Au-Cu and Cu-Au mineralisation in the Northern Paterson Province, Western Australia; new insights into an important intrusion-related gold district

The undercover northernmost part of the Neoproterozoic Paterson Province, the Anketell Shelf, has geological characteristics that are different from those of the main outcropping part in the south. Sedimentary sequences are thicker, represent deeper-water equivalents and are dominated by siliciclastic rocks with lesser carbonates. The thickness and abundance of intrusive mafic sills increase towards the north, as does the regional metamorphic grade, which reaches lower granulite facies in the northernmost parts. The structure is dominated by large, gently SSE-plunging open anticlines separated by narrow sheared synclines instead of the dome and basin geometry that typifies the outcrop patterns in the exposed parts of the province. In contrast to the outcropping parts of the province where the dominant structural framework was formed during the Miles Orogeny (ca 840-654 Ma), major folds of the Anketell Shelf are interpreted to have formed during the Paterson Orogeny (ca 654-550 Ma). Several gold-copper and copper-gold deposits have recently been discovered across the Anketell Shelf. These deposits are closely associated with granitoids, with gold-dominated deposits situated near non-magnetic (reduced) granites and copper-dominated deposits near composite magnetic (oxidised)-non-magnetic granites. The structural style of the deposits is strongly controlled by the host lithologies, interpreted to be deeper-water equivalents of the Malu Formation. Deposits hosted in competent sandstones are located near the closures of anticlines and have strongly discordant ore shoots and vein systems whereas, deposits that are hosted in calc-silicate rocks and mafic sills have mostly concordant ore shoots and vein systems. All have a strong gold-bismuth association, with textures indicating that gold was concentrated and precipitated according to the bismuth collector model, scavenging gold from a gold-undersaturated hydrothermal fluid and concentrating it into molten bismuth droplets. Upon cooling, these droplets precipitated together with the gold in quartz veins. In copper-rich systems, an extensive copper-sulfide overprint, which largely follows the gold system, took place after the gold mineralising event. Recent studies have put into question the interpretation of an exclusively intracratonic setting for deformation of the Yeneena Basin. This study provides further support for a collisional orogenic event between the combined North Australian and West Australian cratons and the West Cathaysia-Lhasa block during the Paterson Orogeny. The likely tectonic setting for the deposits described in this paper is interpreted to be well inboard of a convergent plate boundary now hidden below thick sedimentary successions of the Canning Basin and the Northwest Shelf.