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Deposit Synonyms
Cattle Grid; Cattle Grid South; Elizabeth Creek; Gunson; Ml 4247; Ml 5599
Mineral District
Mount Gunson Copper
Deposit Summary
stratabound Cu mineralisation at disconformable contact between red beds of the Pandurra Formation, & overlying Whyalla Sandstone. Production from 1974-86, 7.2 Mt @ 1.7%Cu & 8.3g/tAg.
Deposit Description
CATTLEGRID, the major deposit of the Mount Gunson Mining District, where copper mineralisation was strata bound at the brecciated, disconformable interface between red bed sandstone of the late Mesoproterozoic Pandurra Formation, and overlying Whyalla Sandstone of Marinoan age. The silicified upper surface of the Pandurra Formation was brecciated by Marinoan periglacial activity, creating a discontinuous horizon named the Cattle Grid Breccia, which became the host for copper mineralisation. At Cattle Grid, copper sulphide mineralisation formed a network of fracture filling veins in a tabular quartzite breccia body of palaeo-permafrost origin, averaging 4.5 m thick and occupying an area of 1,400 m x 600 m. Minor quantities of copper sulphide formed a matrix in Whyalla Sandstone in some places.
The principal copper minerals were chalcocite, bornite and chalcopyrite. Mineralisation was asymmetrically zoned on a more or less horizontal plane, with a core of chalcopyrite rimmed progressively by a bornite-rich zone followed by a chalcocite-rich zone. The zoning appeared related to increasing permeability of the host rock. Ore textures indicated repeated dissolution and redeposition of sulphide minerals, with the dominant process being the replacement of copper-iron sulphide phases by copper sulphide phases, although early iron sulphides did not appear as abundant as later copper sulphide. Age dates obtained in 1974 gave a tentative age of mineralisation of 1350 to 920 Ma, with possible remobilisation from 920-500 Ma.
Copper was the major ore metal, but the ore also contained significant quantities of zinc and lead, as well as bismuth and cobalt. There were appreciable quantities of nickel and arsenic, trace amounts of silver, and rare gold, all present as elemental inclusions in various sulphide minerals. Open cut production from Cattle Grid from 1974-86 (excluding blended production from Main Open Cut), was 7.2 million tonne (Mt) of ore, with a recovered grade of 1.7% Cu, and 8.3 g/t Ag. Head grade for ore delivered to the concentrator was about 2.0% Cu. A typical copper concentrate assayed 44.8% Cu, 10.6% Zn, 2.6% Pb, 1.0% Co, 0.15% Bi and 0.08% Ni. The workings consisted of 3 connected open cut pits over a distance of ~1.5km EW. A 2000 resource figure was 5.6Mt @ 2.1%Cu at 1% cutoff (Selley, 2000, pp28).
THZ pty Ltd in 2014 proposed an alternative model for mineralisation at Cattle Grid. They propose a redox interface model where mineralisation occurs where the reduced Whyalla Sandstone is in contact with oxidised strata, eg underlying red-bed Pandurra Formation. They postulate an exploration potential for other redox contacts, for instance Whyalla Sandstone with the overlying oxidised Tent Hill Formation. Petrographic studies indicated ironstone on the Arcoona Plateau is probably of lateritic origin, whilst those on the western margin of Pernatty lagoon might represent the residuals of a roll-front system. Mineralisation of the Whyalla Sandstone is related to the presence of reducing hydrothermal fluids introduced during diagenesis.
Discovery Year
? 1972
Commodities
Copper, Silver, Cobalt, Zinc
Ore Minerals
Argentite, Bismuth, Bornite, Carrollite, Chalcocite, Chalcopyrite, Digenite, Galena, Sphalerite, Wittichite
Gangue Minerals
Barite, Fluorite, Marcasite, Pyrite, Unknown
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