Weetootla Network Geology Walks
These walks take us through many millions of years of geological history through glaciations and
times when the earth’s crust was crushed up and jostled for space, when calm seas allowed sediment
to settle or be moved around by gentle currents, to be later compressed, squeezed sideways or
vertically, or completely worn away.
Balcanoona Creek walk displays, like Italowie Creek the 700 myo sediments, pebbles and boulders
deposited by glaciers and later lithified to form tillite. The huge Paralana Fault, regarded as the
eastern limit of the Flinders Ranges, runs through this area, and is a salutary reminder of the scale of
earth movements that have occurred here and still continue. The land to the west of the fault zone
rode over the eastern land mass for a distance of 5 km along a length of some 50 km. The fault had
its origins about 850 million years ago during the early development of the Adelaide Geosyncline as
the earth’s crust stretched and thinned.
Monarch Mine walk follows the intricacies of the Umberatana Group of rocks laid down on top of
the tillite; they include the Amberoona Formation, Balcanoona Formation and the Tapley Hill
Formation, a name familiar to visitors from Adelaide, and applying to the very same rock which has
survived recognisably over a period of 670 million years in this diverse and contorted sediment pile
some 700 km south in Adelaide’s suburbs.
The sediments of these rocks were laid down in calm seas following the Sturtian glaciation of the
Cryogenian Period, 700 million years ago. Later earth movements and chemical changes to mineral
composition have made this area of interest to the mining industry from time to time.
There are striking rock forms and crystalline structures, delicious springs, evidence of climatic
variation and even early life.
McTaggart Track walk, although not recommended because there are 6.2 km of walking along a
vehicle track, provides views at the top of the hill of Amberoona Formation siltstones beyond
Checkpoint T2. No detailed notes are provided, but the route is shown on the map; geology is similar
to Monarch Mine walk.
Access: There are three locations in the Gammon Ranges National Park where you can access walks in the Weetootla Hike
Network.
Weetootla Camp Trailhead Checkpoint B1 is 7.1 km from Balcanoona - turn off the Arkaroola road at 1.9 km from the
finger post at Balcanoona; 2-WD access is available to Weetootla campground
Grindell Hut Trailhead Checkpoint B6 is 26.5 km from Balcanoona -turn off the Arkaroola road at 8.2 km from the finger
post at Balcanoona; 4-WD recommended (McTaggart Track).
McTaggart track, Checkpoint T1 is 18.2 km from Balcanoona - turn off the Arkaroola road at 8.2 km from the finger post at
Balcanoona, as above; continue about 10 km to reach T1.
Track: Easy grades on formed walking trails; some service tracks and creek bed walking.
Self guided options available from Weetootla Camp or Grindell Hut Trailhead.
1. a 6.0 km one way (12.0 km return) linear walk along Balcanoona Creek.
2. a 10.8 km circuit based on Grindell Hut Trailhead, involving portion of Balcanoona Creek Hike and
Monarch Mine Hike.
3. a 15.6 km walk from Weetootla Camp comprising an out-and-return from B1 to B2 and the
10.8 km circuit.
4. Weetootla Spring can be accessed from T1; walking along the access road to Grindell Hut is not
recommended.
Distances marked in km decrease as you approach your destination.
Balcanoona Creek Geology Walk (6.0 km from B1 to B6, Option 1)
Notes read as for start from Weetootla Camp; use Bush Walk map from the web.
6.0 Checkpoint B1 – Weetootla Camp Trailhead
Track passes along a gravel terrace above the creek with weathered yellow-brown dolomitic
siltstones.
5.7 Passes over the Paralana Fault zone which is not visible and enters Weetootla Gorge, which is
cut through the Balcanoona Range and consists of massive Bolla Bollana Tillite.
5.65 Pebbly tillite and breccias of siltstone fragments – indicating the base (or start) of Sturtian
Glaciation.
5.25 Massive tillite beds.
5.0 – 4.8 Laminated siltstone, interbedded with the tillite, which shows that tillite dips to the north.
Most of the tillite is massive – only a few thin beds of siltstone, shale or sandstone show
bedding which indicates the direction of dip.
