Abstract

Conjugate ductile shear zones developed mostly on granite-greenstone margins are a dominant structural feature of the Yilgarn craton. These greenstone belt–scale shear zones lack both gold deposits and gold-related alteration. Previous interpretations of the shear zones as part of a linked system, as craton-scale terrane boundaries, or as crustal-scale pathways for gold-mineralizing fluids, all appear equivocal. Instead, gold mineralizing fluids in the Yilgarn craton (illustrated here by the gold-rich Yandal Belt) were focused by a network of middle to upper crustal brittle faults in the Late Archean. The faults are 040° to 060° trending dextral, and 090° to 120° trending sinistral; the maximum compression direction is about 075°. Gold mineralization occurs in laminated and other schistosity-parallel quartz veins where brittle faults refract along earlier subsidiary within-greenstone ductile shear zones, and in quartz veins within Late Archean faults.

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