Bruce Mowat & Stuart Smith

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Introduction
 History of exploration and research
 Distribution of systems
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Review key geological aspects of the major deposits
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Characteristics of the Temora porphyry systems
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Future challenges of exploration

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1976 Geopeko/North identifies porphyry style
Cu-Au in the Goonumbla area
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Initial Research, (Paul Heithersay, John Walshe)
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AGSO, NSW DMR (Doon Wyborn)
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Newcrest identify Cadia Hill porphyry system
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AMIRA P425 (Gregg Morrison, Phil Blevin)
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SPIRT (Dave Cooke, Tony Crawford, Dick Glen)
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Ongoing research by Newcrest team

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Macquarie
Arc is a component of the Lachlan
Orogen
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Ordovician to early Silurian
Volcanic
Province
Melbourne
Sydney

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Four Separate
Belts
Junee-
Narromine
(JNVB)
Molong (MVB)
Rockley-
Gulgong
(RGVB)
Kiandra (KVB)
JNVB
-3 2 °
Narromine

MVB

RGVB
Orange
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-3 4 °
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Temora

Parkes
KVB
0 km
100

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24 porphyry systems
Most (22) occur within definable districts
17 including all operations within
Cadia and
Northparkes
Districts defined by coherent geological character
Clustered
-3 2 °
-3 4 °
Narromine
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Northparkes District
Orange
Cowal District
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Cadia District
Parkes
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Temora 
Rain Hill District
0 km
100

Northparkes District
Cadia
Lake Cowal
Copper Hill
Cargo
Macquarie Arc – Summary Time-Space Plot

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Macquarie arc - Australia's only economic porphyry province

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Higher proportion of intrusive rocks
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More complex (but not unique) magnetic signatures - most related to intrusive activity
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Gravity lows
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Overall more felsic
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Overall more potassic

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455 Ma
 E43, Cargo, Copper Hill,
 Low K, dacite association
 adakites
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440 Ma
 Cadia District, Northparkes, Rain Hill
 Medium to High K, monzonite association

440
450
465
480
Late intrusive shoshonites
(monz)
Evolved shoshonitic lavas suites
Copper Hill-type adakitic dacite-gdt suites
Middle Ord high-K to (higher) shoshonitic lavas
Narromine and Cowal
Middle Ord Intrusive
Monzodiorites etc (hi-K CA)
Nelungaloo Volcs and Mitchell Fmn-
- Hi-K calc-alk and shoshonitic

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Macquarie Arc dominated by basalts and andesite compositions
Productive districts tend to be more felsic on average
E43, Cargo and Copper Hill low-K Calc-alkaline
 Dacite porphyry association (adakites)
Rain Hill District medium to high-K Calc-alkaline
Cadia and Northparkes districts are high-K to shoshonitic in character, the most potassic regions in the arc
 Monzonite, syenite, latite, trachyte

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Core:
 potassic (biotite-mt; orthoclase-qtz-sulphide-hematite)
 calc-sodic (act-mt-ab)
 Phyllosilicate (sericite, hm, ab)
Distal:
 propylitic (chl-carb-epi-ab-hm)
 sodic (ab-chl-tm)
 Phyllosilicate (sericite, albite)
Late faults:
 phyllic (QSP-carbonate-base metals)
Distinctive pink rock hematite alt of intrusions & volcanics

GOONUMBLA
Schematic Intrusives -
Alteration - Mineralisation
G Morrison & P Blevin 3/96
Ap
MZp
ALTERATION
K Feldspar-quartz
MMZp
K Feldspar destructive
Sericitic
Kf network + biotite spots
DI
MZD
MMZc
GRp
MMZm
MZD
MMZc
MMZp
MMZa
MMZa MMZp

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Cadia East, Ridgeway, E26, E48 have sericite and/or albite bearing zones
 These can be
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Central and directly associated with ore
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Proximal and directly associated with ore
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Peripheral and not associated with ore
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Minor associated with narrow fault zones
 Distinguishing these is critical but can be very difficult

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Extensive alb-ser-tourpy-hem zone
 Above and peripheral to orebody
 Obscures outcrop of the orebody
After Tedder et al., 2001
500m
Reg Prop
Skarn
Skarn Prop
Alb-ser
Alb-qz-hem
Calc-sodic
Inner Prop
Outer calc-pot
Inner calc-pot

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Widespread and generally high level qtz-ser-py-alb
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Highly bleached
Unaltered or Propylitic
Qtz-ser-py-alb
Weak K-fs
Strong K-fs
Weak mt-bi
Strong mt-bi

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E26 & E48 both have a core zone of magmatically derived sericite +/-albite, alunite
 Associated directly with bornite, chalcocite, covellite, digenite, tennantite, enargite
Generally > 2%Cu

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One of the greatest unknowns in Macquarie
Arc porphyries
 Cadia has both distal and proximal
 Northparkes, possibly has distal
 Strong and very widespread regional assemblage that is definitely unrelated to mineralisation
 Use with extreme caution

Ridgeway
Cadia East
Outer Propylitic
Inner Propylitic
Albite-pyrite
Potassic
Calc-Potassic
Garnet-silica
After Wilson et al., 2003
200m
After Tedder et al., 2001
500m
Reg Prop
Skarn
Skarn Prop
Alb-ser
Alb-qz-hem
Calc-sodic
Inner Prop
Outer calc-pot
Inner calc-pot

