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

本文基于区域地质背景和矿床地质特征,通过元素地球化学、流体包裹体地球化学及同位素地球化学研究,探讨了甘孜-理塘缝合带阿加隆洼金矿床的成矿物质和成矿流体来源,以及成矿物理化学条件。阿加隆洼金矿赋存于日则-萨马隆洼深大断裂的喜山期次级阿加隆洼剪切破碎带中,赋矿围岩是上三叠统瓦能蛇绿岩组。矿石矿物以毒砂和含砷黄铁矿为主,呈微细浸染状分布;脉石矿物有石英、碳酸盐矿物、绢云母等,矿化元素组合为Au、As、Sb、W、B、Hg。矿石和围岩稀土配分曲线一致,矿石和围岩硫化物硫铅同位素组成一致(δ34S=-13.249‰～-8.091‰,铅同位素组成靠近Zartman图解的上地壳增长曲线),表明成矿物质来自围岩。矿化期石英与方解石中仅发育单相和两相水溶液包裹体(H2O含量91.80mol%～97.63mol%),成矿流体低温(Th=120～215℃)、低盐度(0.18%～6.16%NaCleqv)、低CO2含量(2.015mol%～7.297mol%),包裹体捕获压力小(2.21～19.62bar),成矿流体具弱还原性(还原参数为0.087～0.230),氢同位素组成(δD)为-124.243‰～-114.968‰,氧同位素组成(δ18O水)为-0.36‰～1.91‰,变化范围窄,这些不仅指示成矿流体为浅部循环后的大气降水,还反映了成矿时的物理化学条件。矿石矿物组合、流体包裹体均一温度与成分以及矿石的元素与同位素特征都显示阿加隆洼矿床为一类卡林型金矿,成矿时代可能为新生代。

Geological characteristics and genesis of Ajialongwa gold deposit in Ganzi-Litang suture zone, West Sichuan

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.