SHEAR ZONES, FAULT NETWORKS, AND ARCHEAN GOLD

Conjugate ductile shear zones developed mostly on granite-greenstone m argins are a dominant structural feature of the Yilgarn craton, These greenstone belt-scale shear zones lack both gold deposits and gold-rel ated alteration. Previous interpretations of the shear zones as part o f a linked system, as craton-scale terrane boundaries, or as crustal-s cale pathways for gold-mineralizing fluids, all appear equivocal. Inst ead, gold mineralizing fluids in the Yilgarn craton (illustrated here by the gold-rich Yandal Belt) were focused by a network of middle to u pper crustal brittle faults in the Late Archean. The faults are 040 de grees to 060 degrees trending dextral, and 090 degrees to 120 degrees trending sinistral; the maximum compression direction is about 075 deg rees. Cold mineralization occurs in laminated and other schistosity-pa rallel quartz veins where brittle faults refract along earlier subsidi ary within-greenstone ductile shear zones, and in quartz veins within Late Archean faults.