. Mineralised conjugate strike-slip faults formed at Mt Wills and in a zone of transtension
between the bounding Ensay Shear Zone and the Haunted Stream Fault.
Mineralised faults cut across Early Devonian granites i.e. post-date
Bindian Orogeny.
Key minerals: Mostly sulphide-rich, as high as 60% at Bethanga, and
up to 20–30% in other places. Sulphides are predominantly arsenopyrite–pyrite, but chalcopyrite, sphalerite and galena are locally important
(e.g. Bethanga produced more than 600 t of copper). Pyrrhotite is sometimes present. Ores and gold are silver-rich. Some veins have low sulphide.
Table 3.10 Stawell Zone—Structure in low-strain zones
Regional folds (F2) have a ‘similar’ style with horizontal to gently plunging hinges. A strong to weak slaty cleavage is axial planar to F 2 folds and
varies from a spaced non-penetrative cleavage in sandstone to a slaty
cleavage in siltstone. Folds between the Landsborough and Percydale
faults are much tighter and have shorter wavelengths than those east of
the Concongella Fault (Fig. 3.10C). Interlimb angles are 2 to 10 and
wavelengths range from 1 to 50 m. Between the Concongella and Landsborough faults, interlimb angles vary greatly from 5 to 60 and wavelengths vary from a few metres to kilometres (inferred from large-scale
younging reversals; Cayley & Taylor, in prep.).
Late brittle structures are designated D3–D4 and overprint D1–D2
ductile structures. NW-trending faults dipping 20–90 commonly have
associated quartz veins and gouge zones up to 1 m wide with fragments of
quartz and cleaved sedimentary rock. Some mineralised faults have been
traced for several kilometres along strike. In the low-strain zone east of
the Landsborough Fault, NE-trending subvertical cross faults are welldeveloped N of Beaufort. They appear to offset mineralised faults (D3?) by
dextral strike-slip and are therefore D4 structures. Small-scale subvertical cross faults and kinks elsewhere are similarly attributed to D4.
Table 3.11 Stawell Zone—High-strain zones
Landsborough high-strain zone
Displays a W-dipping penetrative schistosity, widely overprinted by NWtrending, asymmetric, E-verging folds and crenulations probably related
to polydeformation. Alternating pelitic and psammitic layers up to 1 m
thick that lie parallel to the intense schistosity appear to be transposed
bedding. In some outcrops the main schistosity is axial planar to rootless
isoclinal fold remnants that preserve fragments of bedding indicating
that folding accompanied cleavage development. The strong W-dipping
cleavage in the hanging wall zone is transitional with the S2 cleavage of
the low-strain zone to the W. A west over east shear sense is indicated by
these structures and by S–C fabrics, asymmetric pressure shadows and
asymmetric boudins. Mineralised W-dipping faults overprint the early
schistosity. The fault zone is stitched by Early Devonian granites. Common late brittle faults, kinks, crenulations and joints that overprint contact metamorphic mineral assemblages are probably related to the Tabberabberan Orogeny (Cayley & McDonald, 1995).
Percydale high-strain zone
Slate and schist have pervasive foliation (S2) that dips 50–80 W and was
formed during the regional D2 event. This cleavage forms axial planes to
rootless isoclinal fold remnants that are overturned to the E. Bedding is
often transposed parallel to the dominant cleavage. Small beddingparallel boudinaged quartz veins are sometimes folded. Pyrite crystals in
the Fiddlers Creek mine have well-developed pressure shadows that
parallel down-dip lineations in the plane of S2 cleavage. Cayley &
McDonald (1995) interpret these as resulting from later stage movements
along the Fiddlers Fault. D2 folds and cleavages weaken southward where
relatively open folds and weak cleavages strike NE, at almost 90 to the
regional D2 trend. The dominant S2 fabric is transitional with the secondgeneration fabric in the low-strain zone farther W. D2 structures are
overprinted by late brittle SW-dipping mineralised and unmineralised
faults, quartz veins, kinks and crenulation folds and cleavages, all attributed to D3–D4. Strike of brittle faults parallels D2 fabrics but many
faults have N or S-plunging slickenlines and the regional predominance
of NE-trending dextral faults (D4) suggests that D3–D4 was characterised
by progressive dextral transpression (Cayley & McDonald, 1995).
St Arnaud high-strain zone
49 TASMAN FOLD BELT SYSTEM IN VICTORIA
F3 folds in high-strain zone deform a prominent S2 cleavage as well as
concordant and discordant quartz veins. F3 folds have a chevron style, are
tight, predominantly subvertical, typically asymmetric, with a sinistral
vergence. Amplitudes and wavelengths range from 1 cm to tens of metres.
This strike-slip style of folding is superimposed on sub-horizontal regional
F2 folds, apparently developed during simple E–W shortening. North of
the Coonooer pluton, steeply NE-plunging Z-shaped folds (average 50)
and dextral asymmetry (Evans, 1993) may be equivalent to the F3 folds.
The fault zone has localised subvertical, NNE-striking crenulation
cleavage and a spaced cleavage axial planar to the F3 folds striking NNW.
In more pelitic rocks the cleavage grades becomes slaty and sometimes
schistose. Locally it grades into a set of subparallel fractures that are
longitudinal to F3 fold hinges. Many mesoscopic F3 folds merge into zones
of intense cleavage. Layer-parallel stretching shortening in folds is common, with inner arcs of larger F3 folds showing numerous small-scale
parasitic folds while outer arcs have a spaced S3a cleavage filled with
quartz. Neutral surfaces of no strain are common (Krokowski de Vickerod
et al., 1997).
Avoca high-strain zone
Earliest recognisable fabric is a differentiated quartz–mica layering sporadically preserved in millimetre-scale intrafolial folds—it is absent away
from the fault. Dominant fabric is a strong schistosity of differentiated
millimetre-scale layering of quartz and mica generally with steep W dip
except where reoriented (Fig. 3.18). With increasing strain towards the
fault the schistosity develops by intensification of the regional slaty
cleavage and begins to transpose bedding. It is subparallel to the limbs of
the nearly transposed isoclinal folds, overprinted and in places transposed by a patchy to pervasive zonal to discrete crenulation cleavage. The
late crenulation cleavage strikes slightly more westerly and in many
places has overprinted the schistosity at a low angle or completely transposed it so that a single composite foliation is preserved. Lineations and
kinematic indicators are largely lacking. In the most highly strained
exposures, sheared and boudinaged quartz veinlets lie subparallel to the
main schistosity with lineated surfaces plunging steeply to the S, almost
down-dip.
Table 3.12 Main faults
Moyston Fault
The fault is prominent on magnetic images as the boundary between a Ntrending set of cuspate magnetic anomalies (interpreted to represent
amphibolite), and less magnetic rocks in the footwall (variously interpreted as Glenthompson Sandstone and Mount Stavely Volcanics). N of
the Stawell Granite, a weak but straight and continuous linear magnetic
high, which links with exposures of the fault adjacent to Mt Drummond is
interpreted as a magnetic dyke intruded along the fault. Farther N, under the Murray Basin, the fault is generally taken as the W edge of a
magnetically distinctive package that may be the Moornambool Metamorphic Complex. This package extends north into New South Wales,
where it forms the E edge of the Wentworth Trough. To the S, the fault is
covered by Newer Volcanics and the Otway Basin but is visible in the
gravity data where it can be traced as far as the coast. Just offshore, it
appears to be cut off by the Sorell Fault as it swings NE to become the
Bambra Fault. The position is also constrained by drilling traverses and
scattered outcrops in the Ararat region. Manifestations are changes in
the geochemistry of the granites and Newer Volcanics and significant
Mesozoic and Cainozoic uplift to the E (Foster & Gleadow, 1992).
Mt Drummond: forms a 50-m wide breccia zone separating gently deformed but overturned Glenthompson Sandstone from more strongly
deformed sedimentary and volcanic schist to the E. The breccia zone is a
belt of polydeformed schist with a folded main transposition schistosity
with parallel boudinaged quartz veins. The schist dips 85º NE with overprinting tight crenulation folds plunging S. Schist in the hanging wall
consists of intercalated metasedimentary and metavolcanic rocks metamorphosed to hornfels. Slickenside lineations on minor faults indicate
predominant dip-slip, subparallel to bedding (Cayley & Taylor, in prep.).
Moyston: separates intensely polydeformed mafic schist from low-grade
Glenthompson Sandstone to the W. In its only exposure, sheared cataclasite and talc–chlorite schist with a ramifying network of thin boudinaged quartz veins has been thrust over steeply E-dipping Glenthompson
Sandstone along a somewhat irregular fault plane that locally dips moderately SE. The final movement post-dates the formation of the highgrade minerals and ductile structures in the rocks in the hanging wall.
Late brittle fractures and cataclastic gouge zones and NW-verging folds
and kinks in the hanging wall schist in some outcrops indicate late brittle, sinistral-reverse movement. Glenthompson Sandstone in the footwall
has a single weak cleavage and has near-vertical pods of sandstone and
mudstone, probably relict bedding, partly disrupted into a tectonic mélange.
Coongee Fault
At the Ararat tip, a 50-cm wide zone of cataclasite and ferruginisation
dipping 80º SW is exposed. The fault plane separates simply deformed
low-grade slate (Warrak Fm) in the footwall from a tectonic mélange of
strongly sheared mylonitic chlorite schist and boudinaged siltstone. Other exposures are of highly strained chloritic schist grading to mylonite in
the hanging wall, with strongly transposed, steeply W-dipping fabric and
relicts of earlier, overprinted crenulation cleavage fabrics preserved between strong cleavage domains. The transposition schistosity is cut by
small, E-verging subhorizontal crenulations with axial planes-dipping
moderately E. Geometry of these structures is consistent with W over E
movement on the fault. Less deformed rock in the footwall is folded by
moderately N-plunging regional folds with E-dipping axial plane cleavage.
At Armstrong, the hanging wall is polydeformed quartz–sericite–
chlorite schist with a strong, steep SW-dipping transposition schistosity
and numerous parallel rodded quartz veins. In places metavolcanic rocks
are infaulted with schist. Mudstone in the footwall shows gently Nplunging open folds with a single axial plane slaty cleavage. To the N of
Armstrong, the hanging wall schist is a tectonic mélange metamorphosed
to biotite–cordierite hornfels in the aureole of the Stawell Granite. The
mélange consists of broken formation, aligned along a fabric with a moderate NE dip.
Concongella Fault
In outcrop just SE of Concongella Hill it breaches a regional-scale anticline defined by vergence of smaller-scale folds. The fault lies parallel to a
strong slaty cleavage that dips 65–70º NE and is axial planar to tight,
often slightly overturned folds. Metamorphic biotite along the fault trace
suggests locally higher metamorphic conditions. The fault plane is a ~50
m wide zone of strong cleavage and numerous thin parallel quartz veins
dipping 70º NE, refolded by tight, E-verging, S-plunging crenulation folds.
In slate nearby, cleavage dips 70º E and has a strong down-dip lineation
interpreted to lie parallel to the transport direction. Rock in another
outcrop shows stretched and folded parallel quartz veins and a strong
NE-dipping cleavage.
South of the Stawell Granite the trace may parallel a suite of Edipping quartz veins that appears to have intruded its footwall (Krausé,
1873). A smaller parasitic fault just to the E and visible in the magnetic
data has vergence that shows it also breaches a broad anticline.
Avoca Fault
The fault is exposed in the Devils Kitchen at Piggoreet 25 km
southwest of Ballarat. The fault separates pelitic schist with steeply plunging mesoscale folds in the hanging wall to the west, from
simply cleaved turbidites in the foot wall. The faulted contact between these rock types is exposed in mine workings 250 m downstream from the Devils Kitchen, on the north bank of the river. A
metre wide zone of cataclasite marks the fault, dips steeply west,
strikes northerly and is intruded by a subparallel 50 cm wide laminated quartz vein. The cataclasite zone consists of a scaly fabric
of disrupted schist that internally dips steeply east, suggesting
west-over-east shearing along the fault.
Table 3.13 Principal Stawell Zone goldfields—production and mineralisation styles
Stawell—102 t orogenic 78 t; placer 24 t
(Fredericksen & Gane, 1998; production to end 1996)
Ararat—19 t orogenic negligible; placer 19 t (O’Shea et al., 1991)
Main mineralisation is in ductile–brittle reverse shear zones related to
movement on the Stawell Fault. Faulting probably occurred during exhumation along the Pleasant Creek and Moyston faults. Mineralisation
at the Magdala deposit is concentrated in high-strain zones at the contact
between competent Magdala Volcanics and less competent sedimentary
rocks. Structural style and mineral assemblage point to high formation
temperatures. Main mineralisation is dated at 440 Ma with less significant, lower-temperature mineralisation within early shears and NEstriking sinistral strike-slip faults emplaced between 420 Ma and 400 Ma
coincident with the intrusion of dykes and granites.
Moyston—2 t orogenic 2 t; placer negligible (O’Shea et al., 1991)
Mineralisation occupies NNW-trending splays off the Moyston Fault.
Veins have a quartz–carbonate–pyrite alteration envelope.
St Arnaud – Stuart Mill—>13 t orogenic 13 t; placer negligible
(Krokowski de Vickerod et al., 1997
At Lord Nelson mine, richest in the field, NE-trending veins occupy steeply SW-dipping ductile–brittle faults. Veins contain abundant pyrite, chalcopyrite, arsenopyrite, galena and silver; host rocks are carbonate–
pyrite–chlorite altered (Forde & Bell, 1994). Carbonaceous beds in the
host Pyrenees Formation may have been an important control on gold
segregation. Elsewhere veins mostly trend N–S. Cross faults which truncate early structures trend NE (Krokowski de Vickerod et al., 1997).
Redbank–Moonambel–Percydale—unknown orogenic negligible; placer
unknown
Mineralisation occurs in a narrow belt of carbonaceous rocks in the hanging wall of the Percydale Fault. The Fiddlers Creek mineralisation occurs
in the hanging wall of a moderately W-dipping reverse fault with a sinistral strike-slip component that post-dates this main cleavage (Cayley &
McDonald, 1995). Rocks show sericite–carbonate  chlorite alteration and
51 TASMAN FOLD BELT SYSTEM IN VICTORIA
abundant pyrite–chalcopyrite–sphalerite–galena (Marek, 1997) typical of
the region. Unmineralised Early Devonian felsic dykes (~400 Ma; Ar/Ar;
Bierlein et al., 1999c truncate and post-date mineralisation. Bierlein et al.
