The Bararranna walk has complicated geology, because the orderly sequence of sediment layers as shown in the stratigraphic column has been disrupted by earth movements associated with the giant Paralana Fault (which here has two arms) and other minor faults. As a result some rocks have been displaced and dragged from their normal positions. Some in the sequence have disappeared or are insignificant because of erosion.
We are moving into lower layers of the sediment pile from the tillite of the Umberatana Group into sediments of the Burra Group with characteristic Skillogalee dolomite, Blue Mine Conglomerate and Woodnamoka Phyllite. Below these again are rocks which did not originate as sediment – the
Wooltana Volcanics.
These layers of lava originated when the earth’s crust stretched and thinned as the Adelaide
Geosyncline began to form. Molten rock emerged through fissures and flowed on to the surface of the accumulating sediments. In places on this walk, lava is now exposed on the surface.
Distance and time: 6.8 km circuit walk; allow 3.5 hours.
Altitude range: 210 m (Stubbs Waterhole) to 280 m (saddle above Welcome Mine).
Access: The Welcome Mine Trailhead is generally accessible to 2-WD vehicles. Welcome Mine is about 10 km from
Arkaroola along the Paralana Hot Springs road.
Track: Some road and vehicle track walking; some rock scrambling
Distances, marked in km, increase as you return to Welcome Mine.
Notes read for an anticlockwise circuit.
0.0 Checkpoint B1 Welcome Mine Trailhead – car park
The mine is 50 m to the east and consists of old and more recent workings. The mine was originally operated in the 1860s by H C Gleeson. Three miners raised 23 tons of ore and dressed and bagged it. The ore contained 40% of copper and was valued at £35 per ton; it was carted to Port Augusta and then shipped to smelters in Wales. Drought in 1864 meant that draught animals could not work and 19 tons of ore waited at the mine until the drought ended in 1867.
Beach Petroleum Ltd drilled extensively in 1970, but copper grades decreased with increasing depth.
The trailhead is located is on Blue Mine Conglomerate weathered to a pink colour, with excellent examples of heavy mineral laminations and cross bedding.
0.2 The road curves slightly and passes on to thinly laminated fissile buff siltstones of the Tapley Hill
Formation, well exposed in the gutter on the right of the road. The bluffs on the top of the slope to the right are dolomites of the Balcanoona Formation, lying above the Tapley Hill
Formation.
0.4 From the saddle here to the east is Welcome Pound, floored by Tapley Hill Formation; behind it are the looming dark hills of Merinjina Tillite which include Mt Jacob.
0.9 Checkpoint B2 Leave the road, following east.
1.2 Leave Mt Jacob track. Tapley Hill Formation siltstone continues under foot.
1.3 Here there is a thin bed of yellow-brown laminated dolomite, which forms a cap to underlying
Merinjina Tillite. Just past this, the coarse tillite contains large quartzite erratics up to 2 m across, some of which are facetted and striated (scratched). Large erratics of Blue Mine
Conglomerate are common here also.
1.4 The track enters a creek with small waterfalls. Good tillite is exposed; the very coarse boulder tillite has a green matrix which weathers a deep red. Going down the second small waterfall, you step on a large quartzite boulder well striated by glaciers. Erratics of purple oxidized
Wooltana Volcanics can be seen here, and at about 1.8 km is a quartzite erratic, over one metre across with very well developed striations, in three different directions. Not to be overlooked!
Between here and Arkaroola Creek there are spectacular exposures of coarse purple boulder tillites including numerous locally derived erratics of Blue Mine Conglomerate and Wooltana
Volcanics.
1.9 Checkpoint B3 This section of Arkaroola Creek has wonderful exposures of massive boulder tillite in the walls and creek bed.
2.0 Here is the creek and (sometimes) a waterhole; the tillite shows attractive brown and purple bands of iron staining called Liesegang Rings. The concentric bands occur through the body of

the rock; they are of uncertain origin but seem to arise as chemicals are precipitated from solution in sandstone rock. Tillite cliffs continue.
