Study On The Genesis Of Porphyry Pb-Zn Deposits In Continental Settings Of China

Porphyry copper(molybdenum,gold)deposits are widely distributed in island arcs,continental margin arcs that related to subduction and continental environments that unrelated to subduction.As well known,the formation of porphyry copper(molybdenum,gold)deposits is closely related to the nature and source of magma,while whether the porphyry-magma-hydrothermal system can form large-scaled lead-zinc deposits has not been reported yet.In this study,we took Narusongduo lead-zinc deposit in Tibet and Lengshuikeng lead-zinc deposit in Jiangxi Province to do the comparative research.The detailed process of metamorphic evolution of the porphyry-type lead-zinc deposit was studied by detailed field geological investigation and laboratory experimental analysis.A detailed research and discussion of diagenetic and mineralization process of the porphyry lead-zinc deposit is carried out through the detailed field geological investigation and laboratory experimental analysis.The results show that there is a consistency between Narusongduo and Lengshuikeng deposit in the origin and evolution of magma,the source and the enrichment mechanism of ore-forming materials,the deep process and the dynamic background.There are two periods of magmatic activity in each deposit.The extrusion environment and following stress relaxation are the dominant dynamic mechanism of the magmatic activities in Narusongduo and Lengshuikeng deposit.The ore-forming porphyries of the two deposits do not have the affinity to adakite,but have the characteristics of high silicon,depleted in sodium,enriched of potassium and have high degree of magmatic differentiation.The ore-forming porphyry magma originated from the crust.There are different types of orebodies,namely cryptoexplosive breccia type orebody,skarn type orebody,vein orebody and stratiform orebody in Narusongduo deposit,while porphyry orebody and stratiform orebody in Lengshuikeng deposit.In situ electron microprobe and LA-ICP-MS analysis of the sphalerite from different orebodies in Narusongduo and Lengshuikeng deposit show that the precipitation of ore-forming material in sphalerite of the two deposits has the characteristics of magmatic hydrothermal action.The characteristics of the ore-forming fluids in the two deposits are similar: both are formed in low temperature and low-salinity environment;the hydrothermal fluids are from magma with the later meteoric water continuously added.The formation of the deposit is similar in depth,about 2.0~2.8km,and the fault or the cryptological explosure may provide incentives and metallogenic space for mineralization.In Narusongduo deposit,zircon trace element of quartz diorite show that the Ce(?)/ Ce(?)ratio of most zircons are lower than 100 with th>0.4,it is concluded that the magmatic rock of quartz diorite may not be able to have similar metallogenic ability with granite porphyry.There are many similarities and uniqueness in the general characteristics of Narusongduo deposit and Lengshuikeng deposit,which belonged to different tectonic-metallogenic belts.The metallogenic study of these two typical porphyry Pb-Zn deposits reveals that the metallogenic processes of continental environment porphyry Pb-Zn deposits have significant similarities,and could help to establish a universal model for metallogenic system of porphyry Pb-Zn in continental setting.