(1999c) considered that the 413 ± 3 Ma age of hydrothermal mica in a
laminated vein is close to the age of gold mineralisation.
Avoca–Homebush—23 t orogenic negligible; placer 23 t
(Phillips & Hughes, 1996)
Small deposits occur within discontinuous W-dipping fault splays in the
hanging wall of the Avoca Fault. Quartz veins generally contain arsenopyrite–galena–pyrite–chalcopyrite–sphalerite (Sandiford & Keays, 1986).
A sericite, carbonate and pyrite alteration assemblage overprints cleavage probably coeval with 440  2 Ma Ar/Ar metamorphic mica along the
Avoca Fault (Foster et al., 1998). The Early Devonian Natte Yallock
Granite post-dates mineralisation at Lower Homebush (Taylor et al.,
1999).
Landsborough—unknown
Splays off the Landsborough Fault trending NNW contain minor mineralisation. The dearth of carbonaceous bed in the Warrak Formation may
explain the rarity of deposits in the hanging wall of the Landsborough
Fault (Cayley and McDonald, 1995).
Beaufort—>8 t orogenic negligible; placer >8 t (O’Shea et al., 1991)
The Beaufort Formation in the Beaufort Anticlinorium is riddled with
small quartz–gold veins along steep W-dipping faults.
Table 3.14 Magdala mineralisation
Central Lode
Structural control was by reverse faults that dip 40–70 SW, cutting the
contact between volcanogenic metasedimentary rocks and schist (Fig.
3.20). Transport on faults was reverse dextral with principal stress along
32238 (Mapani & Wilson, 1994). Thin mineralised shear zones alongside the Magdala Volcanics, and mineralised stockwork above competent
‘noses’ of Magdala Volcanics are interpreted as low-strain zones (Fredericksen & Gane, 1998).
Scotchman’s
This overprints the Central Lode. Mineralisation occurs along ‘master’
faults and ‘contained’ duplex faults, and is richest at the intersection of
these faults. Master faults dip 20–40 NW and contain slickenlines which
plunge gently to 340–350. They are interpreted to have formed under a
sinistral thrusting regime (Mapani & Wilson, 1994).
Table 3.15 Heathcote Fault Zone—faults in the central segment
Heathcote
Fault
Silver
Spoon
Fault
Red Hill
fault slice
A major Benambran décollement separating thruststacked metavolcanic and sedimentary rocks from overlying chevron-folded Castlemaine Group. The fault was
reactivated in the Tabberabberan Orogeny. It extends
from the Cobaw Granite to near Mount Camel and possibly bounds the entire northern segment. South of Heathcote, its dip is 56 SW measured from drill hole intersections (C.E.W. unpublished data). Structures in the hanging wall suggest late strike-slip movement. Turbidites
west of the fault show an eastward transition into a 1-km
wide zone of high strain or intense deformation.
A large internal fault interpreted from magnetic data. It
separates areas of NE–SW magnetic trends to its south
from areas of N–S magnetic trends. It cuts across the
fault zone truncating numerous N–S-trending faults,
separates Lazy Bar Andesite from Sheoak Gully Boninite
and truncates and offsets Knowsley East Shale and is
itself truncated by both the Heathcote and Mount William
faults (Edwards et al., 1998a).
Consists of a package of Cambrian volcanic and sedimentary rocks (Knowsley East Shale?) ~600 m wide and nearly 4 km long. Both margins appear faulted but drill holes
show that the W boundary is concordant with Castlemaine Group bedding (Gray & Willman, 1991a); sedimentary younging is consistently to the west. Some parts of
this boundary may preserve a conformable CambroOrdovician succession disrupted only by minor beddingparallel faults. The Heathcote Fault truncates the SE
margin of the slice. The Red Hill fault slice was probably
detached from the main belt by reactivated group 2 Tabberabberan thrusts.
‘Tuning
fork’ and
vicinity
Ladys
Pass area
Trilobite
Gully area
North of Heathcote the central segment widens to about 3
km and in addition to the mélange zone, contains fault
slices of both Ordovician and Cambrian rocks. Internally,
these vary in structural complexity from moderately
deformed Ordovician rocks with well preserved sedimentary structures and fossils, to variably foliated Cambrian
volcanics with patches of preserved igneous textures, and
highly contorted Cambrian sedimentary rocks.
A highly deformed fault slice of Goldie Chert(?) at the N
end of the central segment (Gray & Willman, 1991a)
contains numerous fault slices, each with homoclinally Wdipping and variably plunging folds. Zones of steeply NWplunging F2 folds are interspersed with, and refold, F1
folds that plunge gently N and S. Folds are mostly tight,
with upright to inclined W-dipping limbs. A refolded and
fault-bounded recumbent fold occurs near the base of the
fault slice Ladys Pass.
In a fault slice at Trilobite Gully, panels of Knowsley East
Shale dip mostly W with cleavage gentler than bedding.
In comparison to the Ladys Pass slice, folds are more open
and have gentler limb dips (30) with plunges of ~20° S
(Edwards et al., 1998a). On the E margin of this slice,
deformed andesite contains rootless F1 fold hinges that
plunge steeply to moderately S and have been refolded by
NW-trending, NW-plunging F2 folds (Gray & Willman,
1991a).
Table 3.16 Heathcote Fault Zone—northern segment
Corop
Fault and
associated
structures
Western
part
Separates the exposed N-trending concordant Cambrian
rocks and volcanics from a buried package of variably
faulted magnetic (volcanic?) rocks. Area east of it consists
of fault slices with alternating intensely and weakly magnetic rocks. Faults here cut across magnetic units but are
themselves truncated by the Corop and Mount William
faults. Internal faults are inferred to be steep, westdipping reverse faults with some strike-slip movements.
Small intermittent outcrops along the fault trace (Green,
1972) are of sheared rock (possibly Sheoak Gully Boninite), including quartz–magnesite cataclasite, locally
with pods of serpentinite and amphibolite (Crawford,
1988). These extend for ~9 km N from Cornella East.
Structures are poorly exposed. In the Mount William
Metabasalt, interbedded sedimentary rocks are folded
into small-wavelength folds (<1 m), upright to steeply
inclined and tight, with moderate NW or SE plunges
(Edwards et al., 1998a). They have NW-trending axial
planar slaty cleavage typically with steep NE dip. Minor
upright to steeply inclined chevron folds and box folds also
occur. Fold hinges are commonly truncated by small reverse faults that have a listric (concave up) geometry.
Table 3.17 Bendigo Zone—Some major faults
Mount William
Fault
North of Cornella the position of the buried fault is
interpreted from the magnetic data. It separates
highly magnetic trends in Cambrian Heathcote Volcanics from poorly magnetic Melbourne Zone sedimentary rocks. North of Rochester it truncates faultbounded packages of Cambrian sedimentary rocks
that form part of an antiformal stack.
Near Kilmore the fault is nearly vertical and in
places dips steeply E (VandenBerg, 1992) but farther
N and just south of Mount Ida, overturned Eyounging beds in the footwall indicate it is a steeply
W-dipping reverse fault (Edwards et al., 1998a). Deep
crustal seismic imaging north of Heathcote (Gray et
al., 1991b) shows some listric reflectors that dip W
but it is not clear that these represent the Mount
William Fault.
53 TASMAN FOLD BELT SYSTEM IN VICTORIA
Campbelltown
Fault
Muckleford
Fault
Whitelaw Fault
Hanover Fault
Near Campbelltown, Lancefieldian rocks are juxtaposed against Chewtonian indicating a dip-slip throw
of at least 800 m. The enveloping surface climbs towards the fault. In geophysical data it matches a
slight gravity rise to the west. On the E side, NW
magnetic trends that bend into the fault may represent dykes along fractures associated with the fault
(Taylor et al., 1999). The fault separates rocks with a
higher sandstone content and greater quartz-vein
abundance to the W compared to rocks to the E (Harris & Thomas, 1948). Post-Permian reactivation (Taylor et al., 1999) probably occurred before early Cainozoic dissection since a fault scarp is not preserved. It
is invisible in radiometric data, unlike in other areas
of Cainozoic faulting (e.g. Whitelaw). The Campbelltown Fault coincides with a small increase in the
oxygen isotope values of quartz veins (Gray et al.,
1991a).
East of Maldon, basal Castlemaine Group (Lancefieldian) in the hanging wall is faulted against Yapeenian
near the top of the group, a total stratigraphic displacement of >1.5 km. Most of this movement is Benambran displacement but some subsequent movements have occurred. Post-Late Devonian movement
is shown by a breccia zone 100 m wide in Harcourt
Granodiorite (G290), north of Maldon (Cherry & Wilkinson, 1994). At Guildford, Cainozoic basalt is faulted
(Thomas, 1935) and farther north an east-facing Cainozoic fault scarp occurs. Some hanging wall sections
have a high-strain zone up to 300 m wide with a
strong transposition foliation (Cherry & Wilkinson,
1994). The fault separates rocks with abundant quartz
veins to the W from rocks with few quartz veins immediately E of the fault.
The enveloping surface on the W side climbs steeply
towards the fault (Willman & Wilkinson, 1992). Hanging wall has narrow zone with much higher strain
than elsewhere. Within 0.5 km W of the fault, cleavage is stronger and pelitic rocks have a well-developed
vertical mineral lineation defined by pressure shadows around framboidal pyrite (Gray & Willman,
1991b). The fault is difficult to map S of the Harcourt
Pluton because of sparse fossil localities. It probably
follows the Taradale valley, which separates eastvergent folds with strong cleavage and lineated shales
on the W from less strained rocks. Fossil information
suggests it may continue S through Barrys Reef. An
alternative is that it links with the Rowsley Fault.
Separates Chewtonian turbidites to the N from
Darriwilian rocks to the S and is associated with a
parallel ‘fracture’ cleavage (Beavis & Beavis, 1968).
Near Steiglitz it is associated with a steep N-dipping
zone of brittle faulting (Willman, 1987c). The age of
movement is pre-Cainozoic; minor associated mineralisation suggests it occurred in either the Benambran
or Tabberabberan orogenies. The brittle nature of the
faulting suggests it is a Tabberabberan structure.
Table 3.18 Principal Bendigo Zone goldfields
Castlemaine–Chewton–Fryerstown—173 t orogenic 30 t; placer 143 t (Willman, 1995)
Mineralisation occurs along W-dipping reverse faults and related structures which strike sub-parallel to bedding and fold hinges but truncate
them in cross section. Many of the small-displacement faults are late-stage fold-accommodation faults but larger faults may have a deep-seated
control (Willman, 1995) (Fig. 3.28). Strongest mineralisation occurs in a simply folded sector, the goldfields structural domain whose abrupt
E margin, the Shicer Gully Fault, marks a transition to strongly E-vergent folds in the hanging wall of the Whitelaw Fault. In contrast, a general trend occurs of decreasing fault intensity and gold production to the W. Along strike a transition occurs from a ‘single’ mineralised fault
(Wattle Gully Fault) to mineralised extensional vein sets between smaller faults. These characteristics suggest a systematic and large-scale
structural control on mineralisation. Willman (1995) argued that mineralised faults are splays of a deep-seated ‘fluid conduit’ structure (Fig.
3.28).
At deposit scale, the best example is the Wattle Gully Fault Zone in the Wattle Gully mine (Fig. 3.29; Willman, 1995; Cox et al., 1995). Mineralisation was protracted, spanning folding through to late-tectonic faulting. The most important site for mineralisation is a dilatant fault jog
controlled by fold geometry, which consists of discontinuous splay faults in en echelon arrangement (Fig. 3.30). Mineralisation occurs along
faults but also in related extensional vein sets. Vein geometry and overprinting relationships indicate that growth has been controlled by cyclic
fluid pressure fluctuations associated with fault-valve behaviour (Cox et al., 1995).
Main sulphide phases are pyrite and arsenopyrite, with sphalerite, galena, chalcopyrite and pyrrhotite also present. Host rock alteration consists of arsenopyrite–pyrite–chlorite–sericite and widespread carbonate (Gao & Kwak, 1995). The highest gold grades at the mine tend to be
localised in vein systems close to carbonaceous slates.
Cox et al. (1995) showed that gold segregated from H2O–CO2–CH4 bearing fluids with near-neutral pH, low-salinity and variable compositions
and densities, at temperatures around 300°C and depths probably around 7–10 km. Segregation was influenced by structural and chemical
factors and triggered by redox reactions, fluid mixing and phase separation in response to fluid pressure cycling. In particular, mixing between
deeply sourced H2O–CO2 fluids and more reduced fluids that evolved during fluid reactions with carbonaceous slates was probably the key factor
controlling gold deposition.
The Ar/Ar age of hydrothermal sericite from a gold–quartz vein (441  3 Ma; Foster et al., 1998) is consistent with structural overprinting relationships which point to synkinematic mineralisation occurring during the Benambran Orogeny. Isotopic and bulk chemistry of fluids indicate
derivation from metamorphic devolatilisation (Cox et al., 1995).
Bendigo—684 t orogenic 529 t; placer 155 t (Willman & Wilkinson, 1992)
Bendigo is the largest goldfield in Victoria. Its main part has a strike length about 17 km, is up to 4 km wide and is remarkable for its regular
trains of chevron folds that have controlled the distribution and geometry of mineralisation (Fig. 3.31A). Most gold came from the hinge zones
and E limbs of just three anticlines, the Garden Gully, New Chum and Hustlers ‘lines’, but significant gold was also mined from other adjacent
anticlines. As in Castlemaine, mineralisation is confined to a zone of symmetric and persistent folds and the E edge of the field is sharply delineated, contrasting with the gradual westward decline in production and in abundance of mineralised structures (Willman & Wilkinson, 1992).
Domal culminations along the main anticlines tend to correspond with well-mineralised portions of the folds. Overall, folds plunge about 10°
away from the centre of the field.
