Geological,Geochemical Characteristics And Genesis Of The Nanmingshui Gold Deposit In The East Junggar,Xinjiang

The Nanmingshui gold deposit is located in the eastern part of the Kalamaili metall-ogenic belt in the east Junggar,Xinjiang,sandwiched between the NWW-NW-striking Kalamaili Fault and Qingshui-Sujiquan Fault.Studies on this gold deposit were extremely weak,especially lacking of the systematic research on geological characteristics of ore deposits,characteristics of ore-forming fluids,sources of ore-forming materials and metallogenic age.Therefore,up to now,the genesis of this deposit is still ambiguous.In this paper,we report results obtained from field investigations,ore geology,fluid inclusions,C-H-O-S-Pb isotope studies and hydrothermal zircon LA-ICP-MS U-Pb geochronology,thereby discuss the nature,origin and evolution of ore-forming fluids,and clarify the time of gold mineralization.Meanwhile,we also attempt to constrain the genetic type of the Nanmingshui gold deposit,in order to provide a basis for the study of metallogenic mechanism and enrich the understanding of regional metallogenic regularities and processes.The ore bodies are composed of quartz veins or quartz-tourmaline veins and subordinate altered rock,whih are controlled by NW-NWW trending ductile-brittle secondary faults and hosted in volcaniclastic sedimentary rocks of the Lower Carboniferous Jiangbasitao Formation.The wall-rock alteration has obviously lateral zonation,and silicification,arsenopyritization and pyritization are the most closely associated with gold mineralization.According to the crosscutting relationships and minerals combination between different veins,the hydrothermal mineralization process can be divided into three stages at the Nanmingshui gold deposit:?1?milky white quartz stage?early?;?2?quartz-tourmaline-gold-polymetallic sulfides stage?middle?and?3?quartz-calcite-sericite stage?late?.There are two types of gold ores in the Nanmingshui gold deposit,including quartz-tourmaline-gold-polymetallic sulfides ore and altered wallrocks ore.The major ore minerals include arsenopyrite,pyrite with small amounts of native gold,chalcopyrite and tetrahedrite,which have a total content less than 5%.The gangue minerals are primarily quartz,tourmaline,sericite,with minor calcite,chlorite.The most common ore textures consist of vein-stockwork,disseminated,breccia textures.Ore minerals occur as euhedral to subhedral or anhedral crystals.Meanwhile,the metasomatic,cataclastic and pressure-shadow textures are commonly observed in ores.Based on the studies of fluid inclusions and C-H-O-S-Pb isotopes,three types of primary fluid inclusions were identified,including CO₂-H₂O,H₂O-NaCl and pure CO₂inclusions.The ore-forming fluids in the main-ore stage may have originated from the metamorphic water?medium-high temperature,low-salinity and CO₂-H₂O-NaCl±CH₄ in composition?rather than granitic magma.The carbon in the ore-forming fluids may be derived from the dissolution or decarbonation of marine carbonate rocks.The sulfur source is a mixed sulfur from the stratum and basalt at mining area,and the lead of ore is a mixed source of lead between the orogenic belt and mantle.The weighted average ²⁰⁶Pb/²³⁸U age of the hydrothermal zircons LA-ICP-MS U-Pb in gold-bearing quartz veins is 314.1±3.0 Ma,which is consistent with the age range defined by geological features.This mean age indicates that the Nanmingshui gold deposit was formed during the collisional orogeny-extension environment transition period in the Kalamaili area.By the comprehensive studies of geological background,tectonic evolution,geological characteristics of ore deposits,characteristics of ore-forming fluids,sources of ore-forming materials and metallogenic ages,we confirm that the Nanmingshui gold deposit is a typical orogenic gold deposit.