Characteristics of Ore-forming Fluids of the Nanmingshui Gold Deposit in the East Junggar,Xinjiang: Evidences from Fluid Inclusions and H-O Isotopes
GE Zhanlin;ZHANG Yongmei;GU Xuexiang;CHEN Weizhi;XU Jinchi;WU Ruochen;HUANG Gang;School of Earth Sciences and Resources,China University of Geosciences;No.8 Gold Geological Party of PAP;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences;Regional Institute of Shaanxi Bureau of Geological Exploration;
The Nanmingshui gold deposit is located in the eastern part of the Kalamaili metallogenic belt. Its ore-bodies,controlled by the NW—NWW trending ductile-brittle faults,are hosted in epimetamorphic marine volcaniclastic sedimentary rocks of the Lower Carboniferous Jiangbasitao Formation. Based on the studies of fluid inclusions and hydrogen and oxygen isotopic geochemistry,the properties,source and evolution of ore-forming fluids are discussed in this paper. The ore-forming process can be divided into three metallogenic stages including the early,middle and late stages. Three types of fluid inclusions that include CO_2-H_2O,H_2O-NaCl and pure CO_2 inclusions are identified in the quartz of the Nanmingshui gold deposit. The early-stage quartz mainly contains CO_2-H_2O and pure CO_2 inclusions with homogenization temperatures and salinities ranging from 257 ℃to 339 ℃ and 0. 4% to 2. 2%. All three types of inclusions are trapped in the middle( main)-stage quartz. The homogenization temperatures and salinities of CO_2-H_2O and H_2O-NaCl inclusions vary from 196 ℃ to 361 ℃and 0. 4% to 6. 0%. Only H_2O-NaCl inclusions are found in the late stage quartz with relatively lower homogenization temperatures clustering at 174 ℃ to 252 ℃. Meanwhile,the salinities of H_2O-NaCl inclusions vary from 1. 4% to 3. 2%. According to the estimation from CO_2-H_2O inclusions,the minimum trapping pressures for early and middle stages are 214 MPa to 371 MPa and 236 MPa to 397 MPa,respectively,corresponding to the metallogenic depths of 8. 1 km to 14. 0 km and 8. 9 km to 15. 0 km,respectively. The studies of fluid inclusions in different metallogenic stages indicate that the metallogenetic temperatures and fluid densities show a decreasing trend,as the ore-forming fluids are evolved from CO_2-H_2O-NaCl ± CH_4 system in the early and middle stages to H_2O-NaCl system in the late stage. Fluid inclusions and hydrogen and oxygen isotopic studies show that the ore-forming fluids of the main metallogenic stage were dominantly originated from metamorphic water.The immiscibility of CO_2-H_2O-NaCl fluids is an important mechanism that leads to the gold precipitation and enrichment. The genesis of the Nanmingshui gold deposit is a mesozonal to hypozonal orogenic gold deposit.
【Fund】： 国家自然科学基金项目(41572062);; 中央返还两权价款资金综合研究项目(Y15-1-LQ04 Y15-1-LQ02);; 中央高校基本科研业务费专项资金项目(2652017226)
【CateGory Index】： P618.51
【CateGory Index】： P618.51