Superimposed Mineralization Process On The Ashele Copper-Zinc And Adjacent VMS Deposits,Xinjiang

The Early-Middle Devonian VMS deposits in the Southern Altay have been deformed and modified during regional metamorphism and tectonic events since Late Devonian.However,the studies about deformation,metamorphism and superimposed mineralization in relation to VMS deposit are less constrained.The arguments of the ore genesis are still existed.The Ashele deposit,located in the Ashele basin in the south Altay orogenic belt,is a famous lager deposit.In this paper,ore-forming fluids,metamorphic and deformation characteristics and metamorphic fluids of the Ashele Cu-Zn deposit and Saershuoke Cu-Au deposit are studied based on field geology and laboratory analysis,and new insights of the ore genesis is presented.The Ashele Cu-Zn deposit and Saershuoke Cu-Zn-Au deposit are two typical marine volcano sedimentary deposits.The Ashele Cu-Zn mineralization occurs mainly in the Lower Middle Devonian Ashele formation of basaltic dacitic marine volcano sedimentary formations.According to the characteristics of ore bodies,mineral paragenesis and deformation and metamorphism of the surrounding rocks,two metallogenic periods are identified:marine volcanic sedimentary period and metamorphic hydrothermal superimposed period.Metamorphic hydrothermal superimposed phase is characterized by the formation of metamorphic quartz veins in four stages:less sulfide quartz veins(QI),white bedding coarse grained sulfide quartz vein(Q2),grey quartz sulfide quartz vein(Q3)and white quartz veins(Q4).The deformation and metamorphic textures are well developed in wall rock of ore-bodies.The ore-forming fluids in Q1,Q2 and Q3 are characterized by CO2-rich,medium-low temperatures and low salinities.Those characteristics are typical of metamorphic fluids.The Synchrotron radiation X ray fluorescence(SRXRF)analysis of H2O-CO2 fluid inclusion from Ashele deposit showed that trace elements in fluid inclusions have high content of Au,Cu,Pb,Zn,Fe,Sn.Pb,Cu and Fe elements are obvious in gas phase,and Au and Zn are enrichment in liquid phase.The study of cooper and zinc isotopes reveals that the source of material have genetic connections from the south east to north west direction in Altai area.The ?65 Cu value of chalcopyrite in the vein-type gold mineralization in the Kelan basin is relatively low,which may reflect the superposition of the hydrothermal fluid,while the ?65 Cu value of the Keyinbulake deposit,Ashele deposit and the Sarekuobu deposit are increasing,which may reflect the characteristic of marine volcanic deposits(VMS).The systmatical studies show that the extensional basins after island are along the southern margin of Altay Mountain might result from the subduction of the Erqis ancient Asia oceanic crust in Early Devonian,and then a number of marine volcanic-sedimentation Cu-Zn(Pb)deposit formed from submarine exhalative-sedimentation.The metallogenic process of superposition and transformation with metamorphic fluids in the Altay induced extensive deformation and metamorphism from Early Devonian to late Early Triassic,resulting in intense meltalreworking an enrichment of early-fonning VMS Cu-Zn(Pb)deposit.