Structural controls on gold mineralization on the margin of the Yilgarn craton, Albany-Fraser orogen: the Tropicana deposit, Western Australia

摘要

The Tropicana gold deposit is located adjacent to the margin of the Yilgarn craton in the Albany–Fraser orogen, Western Australia. The deposit is hosted in granulite facies quartzo-feldspathic gneisses of the Archean Tropicana Gneiss. Ore bodies comprise biotite-pyrite alteration concentrated in shear zones that formed during NE–SW shortening in the late Archean, and clearly postdate the formation and deformation of high-grade gneiss fabrics (D1 and D2). The orientation of the ore bodies is controlled by the shear zones that are in turn localised by the gneissic banding. Mineralization also involved solution and coeval microfracturing and veining of more competent pegmatitic units. The mineralizing event (D3) was followed by at least two further deformations, which reactivated and overprinted the biotite fabrics with sericite and chlorite, created new shear zones, and affected gold distribution. D5 consisted of dextral shear on ~E–W shear zones, which subdivide the deposit into five major structural domains. The importance of structurally controlled permeability at Tropicana is similar in cratonic lode gold deposits, as is the protracted deformation/fluid flow history. Like Renco mine in Zimbabwe, Tropicana gold deposit was formed by hydrothermal fluid flow peripheral to the craton: economic gold mineralization was clearly post-peak metamorphism.