Iron Oxide Cu-Au Monograph - Volume 3, Abstract

The Prominent Hill iron oxide copper-gold deposit (278.8 Mt @ 0.98% Cu, 0.75 g/t Au) is located on the southern margin of the Mount Woods Domain in South Australia's Gawler craton. It is hosted by a sequence of unmetamorphosed lithic quartz sandstone, conglomerate, argillite and dolomite, and mafic to felsic volcanic rocks. The age of the sedimentary rocks remains unresolved. Basalt, andesite, dacite and rhyolite are possible correlatives of the lower Gawler Range Volcanics. Mineralisation comprises disseminated chalcocite, bornite and chalcopyrite in the matrix and clasts of hematite-rich breccias. A large portion of the mineralisation is strata-bound, occurring parallel to stratigraphy within steeply dipping fragmental sedimentary rock units that have undergone extensive hydrothermal alteration and brecciation. Upper greenschist to mid amphibolite facies metamorphic rocks north of the Prominent Hill deposit consist of intercalated iron and calcium-rich chemical sediments, possible meta-evaporites and pelites. They may be correlatives of the Palaeoproterozoic Wallaroo Group of Yorke Peninsula, and have been intruded by felsic magmas and layered sequences of mafic and ultra-mafic cumulate rocks. Drillholes 30 km east of Prominent Hill have intersected a bimodal suite of tholeiitic volcanic rocks, geochemically distinct from the Gawler Range Volcanics and probably Archaean or Palaeoproterozoic in age. Pre- and post-discovery exploration drilling has highlighted the occurrence of numerous iron-oxide (±copper ±gold) systems within both the metamorphosed and unmetamorphosed domains that make up the southern Mount Woods Domain. These include a full spectrum of magnetite, magnetite-hematite and hematite rich prospects and deposits with variable copper and gold tenor.