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投稿时间：2023-03-29 修订日期：2023-08-15 网络发布日期：2023-11-01
中文摘要:广西隆或金矿床位于右江盆地隆或孤立碳酸盐岩台地内部，为一产于C/D不整合面上的层状卡林型矿床。为了查明隆或金矿的成矿流体来源，探讨矿床成因，本次工作对其开展了详细的野外地质考察，对不同成矿阶段石英、方解石进行了系统的包裹体岩相学观察、显微测温及C-H-O-He-Ar同位素分析。包裹体岩相学及测温结果显示，石英、方解石中主要发育富液相气液两相水溶液包裹体，含有少量CO2三相包裹体。其中石英中包裹体均一温度集中在170.4~282.6℃，盐度w （NaCleq）集中在2.57%~8.41%，密度为0.774~0.938 g/cm3；方解石中包裹体的均一温度集中在178.5~237℃，盐度w （NaCleq）集中在2.9%~7.17%，密度为0.845~0.935 g/cm3，为中低温、低盐度、低密度的H2O-NaCl体系。通过计算得出成矿流体的成矿压力为45.83~74.17 MPa，成矿深度为1.611~2.472 km。石英的δ18OV-SMOW值为25.5‰~28.7‰，对应的δ18OH2O为14.10‰~17.18‰，δDV-SMOW值为-79‰~-51‰，两个阶段石英H、O同位素投点虽位于变质水区域及附近，但Ⅱ阶段石英具有向岩浆水漂移的趋势。方解石的δ13CPDB集中在-6.5‰~-4.6‰，δ18OV-SMOW分布在19.9‰~21.1‰，其投点靠近海相碳酸盐岩区域，表明方解石的形成主要来源于碳酸盐的溶解。石英包裹体中3He/4He的值为0.351~0.744 Ra，位于地幔氦和地壳氦之间，幔源He （%）值为5.11%~11.17%，说明地壳流体占主导地位；方解石中3He/4He值为0.038~0.073 Ra，位于地壳氦附近。石英、方解石的40Ar/36Ar值为303.1~436.4，经计算得成矿流体中大气40Ar贡献介于67.71%~97.49%，表明了成矿流体具有壳幔混合的特征，并且有大量大气水的参与。综上分析，文章推测隆或金矿床中原始成矿流体来自深部岩浆流体，原始成矿流体在上升过程中与盆地建造水发生混合，形成了多流体混合的成矿流体，并且随着成矿的进行，大量的大气降水或地下水的渗入。结合构造环境、矿化蚀变等特征，文章认为隆或金矿床为中低温低压浅成热液卡林型金矿床。
Abstract:The Longhuo gold deposit in Guangxi is a layered Carlin-type deposit located in the interior of the Longhuo isolated carbonate platform on the C/D unconformity surface of the Youjiang Basin. A detailed field geological investigation was carried out in this work to investigate the source of ore-forming fluid of the Longhuo gold deposit and discuss its genesis, and systematic petrographic observation, microscopic temperature measurement, and C-H-O-He-Ar isotope analysis were carried out for fluid inclusions in quartz and calcite formed in different metallogenic stages. Petrography and inclusion temperature measurements revealed that liquid-rich gas-liquid two-phase aqueous solution inclusions developed primarily in quartz and calcite, with a tiny amount of CO2 three-phase inclusions. The homogenous temperature of the inclusions in quartz is between 170.4~282.6℃, the salinity w(NaCleq) is between 2.57%~8.41%, and the density is 0.77~0.93 g/cm3. The homogenous temperature of the inclusions in calcite is between 178.5~237℃, the salinity w(NaCleq) is between 2.9%~7.17%, and the density is 0.845~0.935 g/cm3, which are H2O-NaCl system with medium-low temperature, low salinity, low density. It is calculated that the ore-forming fluid's metallogenic pressure is in the range of 45.83~74.17 MPa, and the metallogenic depth is 1.611~2.472 km. Quartz has an 18OV-SMOW value of 25.2‰~28.7‰, a matching 18OH2O value is 14.10‰~17.18‰, and the δDV-SMOW value is -79‰~-51‰, Although the H and O isotope plotting sites of the two stages of quartz are in or near the metamorphic water region, but stage Ⅱ quartz tends to shift to the magma water. The calcites δ13CPDB and δ18OV-SMOW values are concentrated in the range of -6.5‰~-4.6‰ and 19.9‰~21.1‰, respectively. The plotting points are close to the marine carbonate area, indicating that the formation of calcite is mainly from the dissolution of carbonate rocks. The 3He/4He values of fluid inclusions in quartz range between 0.351~0.744 Ra, which is placed between mantle helium and crustal helium, the values of mantle-derived He(%) is 5.11%~11.17%, indicating the domination of crustal fluid. The 3He/4He values of fluid inclusions in calcite are 0.038~0.073 Ra, which is located near crustal helium. The 40Ar/36Ar values of quartz and calcite are 303.1~436.4. The calculated contribution of atmospheric 40Ar ranges between 67.71%~97.49%, indicating that the ore-forming fluid possesses crust and mantle mixing features, and there's a significant amount of atmospheric water involved. Based on the above analysis, it is deduced that the original ore-forming fluid in Longhuo gold deposit comes from deep magmatic fluid, and the original ore-forming fluid mixes with basin formation water during the ascent process, forming a multi-fluid mixed ore-forming fluid, and there is a large amount of atmospheric precipitation or groundwater infiltration with the progress of mineralization. Combining the characteristics of tectonic environment and mineralization alteration, it is ascertain that the Longhuo gold deposit is a medium-low temperature and low-pressure epithermal Carlin-type gold deposit.
keywords:fluid inclusion C-H-O-He-Ar isotope ore genesis Longhuo gold deposit isolated platform in western Guangxi
AN Peng,CHEN MaoHong,KONG ZhiGang,CHEN Gang,WANG Yu.2023.Restriction of source of ore-forming fluid by fluid inclusions and C-H-O-He-Ar isotopes of Longhuo gold deposit in western Guangxi[J].Mineral Deposits42(5):907~926