Mineralisation is mostly in W- and E-dipping reverse faults which truncate fold hinges. Many of the smaller faults appear to be true limb
thrusts—they have short dip lengths and were generated as fold accommodation structures after fold lock-up. However, some of the larger mineralised structures may a deep-seated origin and be more significant regionally. The famous saddle reefs are composite fault structures controlled by thick, competent sandstone beds. They range from simply folded bedding-concordant veins through to complex structures involving
the interaction of limb thrusts, fold hinges and bedding-concordant veins (Willman & Wilkinson, 1992; Figs 3.32, 3.33). A significant proportion
of gold came from W-dipping reverse faults and associated extensional vein zones. The Deborah Fault shown in Figure 3.33 is interpreted to
have a strike length of more than 1 km and is associated with minor E-dipping splay faults (Turnbull & McDermott, 1998). Hydrothermal sericite from an extensional vein along this fault gave an Ar/Ar age of 439  2 Ma (also ~420 Ma; Foster et al., 1998). Other dating methods give
younger ages (e.g. Pb/Pb model age for galena in contact with gold = 430 Ma, and for arsenopyrite = 350 Ma; Rb/Sr age for vein albite–sericite =
424  7 Ma; Kwak & Maas in Foster et al., 1998).
At the Nell Gwynne anticline Li (1998) distinguished six stages of quartz veining: (1) mineralised bedding-parallel veins with minor pyrite–
arsenopyrite and high levels of antimony–lead–zinc; (2) mineralised tensional vein arrays containing coarse-grained gold and base metal sulphides, and traces of arsenopyrite; (3) barren massive veins; (4) mineralised breccia with abundant arsenopyrite–carbonate–pyrite and high
levels of copper–zinc–lead; and (5 & 6) barren carbonate–quartz and quartz veins. The bulk of gold occurs in stage 4 breccia. This timing is consistent with Forde (1991) who found that the main mineralisation was late and related to breccias with distinctive local alteration envelopes.
Carbonic fluid inclusions in mineralised veins contain high concentrations of CO 2–CH4 and have high trapping temperatures (320–400C). The
anticline is enveloped by carbonate–phengitic sericite–chlorite–sulphide alteration (Li, 1998).
Aeromagnetic data show that magnetic dykes are more abundant in the goldfield than in the surrounding unmineralised areas (Edwards et al.;
1998b). The dykes post-date mineralisation and are Late Jurassic (McDougall & Wellman, 1976).
Ballarat—>164 t orogenic 76 t; placer >88 t (Finlay & Douglas, 1992)
55 TASMAN FOLD BELT SYSTEM IN VICTORIA
Mineralisation was controlled by W-dipping reverse faults with throws of tens of metres. These generally follow bedding on the W limbs of anticlines and form more gently dipping anastomosing faults called ‘leather jackets’ where they cross fold hinges. At a regional scale, most of the
mineralisation occurs in three anticlinorial structures (Taylor, 1998). Three mineralised corridors that broadly correspond with these are from
W to E: Ballarat West, Ballarat East and Little Bendigo (or Nerrena).
Little Bendigo lies in the W limb and hinge zone of the Monte Christo Anticlinorium which shows vergence towards the major W-dipping
Williamson Creek–Campbelltown Fault, about 3 km to the E (Taylor, 1998).
Ballarat East, the most productive mineralised corridor, lies along the E limb of the Ballarat Anticlinorium. Mining was concentrated in a zone
0.5 km wide and 6.5 km long but extended S for a total strike distance of 14 km. Taylor (1998) suggested that the concentrated mineralised zone
corresponds to a domal culmination in the anticlinorium. The mineralised structures are part of a W-dipping fault zone in which individual
reverse faults are stacked 50 to 100 m apart. Mineralisation occurs in faults and subhorizontal extension veins up to 30 m wide (Baragwanath,
1923). Steeply dipping stockwork zones occur at the intersections of some faults and anticline hinges (Ransom & Hunt, 1984). Best gold lies at
the intersection of reverse faults and carbonaceous slate or silky green fine-grained sericite layers (K. Weston pers. comm.). These layers contain
abundant detrital zircon and spinel suggesting bulk metasomatic removal of silica.
1. Vein mineral assemblages consist of several generations of quartz, with minor chlorite–sericite–albite–carbonate. Arsenopyrite–pyrite are
the dominant sulphide phases, with minor galena, sphalerite, chalcopyrite and stibnite also present (Baragwanath, 1923; Bierlein et al.,
1998a). Host rocks show distinctive bleaching and contain abundant carbonate aggregates, disseminated pyrite–arsenopyrite and pervasive
sericitic alteration.
Ballarat West is completely concealed by Cainozoic lavas. Mine cross sections (Taylor, 1998) show that the three separately mined reef systems
are largely confined to the western limbs of three anticlines verging westward into the hinge zone of the Albion Anticlinorium. The three lodes
are thin laminated reefs 1–5 m wide, subparallel to bedding, that are mainly confined to western limbs. Descriptions suggest that they are
crack-seal veins in bedding-parallel fault zones, perhaps associated with a single horizon of black shale (Baragwanath, 1923). Drilling has confirmed that the fault zones extend across fold hinges into the eastern limbs where some spurry quartz bodies up to 25 m thick occur in a similar
fashion to the Ballarat East leather jacket reefs. Overprinting relationships between alteration minerals show that the Ballarat West goldfield
has a complex history involving cyclic hydrothermal fluid flow spanning folding through to late-tectonic faulting (Bierlein et al., 1998a):
1.
Initial pervasive sericite alteration occurred during folding and cleavage growth, possibly accompanied by growth of pyrite–arsenopyrite
porphyroblasts and carbonate spots.
2.
Assemblages formed in veins immediately after initial faulting show evidence of subsequent deformation and alteration. Quartz is sutured,
interlocking dolomite grains show undulose extinction, albite crystals are kinked. Chlorite replaces quartz.
3.
Second stage carbonates (iron-rich) overprint early alteration assemblage. Chlorite is replaced by kaolinite and magnesiosiderite. Sericite
partially replaces albite. Sulphides and gold were deposited.
4.
Growth of late-stage siderite–ankerite and arsenopyrite–pyrite porphyroblasts.
Ar/Ar data show hydrothermal sericite growth at ~440 Ma and at 455–465 Ma (Bierlein et al., 1999b). The younger age broadly consistent with
the timing suggested by structural overprinting relationships. The significance of the older ages is unclear—they correlate with the final phase
of Castlemaine Group sedimentation and predate the onset of the earliest regional deformation (see Box 6—What is the Benambran Orogeny,
and how old is it?).
Tarnagulla—23 t orogenic 15 t; placer >8 t (Maher, 1996)
The main deposit at Tarnagulla is the steeply W-dipping Poverty Reef. It lies on a reverse fault that has breached a tight synclinal axis. The
fault zone has a complex movement history that began with oblique reverse faulting with a sinistral strike-slip component (Cuffley et al., 1998).
Massive quartz, hydraulic breccia and spurry veins in a low-grade gold phase were generated during brittle–ductile reactivation of oblique–
reverse faults. Stylolitic laminations containing high-grade gold formed in dilatant zones at the margin of the massive quartz (Fig. 2.47). Later
brittle–ductile low-angle reverse faults under mainly E–W compression resulted in a medium-grade gold phase. Mineralisation is dated at
420 Ma  2 Ma (Ar/Ar, hydrothermal sericite, Poverty Reef; Bierlein et al., 1999a; also 419  2 Ma, New Cambrian deposit; Foster et al., 1996a).
It predates emplacement of the Early Devonian Tarnagulla pluton (see appendix; Marlow & Bushell, 1995; Molloy et al., 1995). NW-sinistral and
NE-dextral faults which segment the reef are unmineralised.
Early wall-rock alteration is predominantly sericite–silica  carbonate-type and quartz veins contain pyrite–arsenopyrite. High-grade veins have
a distinctive assemblage which includes galena–sphalerite–chalcopyrite. Gao and Kwak (1995) found trapping temperatures for ore fluid of
around 300C and observed similar assemblages at the nearby New Cambrian mine.
Fosterville—8 t orogenic 8 t; placer negligible (Edwards et al., 1998a)
Although just 25 km E of Bendigo, the Fosterville deposit is uncharacteristic of most Bendigo Zone deposits and is broadly similar to deposits in
the Melbourne Zone. Gold chiefly occurs as minute (1–3 m) inclusions in disseminated pyrite and arsenopyrite in sandstone (Fig. 3.34; Nand,
1989). Sulphides are closely associated with quartz–carbonate stockwork veins but these veins do not carry gold and probably represent late,
waning hydrothermal activity (T. Jackson pers. comm.). The controlling structure which envelops the stockwork is a steep W-dipping reverse
fault set which has interacted with fold hinges and favourable rock types to produce dilatant structures hosting the mineralisation (Zurkic,
1998).
The fault set comprises strike-parallel strands in en echelon segments with mainly reverse oblique slip, with later sinistral strike-slip movement (Wang & White, 1993). Two main lines are recognised—Fosterville Fault mineralised over 7 km and O’Dwyers Fault mineralised over
3 km.
O’Dwyers Fault is intruded by rhyolite dykes (Callinan, 1993; Leins, 1994). These contain brittle fractures created during late faulting that are
mineralised. The dykes give a poorly constrained Early Devonian age (Arne et al., 1998a; Bierlein et al., 1999c). Ar/Ar ages along the Fosterville
line give poorly constrained early sericite growth at ~440 Ma, and younger sericite growth (or partial argon loss due to fault reactivation) at
~360 Ma (Foster et al., 1996a). Dating points to episodic mineralisation related to movement along faults linked to the Benambran (Bindian)
and Tabberabberan orogenies.
Host rocks to primary mineralisation have elevated K2O, CO2, arsenic, antimony and sulphur corresponding to destruction of metamorphic
chlorite and detrital albite, and production of ankerite, illite and sericite during hydrothermal alteration (Arne et al., 1998b). Fluid inclusions
show CO2-rich ore fluids with a broad range of trapping temperatures and depths (140–385°C and 2.6–5.7 km depth; Nand, 1989; Mernagh,
1998; Leins, 1994). Phase separation and fluid mixing were important in gold segregation (Mernagh, 1998). High CH 4–N2 levels in some inclusions indicate interaction between fluids and carbonaceous rocks. Mixing of these reduced fluids and gold-bearing fluids is likely to have precipitated gold.
Six million tonnes of oxide ore from a 40-m weathering profile was mined to April 1999, giving 7700 kg of gold at 1.4 g/t. Additional oxide reserves of 1.1Mt @ 1.6 g/t, as well as protore sulphide reserves of 3.2 Mt @ 3.5 g/t were proved at that time. Development of the sulphide resource
awaits financing of a bio-oxidation facility to extract the gold.
Heathcote—3 t orogenic 3 t; placer negligible (Edwards et al., 1998a)
The Heathcote area has been strongly affected by both the Benambran and Tabberabberan orogenies and mineralisation has been episodic as a
consequence. The post-tectonic Late Devonian Pyalong Granite (G283) constrains the latest movement on the fault and hence the minimum age
of mineralisation. Early mineralisation is related to reverse faults that strike-parallel to the trend of the folded Lower Ordovician host rocks.
Younger mineralisation is characterised by gold–quartz–stibnite ores just W of the Heathcote Fault. The best example is Hirds deposit, just S of
Heathcote, where mining of oxide ore in 1992–1995 produced over 1000 kg from nearly 1.5 Mt of ore (Edwards et al., 1998a). Mineralisation was
controlled by NE-trending Tabberabberan group 3 faults—i.e. at 90° to the regional structural grain—with gentle SE dips. Faulting was probably associated with strike-slip movement along the reactivated Heathcote Fault (Gray & Willman, 1991a; Merriner, 1995; Wang & White, 1993).
The mine fault is a reverse dip-slip brittle structure dipping about 25–40 S, with displacement decreasing away from the Heathcote Fault
(Gunn, 1993). Highest grade mineralisation occurs in sub-horizontal extensional arrays adjacent to the fault with pyrite–arsenopyrite, minor
chalcopyrite and traces of silver. Trapping temperatures were around 300C (Fig. 3.33; Morgan, 1991). Low-grade ‘cooler’ gold–stibnite was
probably introduced after main mineralisation (Merriner, 1995; Morgan, 1991; Gunn, 1993).
Maldon—66 t orogenic 56 t; placer 9 t (Whiting & Bowen, 1976)
Mineralisation was controlled by faults with steep E and W dips associated with tight to isoclinal folds with W vergence. These are probably
high-order splays off the Muckleford Fault which lies 3 km farther E. In the Eaglehawk–Linscotts Reef, the main mineralisation occurred after
folding but early in a complex series of events during a prolonged deformation sequence (Ebsworth et al., 1998). The main fault is beddingparallel on the W limb of the host anticline and truncates bedding on the E limb where it widens to tens of metres thick. The fault zone includes
complex en echelon vein arrays bounded by ductile shears. Movement was dominantly reverse dip-slip with a later component of sinistral strikeslip post-dating mineralisation. The latter was associated with a change in the regional compression field from horizontal E–W to inclined at 35°
towards WSW. An even later phase of dextral strike-slip movement was probably contemporaneous with intrusion of the Late Devonian Harcourt Granodiorite (see appendix) which cuts and has enriched mineralisation (Gregory, 1994; Ebsworth et al., 1998; see below, Orogenic gold
and granites).
Clunes—36 t orogenic 34 t; placer 2 t (Taylor et al., 1999)
One of the State’s richest and earliest goldfields in which most gold came from a single mine. Mineralisation occurs in the doubly plunging
Clunes Anticline which trends 010 (Coldham, 1953). The fold, whose regional context is masked by Cainozoic cover, is tight and rocks have an
intense differentiation schistosity (Glasson & Keays, 1978). Veins formed incrementally in dilational structures. Early mineralisation occupies
veins along bedding slip planes, in fold hinges and in extension arrays and are crosscut by mineralised reverse faults and extension vein arrays
that formed in response to fold tightening. Most mineralised veins locally overprint microfolds and dominant cleavage, as well as a second crenulation cleavage that appears in some veined phyllites. Carbonate porphyroblasts mostly overprint the cleavage but some polycrystalline aggregates and veinlets lie subparallel to cleavage (Binns & Eames, 1989).
