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Deposit Synonyms
Brennans; Eml 6192; Main Open Cut; Ml 3717; Ml 3718; Ml 3719; Ml 3720; Ml 3721; Ml 5598; Musolino; Plateau
Mineral District
Mount Gunson Copper
Deposit Summary
Cu-Ag-Co-Zn-Pb mineralisation at Marinoan disconformity at base of Whyalla Sandstone. Most production from 1984-90 for 830,000t @ 1.6% Cu.
Deposit Description
MOUNT GUNSON, copper oxide mineralisation was discovered in 1875, probably at the location now known as Main Open Cut. Mineralisation was developed over a horst of Mesoproterozoic Pandurra Formation, a fluviatile red bed sequence, representing a basement high during Neoproterozoic sedimentation. It formed a core surrounded by onlapping Whyalla Sandstone, a mature quartzose sandstone in part aeolian, which was overlain by Woomera Shale. Lower in the sequence, the Tapley Hill Formation lapped onto the basement horst. This basement high is known as the Pernatty Culmination.
Mineralisation formed at the Marinoan disconformity (~630Ma), represented by the base of the Whyalla Sandstone. Cattlegrid Breccia, a permafrost breccia formed on the silicified palaeo-surface of the Pandurra Formation, was the principal ore host, but there was also significant mineralisation as veins in fractured Pandurra Formation beneath, and as cement in porous Whyalla Sandstone above this breccia. A WNW-trending linear structure influenced the orientation of the sulphide portion of the ore body.
Timing of mineralisation from field relations suggests post deposition of the Whyalla Sandstone, which itself acted as an aquifer for the introduction of mineralising fluids and prior to the lithification of the underlying Neoproterozoic host.
Locally, sub-vertical NE-trending fractures in the Pandurra Formation were well mineralised. Above the modern water table the ore was oxidised, consisting of atacamite with subordinate malachite and traces of chrysocolla and azurite. Mixed oxide and sulphide ore was found below the water table. The sulphides occurred mainly as chalcocite ore, composed of djurleite and digenite, with an oxidation coating of covellite in places. Traces of bornite, chalcopyrite, pyrite and tenorite were also present. Gangue minerals included iron oxide, mainly goethite, and manganese oxides.
Copper was the main metal recovered, but about 10 g/t silver was also recovered from the sulphide ore. Cobalt, zinc and lead were also present in significant quantities. Except for some early shafts, mining was from open cuts, with a maximum depth of 20 m. Production from 1937-43 was 32,000t ore sent for processing to the Port Pirie smelters. Several million tonne of ore was identified during exploration from 1966-68. The ore was mined by Mount Gunson Mines Co. Ltd from 1969-71. Ore was mined from 1984-90, with a total production of about 830,000 tonne @ 1.6% Cu. At the heap leaching site a bi-product was sandstone.
Discovery Year
? 1875
Commodities
Copper, Sandstone, Silver
Ore Minerals
Atacamite, Azurite, Bornite, Chalcocite, Chalcopyrite, Chrysocolla, Covellite, Cuprite, Digenite, Djurleite, Malachite, Pyrite, Tenorite
Gangue Minerals
Goethite, Manganese Oxide
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