Geological and Geochemical Characteristics and Genesis of the Jiama Polymetallic Copper Deposit in Tibet

The Jiama polymetallic copper deposit is a superlarge deposit in the Gangdese metallogenic belt in Tibet with large quantity resources of copper,molybdenum,lead+zinc as well as associated gold and silver.It is also a typical deposit indicative of breakthrough in ore-search through the practice guided by the metallogenic series theory.The main skarn bodies are of layered and thick plate-like occurrence produced in the expansion space due to overthrust and sliding between the beds of K1l sand-slate,hornfels and of J3d limestone and marble.The main skarn body extends 3000m along the strike,and 2200m in the dipping direction,and its true thickness is up to 250m.The hornfels type molybdenum(copper)body and porphyry type molybdenum(copper)body both have a certain scale besides the main skarn body.The hornfels type bodies with tube-like form are distributed in the hornfels of the upper of the skarn body marked by 0~40 exploration lines with an area about 0.8 km2 on plane,extending 800m in vertical direction.The porphyry type bodies have an inkling of existence,which lie largely in the lower of skarn body or partially cutting through it.Disseminated-veinlets are main structure of ores,which are dominated by structure of thermal-liquid replacement.The primary ore minerals include chalcopyrite,bornite,molybdenite,tetrahedrite and chalcocite.The vein minerals are composed of skarn minerals and quartz.The molybdenite Re-Os age dating on different ores suggests that the Jiama polymetallic copper deposit formed between 18Ma and 10Ma,associated with mineralization in a post-collisional extensional setting in the Tibetan plateau.Its REE geochemical characteristics indicate that the Jiama skarn was generated by magmatic hydrothermal solution separated from magma replacing marble.Finally,through detailed analysis of geological and geochemical characteristics of the study area,this article suggests that it is a porphyry-skarn-hornfels type deposit associated with porphyry mineralization.