The best ore was associated with the fold culmination, and the average gold grade decreased from 17 g/t in its centre to 7 g/t in the S (Glasson &
Keays, 1978; Binns & Eames, 1989). Gold enrichment at the intersection of ‘flat’ quartz veins and ‘indicator’ (carbonaceous slate; Bradford, 1903)
may be due to reduction of hydrothermal fluids by carbonaceous host rock causing gold immiscibility.
Gold-bearing veins consist mainly of quartz with H2O–CO2 fluid inclusions, and minor carbonate, chlorite, and albite. Scarce sulphides include
arsenopyrite, pyrite, minor galena, sphalerite, chalcopyrite (Binns & Eames, 1989). Chlorite–pyrite selvages (which sometimes carry gold) of
veins indicate retrograde metamorphism probably associated with late faulting.
Host rocks display an intense cleavage, are bleached (particularly close to veins), and have common ankerite and siderite. Apart from enrichment in CO2 and As, however, little geochemical contrast exists with unaltered rocks a kilometre away (Binns & Eames, 1989). Enrichment in
CO2 and As is due to ankerite–siderite porphyroblasts and veinlets and accessory cobaltite. Subtle K-enrichment close to veins is due to higher
muscovite content (and minor siderite and kaolin) and less chlorite (Binns & Eames, 1989). Sulphur isotope values show hydrothermal pyrite
(34S = –2.7 to 2.7) is depleted in 34S when compared with values measured on diagenetic pyrite (34S = 5.7 to 7.8; Gulson et al., 1988).
Table 3.19 Tabberabberan structures formed by north-south shortening
Waranga
Domain
Darraweit
Guim
Province—
northwestern portion
West Darraweit Guim
Province
Mount
Easton
Province
Melbourne
Zone gold
deposits
Regional
cleavage
Northsouth shortening is most evident, with eastwest
folds and north-dipping reverse faults dominating (Gray
& Mortimer, 1996; Morand et al., 1997). Along the
northern margin in the hanging wall of the Governor
Fault, north-dipping mylonitic fabrics and associated
shear bands indicate that Cambrian rocks were thrust
southward over the Melbourne Zone (Tickell, 1989;
Gray & Mortimer, 1996).
This is a broad transitional zone where northwesttrending folds are transitional with eastwest folds
(Fig. 2.93). The sigmoidal interference pattern suggests
that group 3 structures have modified group 2 structures, with no cases of the reverse occurring. Edwards
et al. (1998a) observed that some north-trending folds
are overprinted by a northwest trending cleavage which
is consistent with the regional structural relationship.
Northwest-trending folds dominate, have curvilinear
traces of fold axial surfaces and dome-and-basin structures suggesting interference between north-trending
and east–west trending structures.
A late period of northsouth shortening has resulted in
strike-slip movement along the Fiddlers Green Fault
(VandenBerg et al., 1995). This movement is constrained to late in the Tabberabberan Orogeny as the
fault post-dates major group 1 and 2 structures and
predates the Upper Devonian Delatite Group.
Many of the deposits are controlled by structures that
either have a major component of northsouth shortening or are north-trending structures that show evidence
for late strike-slip reactivation. These include Nagambie, Bailieston and Walhalla (Cohens Reef). Ar/Ar dating has constrained the main period of gold mineralisation to between 385 and 365 Ma (Bierlein et al., 1999b),
after the major part of the Tabberabberan Orogeny
(390380 Ma).
A NW-trending cleavage that occurs over much of the
Melbourne Zone was interpreted as indicating a late
NESW compressional event post-dating all folding in
the zone (Morand et al., 1997). It is a regional feature
and is unlikely to be associated with either transpression or localised strike-slip movement. The cleavage
57 TASMAN FOLD BELT SYSTEM IN VICTORIA
may be recording an event after the close of the Tabberabberan Orogeny that was caused by minor compression associated with SW movement of the Benambra Terrane against the NE margin of the Melbourne
Zone (Morand et al, 1997). An alternative explanation is
that it was generated late in the orogeny by the interaction of northsouth and NESW components of compression ( Gray & Mortimer, 1996).
Table 3.20 Models proposed for north–south shortening
Gray and Mortimer (1996)
The development of both east-trending and northwest-trending structures is a reflection of two concurrent and diachronous deformation
fronts. They envisaged that a south-directed deformation front was initiated along the northern margin of the Melbourne Zone by thrusting of the
southward moving Tabberabbera Zone over the Melbourne Zone. This
occurred at the same time as eastwest shortening over the remaining
and major part of the Melbourne Zone. The deformation fronts met in the
NagambieRushworth area, giving rise to fold interference structures
(Fig. 3.39). Continued southward migration of the south-directed deformation front led to local overprinting of northwest-trending folds by
eastwest folds. The northwest-trending cleavage found by Morand et al.
(1997) was explained as a combination of the superposition of strains
between the two main shortening fields.
Morand et al. (1997)
Similar in some respects to the above as it involves southward thrusting
of the Tabberabbera Zone over the northern margin of the Melbourne
Zone to produce east-trending folds in the Waranga Domain. However,
these authors suggested this was a separate and earlier event and was
then followed by open, north-trending folds formed during eastwest
convergence with the Tabberabbera Zone, an event that was more strongly expressed south of the Waranga Domain. It was pointed out that the
Waranga Domain is structurally distinct from the rest of the zone and
does not include the belt of strongly deformed rocks in the Mount Useful
Fault Zone. These authors suggested that a major discontinuity may exist
along the southern margin of the Waranga Domain to account for the
small amount of eastwest shortening in the domain compared to the
region farther south. They concluded that this discontinuity was originally a south-verging thrust but was subsequently subjected to dextral
strike-slip. They also described a late northwest-trending and non-axial
planar cleavage found throughout much of the Melbourne Zone (Fig.
3.39), attributed to a late episode of northeastsouthwest shortening
which overprints all other structures.
Edwards et al. (1998a)
The eastwest and northsouth shortening events are two separate but
closely related episodes across the entire area. Northsouth structures
were formed by the earlier of the two, then overprinted by eastwest
structures. This was partly based on the finding that a northwesttrending cleavage, which they interpreted as axial planar to major east–
west folds, overprints earlier north-trending folds in the Waranga Domain (Edwards et al., 1997).
Table 3.21 Structures in the Waranga Domain
Mine Hill
Anticline
Whroo
Anticline
Cattanach
Anticline
Balaclava
Fault
Doubly plunging, E–W-trending fold in the Hill 158 gold
mine near Nagambie. Limb dips average 50–60. Hinge is
truncated by mineralised faults that dip moderately to
steeply N and have small reverse dip-slip displacements
(Fig. 3.43; Edwards et al., 1997). Mortimer (1992) and
Gray and Mortimer (1996) suggested that N-trending
structures in the mine overprint the main E–W fold,
whereas Edwards et al. (1997) regarded the main fold as a
late structure.
In exposure in the Balaclava mine (Fig. 3.43C) it is inclined with a steeply dipping overturned S limb and its
hinge faulted by the Balaclava Fault. The fold limbs are
steep due to local faulting, but the fold is more upright
and open towards the E. At the mine the anticline plunges
to the W.
One of the larger group 2 folds in the area—a broad NWtrending inclined fold with a steeply dipping overturned
NE limb and a NE vergence. The hinge contains a large
W-dipping thrust and associated back-thrusts (Edwards et
al., 1997).
Has a N dip with a N over S displacement and has caused
local drag, overturning the beds in the S limb of the
Whroo Anticline. This suggests southward tectonic
transport.
Table 3.22 Darraweit Guim Province—Tabberabberan folds and faults
Mount Ida
Syncline
Bailieston
Anticline
Graytown
Anticline
Moorooduc
Anticline
Studley
Park Fault
Zone
Selwyn
Fault
Brokil Fault
Yellingbo
Fault
In the south this fold becomes overturned and tightens
to an interlimb angle of 24, significantly tighter than
other folds in the domain—suggesting tightening in
association with continued movement along the Mount
William Fault. The northerly plunge (~ 30º) is much
steeper than any other fold in the domain, possibly because of interference from group 3 folding which becomes
important in this region.
A doubly plunging structure with a dome centred on
Bailieston and with a hinge containing a set of group 3
mineralised faults. Some parasitic folding occurs S of
Bailieston. Fold trace is curvilinear but generally strikes
northerly (group 2) but in the N it forms a branching Yshaped trace where it divides to the SW and SE. The SE
branch, interpreted by Edwards et al. (1997) as a later
structure, plunges to SE and has limbs dipping ~60.
The branching anticline here forms a structural high or
dome, with its limbs forming the rims of adjacent structural basins.
N portion is deformed in similar manner to Bailieston
Anticline—near Mount Black it branches into a Yshaped structure with the Uncle Bills Anticline and
Scrubby Anticline forming the arms. These plunge
NW and SE respectively, and together with the N part of
the Graytown Anticline form a regional structural high.
Open fold with broad hinge zone and little development
of cleavage. Both limbs dip relatively gently, generally
<50°, with few parasitic folds. Bedding and graptolites
indicate a consistent N plunge, with Lancefieldian graptolites in the core in the S outcrops and Darriwilian ones
in the core in the N outcrops. Parasitic folds are box-like
with incompetent chert showing a tight to open style;
locally strata are overturned. Elsewhere folds are so
open that they are only traced from strike swings (VandenBerg, 1998).
Average dip of faults is 50° W with a reverse sense of
dip-slip; a significant number of normal faults also occur.
Hills (1941a) concluded that faulting and folding are
related although in some areas the trends of faults deviate slightly from those of folds. Minor ‘drag folds”, some
with plunges, are associated with slickensided fault
surfaces. Folds generally verge W and plunge S.
In magnetic data the fault can be traced S to the Proterozoic rocks of King Island as the western margin of
magnetic rocks of the King Island–Mornington High.
Mapping in the Mornington Peninsula area has found
little evidence for the numerous faults shown by Keble
(1950), which must be small structures with offsets of
metres or perhaps tens of metres (VandenBerg, 1998).
However, the occurrence of Lancefieldian graptolites
well to the NW of the large Moorooduc Anticline indicates the existence of a reasonably large fault west of
this anticline. This Brokil Fault is likely to be a westdipping high-angle reverse fault with a throw in the
order of 1000 m or so (VandenBerg, 1998). Some smallscale faults that are associated with small parasitic folds
of thin-skinned style are probably fold accommodation
structures.
Links the Mount Dandenong Igneous Complex and Acheron Cauldron and is easily traced by a quartz porphyry
dyke intruded along its entire length (AHMV, unpubl.
data). In the NE-trending section it separates Devonian
Humevale Siltstone with NE-trending folds on the north
from Silurian Anderson Creek Formation with Ntrending folds to the south, suggesting substantial Nside down movement.
Table 3.23 Character of the Mount Easton Fault Zone
Northern section—Lake Eildon district (after Hartley, 1993)
Cleavage is weak to moderate, strongest in pelites. Folds within the fault
zone have shorter wavelengths and are tighter than folds to the W indicating higher strain. Fold tightness and cleavage (including pencil cleavage) increase eastward towards the Enochs Point Thrust where strain
was greatest. Reverse faults truncate the limbs of folds and Hartley
(1993) suggested that most developed late in the structural history. Some
early-formed bedding-parallel faults are associated with faultpropagation folds.
Central section—Enoch’s Point to Mount Matlock
59 TASMAN FOLD BELT SYSTEM IN VICTORIA
The eastern boundary of the fault zone, the Enochs Point Thrust, is
sharply defined with a half-metre wide slice of Mount Easton Shale lying
between Jordan River Group in the hanging wall and Walhalla Group
(Norton Gully Sandstone) in the footwall. The fault slice of Mount Easton
Shale widens to several tens of metres farther N, but near Enochs Point
becomes discontinuous and the fault separates Jordan River Group from
Norton Gully Sandstone. The hanging wall structure is complicated by
the presence of a stratabound fault that separates the Mount Easton
Shale from the Jordan River Group—probably the same structure as the
Queen Bee Fault in the Mount Useful Fault Zone. The lowermost two
formations of the latter are missing on this fault. The stratabound fault is
a group 1 structure that has been folded, together with the other hanging
wall rocks, into a series of closely spaced open group 2 folds. The folds are
tighter below the detachment surface than above it, where the lowest
unit is the competent McAdam Sandstone. Cleavage varies from strong to
very weak. The folds are quite asymmetric, with eastward vergence.
Southern section—Coopers Creek area
The fault zone becomes unmappable near the Thomson–Jordan confluence where the Jordan River Group disappears in a series of SE-plunging
folds. Farther south, between “Beardmore’s” and Coopers Creek, the
Jordan River Group re-emerges in a major anticlinal structure in which
there appears to be a detachment fault between the Wilson Creek Shale
and overlying Norton Gully Sandstone. The structure here is poorly
known but is more complex than first appears, shown by the presence of
several very small fault slices of Mount Easton Shale along this detachment zone.
Table 3.24 Mount Useful Fault Zone—main faults
Thomas
Fault
Frog
Hollow
Fault
Fiddlers
Green
Fault
Barkly
Fault
With the possible exception of the fault below the Howqua
Chert, this is the earliest major stratigraphically controlled
detachment fault in the fault zone (group 1 fault). It forms
the main décollement above the Selwyn Block and its hanging wall in all places is Mount Easton Shale. It is characterised by mylonitic fabrics indicating west over east shear
sense. Best exposure is in the SE corner of the Licola Window where Serpentine Creek Sandstone is thrust over
Cambrian volcanics and in places, over thin Mount Easton
Shale (VandenBerg et al., 1995). The fault locked up and
was subsequently folded into gentle to open folds.
Lies along the SW margin of the Jamieson Window and NW
margin of the Fullarton Spur Window. It dips steeply W
and truncates the Fullarton Fault and therefore is interpreted as a late-stage accommodation fault associated with
the late stages of the folding of the fold and thrust stack in
the Mount Useful Fault Zone.
Forms the W margin of the fault zone and is a major strikeslip fault. Strike slip post-dates the major east-vergent
deformation and occurred late in the orogeny but thin slices
of Mount Easton Shale indicate significant early dip-slip.
