Identification of a ductile shear zone in quartz-magnesitite and its controlling on gold deposits in the Sartohay region, western Junggar, Xinjiang
新疆萨尔托海石英菱镁岩中发育的韧性剪切带及其对金矿的控制

The Sartohay gold deposit is located in the Darbut ophiolitic mélange, western Junngar, Xinjiang. It is the first time to recognize the ductile shear zone in this ore district. Fuchsite and quartz, representing the foliation of mylonite or mylonitized quartz-magnesitite, formed during ductile shearing deformation process. The calcite-quartz-chalcopyrite-muscovite vein, cutting off the mylonite foliation, represents the fluid activity during brittle deformation. On the basis of the correlation of mineral assemblages, three structural deformation stages could be recognized: early ductile deformation forming fuchsite-quartz assemblage, stress fracture in an obviously different direction filled with calcite-quartz-chalcopyrite-muscovite vein, and brittle structural deformation at shallow level in the direction similar to the direction of the early ductile deformation formed muscovite-quartz veinlets(or micro-veins). Quartz-carbonate vein containing sulfide and native gold frequently was formed during the period of transformation from a ductile to brittle deformation regime, which represents the main ore-forming period. The distribution of gold deposits in the Sartohay district is controlled by shear zone. The calcite-quartz-chalcopyrite-muscovite vein cross-cutting mylonite foliation is a major ore prospecting indicator. The ductile shear zone controlling gold deposit indicates that, sulfide-quartz-carbonate vein formed during ductile-brittle transformation and associated hydrothermal alteration, induced gold enrichment and ore formation. Ore bodies always occur in the expansion part of fracture structure. The genesis of the Sartohay gold deposit has no relation with the Darbut ophiolite and its evolution. A systematic study on ductile shear zone in this area is the critical factor to make a breakthrough in further exploration.