ANALYSIS OF ORE-CONTROLLING STRUCTURE OF THE XORKOL BEISHAN Cu-Ag DEPOSIT IN THE NORTHERN ALTUN MARGINAL AREA,NORTHWESTERN CHINA

The Xorkol Beishan Cu-Ag deposit,located at the northern side of the Xorkol Corridor at the northern margin of the Altun(Altyn Tagh) Mou ntains,is a hydrothermal deposit controlled by second-order faults in the thrust block of nappe structure.There outcrop the thich-bedded lime stone member and medium-bedded limestone member of the Jinyanshan Formation of the Jixianian System and the thin-bedded schist member of the Xiaoquandaban Formation of the Qingbaikouan System in the ore district.The closed folds and foliation substitution in the autochthonous block of nappe structure formed by the th in-bedded schist member,the intermediate,open folds in the allochthonous block formed by the thick-bedded limestone member and medium-bedded limestone member,nappe structure and late-stage steep-angle strike-slip fault make up the basic structural framework of the ore district.The nappe is overthrust from south to north and cut by the late-stage Altum strike-slip fault.The secondary faults developed in the thrust block at the inflection point of the nappe structural plane are the principal ore-hosting structure.The shape,attitude,distribution and size of the mineralization zone and orebodies are strictly controlled by ore-hosting structure.