Geological characteristics and genesis of Ajialongwa gold deposit in Ganzi-Litang suture zone, West Sichuan
川西甘孜-理塘缝合带阿加隆洼金矿床地质特征及成因探讨

Based on regional geological settings and characteristics of ore geology,this article made research on element geochemistry,fluid inclusion geochemistry and isotope geochemistry to make an estimate of the origins of ore-forming materials and fluids as well as metallogenic physicochemical conditions for Ajialongwa gold deposit located in Ganzi-Litang suture zone.It was hosted in the Ajialongwa fracture zone that developed at Himalayan stage and secondary to the Rize-Samalongwa deep fault,and the ore-hosting rock was ophiolite of Upper Triassic Waneng Formation.Ore minerals were mainly arsenopyrits and arsenian pyrits,fine disseminated of the distribution,while gangue minerals included quartzes,carbonate minerals,seristes,and so on.Mineralizd element association was Au,As,Sb,W,B and Hg.Chondrite normalized rare earth element patterns of ore and host rocks as well as δ34S and Pb isotope compositions of their sulfides were consistent(δ34S=-13.249‰～-8.091‰;the composition of Pb isotope was near to the growth curve of upper crust in Zartman graphic) ,proving that the ore-forming materials were sourced from host rocks.There were only single-and two-phases aqueous ore-forming fluid inclusions in quartzes and calcites of mineralization stage(the H2O content was 91.80 mol%～97.63mol%) ,which were low in homogenous temperature(Th=120～215℃) ,salinity(0.18%～6.16% NaCleqv) ,CO2(2.015 mol%～7.297mol%) and trapping pressure(2.21～19.62bar) ;the ore-forming fluids were in weak reduction,which parameters ranged from 0.087 to 0.230;the δD values ranged from-124.243‰ to-114.968‰,and the δ18O from-0.36‰ to 1.91‰,which variation ranges were narrow.It not only showed the ore-forming fluids were meteoric water,having taken circulation at shallow depth,but also reflected metallogenic physicochemical conditions.The evidences,including ore mineral assemblage,fluid inclusions temperature and compositions,elemental and isotopic features of ores,all supported a Carlin-like type genesis for the Ajialongwa deposit possibly formed in Cenozoic.