2.5 Stubbs Waterhole car park; the cliff to the left has a bed of close packed quartzite boulders as part of the tillite at the base of the cliff; fine sediments may have been washed out by currents.
2.7 Underlying Burra Group dolomites are exposed to the left. Ahead is the dark Bararranna Hill of
Humanity Seat Formation
2.9 Checkpoint 5 – Bararranna car park; track junction.
An outcrop of iron and manganese oxide stained Burra Group dolomites is just to the left; the dolomites have been broken up by an adjacent fault which has allowed ground water to deposit surface oxide concentrations. The fault (an arm of the Paralana Fault) has brought the dolomite into contact with the Wooltana Volcanics at . . .
3.0 to 3.2 . . . where the track passes brecciated dark green rocks of the Wooltana Volcanics with dolomite and quartzite occurring in or next to a fault zone. This is a branch of the Paralana
Fault.
3.3 Good exposures of Blue Mine Conglomerate on the left show cross bedding with heavy mineral laminations and well rounded pebbles of vein quartz, chert and pink fine grained granite.
3.4 The track passes into Humanity Seat Formation, a grey to pink fine grained laminated quartzite with numerous examples of small symmetrical ripple marks – these are due to wave action in shallow water; examples of heavy mineral laminated and cross bedding are also common.
3.6 to 4.0 (Checkpoint 6) The left wall of Bararranna Gorge has spectacular exposures of the steeply dipping beds of the Humanity Seat Formation quartzite, showing the numerous 1 to 2 m thick individual beds, forming the lowest layer of the Burra Group.
4.0 Checkpoint 6 – creek junction.
One can deviate further up the gorge if water levels permit to see more spectacular examples of the quartzite layering; here the orientation of the creek allows large exposures of ripple marked bedding planes – both symmetrical wave and asymmetrical current types are visible. It is interesting to realise that the Humanity Seat Formation, is here more than a kilometre thick, yet the water was always a just few metres deep, as the seabed kept slowly sinking as sediments accumulated, a shallow depth of water always being maintained.
From Checkpoint 6 the track leaves the Bararranna Gorge via a tributary on the left.
4.2 Blue Mine Conglomerate in its familiar form overlies Humanity Seat Formation. Laminated quartzite and green soft talcy siltstone form beds in the conglomerate; a bed of iron stained siltstone forms a bar across the creek at 4.35 km. Coarse conglomerate with interbeds of ripple marked sandstone continue as far as . . .
4.5 Checkpoint 7—junction with spotted Schist Pass Track.
The trail follows the track south, parallel to and about 300 m east of the Paralana Fault; the dark range to the west is Woodnamoka Phyllite, which is west of the fault. The track follows creeklines which exploit weakness caused by the fault. The abundant pebbles of grey banded phyllite with mica sheen, and grey spotted rocks are derived from these hills. The spots are the remains of andalusite grains which formed under high temperature and pressure deep in the crust but have ‘retrograded’ to lower temperature minerals, mainly micas, as the rock came close to the surface.
Track is over green talcy Opaminda Formation with a few dolomite beds, but at . . .
5.5 . . . it passes back into Blue Mine Conglomerate.
5.8 The minor workings of the Wheal Hancock copper mine are on the right, in dolomite broken up by the Paralana Fault.
6.0 North-running white quartz veins within the fault can be seen about halfway up the hillside.
Burra Group brown dolomite to the right overlies a thin bed of Blue Mine Conglomerate.
Along this part of the track, close to the fault, the rocks have been dragged, twisted and disrupted so that many are displaced from their normal relative positions.
6.4 to 6.5 Wooltana Volcanics of the Callana Group are here; they are dark green altered basalts, stained by green copper carbonates and can be seen on the track cutting. The volcanics host numerous small copper occurrences in the Mt Painter province. The track crosses a thin bed thin bed of Blue Mine Conglomerate before passing over a hill of Wooltana Volcanics on the way to the trailhead. Along the track to the left are many good examples of basalt with vesicules (holes); the pale spots in the dark green basalt were originally vesicules produced by gases in the lava, which were later filled by other minerals, mainly fine grained quartz; this is

called ‘amygdaloidal’ texture and is convincing evidence that they were formed as lavas. The red zeolite mineral stilbite can be found in vesicules here also.