4.4 Hell’s Gate – the narrowest part of the gorge; the walk traverses large boulders of coarse tillite
in the creek bed, with a variety of fragment sizes.
3.6 Checkpoint B2 – Junction of Balcanoona and Wortupa Creeks (start of Monarch Mine Walk)
There are usually permanent pools of water here, which flows down Wortupa Creek from Weetootla
Spring. Our track continues on up Balcanoona Creek, with the dark red-brown tillite of the
Balcanoona Ranges to the left and paler yellow-brown hills of Balcanoona Formation to the
right.
3.4 Track passes huge boulders of magnesite derived from the Balcanoona Formation Hills; several
other huge boulders can be seen on their slow progress over the slope of Tapley Hill Formation
from the dark crags on the skyline to the right. Exposures of tillite appear a little further on.
3.0 Cross the creek to the southern bank.
2.8 Here is a section of an old vehicle track, which crosses an island in the middle of the creek.
2.6 Checkpoint 3 – track junction near magnesite heaps.
This is positioned on laminated siltstones of the Tapley Hill Formation which is sandwiched between
the Bolla Bollana Tillite and the Balcanoona Formation.
There are several rows of magnesite heaps which result from BHP exploratory mining in 1956. The
magnesite is 96% pure and was an attractive prospect as feedstock for magnesium metal
production. The ore is bright white, crystalline and formed by replacement of Balcanoona
Formation dolomite. Although the leases were held for a long time, they have been
surrendered and mining cannot now occur. There are a number of fenced off adits that you can
peer into if you follow the creek bed (see below).
You may choose to follow the old vehicle track over shales of the Tapley Hill Formation where
Flinders Range Corkwood trees are common the slopes above the track; or you can follow the
creek bed upstream where you can look into the mine adits and walk across white boulders of
magnesite.
The creek bed is a beautifully sculpted white floor, displaying a range of magnesite replacement
textures, the most spectacular being bands of coarse crystals cutting across the bands which
are the ghosts of the original bedding. There are adits in the left and right banks.
Eventually the gorge passes into Tapley Hill Formation clearly showing in a cliff section on the left. It
consists of alternating bands of laminated siltstone and darker dolomite rich siltstones, similar
to that seen south of Adelaide.
2.0 Checkpoint 4 – track junction above creek.
The siltstones continue on and looking to the steep hillside to the north Balcanoona Formation (the
craggy top two thirds) overlies the layered Tapley Hill Formation dipping away to the north.
1.2 Track passes back into Balcanoona Formation, and there are good crystalline magnesite
exposures can be seen at the side of the track.
0.8 Blocky green laminated siltstones and dolomite of Amberoona Formation appears at a fault and
it is disrupted with isolated blocks of dolomite occurring within the contorted green siltstone.
0.4 Checkpoint 5 – junction with road to Grindell Hut.
This marks the end of the gorge with an uphill walk to the trailhead.
0.0 Checkpoint 6 – Grindell Hut Trailhead.
If you have not already done so walk up behind the main house to see the original hut and read
the plaques.
Monarch Mine Geology Walk (6.8 km from B2 to B5; Option 2 or 3 includes section
to Grindell Hut, B6).
Notes read as for a start at Checkpoint B2; use Bush Walk map from the web.
Distances marked in km decrease as you approach B5
6.8 Checkpoint B2 – junction with Balcanoona Creek walk.
Cross the creek which is often wet and follow the trail over grey thinly laminated dolomitic siltstones
of the Tapley Hill Formation.
6.2 Track crosses creek at right angles on a white magnesite pavement (take care – wet and
potentially slippery); just over the creek well preserved centimetre scale banding in the
magnesite shows that the replaced rock was the Tapley Hill Formation. This Formation consists
of thin beds of siltstone which contain varying amounts of dolomite giving an overall banded
appearance. When it is replaced by magnesite the banded appearance is preserved.
Close by, the magnesite shows angular WWWW folds perfectly preserving the original bedding
layers.
6.0 Grey unreplaced grey Tapley Hill Formation siltstones can be seen with identical “W shaped”
chevron folds.
Magnesite pavement continues in the creek bed with unreplaced Tapley Hill Formation on the right
and Balcanoona Formation – replaced by magnesite on the left.