Strike-slip movement is best expressed by kink bands and
kink-related crenulation cleavages along the E side of the
fault, and folds that plunge steeply in the fault zone but
gradually become horizontal to the W. Kink bands form two
main complementary sets, one sinistral striking 052° and
the other dextral striking 090°, that resolve to give a compression direction approximately parallel to the strike of
the sedimentary rocks and the Fiddlers Green Fault. Fault
zone up to 30 m wide consists of cataclasite and tightly
folded siltstone with a pencil cleavage.
Late Devonian or Early Carboniferous fault dips about 45°
W in the south but steepens farther north to become vertical indicating it has a curved profile.
Table 3.25 Waratah Bay faults
Waratah
Fault
Bell Point
Fault
Subvertical NE-striking brittle fault. S–C fabrics along
fault trace S of Walkerville indicate sinistral displacement
(Fig. 3.47). Effects of faulting in turbidites to W include
100–150 m wide zone of tectonic mélange, and steeply
plunging refolded folds (Gray & Foster, 1998). Limestone in
footwall at Walkerville and at Grinder Point is affected by
veining and cataclasis.
Subvertical, NE-striking brittle fault zone exposed south of
Digger Island. Fault zone consists of sinistral anastomosing
fault array in Maitland Beach Volcanics, incorporating
clasts of Corduroy Creek Gabbro, peridotite, rhyolite, Digger Island Marlstone and Waratah Limestone. Fault is
associated with plunging folds and thrust-fault arrays in
adjacent Waratah Limestone, and strong, steep stylolitic
cleavage in adjacent Digger Island Marlstone (Figs 3.48,
3.49).
Table 3.26 Principal Woods Point mineral domain orogenic goldfields
Walhalla—68 t predominantly orogenic
Cohens reef is the principal deposit and was one of Victoria’s major gold
producers with a total of 46 059 kg from 1 429 298 tonnes of ore at an
average grade of 32.2 g/t (Bowen & Whiting, 1975). Mineralisation was
controlled by the steeply west-dipping Cohen’s Shear Zone in Norton
Gully Sandstone (Fig. 3.51). Tomlinson et al. (1988) interpreted the main
shear zone to be a reactivated reverse fault developed in an east-vergent
regime that may have been initiated as a listric thrust fault during folding. Faults associated with mineralisation post-date the main Middle
Devonian deformation and displace several dykes (Tomlinson et al., 1988)
although Edwards (1953) noted that the dyke in some places encloses the
reef, suggesting that mineralisation and dyke emplacement may have
overlapped. Similar controls on mineralisation occur elsewhere at Walhalla (Moy, 1994), as well as farther N at Gaffneys Creek (Cobcroft,
1996). Well-defined hanging wall and footwall faults enclose a 20–50 m
wide shear zone characterised by tight, often steeply plunging folds and
intense deformation compared to the more open and horizontal folding to
the west (Tomlinson et al., 1988; Tomlinson, 1990). The style of folding
indicates that faulting was initiated by reverse dip-slip although structures in the mine show a component of strike-slip. Gold mineralisation is
mainly in laminated quartz veins in the early reverse faults, associated
with pyrite, arsenopyrite, galena, chalcopyrite and sphalerite. Pyrite
alteration envelopes extend 10 m into host rocks, more abundant arsenopyrite to 2 m. Hydrothermal sericite is dated at 372  2 Ma (Ar/Ar sericite; Foster et al., 1998). Tomlinson (1990) suggested that gold occupies
dilatant zones formed during late movement, following main vein emplacement, and is localised by ‘perturbations and rolls’ in early veins.
This agrees well with structural overprinting relationships which show
that gold segregation occurred late in the vein history. The laminated
veins are sometimes boudinaged, recording a phase of extension in the
direction of the earlier reverse fault movement. Other mineralised quartz
veins include en echelon veins adjacent to shear zones and small ptygmatically folded veins in shear zones. The ptygmatic veins were formed
early in the reverse faulting and were subsequently folded into eastvergent minor folds by continued compression. A set of normal faults
developed late in the deformation, with initial normal dip-slip movement
followed by strike-slip movement. A set of late conjugate cross-faults
produced during north–south compression truncates all older faults and
veins.
Woods Point Dyke Swarm—52 t orogenic 40 t; placer >12 t
Significant gold production has come from faulted dykes in a NNWtrending zone from south of Walhalla to Eildon (see Ch. 5). The dykes are
Middle Devonian and trend parallel to the regional structural grain. They
are usually only a few metres thick but several have bulges up to 120 m
wide and 500 m long (Edwards, 1953). Best examples are the A1 (Whiting
& Bowen, 1970; Green et al., 1982), Loch Fyne (Whitelaw, 1923) and
Morning Star mines (Clappison, 1953; Carmichael, 1994). In these, reverse faults resulting from east–west compression form conjugate sets in
competent dykes. Gold is contained in quartz–carbonate veins in these
conjugate faults (ladder veins; Fig. 3.52), and is associated with pyrite,
arsenopyrite, sphalerite, galena, bournonite, tetrahedrite, jamesonite and
occasionally stibnite (Edwards, 1953). Thin chlorite–sericite–pyrite–
carbonate–hematite alteration envelopes along veins overprint deuteric
and regional propylitic alteration of the dykes (Carmichael, 1994). Fluid
inclusions at the A1 mine show that gold segregation probably occurred
below 360C after main vein formation (Green et al., 1982). Orthomagmatic precious metal-rich copper–nickel sulphides occur in dykes at many
mines (e.g. Shamrock, Hunts, New Loch Fine, Maynards Gully and Morning Star gold mines and the Kellys, Toombon and Aberfeldy dykes), the
best studied being the Thomson River ultramafic differentiate (see Box
10—Magmatic sulphides in the Woods Point Dyke Swarm, and 4.7 Dykes).
Production is taken from Phillips and Hughes (1996).
Table 3.27 Principal Melbourne Zone orogenic goldfields (outside the Woods Point mineral domain)
Nagambie mine—4 t orogenic 4 t; placer negligible (Edwards et
al., 1997)
The Nagambie deposit lies 6 km E of the township and is hosted by Early
Devonian Waranga Formation (Edwards et al., 1997). The large stockwork system was controlled by sets of N-dipping faults which strike subparallel to the axis of the Mine Hill Anticline, a major E–W-trending and
doubly plunging anticline (Mortimer, 1992; Gao et al., 1995). It is regarded as a late Tabberabberan structure (Edwards et al., 1997; Gao et al.,
1995; group 3 of this book). Most of the mineralisation is located on the
steep S-dipping limb. Mining in the oxide zone has yielded a total of 4192
kg to May 1998. Five phases of quartz veins occur, with the two early sets
parallel to the fold axis and containing no gold. The next two phases are
mineralised and include stibnite-bearing quartz veins and stibnite–gold-
61 TASMAN FOLD BELT SYSTEM IN VICTORIA
bearing quartz stockwork veins associated with pervasive silicification of
siltstone. The youngest set, of quartz veinlets, is barren (Gao et al., 1995;
Gillies, 1990).
Costerfield—2 t gold, 22 t antimony (Edwards et al., 1998a)
This goldfield lies on a regional structural high that O’Shea et al. (1992)
attributed to ascending magma; Edwards et al. (1998a) argued that it is
due to modification of N-trending folds by later N–S compression. At the
Brunswick deposit, gold–antimony–quartz veins are related to subvertical N–S faults in Costerfield Siltstone consistent with early E–W compression (Hill, 1980). Siltstone close to veins contains carbonate, sericite,
pyrite and chlorite alteration (Figs 3.53, 3.54). Barren carbonate veins
occupy later east–west and oblique faults which offset N–S faults (Gao &
Kwak, 1995).
Bailieston—<1t orogenic <1 t; placer negligible
(Edwards et al., 1997)
Mining recommenced at Bailieston in 1996 with 266 kg of gold produced
to date (Perseverance, 1998). New development occurs along a WNWtrending dextral strike-slip fault zone parallel to the hinge of a major
open anticline in Silurian Dargile and Broadford formation (Sebek, 1998;
Edwards et al., 1997). Mineralisation is associated with N-trending minor
faults accompanied by silicification, narrow quartz veins and <2% sulphides including arsenopyrite, pyrite, sphalerite, galena, minor pyrrhotite, chalcopyrite and bournonite. Favourable hosts include porphyry
dykes that occupy the WNW-trending shear zones, and sandstone beds.
Sebek (1998) attributed all veining to dextral shearing but Gao and Kwak
(1995) observed features that point to separate mineralising events (e.g.
N–S veins have a chlorite–carbonate–arsenopyrite assemblage, and are
truncated by E–W veins with a pyrite–stibnite assemblage.
Yea—unknown
Gold occurs in NNW-trending shears and faults in the Yea Anticline
(Kwak & Roberts, 1996). Gold–silver occurs in quartz–adularia veins with
abundant
sulphides
(pyrite–arsenopyrite–sphalerite–chalcopyrite–
galena) from a pair of parallel breccia zones at the Providence deposit
(McKnight et al., 1998). Host rocks are silicified and sericitised near veins
and contain disseminated gold.
Table 3.28 Melbourne Zone orogenic(?) gold deposits related to magmatism
Tallangalook—4 t orogenic <1 t placer 4 t (Maher et al., 1997b)
Mineralisation at Tallangalook (Golden Mountain) is distinctive. Gold,
with relatively little quartz, is disseminated in cordierite–biotite hornfels
adjacent to the Late Devonian Strathbogie Granodiorite (see appendix).
Production from three oxide-ore open cuts totalled 268 kg of gold (Griffiths, 1981), and about fifteen times this amount was taken from nearby
placer deposits. Mineralisation was localised by carbonaceous beds and
steep-dipping N–S-trending faults (Sandl, 1989), as well as coarse sediment-dominated packages (Phillips, 1973). Gold was emplaced with biotite and pyrite during contact-metamorphism, and also with arsenopyrite
during retrograde metamorphism (Sandl, 1989; Wall & Taylor, 1991). The
main gold phases, fine grained (15 m) electrum and calaverite (AuTe2),
are unrelated to sulphides.
Steels Creek
Steels Creek occurs 40 km E of Melbourne at the intersection of an anticline in Dargile Formation with the Tarrawarra ring fault and dyke (Fig.
2.112). This structure may be a ring fracture of the Early Devonian
Mount Dandenong Cauldron although an age of 382  2 Ma of hydrothermal sericite in the Steels Creek dyke (Foster et al., 1996a) suggest
that the dyke is too old. Main gold veins occupy N–S joints in the
porphyry and are surrounded by sericite–carbonate–pyrite alteration
(Hawkins, 1980). Dominant sulphides are stibnite–pyrite–arsenopyrite–
pyrrhotite–chalcopyrite–berthierite. Fluid inclusions from this, and nearby orogenic gold deposits not clearly related to magmatism (Black Cameron and One Tree Hill), show broadly similar salinities (<10 wt.%) and
trapping temperatures (295–375C; Noble, 1990)
Mount Piper
Gold-bearing quartz–sulphide veins and silica–tourmaline–illite–
carbonate–sericite alteration surround a small porphyritic stock 12 km
NW of Kilmore (Kwak & Roberts, 1996). Overprinting relationships between mineralisation and the stock, and the alteration style, point to a
genetic relationship between mineralisation and the intrusion. Hydrothermal sericite with a 379  2 Ma age dates this events (Ar/Ar; Foster et
al., 1998). Dominant sulphides are arsenopyrite–pyrite–stibnite.
Table 3.29 Faults in the Tabberabbera Zone
Governor
Fault
Forms the boundary between Whitelaw and Benambra
terranes. N to NE-dipping thrust fault with local mylonite foliation showing N over S movement sense, plac-
Wonnangatta Fault
Zone
Barmouth
Fault
Haunted
Stream Fault
ing Cambrian volcanics and Ordovician–Silurian sedimentary rocks over Silurian–Devonian Yarra Supergroup.
This largest internal fault in the Tabberabbera Zone
consists of numerous parallel northeast-dipping faults
reflecting SW vergence. Fergusson (1987a) noted the
presence of mélange-like deformation suggesting that
rocks at the base of the hanging wall were watersaturated. The mélange consists of phacoidal fragments of sandstone in a matrix of mudstone with a
scaly fabric (Fergusson, 1987a—Fig. 3.59). Farther
north the fault zone loses displacement and branches
into several smaller structures, many with slices of
Bendoc Group. Best known in the S of the zone in excellent outcrop in the Wonnangatta R, 15 km NW of
Dargo. Hanging wall here consists of basal Pinnak
Sandstone and underlying Howqua Chert, and possible
Cambrian volcanogenic sedimentary rocks, footwall
consists of faulted Cobbannah Group (GSV unpublished
mapping), in places with Warbisco Shale.
A major NE-dipping and SW-verging compressional
fault in the south of the zone. Coincides with a significant gravity gradient, with a large gravity high on the
NE side (Willman et al., 1999a). This suggests that the
fault is, or at least overlies, a major crustal structure.
The gravity high is interpreted as a body of dense rock
in the middle to upper crust. It is nonmagnetic and
therefore most likely composed of high-grade metasedimentary material of Omeo Metamorphic Complex
type. The body does not outcrop but it is consistent
with SW-directed compressional faulting having raised
denser mid-crustal rocks closer to the surface against
less dense low-grade rocks to the SW. However, the
lack of a change in metamorphic grade across the fault
is problematic. The fault is regarded as having initiated in the Benambran Orogeny with subsequent movement in the Bindian Orogeny deforming the Barmouth
Group. Benambran(?) dip-slip is shown by early-formed
quartz veins associated with layer-parallel shearing in
pelites between less-deformed sandstone beds. Bindian
phase involved components of (1) strike-slip movement
that produced steeply plunging F2 folds, and (2) eastover-west dip-slip movement which further deformed
the Barmouth Group. Dextral Bindian strike-slip is
suggested by clockwise rotation with respect to the
fault of a related cleavage and by comparison with
Bindian movement along the Kiewa Fault and Cassilis
Shear Zone. The Barmouth Fault is mapped for 10 km
SE of the Barmouth Group but it probably extends a
further 24 km where an 8-km wide NW-trending zone
shows strong crenulation cleavage (S2 S3a cleavage of
Simpson et al., 1996—Fig. 3.57).
