Deciphering the tectonic evolution of Archaean greenstone belts: the importance of contrasting histories to the distribution of mineralization in the Yilgarn Craton, Western Australia

Abstract

Abstract The distribution of Archaean metallic mineral deposits reflects tectonic controls operating during the evolution of granitoid-greenstone terranes. Tectonic analysis of these terranes not only allows recognition of parameters that may be important in interpreting the tectonic histories of greenstone belts, but also the resultant tectonic control on mineral deposit distribution. In the Yilgarn Craton of Western Australia, the late Archaean (∼ 2.7 Ga) Norseman-Wiluna Belt is most intensely mineralized with both komatiite-associated Ni-Cu deposits and epigenetic gold deposits. This belt is dominated by ∼ 2.7 Ga supracrustal successions, and its tectonic history is that of an orogenic belt at an obliquely convergent craton or proto-craton margin. Tectonostratigraphic associations preserved resemble younger volcanic arc and back-arc basin crust, and many represent the remains of a volcanic arc and back-arc basin complex developed in response to westward-dipping subduction. These sequences were deformed, metamorphosed and intruded by granitoids relatively soon (30 Ma) after the major period of volcanism, with gold mineralization, occurring late in the orogenic event, possibly during uplift. In contrast, greenstone belts in the Murchison and Southern Cross provinces are dominated by older supra-crustal successions that contain > 2.9 Ga volcanosedimentary associations characterized by extensive oxide-facies banded iron formations (BIFs). BIFs appear to have been deposited in shelf or platform environments in intra-oceanic or passive craton margin settings. Komatiite-associated Ni-Cu mineralization and volcanogenic Cu-Zn mineralization are locally hosted by favourable tectonostratigraphic associations. The main period of deformation, metamorphism, and gold mineralization in these provinces was broadly synchronous with that in the Norseman-Wiluna Belt, as was regional granitoid emplacement. During this event, strain was probably transmitted from the eastern margin of the craton via a Yilgarn-wide system of shear zones, faults and fold belts. Gold mineralization is developed best in greenstone belts, such as the Meekathara-Mt. Magnet Belt, that contain large-scale fault systems and internal granitoids. Similar tectonic controls on the distribution of mineral deposits can also be recognized in other Archaean cratons, and the heterogeneous distribution of Archaean mineral deposits probably reflects a range of tectonic settings as well as different stages in the evolution of individual cratons.