Xitiesan Pb-zn Deposit Exhalative Sedimentary Features And Tectonic Environment

The Xitieshan Pb-Zn ores is the large-scale sulfide deposit located in northwestern China, some primary researches had been carried out since 1960's ,but systemic study about geochemistry of exhalation mineralization is less. In this paper, the author consults a lot of papers about exhalative deposit and summarizes some new studying progresses.On the basis of former studies and by field investigations to geological appearances and observation of mine gallery, the geological characteristics of Xitieshan Pb-Zn ores and the rule of spatial distribution have been obtained, these new and valuable datum can be used to explain the genesis of ore ,the writer also classfied the types of exhalative rocks through study of lithology and geochemistry about the wall rock of ore-body.Ore-body of Xitieshan Pb-Zn deposits mostly occurenced in marble and controlled by lithof acies obviously. Wall rock of ore-body is sedimentary rock and including marble, carbonaceous schist , chlorite schist ,summarily, they has less volcanic component, it shows that contribution of volcanism to mineralization is not notable. Negative Ce anomaly (0.47~0.9 ) implies that rock is typical sedimentary rock in submarine, some trace elements (Ag, Hg, As, Sb, Ba etc) in wall rock of ore-body have high values,it suggests that sedimentary rockes formed through hydrothermal exhalation.Along ore-body tending, variety of cerium anormaly in the carbonaceous schist(for exemple Ce=0.84 in Wuminggou Ce=0.47 in Xitieshangou) implies that sedimentary deepness of carbonaceous schist is bigger than Wuminggou's, it approves that Xitieshangou is the center of exhalative mineralizion(prospection line 55).Research on ore formation indicates that ores remain sediment fabric of early exhalative period ,fine-grain Pb-Zn ores in eastern part of ores macroscopically conformitily contacts with wall rock, ribbon pyrite develops circle-zone of colloidal pyrite,these features strongly show that it develop fabrics of exhalative sedimentary.In this paper , according to chemistry componentof basalt, geological background of deposit was discriminated as rift valley in inner plate.In conclusion ,by studying on lithology ,petrochemistry and geochemistry of wall rock of ore-body and sedimental fabris of representative ores, the author considers that Xitieshan Pb-Zn ores is of Sedex exhalative sedimentary deposit occurring in sedimentary rock ,it can be compared with other Sedex deposits in the world.