The very straight course of the creek between B2 and M1 suggests that Wortupa Creek follows a
faultline. Faulting may have caused the local sharp chevron folds in the Tapley Hill Formation.
At the crossing thinly banded water rounded magnesite pavement again shows that it replaced
Tapley Hill Formation.
5.3 Checkpoint M1 – track junction at Weetootla Spring.
Head north-west up the hill, into the largely bare pale yellow magnesite hills of the Balcanoona
Formation. The original dolomitic rocks have been entirely replaced by magnesite. Any freshly
broken surface show fine grained pure white magnesite – noticeably denser than the original
dolomite (Specific Gravity of 3.2 as opposed to 2.8).
4.9 A fallen slab on the left contains some partly replaced stromatolites – signs of early life.
4.0 A patch of curly mallee – trees are rare on the magnesite probably because of thin soils – but
curly mallee seems to prefer substrates containing magnesium.
3.8 Sharp fluted weathering on these magnesite boulders is an example of small scale karst. Karst
weathering is characteristic of carbonate rocks including limestone, dolomite, magnesite.
3.3 Checkpoint M2 – viewpoint over ridge.
Take in the view and identify distant features using the topogram.
3.2 Massive Balcanoona Formation passes abruptly into blocky laminated green siltsones and
interbedded laminated dolomites of the Amberoona Formation. Siltstones are spotted with
white scapolite, sometimes forming half the rock.
3.3 Grindell Hut is visible.
The dolomites may be recrystallised to form dolomite marble. These finely laminated marble beds
are beautifully ‘fluted’ by karst weathering.
2.6 to 2.4 Track passes between several bands of brown dolomite marble within green scapolite
spotted siltstones. The marbles contain abundant randomly oriented clusters of needle-like
pale tremolite crystals, resulting from heating of the dolomite.
Stromatolites have survived this process and delicate traces of their domes can be seen in the marble
at 2.4 km.
2.3 Checkpoint M3 – remains of Monarch Mine.
Located in the Amberoona Formation, a small tonnage of copper ore was extracted here between
1906 and 1908. Although there is an abundance of green copper carbonate (malachite)
staining, there is little copper here. Only 12 tons of ore were treated.
A variety of secondary copper minerals occur, blue azurite, pale blue green chrysacolla, cuprite, and
chalcocite. The ore fragments at the foot of the sloping slab floor suggest it was used to sort
and bag ore for carrying it out on horseback. Wooden boughs supported canvas for shade.
1.9 A similar disappointing copper prospect.
1.85 From this prominent point the geology is laid out. A set of dark dolomite beds to the southwest outlines a large synclinal fold in Amberoona Formation – the knob of dolomite here is part
of one of them. These are the lower beds as they occur near the base of the Amberoona
Formation, just above the Balcanoona Formation. A second set of dolomite layers occurs near
the top of the Amberoona Formation on the flanks of the hills (looking towards Grindell’s Hut).
They are capped by red-brown Elatina Formation with minor tillite, which reflects a second
minor glaciation (Elatina Glaciation 630 million years ago), some 100 million years after the
Sturtian glaciations.
Note that a period of prolonged erosion has been identified between the Amberoona and Elatina
Formations. This could have been glacial or coastal in origin.
The curve of these hills reflects the shape of the fold. Pale cream bare hills of magnesite (replaced
Balcanoona Formation) can be seen to the south-east with dark Bolla Bollana tillite of the
Balcanoona Range beyond. To the west are the Rawnsley Quartzite peaks of the Gammon
Ranges.
The distinctive high level terrace of the Gibber Plain can be seen to the south-west.
1.6 The trail continues down though a small grove of pines which are located on the upper band of
dolomite layers within the green siltstones of the Amberoona Formation.
Trail enters a small gully cutting through several dolomite beds.
1.0 A thin bed of red-brown Elatina Formation sandstone is crossed, followed by a layer of thin
dolomitic bands of Nuccaleena Formation – a marker layer between the Umberatana Group and
the Wilpena Group. The Wilpena Group is here represented by buff coloured Ulupa Formation
siltstones (equivalent to the Brachina Formation further south).
