Extension and gold mineralization in the Archean Kalgoorlie Terrane, Yilgarn Craton

This paper focuses on two extensional events affecting late Archean crust of the Kalgoorlie Terrane in the Eastern Goldfields, and which are associated with gold mineralization. These events bracket the duration of the crustal shortening event known as the Kalgoorlie Orogen. The early extension phase is preserved around the Raeside Batholith and gave rise to the earliest recognized structures, D1e. This event is characterized by multi-directional horizontal extension, in contrast to unidirectional extension associated with core complexes. Extension uplifted the batholith in relation to the overlying greenstone sequence and produced recumbent folds. Gold, including the large deposits at Leonora, was deposited in normal shear zones around the batholith. We propose that extension triggered doming of gravitationally unstable granitic rocks buried under a greenschist sequence, and amplified the growth of extensional nappes.The late phase of extension is evident in a number of gold deposits in the Kalgoorlie Terrane. This phase is characterized by (a) overprinting crustal shortening structures that suggests it is the latest structure in all localities; (b) gently dipping foliation, associated with recumbent folds, which are dragged into moderately dipping, normal shear zones; (c) maximum stretching axis, NW–SE or N–S, at high angles to the maximum shortening axis inferred from regional shortening phases of the Kalgoorlie Orogen and (d) hosting gold. This phase records relaxation of the Kalgoorlie Orogen and the findings suggest that gold mineralization was not restricted to a single deformation phase but started before the Kalgoorlie Orogen and waned at the end of the orogeny.