Large-Scale Structural Controls on Gold Mineralization Along the Kalgoorlie Rift From Seismic Reflection Imaging in the Neoarchean Yilgarn Craton, Western Australia

Abstract

Archean granite-greenstone belts are highly prospective for structurally controlled Au, Ni, and Li mineralization, but determining the deeper structural architecture is challenging. Three regional seismic reflection surveys over the highly mineralized Neoarchean Kalgoorlie terrane in Western Australia have been reprocessed and reinterpreted using 3-D reflector orientation estimates, partial 3-D images, and geologic constraints. We divide the Kalgoorlie terrane between Ora Banda and Kambalda into northern, central, and southern domains, based on significant structural along-strike variations, including the extent to which a structural discontinuity (decollement) at 5- to 8-km depth is observed. In the northern domain, near Ora Banda, NW-striking upper crustal faulting is restricted to narrow zones between broad granite domes, and the decollement is faulted into discrete segments. In the central domain around Kalgoorlie, up to 8-km-deep structural basins of volcaniclastic rocks, separated by wedge-shaped blocks comprising mostly mafic volcanic rocks, are imaged above a largely continuous decollement. In the southern domain around Kambalda, the decollement is not observed; here, the W-dipping Boulder-Lefroy fault is part of a major fault system extending from the surface to >10-km depth, where the fault truncates against an E-dipping midcrustal shear zone that underlies the entire region. The deep structural basins, which lie below late-stage siliciclastic basins, accommodated deposition of the volcaniclastic Black Flag Group associated with mantle-derived sources for fluids and melts potentially related to Au and Li mineralization. We speculate that along-strike structural variations of the Kalgoorlie terrane, which affected both pathways and traps for Au mineralization, arose from structural inheritance and strain partitioning during rifting and subsequent crustal shortening.