0.8 Here there is a return to contorted green Amberoona Formation siltstones, with isolated blocks
of dolomite and quartzite, part of a large breccia body which extends as far as . . .
0.0 Checkpoint 5 . . . and 0.4 km beyond to Grindell Hut. End of Monarch Mine walk.
GLOSSARY OF GEOLOGICAL TERMS
For composition of different rock Formations and Groups, see Stratigraphic Column.
Adelaide Geosyncline A deep subsiding trough into which over about 350 million years, material eroded from
adjacent land masses was deposited.
azurite dark blue copper carbonate.
banded parallel stripes of different colours, generally, but not always, representing bedding in sedimentary
rocks.
bedding, layers, interbedding Bedding is the original surface on which successive layers of sediments were
deposited. Originally these were essentially horizontal.
Bolla Bollana Tillite product of the Sturtian glaciations; occurs west of Paralana Fault (see Merinjina Tillite).
breccia Broken up rock; can be formed by wide range of processes.
chalocite Grey copper sulphide – a high grade copper ore.
chrysocolla Blue-green copper silicate, common in arid climates.
copper Bright pink metal, Cu. Important industrial commodity.
copper carbonate Brightly coloured, hence easily recognised secondary copper minerals formed by the
weathering of primary copper sulphide minerals. Most common are malachite (green) and azurite (blue).
Cryogenian Period The base of this Period is defined at 850 million years ago, and its top is the base of the
Ediacaran Period, which as yet is not defined by a precise time, but is about 630Ma.
cuprite Red copper oxide.
dip The angle at which a rock layer is inclined to the horizontal.
dolomite Rock that is largely composed of the dolomite mineral, CaMg(CO3)2
fault, faultline, fault plane, fault zone A fault is a physical break in a body of rock. Faults may be of huge
displacement, many kilometres (e.g. Paralana Fault), or only a few centimetres.
Formation A sedimentary or volcanic rock unit which can be physically mapped and defined by features
observed in the field.
gibber Rock fragments which have accumulated as pavement due to the removal of all fine sediment by wind.
Individual fragments are darkened by a thin layer of iron oxide ‘desert varnish.’
Group a unit which includes several Formations of usually sedimentary rocks.
interbedded layers of sediment lying in or parallel to layers of other material.
karst Irregular surface and subsurface topography produced in carbonate rocks (limestone, dolomite) by
ground water solution.
laminated Thinly, regularly banded: almost always reflects bedding – siltstones, shales.
limestone Sedimentary rock made of calcium carbonate.
lithified Turned into stone.
magnesite Heavy mineral, magnesium carbonate MgCO 3; source of magnesium and used as a refractory in
steelworks.
magnesium A metal found only in other compounds such as magnesite, MgCO 3 and dolomite, CaMg(CO3)2
malachite Bright green copper carbonate.
marble Recrystallised carbonate sedimentary rock.
Merinjina Tillite product of the Sturtian glaciations; occurs east of Paralana Fault (see Bolla Bollana Tillite).
quartzite A rock which was originally quartz sandstone which has been heated or compressed sufficiently to
fuse the grains together, producing a tough resistant rock.
recrystallised When rocks are heated , they undergo physical and eventually chemical changes The most
common is the recrystallisation of low temperature sedimentary rocks where the original fine grains are
enlarged by grain growth, often as individual crystals. Common examples are the formation of marble
from limestone, or quartzite from quartz sandstone.
replacement When one mineral takes the place of another by chemical transformation- a new chemical
element comes in, otherwise merely recrystallization.
scapolite, scapolitic A complex calcium-sodium alumino-silicate, which can accept large amounts of
carbonate, chloride or sulphate in its crystal structure. Often occurs as matchstick shaped crystals in
altered limestones.
siltstone A rock composed of silt sized mineral grains – usually mainly quartz.
specific gravity Ratio of the weight of equal volumes of the substance and water.
stromatolite Domal or columnar layered structures built up by microbial organisms. Among the earliest life
forms and some survive to the present.
syncline, synclinal A concave downwards fold.
tillite Rock formed by glacial activity, containing a very wide range of grain sizes, usually including some large
fragments obviously not locally-derived, known as erratics.
tremolite A magnesium rich alumino-silicate commonly with a fibrous habit.