A brittle fault characterised by up to 60 m of cataclasite originating late in the Bindian Orogeny. The
crush zone includes fragments of vein quartz in a matrix of brecciated Pinnak Sandstone—with some evidence of an overprinting Tabberabberan cleavage. The
fault is inferred to lose displacement in the SE where it
is replaced by a set of minor conjugate mineralised
faults in a jog zone. The mineralised faults are aligned
along the Haunted Stream Fault for a distance of 8 km
and they fall into three main sets of preferred orientations resembling a Riedel shear system produced by
NNW–SSE compression.
Table 3.30 Principal Tabberabbera Zone goldfields
Chiltern–Rutherglen—>34 t orogenic >3 t; placer >31 t
(post-1964; Maher et al., 1997b)
This goldfield is special on two counts: (1) despite modest orogenic gold,
placer gold mining was very successful and (2) it contains enigmatic very
fine-grained gold disseminated in sediment (see Box 16—Disseminated gold
at Chiltern). This gold was mostly too fine to recover but was occasionally
worked profitably. Mineralised faults dip steeply and trend NNW and N–S;
and are truncated by sinistral strike-slip faults (Hunter, 1903). Veins contains a small amount of pyrite–arsenopyrite and traces of silver, chalcopyrite and scheelite, and are surrounded by carbonate alteration (Ivett, 1982).
Beechworth–Yackandandah–Myrtleford–Eldorado—>16 t
orogenic >4 t; placer >12 t (post-1964; Maher et al., 1997b)
Mineralisation trends NE, N–S or NNW and dips steeply W (Easton,
1912a, b; Meltech, 1985). The Wallaby deposit near Stanley was a major
producer and is one of many mines within a 100-m wide shear zone where
NNW-trending mineralised shears cross-cut barren bedding-parallel NWtrending veins (Ivett & Oldfield, 1988). In other areas, mineralised veins
63 TASMAN FOLD BELT SYSTEM IN VICTORIA
are displaced by complex late cross- and low-angle faults which hampered
mining. Veins contain small amounts of pyrite–arsenopyrite and traces of
galena, sphalerite and chalcopyrite and are surrounded by chlorite and
carbonate alteration (Foster & Roberts, 1988).
Bright–Wandiligong–Buckland–Harrietville–Freeburgh—>15 t
orogenic >11 t; placer >4 (post-1964; Maher et al., 1997b)
Mineralised faults are steeply E-dipping NNW-trending reverse faults
usually in W-dipping Ordovician rocks. Mineralisation branches into hanging walls while footwalls commonly contain mineralised extension arrays
(Cuffley, 1985). At the Red Robin mine Dugdale (1986) described three
vein generations: (1) unmineralised ptygmatically folded veins that crosscut bedding and the S1 cleavage are crosscut by (2) mineralised laminated
veins on reverse faults and related tension gash veins. A late unmineralised vein set (3) lies on strike-slip faults with mainly NE dextral trends and
less common NW-trending sinistral faults. This is consistent with E–W
compression, probably during or after the Middle Devonian. Mineralised
veins contain minor arsenopyrite–pyrite and traces of galena, chalcopyrite
and sphalerite and are surrounded by sericite–chlorite–carbonate–albite
alteration (MacKay, 1984). Mineralised veins at Wandiligong and Buckland
are associated with dykes which sometimes host mineralisation (Kenny,
1908).
Haunted Stream—<1 t orogenic <1 t; placer < 1 t
(Willman et al., 1999a)
Mineralised faults form a NW-trending zone approx. 7 km long and 1 km
wide aligned with the SE end of the Haunted Stream Fault. Faults form a
Riedel shear system (see Table 3.29). Mineralisation overprints Benambran
cleavage and folds and is possibly overprinted by Tabberabberan folds.
Mineralised faults are characterised by strongly sheared black chloritic
ductile shear zones. Veins contain quartz  calcite and minor pyrite–
arsenopyrite, and traces of chalcopyrite, sphalerite and galena (MacKenzie,
1986).
Table 3.31 Structures in the Omeo Metamorphic Complex
Structural variations with increasing grade
In the cordierite zone the dominant foliation is a second-generation
schistosity (S2) defined by well-aligned micas with the earlier S1 foliation
only preserved within cordierite porphyroblasts. F2 folds are usually
upward-facing, tight, have half-wavelengths up to hundreds of metres.
Close to the cordierite isograd, F2 folds appear indistinguishable from
first-generation folds in low-grade Pinnak Sandstone suggesting that the
‘S1’ in cordierites is not associated with the major folds in the low-grade
rocks—its equivalent may be the S* fabric (see Box 17—Early S* foliation). ‘S1’ in low-grade rocks may therefore be the equivalent of ‘S2’ in
metamorphic rocks.
In the south of the subzone, most rocks in the andalusite–K-feldspar
and sillimanite–K-feldspar zones have a single S2 gneissosity with
bedding commonly preserved. Mesoscopic F2 folds are tight to isoclinal
and commonly have faulted hinges (see fig. 3.55B). F2 folds are rarely
seen but variations in dip and younging direction of bedding indicate the
presence of large-scale F2 folds with half-wavelengths of 200–800 m.
Small-scale F3 folds occur locally in some schist but more commonly in
gneiss and occasionally form map-scale structures. Faults are usually
parallel to S2 and form steeply dipping shear zones associated with
quartz veining up to several metres thick. Closer to the migmatite zone,
bedding disappears and the main penetrative structure is S 2 sometimes
folded into small tight F3 folds. Structure in migmatite is typically complex because the dominant layering (usually S2) is irregular and cut by
shear zones and several generations of granitic segregations and dykes.
Small shear zones with various orientations are common in migmatite.
Multiply deformed upper amphibolite facies gneiss and migmatite and
rare calc-silicate rocks occur in the north of the subzone near Lake Hume
(Steele, 1993).
Structural vergence patterns
Difficult to map in the Omeo Metamorphic Complex because of limited
exposure. A section near the S margin of the subzone at Cassilis shows Sverging F2 folds with an axial planar S2 schistosity (see fig. 3.55B; Willman et al., 1999a). Folds are upward facing, tight, vary from upright to
inclined to N. Many have faulted hinges. Fold half-wavelengths are ~10–
50 m with folds in small groups separated by unfolded zones ~100 m
wide. S2 dips vary from 90º to 30 N, possibly as a result of low-dipping, Sdirected reverse shear zones.
Table 3.32 Faults in the High Plains Subzone
Kancoona
Fault
NW-trending strike-slip fault active in the Bindian and Tabberabberan orogenies. Forms part of W boundary of the Omeo
Zone. S–C fabrics and a near-horizontal stretching lineation in mylonite indicate main early dextral strike-slip movement
which post-dates Benambran structures (close to its W side, low-grade sedimentary rocks have a second-generation cleavage
and locally downward-facing folds). Subsequent sinistral strike-slip that has displaced the Mudgeegonga Granite (G179) is
Ensay
Shear Zone
Kiewa Fault
Jarvis
Creek Fault
Talgarno
Fault
Cassilis
Shear Zone
Tokes
Creek Fault
Zone
Mount
Hopeless
Fault
recorded in S-C fabrics (Sandiford et al., 1988—Fig. 3.61) that are overprinted by Middle Devonian folds. Dextral movement
is therefore assigned to the Bindian Orogeny, in agreement with Ar/Ar ages from micas in the Kancoona Fault (409 ± 2, 403 ±
2, 395 ± 2 Ma; Foster et al., 1999). The granite is very late Early Devonian (see Appendix) suggesting that sinistral reactivation was Tabberabberan.
A major Bindian NW-trending dextral strike-slip fault closely associated with foliated magnetic tonalites (Fig. 3.64). The
Doctors Flat Tonalite (G517) follows the fault for about 37 km, and the Polar Star (G146), Livingstone Creek (G145), Hallets
Road (G148) and Holstons (G518) tonalites, and Dry Hill Granodiorite (G147), are elongate plutons of foliated granite lying
entirely or partly within the shear zone. SE of Ensay it widens to 3 km, swings E and has strongly foliated and fractured the
whole width of the Doctors Flat Tonalite. The large width of the Ensay Shear Zone here seems to result from the Jam Tin
Fault merging with it at Ensay. SE-trending splays within the shear zone may be large-scale Riedel shears. Steep stretching
lineations and horizontal asymmetric folds occur in the E–W-trending part, suggesting a component of dip-slip and consistent
with movement direction to the SE. A strong reverse dip-slip component must be present where the shear zone changes to E–
W trend. Cataclasite is common in the Doctors Flat Tonalite (G517) around Ensay.
Major dextral strike-slip fault forming part of the W boundary of the Omeo Zone. Composed of 2-km wide mylonite zone,
characterised by a subhorizontal lineation. The mylonites are gradational into high and low-grade rocks at its W and E margins respectively (Scott, 1985; Morand & Gary, 1991; Gray & Foster, 1998). South of the Tawonga Fault ultramylonite separates schistose and gneissic mylonites. Folds near the E margin of the gneissic mylonite have steep plunges and are orthogonal to the mylonitic lineation in the shear zone.
Arcuate shear zone in the N of the subzone. Movement sense indicators in the south-dipping mylonite vary systematically
along the shear zone and show that overall tectonic transport was to the north (Sapurmas, 1993). Where the shear zone
trends east–west, at right angles to the transport direction, dip-slip movement predominates but the northwest-trending
portion shows oblique slip with dextral strike-slip and thrust components. This is consistent with the early sinistral strikeslip movement on the Talgarno Fault, indicating that they were linked, possibly during the Benambran Orogeny. The northwest-trending segment of the Jarvis Creek Fault may have formed a linked splay with the Tallangatta Creek Fault Zone
during their early movements. Later movement along the Talgarno Fault truncated the Jarvis Creek Fault.
Fault in the N part of the subzone that links with the Jarvis Creek Fault. Mylonitic fabrics dip about 45° southeast. Sapurmas (1993) has shown that early ductile movement along the fault was oblique with sinistral strike-slip and thrust components. This resulted in northward thrusting along it, and the Jarvis Creek Fault, which at that time formed a continuous
curved system—the Talgarno Fault probably curved eastward and linked with the Jarvis Creek Fault, a dip-slip thrust fault.
A later ductile event truncated the Jarvis Creek Fault and propagated the Talgarno Fault another 12 km northeast until it
linked with the pre-existing Tallangatta Creek Fault Zone. The reactivated section of the Talgarno Fault displays consistent
evidence for oblique dextral slip with a normal displacement. Structures in the southern section, south of the Jarvis Creek
Fault, show that this late movement overprints the early oblique sinistral movement. The late dextral movement is consistent with the initial dextral strike-slip movement on the Kiewa Fault, indicating it may have occurred during the Bindian
Orogeny. Some of this late dextral strike-slip on the Talgarno Fault may be related to east–west compression during the
Tabberabberan Orogeny (Sapurmas, 1993). A late brittle event is recorded by vertical slickenlines.
Dextral strike-slip fault along the N margin of the Swifts Creek Igneous Complex. Main movement was in the Bindian Orogeny. The shear zone truncates metamorphic isograds to the N therefore post-dates the Omeo Metamorphic Complex. This
contrasts with metamorphic rocks on the S side which follow the general trend of the shear zone and curving around the
syntectonic granites—indicating that metamorphism on this side accompanied both faulting and igneous intrusion. The
Rileys Creek Granodiorite (G137) is syntectonic with the mylonitic zone. Its ‘tail’ (Fig. 3.64) lies within the shear zone for a
distance of at least 10 km and tapers to the SE. Sense of movement criteria are inconclusive with both dextral and sinistral
rotations occurring. The shape of the Rileys Creek Granodiorite suggests that granite emplacement occurred during a period
of dextral strike-slip movement.
NW-trending fault in the east of the High Plains Subzone. It consists of fault slices of Pinnak Sandstone, Bendoc Group units,
Yalmy Group (Tongaro Formation) and Wombat Creek Group (Gibbo River Siltstone) (Fig. 2.65). These fault slices peter out
to the NW where the fault zone is recognised from structural complexities in Pinnak Sandstone with structural style varying
from N to S. The northern part, ~2 km wide, is most intensely deformed, characterised by numerous steep NE-dipping faults
separating fault slices of Pinnak Sandstone. The S half, ~1.5 km wide, is characterised by steep SE-plunging F2 folds. It is
inferred that a major NW-trending fault occurs along the N margin of the belt. Pinnak Sandstone immediately N of this
inferred fault generally strikes NE, nearly 90 to the average strike of the deformed zones. Towards the S margin of the zone
many F2 folds are truncated by brittle faults—narrow breccia zones dipping about 50 SW, some showing small reverse displacements. Other late conjugate brittle faults resolve to give a N–S compression direction.
A mostly subhorizontal fault in the S of the subzone (Fig. 3.60B). A narrow mylonite zone with bands of cataclasite separates
migmatite from cordierite schist and gneiss in an area where a complex structural relationship is indicated by nearhorizontal contacts between different metamorphic zones and a rapid change in metamorphic grade from the valley floors to
ridge tops. The Cobungra Granite (G549) and migmatite typically occur in valleys with gradational contacts while the higher
ground is occupied by cordierite schist and chlorite-grade Pinnak Sandstone. Contacts between the Cobungra Granite and
migmatite appear gradational, but the contact between migmatite and gneiss is probably faulted and marked by cataclasite
horizons which appear to be contact metamorphosed. Metamorphic isograds above the horizontal fault are near-parallel to
the fault and have different dip to isograds elsewhere (Fig. 3.60B). The origin of the fault is uncertain—it may have resulted
from doming and sliding off of successive layers above the rising roof of an emerging pluton, or from low-angle faulting caused
by southward movement of the High Plains Subzone. The presence of contact-metamorphosed cataclasite indicates that
faulting took place prior to the intrusion of the Connors Creek Tonalite (G135), possibly during the latter stages of the Benambran Orogeny in the Lower Silurian (Willman et al., 1999a). The fault shows some similarities to extensional faults
formed in metamorphic core complexes (Willman et al., 1999a).
