桂西隆或金矿床流体包裹体与C-H-O-He-Ar同位素对成矿流体来源的制约  

Restriction of source of ore-forming fluid by fluid inclusions and C-H-O-He-Ar isotopes of Longhuo gold deposit in western Guangxi

作　　者：安鹏 陈懋弘[2] 孔志岗[1] 陈港 王昱 AN Peng;CHEN MaoHong;KONG ZhiGang;CHEN Gang;WANG Yu(Faculty of Land Resource Engineering,Kunming University of Science and Technology,Kunming 650093,Yunnan,China;MNR Key Laboratory of Metallogeny and Mineral Assesment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093 [2]中国地质科学院矿产资源研究所,自然资源部成矿作用和资源评价重点实验室,北京100037

出　　处：《矿床地质》2023年第5期907-926,共20页Mineral Deposits

基　　金：国家自然科学基金面上资助项目《桂西孤立台地内部寒武系中卡林型金矿成矿机理研究》(编号:42072110);广西找矿突破战略行动地质矿产勘查项目《桂西隆林孤立台地卡林型金矿的“梯式”结构模型及找矿前景》(编号:桂国土资函[2018]377号)联合资助。

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CO_(2)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/cm^(3);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/cm^(3),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δ^(18)OV-SMOW值为25.5‰~28.7‰,对应的δ^(18)O_(H2O)为14.10‰~17.18‰,δD_(V-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δ^(13)CPDB集中在-6.5‰~-4.6‰,δ^(18)OV-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3 He/4 He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3 He/4 He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 in-vestigation 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-HO-He-Ar isotope analysis were carried out for fluid inclusions in quartz and calcite formed in different metallo-genic 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 CO_(2)three-phase in-clusions.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/cm^(3).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/cm^(3),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 theδD_(V-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 stageⅡquartz tends to shift to the magma water.The cal-citesδ^(13)CPDB andδ^(18)OV-SMOW values are concentrated in the range of-6.5‰~-4.6‰and 19.9‰~21.1‰,respective-ly.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 3 He/4 He values of fluid inclusions in quartz range between 0.351~0.744 Ra,which is placed between mantle helium

关 键 词：流体包裹体 C-H-O-He-Ar同位素 矿床成因 隆或金矿 桂西孤立台地 

分 类 号：P618.51[天文地球—矿床学]