GEOCHEMICAL ANOMALY OF SAHENTUOHAI GOLD DEPOSIT IN XINJIANG,CHINA

Sahentuohai gold field of Hejing County,Xingjiang lies in the Sahentuohai shearing fault belt inside the Sahentuohai-Dashankou foreland basin in Southern Tianshan on Tarim Plate,with simple strata,gentle folds,developed faults and less magmatic activities.The 3rd lithologic member of Dashankou formation,Upper Silurian-Lower Devonian and Saerming formation of Devonian are dominant in the ore field.They are distributed in a NWW-trending zone and contacting each other by fault.The rock association consists of metamorphic sandstone,ferriferous dolomitic sandstone,sericitized siltstone,phyllitic siltstone and phyllite.The orebody is registered in the central area of 1:500 000 Sahentuohai Au anomaly,1:200 000 Au-scheelite heavy concentrate anomaly and 1:100 000 Au₃ anomaly,and hosted in No.1,No.2 and No.3 faulted alterati on zones within Sahentuohai shearing fault belt.The rocks in the fault belt are intensively fractured,with strong schistosity,fragmantation and mylonitization.The fractured alteration zone is the prin-cipal ore-controlling structure in the region.Quartz veins and carbonate-quartz veins are developed along the schistosity and fracture.The wall rock alterati ons are mainly ferrodolomitization,silicification,sericitization and pyritization,with minor chloritization.The metalliz ation are chieflypyrite with a little chalcopyrite and galena.There is no distinct demarcation line between the ore body and wall rock.The mineralization is positively correlated to the alteration.The more comprehensive and stronger the alte rations are,the better the metallization is.Conversely,the metalliza tion becomes weaker and gradually transits to normal wall rock.The ferroan dolomite sandstone and marl of the 3rd member of Dashankou formation are the major source of the regional Au anomaly.The gold orebody occurs in the Au_3-2 sub-anomaly with element composition of Au,Ag,A s,Sb and Bi.The anomaly presents a good recurrence,high correlation between the anomalous elements and multi-element composition.The element composition demonstrates the feature of front halo,indicating that the orebody is in the front part and there might be an even larger orebody with higher grade in the deep.