Stuart Shelf-Adelaide Geosyncline copper province, South Australia

Abstract

Copper mineralization of several different types formed in the Stuart shelf-Adelaide geosyncline region from the middle Proterozoic to the early Paleozoic. Hydrothermal, unconformity-related, and bedded deposits have been distinguished and these are discussed in the light of the geologic evolution of the province.The basement rocks beneath the Stuart shelf were metamorphosed and deformed during the Kimban orogeny, commencing about 1.82 b.y. ago. Between approximately 1.63 and 1.51 b.y. ago there was major bimodal alkali-rich igneous activity, accumulation of volcano-sedimentary graben sequences, and hydrothermal activity. During this period the largest copper (gold, uranium) deposit in the region, Olympic Dam, formed from hydrothermal fluids in a graben sequence and other important middle Proterozoic hydrothermal copper (gold) mineralization formed in fracture zones in feldspar porphyry and schists at Moonta and Wallaroo. In the late Proterozoic (Adelaidean), the Stuart shelf was a stable platform on which only a few hundred meters of sedimentary cover accumulated. Copper (lead, zinc) mineralization formed in permeable zones and is associated with the unconformity at the base of the late Proterozoic sequence at Mount Gunson and elsewhere, where metalliferous fluids from middle Proterozoic red beds and igneous rocks encountered biogenic H 2 S and pyrite.To the east, late Proterozoic sequences locally more than 10 km thick accumulated on crystalline basement in the Adelaide geosyncline, which was a rift in the early stages of its evolution. Low-temperature, bedded and disseminated mineralization formed in these strata where cupriferous fluids reacted with biogenic sulfide, but such copper mineralization is not of economic importance. The main copper deposits in the Adelaide geosyncline sequence were at Kanmantoo and Burra, both of which are considered to have formed from hydrothermal fluids during the early Paleozoic. Uranium (copper) mineralization in breccias in the Mount Painter inlier also appears to have formed primarily as a result of hydrothermal activity during or after the early Paleozoic Delamerian orogeny.The largest of the copper deposits in this region, regardless of type or age, fall on two alignments subparallel to the major fault zone separating the Stuart shelf from the variably metamorphosed and deformed sequence of the Adelaide geosyncline. This implies a general regional tectonic control on ore formation.