Table 3.33 Faults in the Corryong Subzone
Indi Fault
Major NW-dipping thrust fault at SE corner of Corryong Subzone. A mylonite zone about 1 km wide
separates Omeo Metamorphic Complex from the
Limestone Creek Graben along the fault (Allen, 1987;
Morand & Gray, 1991; Willman et al., 1999a). The SE
portion consists of fine sericite-rich mylonite apparently derived from the adjacent Gibsons Folly Formation, while the NW portion is derived from gneiss
and Kimberly Park Granite (G79). Outcrop-scale
structures are complex, but S–C fabrics, a down-dip
stretching lineation and asymmetric folds with horizontal axes indicate SE-directed thrust movement
(Morand & Gray, 1991). Mylonite foliation is parallel
to that in the folded Limestone Creek Graben rocks,
and deformation in the graben increases toward the
Indi Fault. Metamorphic grade in the mylonite is
65 TASMAN FOLD BELT SYSTEM IN VICTORIA
Tallangatta
Creek Fault
Zone
Minute Creek
Fault
Larsen Creek
Fault
Saltpetre Gap
Fault
Sassafras
Gap Fault
Murtagh
Creek Fault
Livingstone
greenschist facies, the same as in the Limestone
Creek Graben, indicating that thrusting was coeval
with Bindian deformation of the Limestone Creek
Graben. This is consistent with an Ar/Ar age of 405 ±
2 Ma from muscovite in the mylonite (Foster et al.,
1999).
This very prominent magnetic and radiometric feature (see Encl. 2) extends to the State border. South
of the Dartella Cauldron the fault zone is complex,
bounded on the W by the Minute Creek Fault and
on the E by the Larsen Creek Fault (Fig. 2.65;
VandenBerg et al., 1998). It consists of a broad zone of
fault slices of Pinnak Sandstone and Bendoc Group.
Near Lake Dartmouth the E boundary is gradational
into relatively simply deformed Pinnak Sandstone
and occasional belts of Bendoc Group and the intensity of deformation decreases to E, away from the Minute Creek Fault. Farther S, in the Eustace Gap
area, both the W and E margins are faulted by the
Minute Creek and Larsen Creek faults respectively.
Structures within the fault zone include steeply
plunging folds and numerous internal faults that
frequently separate fault slices of Bendoc Group.
Bedding and faults in the fault zone generally strikes
NW–NNW, which is at an angle to the N–S strike of
bedding in the Corryong Subzone. F2 folds plunge
steeply NW (~60°) and S2 consistently dips N. South
of Benambra township the fault zone consists of a
fault slice of Yalmy Group and Bendoc Group lying
between the Minute Creek and Morass Creek
faults. It continues S of Triassic granites where it
has a broad S-shaped bend and consists of thin belts
of mylonitic Pinnak Sandstone, Bendoc Group and
Yalmy Group lying between the Bindi Granodiorite
(G121) to the S and Mount Tambo Group to the N.
Forms the W boundary of the Tallangatta Creek
Fault Zone. Separates Omeo Metamorphic Complex
rocks to the W from low-grade Ordovician and Silurian sedimentary rocks to the E (VandenBerg et al.,
1998).
Forms the E boundary of the Tallangatta Creek Fault
Zone, separating Pinnak Sandstone from Bendoc
Group (VandenBerg et al., 1998). Where exposed it is
a fault zone several metres wide of quartz-veined and
sheared Ordovician rocks. Has minor displacement
increasing to N. The fault appears to cut structures in
the fault zone, indicating it is a young structure. It is
interpreted as a steeply dipping reverse fault (E over
W) formed as a result of E–W compression, probably
in the Tabberabberan Orogeny. The Larsen Creek
Fault is defined in the magnetic data as the easternmost N-trending magnetic break within the Tallangatta Creek Fault Zone.
NE-trending fault in the central Corryong Subzone.
May have some Cainozoic movement but offset of
metamorphic grades indicates significant Palaeozoic
displacement (VandenBerg et al., 1998). Forms a
faulted boundary of a belt of Bendoc Group with spotted phyllites in the hanging wall, indicating reverse,
NW over SE, movement. The fault is composed of
numerous smaller faults that are locally associated
with kink-like F2 folds.
Steeply E-dipping set of anastomosing cataclasite
bands up to 30 cm wide lying parallel and subparallel
to bedding and dipping at low angles (40–50) to the
E. Minor kink folds occur in the footwall and small
bedding-parallel faults in the hanging wall suggest Sdirected movement (VandenBerg et al., 1998). Wverging folds E of the fault indicate reverse (E over
W) movement. The relationships between the kink
folds, minor thrusts and the cataclasite bands indicate a component of dextral strike-slip. This may be a
consequence of sinistral movement along the Saltpetre Gap and Indi faults during the Bindian Orogeny.
Mines in the Glendart goldfield occur in the hanging
wall of the fault. The Sassafras Gap and Brown Creek
faults do not offset NE magnetic trends, including the
Dart Fault, which are presumably younger.
A minor fault which has affected rocks in the Dartella
Cauldron (VandenBerg et al., 1998) and is probably
related to cauldron collapse.
A Cainozoic fault in the Corryong and High Plains
Creek Fault
subzones that may have had an earlier Palaeozoic
movement (VandenBerg et al., 1998).
Table 3.34 Omeo Zone orogenic gold deposits
Omeo–Swifts Creek—6 t orogenic 3 t placer >3 t
(Willman et al., 1999a)
This narrow N–S mineralised corridor lies between the Ensay and
Haunted Stream faults, straddling the boundary between the Omeo and
Tabberabbera zones (Fig. 3.55). The earliest age of mineralisation is
constrained by mineralised faults which have cut the Swifts Creek Igneous Complex (G137, G526, G541, G545, G546) which is Early Devonian
(see appendix). The faults and Tabberabberan structures (cleavage and
folds) all trend approximately north–south so that no clear overprinting
relationship can be established. The Cassilis Mine is the major producer
and covers two main sets of mineralised faults which trend N to NE and
NW. Slickenlines on fault surfaces are predominantly horizontal indicating strike-slip movement with a geometry consistent with conjugate
faulting under N–S compression (Willman & Carney, 1998). The faults
are brittle with mineralisation occurring in breccia zones up to 5 m wide.
Mineralisation has been displaced by unmineralised sinistral cross-faults
(Willman et al., 1999a).
The Cassilis reef is sulphide-rich containing pyrite, arsenopyrite, pyrrhotite, chalcopyrite, galena and sphalerite (Fig. 3.65; MacLennan, 1987).
Gangue is mostly quartz with minor carbonate and sericite. The generalised paragenetic sequence is: (1) pyrite–arsenopyrite–gold; (2) pyrrhotite–
sphalerite–galena and (3) chalcopyrite–pyrite. Alteration envelopes surround veins and are widest around zones of cataclasis. Alteration minerals are dominantly white mica and carbonate which overgrow prograde
metamorphic minerals. Fluid inclusions indicate that fluids cooled progressively from ~400°C to 220°C. Isotopic data suggest the fluids were
derived from a magmatic source (MacLennan, 1987).
Mount Wills—8 t orogenic 8 t; placer negligible
(Oppy et al., 1995)
The Mount Wills goldfield, also known as Glen Wills–Sunnyside, covers
two main sets of steeply E-dipping mineralised faults near the E margin
of the Silurian Mount Wills Granite (G111; see appendix). These faults
post-date the granite and Benambran peak metamorphism, constraining
the maximum age of mineralisation. The faults form N and NE-trending
sets and have variable but predominantly horizontal slickenline directions (Crohn, 1958). Relationships indicate a conjugate fault set formed
largely by strike-slip movement under N–S compression (Willman &
Carney, 1998).
About 50% of recovered gold was processed from sulphide minerals which
form about 4% of the ore (Crohn, 1958). The paragenetic sequence is (1) a
pyrite–arsenopyrite–gold phase followed by (2) sphalerite–tetrahedrite
and a range of silver sulphosalts (Birch, 1981). Assuming pyrite and
arsenopyrite crystallised together, the estimated formation temperature
was 350°C.
Bethanga—3 t orogenic 3 t; placer negligible (Oppy et al., 1995)
Bethanga covers a group of distinctive sulphide-rich deposits. Typical ore
contains 10–80 g/t gold, 10–200 g/t silver, 0.5–6% copper and 1–10%
arsenic. Veins contain abundant pyrite, arsenopyrite, pyrrhotite, chalcopyrite and minor galena, sphalerite and native bismuth, consistent with
formation temperatures of about 310–350°C (Williams, 1969). This assemblage is overgrown by a late phase of carbonate–pyrite–marcasite
alteration. Strong sericite–pyrite–carbonate alteration surrounds veins.
Mineralised shears dip steeply and trend NNE with slickensides that
record a complex movement history with predominant strike-slip (Morrison, 1990). Mineralisation is widest where these shears cross ENE faults.
Faults clearly post-date peak metamorphism of host biotite gneiss.
Table 3.35 Faults in the Nunniong Domain
Emu
Egg
Fault
Deddick
River
Fault
Garron
Point
Fault
Syn-volcanic steeply-dipping structure with east-side down
movement. Forms the main western margin of the Buchan
Rift but loses displacement and ultimately disappears in the
south. Last significant movement in the Tabberabberan
Orogeny.
Large Tabberabberan NW-trending sinistral strike-slip
fault. Variable offsets along the fault suggest a component of
dip-slip movement. The Amboyne Granodiorite (G71) is
offset by 7.7 km and has a shear zone several hundred metres wide.
S-dipping thrust in the Limestone Creek Graben with Blueys Creek Formation thrust over Thorkidaan Volcanics.
Forms the northern limit of Blueys Creek Formation and
links with the Jam Tin Fault. Movement on the NNWtrending section is probably dominantly dextral strike-slip.
The fault was probably active in the Tabberabberan Orogeny.
67 TASMAN FOLD BELT SYSTEM IN VICTORIA
Table 3.36 Main structural features of the Kuark Zone
Western
Central
Eastern
Sardine
Creek
Graben
Area
F1 folds are upright, open to tight and are associated with
an axial-planar cleavage that varies from slaty to a crenulation, the latter having formed where S* is well developed
(see Box 17—Early S* foliation). F1 folds plunge gently SW
and have wavelengths of 100–600 m, probably averaging
about 300 m (Fig. 3.67B). Many hinges are truncated by
brittle faults. The fold enveloping surface is generally subhorizontal although locally vergence is to the SE (along the
Snowy River) or NW (Buchan–Orbost Rd S of Bete Bolong
Granite—G57). F1 folds are ascribed to the Benambran
Orogeny. Folded joint surfaces with slickenlines along the
Buchan–Orbost Road were interpreted as Tabberabberan
by VandenBerg et al. (1996).
Main structural trend is close to E–W in the Yalmy Rd area
but farther E along the Bonang Highway and Sardine
Creek Rd, trend varies from W to NNE, probably due to
fold interference patterns between E-trending Benambran
structures and N-trending Tabberabberan buckle folds
(Hendrickx et al., 1996). In the north-central part, variable
structural trends were produced by multiple deformation at
Delegate (VandenBerg et al., 1992).
Characterised by consistent NE trends within a zone of
highly strained and metamorphosed rocks produced in the
Benambran Orogeny. The Kuark Metamorphic Complex is
a major feature. To the N of the complex in the Hensleigh
Creek Rd area, lower-grade rocks have small-wavelength
isoclinal F2 folds associated with a predominantly Wdipping S2 cleavage (Simpson et al., 1997). E-verging isoclinal folds occur S of the complex at Cape Conran just W of
the Pheasant Creek Fault (Burg & Wilson, 1988; Hendrickx
et al., 1996).
Outcrop is poor but the evidence suggests that Silurian
Sardine Conglomerate is fault-bounded (VandenBerg et al.,
1992). A thin slice of Warbisco Shale along the S margin is
probably associated with a major fault affecting both Ordovician and Silurian rocks. The graben trends WNW, at an
angle to general trends in the far W of the zone, but is
parallel to the trends in Pinnak Sandstone immediately to
the S and is similar to trends in the Sardine Creek Rd area.
The graben may have been deformed at any time between
the latest Silurian and Middle Devonian.
Table 3.37 Faults in the Kuark Zone
Lucas Point
Fault
McLauchlan
Fault
Brodribb
Fault
Tooti Creek
Fault
Woodglen
Fault
Ellery Fault
Deddick
River Fault
Youngs
Creek Fault
Combienbar
Defines the E margin of the Buchan Rift and is possibly the SW margin of the Kuark Zone. Main fault formed during
Early Devonian rifting and was reactivated in the Tabberabberan Orogeny but may have had an earlier history. Downthrow to the west is in the order of several kilometres of (Orth et al., 1995). Continuous with the McLauchlan Fault to the
NE.
Comprises a narrow belt of complex faulting separating Yalmy and Bendoc groups from mainly Pinnak Sandstone. In its
best-exposed section along Yalmy Road it consists of a 500-m wide fault zone in which cataclasite bands metres to tens of
metres wide separate relatively undisturbed Pinnak Sandstone packages (Fig. 3.69). Cataclasites become wider and more
intense as the fault is approached; downfaulted Yalmy Group on the NW side are relatively undisturbed but show contact
metamorphism not evident in the Pinnak Sandstone. Glen and VandenBerg (1987) interpreted it to be a relatively late
structure (Bindian or Tabberabberan).
Marks the W boundary of a small belt of Lower Devonian Volcanics that trends to the NNE for approximately 3.5 km.
Subvertical fault with a length of at least 12 km, displaced in the S by at least three NE-trending dextral cross faults.
Separates a narrow belt of muscovite–biotite phyllite from lower-grade Pinnak Sandstone suggesting W over E movement
(Fig. 3.67B). Well defined on the aeromagnetic images (see Encl. 2) and may have acted as a conduit for dykes.
Lying close to the NW margin of the Kuark Zone, this fault has dismembered the Bonang Granodiorite (G49–G52) with
offset suggesting mainly dextral strike-slip with a component of dip-slip (VandenBerg et al., 1992). Within the granodiorite, the fault is marked by a foliation defined by reoriented hornblende grains. The fault is offset by the Deddick River
Fault and a series of related NW-trending sinistral strike-slip faults (Oranskaia, 1997a).
This is the main member of a set of NE-trending structures. The fault is represented by a narrow mylonite zone along the
NW margin of the moderately foliated Ellery Granite (G37) and runs along part of the SE margin of the foliated
Goonmirk Rocks Granodiorite (G34).