► eg. Cadia East
Extensive alb-sertour-py alteration
500m
Reg Prop
Skarn
Skarn Prop
Alb-ser
Alb-qz-hem
Calc-sodic
Inner Prop
Outer calc-pot
Inner calc-pot

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Some clues - but a lot more work needed
 Fracture control
 Overlap with most distal magnetite-biotite
 Any low level Cu
 Prehnite/actinolite
Distal Porphyry ep-chl-preh
Regional ep-chl-calc

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Magnetics is the second most common targeting tool (behind simple Cu & Au geochemistry)
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How well do we understand the controls on magnetite distribution and therefore the types of signatures to expect
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What are the controls
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Primary magnetite
Magnetite constructive alteration
Magnetite destructive alteration

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Magnetite constructive alteration
 Occurs in ALL systems, but location is not always the same
 All Macquarie arc systems share an early mt alteration stage
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Associated with early intrusions - can be widespread
-several 100 m from intrusions
Distal magnetite-biotite

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Cadia systems
 Ridgeway - direct association with ore
Ridgeway Cross Section
Contoured Magnetic
Susceptibility values; 10 -5 SI After Harper, 2000

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Fundamentally different character
 In all known systems the ore-bearing stage overprints and destroys earlier magnetite constructive stage
 Amount of early magnetite AND magnetite destruction is variable the degree of
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Mt alteration is in part function of host rock composition
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Intermediate hosts develop large mt halos
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In felsic hosts low 1 o Fe content results in lesser mt

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E26
 Major ore stage is associated with intense
K-feldspar alteration
 This overprints and destroys much of the magnetite-biotite alteration

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E26 - magnetite destructive K-feldspar
Weak
Remnant bi-mt alteration
Moderate
Intense

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Directly associated with Ore
 Ridgeway
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Magnetite destruction with Ore
 E26
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Felsic host less Mt
 Northparkes
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Mafic to intermediate host more Mt
 Cadia Region

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Cu-Au
 Pipe-like systems (eg NPM, Ridgeway) show a strong zoning with Au increasing toward cores
 Can be used as an exploration tool - slight systematic increase in Au:Cu should encourage further drilling

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Systems have traditional Cu, Zn zoning
From Heithersay & Walshe, 1995
Cu anomaly much larger than the systems
Lows within major ?peripheral Zn anomaly

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Remarkably intact, little deformation
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Northparkes
 Intrusives vertical, 30 degree dip volcanics
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Cadia
 Intrusives vertical, stratigraphy flat
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Cowal
 intact
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Rain Hill
 Devonian shear zone overprint

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Goldminco Corporation holds majority of
District
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Junee-Narromine Volcanic Belt
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6 identified systems so far
 The Dam, Mandamah, Culingerai, Estoril, Harold
Bell, Yiddah

Temora
Geology

Belimebung
Volcanics
Boonabah
Volcanics
Currumburrama
Volcanics
Temora
Magnetics
Gidginbung
Volcanics
Rain Hill
Monzodiorite
Gidginbung
0 kilometres
5 10

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Porphyry mineralisation clustered around margin of Rain Hill Monzodiorite
 Similar setting to Northparkes
Medium to high-K calc-alkaline
Mineralisation associated with high level porphyritic monzodiorite dykes and plugs
 435 Ma age on syn to post mineral dyke
Andesitic volcanics and volcaniclastics
 No felsic volcanics
 Qtz poor volcanics and intrusives

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Mineralisation
 Early classic qtz-mt-py-cpy seam veins
 Late coarse qtz-carb-chl-cpy veins
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Alteration
 Core mt-hm-biot-chl±K-feldspar
 Distal phyllic ab-ser-py
 Late propylitic chl-ep-carb
 Devonian ser-py shear overprint

Qz-mt-ksp-cpy veins
Chl-mt-bi alt volc
Qz-mt-cpy seam vein
Ep-chl overprinting
Early mt-ksp alt

Estoril porphyry Au-Cu system
Qz-mt-cpy veins in
Diorite host rock
Sheeted qz-mt-cpy veins
Andesite and MZDR
Intrusive host rock

Qz-mt-ksp-cpy veins
He-mt alt MZDR
Local intense He-mt
Alteration
MZDR

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Geological Setting
 Similar to Northparkes setting
Age
 Late Ordovician early Silurian
Similar alteration facies
 Inner Potassic and overprinting phyllic
Igneous character
 Oxidised High-K intrusives
Mineralisation
 Qtz-mt-cpy seam veins
 Alteration and ore stage mt

Differences to current economic systems
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No Felsic rocks
 Lack of the felsic suites (monz, trach, latite)
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Limited hematite
 Much less alteration hematite than Northparkes
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Post mineral tectonics
 Overprinted by Devonian shear zones

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Ordovician Systems
 Current model prefers the current 4 productive districts (tightly held)
 Under cover Narromine-Junee
 Variations on current model (Less oxidised systems)
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Other Ages
 Siluro-Devonian Systems (Yeoval, Bald Hill,
Vic, Bushranger)