Metallogenesis,Metallogenic Regularity And Prospecting Direction Of The Sanfengshan Copper Deposit In Ruoqiang County,Xinjiang

The Sanfengshan copper deposit,located in the southern part of the Beishan orogenic belt,Northwestern China,is hosted in an early Carboniferous metavolcanic-sedimentary sequence.In recent years,preliminary studies mainly focused on the geological characteristic of the deposit.The metallogenic background,ore genesis and metallogenic regularity have not been systematically studied up to now.In this paper,we provided the first description of the geology,geochemistry,stable isotope,and geochronology of the Sanfengshan deposit.Based on the detailed study,we proposed a definitive interpretation of the ore genesis,summarized the metallogenic regularity,and provided direction for further exploration in this area.Host rocks to the mineralization are major basalts and minor chlorite-sericite schists of the Lower Carboniferous Hongliuyuan Formation.Systematic geochemical investigation shows that the host basalts are predominantly tholeiites with nearly flat rare earth element(REE)pattern,insignificant negative anomalies of high field strength elements(HFSEs),and low Ti/V and Th/Nb ratios.They were most likely derived from partial melting of depleted asthenospheric mantle affected by slab-derived fluids,and formed in a fore-arc setting during initiation of the southward subduction of the Paleo-Asian Ocean.Mineralization occurs as stratiform,stratiform-like and lenticular orebodies,consistent with the host strata.It comprises of laminated,brecciated,banded,massive,and disseminated ores.Sulfide is dominated by pyrite,chalcopyrite and sphalerite.Alteration at Sanfengshan mainly consists of silicification,chloritization,epidotization,sericitization and carbonatation,and displays a clear concentric zoning pattern.The footwall alteration is more intense and thicker than the hanging-wall alteration.The large-scale immigration of MgO,Fe2O3 T and emigration of Na2 O mignt represent the decomposition of plagioclase,albite and formation of chlorite and pyrite,which is closely related to the mineralization.Fe-Mn chert is widely distributed and generally occurs as massive,laminated,bands or lenses,which are consistent with the orebody.It is typical exhalite that formed in a mid-ocean ridge setting.During the formation and evolution,the deposit primarily experienced three periods,including syngenetic sedimentary period,metamorphic reformation and hydrothermal superimposition period,and the supergene period.Fluid inclusion and isotope studies suggested that the ore-forming materials were mainly derived from mantle magma,and might be leached from the host basalt during the hydrothermal circulation process,although a direct magmatic contribution cannot be ruled out.The ore-forming fluids belonged to H2O-NaCl system,with moderate temperature(182 ?~360 ?)and low salinity(0.7 %~4.0 %)and were dominated by seawater.Mineralization occurred in the early Carboniferous(353 Ma),consistent with the age of the host basalts(350 Ma).Comprehensive studies suggested that the Sanfengshan copper deposit is a typical Cyprus-type volcanogenic massive sulfide deposit that formed in an early Carboniferous fore-arc setting in the Beishan orogenic belt.Mineralization is controlled by extensional tectonic setting,host rocks and syngenetic faults.Moreover,metallgenetic regularities of the deposit including the spatial and temporal background,ore-bearing rock series,mineralization zoning,and alteration were summarized,prospecting criteria were confirmed,and prospecting direction of the deposit was pointed out.