On Kalgoorlie (Australia), Timmins-Porcupine (Canada), and factors in intense gold mineralisation

摘要

The Golden Mile gold deposits of Kalgoorlie (Eastern Goldfields Province, Yilgarn craton, Australia: 46 Moz Au) and the gold deposits in the Timmins-Porcupine camp (southern Abitibi Province, Superior craton, Canada: 63.7 Moz Au) are Earth's two biggest Archaean lode gold camps. While similarities at the camp scale are dominant, they differ in that the Golden Mile is a compact camp of one major deposit with two nearby, subordinate deposits separated by less than 10 km along strike, whereas Timmins-Porcupine consists of a relatively large camp with 30 important mines distributed over 20 km strike length. Seismic data show a detachment fault at the base of the supracrustal rocks at Kalgoorlie at between 5 and 9 km, but none is identified in the Timmins-Porcupine camp. Map-scale patterns, ages and lithologies are superficially similar. The gabbros in Kalgoorlie and conglomerates in Timmins-Porcupine are distinctive rock types, but served similar competence-contrast functions. Late-orogenic sediments are an important host at Timmins-Porcupine for competence contrast reasons, but are apparently absent in the Golden Mile area. Gold deposit formation in both camps is of the same age (approx 2.67 Ga), with a long duration of mineralisation. Porphyries, albitites and lamprophyres are characteristic features, but played no major genetic role. Both camps have early elements of mineralisation that have an epithermal character in Cu-Au-W-V~(3+) and fO_2, and both camps lie in belts locally characterised by the abundance of telluride minerals. However, none of these characteristics seem to be necessary or sufficient for intense gold mineralisation. Syn-mineralisation transpressive deformation in both camps involved the imbrication of thrust slices, followed by strike-slip movement along a major crust-scale fault with a dilatational curve in its trend in the centre of both camps. The various deposits in each of the two camps were formed from immediately before to just after strike-slip deformation, and opening of late-orogenic sedimentary basins. Both areas are characterised by an early episode of intense thrust faulting. Extensive, intersecting fracture arrays likely developed as thrusting gave way to strike-slip faulting. These arrays may have enabled access to fertile source rock and also served as fluid conduits throughout deformation. Moreover, both terranes are characterised by a relatively short pre-mineralisation crustal history, thin(ned) subcontinental lithospheric mantle, and input of juvenile, mantle-derived material. The pre-mineralisation crustal history and evolution of the host terranes thus may have been the most important single factor in the formation of giant orogenic gold deposits at Kalgoorlie and Timmins-Porcupine.