This major NW-trending sinistral strike-slip fault displaces the W margin of the Kuark Zone. Apparent horizontal displacement of geological units varies along the fault from a few kilometres to nearly 8 km suggesting a considerable component of vertical displacement (VandenBerg et al., 1992). In the Amboyne Granodiorite (G71) the fault consists of a nearvertical shear zone several hundred metres wide. Slickenlines are variable, mostly subhorizontal. In outcrops the fault is
a sheared granite only a few metres wide that sharply separates Warbisco Shale from normal granite. Aeromagnetic data
show a number of related NW to NNW-trending faults near the SE end of the fault (Oranskaia, 1997a).
Offsets the Eleven Bob Granodiorite (G55) and Dysentery Tonalite (G48) with apparent sinistral strike-slip with a component of west over east dip-slip (Fig. 3.67B). Its topographic expression suggests it is nearly vertical (Hendrickx et al.,
1996).
Defines the NE margin of the Kuark Zone, linking with the Pheasant Creek Fault and Mount Raymond Shear Zone to the
Fault Zone
Pheasant
Creek Fault
Wrak thun
bairlluk FZ
SW. The central portion traverses the Kuark Metamorphic Complex, is generally ~300–400 m wide, dominated by
quartz mylonite with epidote bands. It contains thin slices of sheared granite probably from the Murrungowar (G39) and
Tarlton (G41) granodiorites as well as mylonite from Arte Gabbro (G38). Foliations generally dip NW or are subvertical;
shear sense indicators show largely dextral strike-slip. Slices of Warbisco Shale occur at the intersection of the Combienbar and Pheasant Creek faults.
The southern part, along the W margin of the Mount Raymond Granite (G43), is also known as the Mount Raymond
Shear Zone (Hendrickx et al., 1996). It is marked by prominent topographic and magnetic features. Numerous ductile
shear zones have a strong mylonitic fabric and a rod-like lineation indicating a dominant N–S stretching direction suggesting strike-slip movement. Later movement along N-trending brittle/ductile strike-slip shear zones was accompanied by
intrusion of mafic dykes. Final phase was of low-angle brittle faulting.
Defines the SE margin of the Kuark Zone, linking with the Combienbar Fault Zone to the north. The Bungywarr, Crabhole Creek and McKenzie River faults are probably splays of the Pheasant Creek Fault. The hanging wall is well exposed
at Cape Conran where the syntectonic Cape Conran Granite has intruded strongly deformed Pinnak Sandstone.
This NW-trending structure ~15 km NE of Orbost developed in the Benambran Orogeny but was reactivated during the
Tabberabberan Orogeny. The zone is composed of fault slices of Bendoc Group, Pinnak Sandstone, Lower Devonian volcanics and Lower Silurian Yalmy Group (Hendrickx et al., 1996).
Table 3.38 Structural and sedimentary facies in the Narooma Accretionary Complex (after Powell,
1983b; Miller & Gray, 1997)
Coastal Belt
Facies I
Wagonga beds
Lithological
features
Structural
features
Facies II
Coastal greywacke and slate
Black shale, chert, mafic volFeldspathic and quartzose greywacke,
canics, pillow basalt breccia,
slate, occasional chert.
feldslitharenite.
Early bedding-parallel fabric, isoclinal recumbent folds localised to refolded zones, differentiated cleavage, structural mélange. Dominantly
east verging.
Table 3.39 Mallacoota Zone faults
Goolengook
Fault Zone
Genoa Fault
Zone
Buldah
Shear Zone
Fiddlers
Green Shear
Zone
Cann Valley
Shear Zone
Many early folds have subhorizontal axes suggesting
that deformation was associated with mainly horizontal
NWSE compression. However, the presence of steeply
plunging folds adjacent to some faults suggests that
some strike-slip displacement has occurred and is probably related to dextral displacement along the Combienbar Fault. Later vertical movement is indicated by
the close spatial relationship between the faults and a
subhorizontal to gently dipping crenulation cleavage.
This cleavage overprints all other structures except the
faults and is axial planar to kink folds with wavelengths
up to several metres. The orientation of the cleavage
and kink folds suggests that they were produced by
reactivation of the faults under brittle conditions. Byrne
(1983) argued that kink folds were formed by a late
episode of subvertical compression after bedding had
been rotated to vertical during the main early deformations. This may be related to major dip-slip displacement along the Combienbar–Pheasant Creek
Fault Zone in the Tabberabberan Orogeny that raised
the Kuark Zone relative to the Mallacoota Zone.
A major ESE-verging fold and fault zone in the centre of
the zone. The leading fault has 2 m of tectonic mélange
dipping 85 NW and is associated with a slice of
Warbisco Shale faulted against Pinnak Sandstone.
The Ordovician rocks are strongly cleaved with subvertical isoclinal folds. Shear bands indicate dextral
strike-slip interpreted as late-stage movement (Simpson et al., 1997). Local shear bands in Ordovician rocks
indicate a W over E sense of movement and imply that
the W margin of the shear zone is a steep W-dipping
compressional fault. This W margin is occupied by a
narrow slice of foliated granite with a down-dip stretching lineation that may be continuous with the Fiddlers
Green Granite (G23) to the N. The shear zone terminates against the Weeragua Granodiorite (G24) to the
S. Moderate to steep lineations in the N part of the
shear zone indicate mainly vertical movement with a
component of dextral strike-slip.
A NE-trending ductile shear zone in the Fiddlers Green
Granite (G25). Contains protomylonite, mylonite and
ultramylonite (Fig. 3.72) with average strike of 060
(010–080) and average dip of 85 NW. An elongation
lineation in the mylonites plunges 10–20 NE and indicates dominantly strike-slip movement; S–C fabrics
indicate a dextral sense.
A mainly N-trending zone composed of numerous small
brittle faults. Structural analysis indicates NW–SE
shortening was followed by N–S shortening (Begg et al.,
1987).
Inland Belt
Facies III
Inland greywacke and slate
Quartzose and feldspathic greywacke and
slate with thick graptolitic black shale and
chert bands.
East verging chevron folds with axial planar
slaty cleavage, no early bedding-parallel
cleavage. Reverse faults truncate folds.
69 TASMAN FOLD BELT SYSTEM IN VICTORIA
Rockton
Fault
Bemm Fault
Club
Terrace
Fault
Black Jack
Fault
Blue Gum
Fault
A N-trending structure up to 700 m wide adjacent to
the Loomat Granite (G20). Intensely foliated and mylonitic rocks occur in New South Wales where dextral
strike-slip movement has been documented (Woodfull,
1984; Davies, 1985). The fault weakens to the S and has
a late E-side down vertical movement which has preserved Upper Devonian Combyingbar Formation at
Genoa River.
Lies along the E margin of the Combyingbar Formation
in the Bemm River belt. It probably has an extended
history with early dip-slip in the Silurian? accompanied
by a component of dextral strike-slip movement.
Kanimblan reactivation has controlled the development
of a footwall syncline in the Combyingbar Formation
immediately to the W. Farther S along Poddy Creek Rd
the fault separates hornfels surrounding the Watchmaker Granodiorite (G502) on the W from crenulated
biotite psammites and phyllites on the E. The hornfels
is highly fractured and the foliation in the adjacent
metamorphics shows complex small folds. The presence
of higher-grade rocks on the east side indicates an E
over W movement sense.
A steeply E-dipping, strongly foliated ductile shear zone
in Pinnak Sandstone. Along the Princes Highway it is
represented by an intensely deformed ductile shear
zone with minor folds and folded quartz veins. However,
the fault is surrounded by numerous W-dipping brittle
faults suggesting significant reactivation. Immediately
S of Princes Highway, it runs along the Poddy Creek
gold workings. Aeromagnetic interpretation indicates
that it continues farther S, weakens, then swings to the
SW, becoming parallel with bedrock strike (Hendrickx
et al., 1996). The early ductile movement is probably
Silurian and the late movement is most likely Kanimblan.
This NE-trending fault cuts across the Cann Mountain
(G25), Loomat (G20) and Beehive (G21) granites. Dextral offset of the granites and the Beehive Fault, visible
in the magnetic data, indicates post-Early Devonian
movement. No associated foliated rocks have been observed (Simpson et al., 1997).
Lies on the E side of the Blue Gum Tonalite (G26),
adjacent to weakly to moderately foliated rocks. The
foliation strikes N–S and dips steeply E, but movement
directions have not been determined (Simpson et al.,
1997).
Table 4.1 Magmatic–hydrothermal metallogenesis
Copper
Early Devonian copper mineralised granites are oxidised, intermediate to
mafic I–types. They occur in all zones of the Benambra Terrane. The
granites are emplaced at high levels, commonly fringing coeval volcanic
sequences, and mineralisation is chiefly porphyry style, and less common
skarn style. Copper granites can be subdivided into copper  molybdenum
types, formed during crustal extension, and copper  gold types belonging
to the Boggy Plain Supersuite. Deposits related to extension form a continuum with epigenetic base metal deposits.
Molybdenum
Molybdenum deposits form during late-magmatic hydrothermal activity
related to moderately to highly fractionated, highly oxidised Early Silurian to Early Devonian I–type intrusions. Noteworthy deposits occur in all
zones except Melbourne, part of Bendigo (Melbourne Basement Terrane)
and Deddick. The reduced nature of Melbourne Basement Terrane granites may reflect more chemically evolved Selwyn Block lower crust.
Tin
Tin ± tungsten ± molybdenum ± gold mineralised granites are reduced,
fractionated Early Silurian to Late Devonian I– and S–types. Molybdenum and gold become increasingly important with increasing oxidation
state of I–type granites (Blevin et al., 1996). Tin granites have well defined compositions. They contain 60–70% silica, 20–25% sodium and
potassium in feldspar, and 5–15% femic cations and calcium in micas,
pyroxenes and amphiboles (Hesp & Rigby, 1974, 1975). Unaltered tin
granites have highly ferroan biotite (Scott, 1988). About 10 400 t of tin
concentrate has been produced in Victoria, mainly from Cainozoic placer
deposits related to granites in the Melbourne, Tabberabbera, GrampiansStavely and Omeo zones (Cochrane & Bowen, 1971; Nott, 1988). The only
magmatic–hydrothermal deposits with recorded production are in the
Tabberabbera and Omeo zones.
Tungsten
Tungsten  molybdenum  tin mineralised granites are Early Silurian to
Late Devonian, intermediate, oxidised and reduced, I– and S–types. They
are widespread, occurring in all Lachlan Fold Belt basement terranes.
The chief ore mineral is wolframite, but scheelite is not uncommon. Many
small deposits were mined early this century, particularly during the
Second World War, producing about 140 t of tungsten concentrates (Nott,
1988).
Table 5.1 Similarities and differences between the Whitelaw and Benambra terranes
Whitelaw Terrane
Benambra Terrane
Similarities





Widespread Cambrian volcanism
Widespread Ordovician to Silurian turbidite deposition (restricted thickness only in the Melbourne Zone)
Major deformation in the Late Ordovician  Early Silurian (Benambran Orogeny). However, this did not affect the Melbourne Zone
Major deformation in the Middle Devonian (Tabberabberan Orogeny)
Early and Late Devonian magmatism
Differences
Deep marine sedimentation ceased in the Late Ordovician in the
Stawell and Bendigo zones but was continuous in the Melbourne
Zone to the end of the Early Devonian. Shallow marine to terrestrial sedimentation equivalent to the Grampians Group may have
continued into the Silurian in the western Stawell Zone (see 2.7.1).
No arc volcanism, and no volcanism of any kind in the Middle Cambrian to Early Devonian interval.
Metamorphic grade is generally low except in the Moornambool
Metamorphic Complex.
Early Silurian S-type granites and migmatites are absent.
Eastwest trending Benambran structures are absent—all are
northwest- or north-trending and are associated with a regionally
consistent east–west to northeast–southwest compression.
Structural vergence has a dominant easterly sense except for the
Moyston Fault and for a small area in the Melbourne Zone (Fig.
5.3).
Late Silurian intracratonic volcanic and sedimentary basins absent.
Late Silurian  Early Devonian magmatism is post-tectonic and
less widespread.
Late Silurian – Early Devonian deformation weakly expressed or
absent.
Early Devonian rift basins absent.
Unusually large number of rich gold deposits.
Magnetic dykes uncommon.
Continuous deep marine sedimentation from the Early Ordovician
to Early Silurian over a significant area.
Large edifice(s?) of Ordovician arc volcanics and shallow-marine
sedimentary rocks (Molong Volcanic Arc)
Regional metamorphism and associated polydeformation associated
with the Benambran Orogeny (WaggaOmeo and Kuark metamorphic complexes).
Early Silurian S-type granites and migmatites are common.
East–west-trending Benambran structures indicate early development of localised components of north–south compression associated with orogen-parallel tectonic transport.
Regional vergence directions show a complex pattern (Fig. 5.3).
Late Silurian intracratonic volcanic and sedimentary basins common.
Late Silurian  Early Devonian magmatism is commonly syntectonic and widespread.
Late Silurian – Early Devonian deformation (Bindian Orogeny)
affected much of the terrane.
Early Devonian rift basins with volcanic and sedimentary rocks
common.
Small gold deposits only.
Magnetic dykes abundant.
Table 5.2 Major components of compression and extension in Victoria and their relative influence
in four major orogenies between the Late Ordovician and Early Carboniferous
Orogeny
Kanimblan
(Early Carboniferous)
Tabberabberan
(Middle Devonian)
Early Devonian
Bindian
(Late Silurian–Early
Devonian)
East–west
compression
Dominant
North–south compression or
tectonic transport
Absent
Dominant
Absent except in the Waranga Domain,
caused by docking of the Benambra and
Whitelaw terranes.
Possibly dominant in
the Kuark and Mallacoota zones but weak
or absent in the Omeo,
Tabberabbera? and
Deddick zones.
Dominant in the Omeo, Tabberabbera
and Deddick zones where large crustal
fragments were transported southward
along strike-slip faults with compressional tectonics at their leading edges.
Rifting
Mainly Late Silurian
Benambran
(Early Silurian)
Extension
Rifting along major
faults. Some rifts
caused by transtension
Dominant over entire
Lachlan Fold Belt
North–south compression locally important in New South Wales such as
along the Gilmore–Long Plain–Indi
Fault Zone. Dominant in the Deddick
Zone and possibly in the southeastern
Tabberabbera Zone and High Plains
Subzone.