In the vicinity of the road crossing is another arm of the Paralana Fault which brings the volcanics up against the Tapley Hill Formation, where normally there are several kilometres of sediment between the two.
6.8 Checkpoint 1 – Welcome Mine Trailhead.
Text prepared from field notes supplied by Nick Langsford
GLOSSARY OF GEOLOGICAL TERMS
For composition of different rock Formations and Groups, see Stratigraphic Column
amygdaloidal Volcanic rock with numerous cavities caused by evolution of gas, often filled by low temperature minerals deposited by warm water.
andalusite High temperature alumina-silicate mineral, common in metamorphic rocks.
basalt Dark green igneous or volcanic rock, made up mainly of feldspar and ferromagnesian minerals – alumino-silicate minerals with notable amounts of iron and magnesium.
breccia Broken up rock; can be formed by a wide range of processes.
carbonate General term for the rock-forming carbonate minerals; mainly calcite which forms limestone, and dolomite and magnesite, all of which are ‘carbonate’ rocks.
chert Very fine grained quartz.
conglomerate Sedimentary rock with a major component of coarse usually rounded rock fragments.
copper Bright pink metal, Cu. Important industrial commodity.
cross bedding Where sediment layers are at an angle to the main stratification, often outlined by dark heavy minerals.
dolomite Rock that is largely composed of mineral dolomite, Ca Mg (CO
3
)
2
erratic In glacial sediments, large rocks which have been transported a considerable distance from their point of origin, by glaciers.
facetted Rock which has been abraded to flattish surface e.g. by glaciation.
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.
fissile Easily split, usually along bedding planes.
Formation A sedimentary or volcanic rock unit which can be physically mapped and defined by features observed in the field.
Group A unit which includes two or more Formations of usually sedimentary rocks.
iron Metallic metal, Fe; with important industrial value.
laminated, laminations Thinly, regularly banded layers of sediment; almost always reflects bedding.
lava Molten volcanic rock.
Liesegang rings Attractive concentric, often highly convoluted colour bands in homogeneous rocks.
manganese A hard grey metal, Mn; used as alloy in steel manufacture.
matrix A rock in which other material is embedded.
metamorphism Change produced in a rock due to dramatic changes in temperature and pressure. While the overall chemical composition may not change much, the minerals present and the ‘fabric’ of the rock can alter dramatically.
mica A series of alumino-silicate minerals which have the property of splitting into thin sheets – hence ‘books’ of mica. The most common are white muscovite and black biotite.
outcrop Exposure of rock layers protruding through the overlying soil and debris.
phyllite A somewhat metamorphosed slate, with abundant mica on splitting planes giving a distinct sheen.
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.
ripple marks Sedimentary structures formed on sandy surfaces by wave or current action. Very common in sandstones and on present day beaches. Has the appearance of corrugated iron.
sandstone A rock made of sand – mostly quartz sand.
schist A fine to medium grained metamorphic rock with structure defined by the parallel alignment of micas .
siltstone A rock composed of silt-sized (less than 0.1 mm) mineral grains, usually mainly quartz.
stilbite A low temperature zeolite silicate mineral commonly found in amygdales (volcanic gas cavities).
talc Complex mineral with soapy feel, Mg
3
Si
4
O
10
(OH)
2
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; e.g. Merinjina Tillite – Bolla Bollana Tillite of
Sturtian glaciations.
vesicules Unfilled gas bubble holes in volcanic rocks, as in vesicular basalt.
volcanics Collective term for igneous and basaltic rocks originating from a from volcanoes.

zeolites A group of low temperature, hydrated alumino-silicate minerals. They have several unusual properties. They can readily exchange calcium and sodium hence are used to ‘soften’ water; and after dehydration will readily absorb organic and heavy metal pollutants.