| The Dapingzhang Cu-Zn deposit,a unique volcanic massive sulfide deposit,is located in the eastern Proto-tethys tectonic domain.A comprehensive study of this deposit will provide constraints on the metallogenic evolution of the eastern Proto-Tethys and enrich the genetic model of VMS deposit.In this contribution,we report the petrology,whole-major trace elements,zircon U-Pb ages and Hf-O isotopes from ore-bearing volcanic rocks to better constrain the emplacement ages,source,and tectonic setting of these rocks.We used detailed field investigations,petrographical analysis,in-situ microanalysis to analyze microfabrics,trace element and sulfur isotope compositions of sulfide.Our aim is to reveal the relationships between metal mineralization,sulfide precipitation,and to get a better understanding and recognition on genesis and preliminarily establish the genetic model of the deposit.The main understandings are as follows:(1)The submarine sodium-rich volcanic rocks are strong peraluminous and belong to the calc-alkaline series.The rocks are characterized by enrichment in large-ion lithophile elements(LILEs,Ba,Th,and U),depletion in high-field-strength elements(HFSEs,Nb,Ta,Ti,Th,and P)and LREEs,and have affinities with subduction-related arc setting.The zircons yield?Hf(t)values of+8.17 to+15 and?18Ozircon values of 3.67to 7.77,which indicates that the parent magma was formed by partial melting of the juvenile lower crust and affected by seawater alteration and hydrothermal alteration or subduction sediments.We speculate that the Proto-Tethys Ocean have been subducted northeastward beneath the Simao block.The subduction causes opening of the Dapingzhang back-arc basin.(2)The massive sulfide ore bodies in the main mineralization period are divided into three mineralization zones:Fe-Cu zone,Cu-Zn-Fe zone and Zn-Pb zone.In Fe-Cu zone,chalcopyrite and pyrite are dominant,and medium-coarsed grain pyrite occurs as euhedral to subhedral crystal,which indicate high-medium temperature ore forming.In Cu-Zn-Fe zone,chalcopyrite,sphalerite and pyrite are dominant,and medium-fine grain pyrite occurs as xenomorphic to subhedral crystal,which indicate medium temperature ore forming.In Zn-Pb zone,chalcopyrite and galena are dominant,and fine grain pyrite occurs as xenomorphic crystal,which indicate low temperature ore forming.(3)In-suit micro-analysis shows that high temperature indicator elements are rich in Fe-Cu zone,such as Mo,Sn,Bi;medium temperature indicator elements are rich in Zn-Fe zone,such as Cu,Au;low temperature indicator elements are rich in Zn-Pb zone,such as Hg,Se,Sb,As.The change of trace elements in different mineralization zones indicates the change of mineralization temperature.The higher contents of Ti,Te,Mn,Mg,Cr and Mo in the veinlet-disseminated ore bodies indicate that they came from the mixed source of felsic and mafic magmas.The changes of trace elements are affected by geochemical affinity of main mineral elements,ore-forming temperature and source of ore-forming materials.(4)In situ S isotopic values of sulfide(-3.70?5.08,n=157)indicate that the ore-forming fluid a combination of magma fliud and water.The ore-forming process experienced thermochemical reduction of seawater sulfate(HSR).From Fe-Cu stage to Zn-Pb stage,?34S value decreases with the decrease of ore-forming temperature.Compared with massive sulfide mineralization,the negative value of disseminated-veinlet mineralization is less,mostly close to zero,indicating that the ore-forming temperature of disseminated-veinlet mineralization stage is higher than that of massive sulfide mineralization.Besides,the effect of HSR on disseminated-veinlet mineralization is less. |
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