湖南新宁星子岩锑矿流体包裹体特征及矿床成因

Fluid inclusion characteristics and genesis of the Xingziyan stibnite deposit,Xinning,Hunan Province

湖南新宁县星子岩锑矿位于钦杭结合带中段湘中盆地内,脉状矿体受NE向硅化破碎带控制,直接容矿围岩为下寒武统香楠组碳质板岩和硅质板岩。文中对星子岩锑矿进行系统的矿物生成序列研究,将成矿过程分为两期3个阶段,即沉积期以碳质板岩内球状黄铁矿为代表,热液期早阶段脉状辉锑矿石英脉(局部夹围岩角砾)和晚阶段辉锑矿方解石脉。为进一步限定其成因,选取热液期与辉锑矿共生的早阶段石英和晚阶段的方解石进行流体包裹体研究。包裹体岩相学研究表明,热液期石英和方解石内广泛发育流体包裹体,主要类型为纯H_2O型和CO_2-H_2O型流体包裹体。激光拉曼测试表明,CO_2-H_2O型包裹体气相主要成分为CO_2,液相主要成分为H_2O。显微测温过程中,当降温时可见CO_2-H_2O型包裹体由气液两相变为三相,其初熔温度为-60.0^-56.6℃,CO_2部分均一温度为3.7~28.5℃,完全均一温度介于113~266℃,CO_2笼合物熔化温度为3.0~9.6℃,对应的流体盐度w(NaCleqv.)为0.8%~12.0%。星子岩锑矿流体包裹体的中低温、低盐度和含CO_2的特征与造山型金矿的变质流体成矿特征相吻合。综合星子岩锑矿的成矿大地构造背景、矿床地质和成矿流体特征,星子岩锑矿的精细成矿过程为:钦杭结合带在印支—燕山期发生强烈的陆壳叠置作用,富碳质含黄铁矿的寒武系地层发生变质变形脱挥发分作用,形成中低温、低盐度、富CO_2和富集锑元素的变质热液;变质热液向上运移过程中,温度压力降低发生相分离,导致CO_2逸失和流体沸腾作用,大量辉锑矿沉淀,最终形成有经济价值的矿体。湖南星子岩锑矿的矿床地质特征和成矿过程与造山型金矿一致,因此其成因类型为造山型锑矿。

The Xingziyan stibnite deposit is located in the Central Hunan Basin（CHB）,the middle section of the Qinzhou-Hangzhou Joint Belt（QHJB）.The stibnite ore bodies,controlled by NW-trending silicified fracture belt,are hosted in the pyrite-bearing carbonaceous and siliceous slate of the Cambrian Xiangnan Formation.In this study,we identified two ore-forming periods exhibiting three ore-forming stages.The sedimentary period typically presents rounded pyrite with recrystallized rims.And in the hydrothermal period,the early-and late-stage features presents stibnite-quartz veins（wrapping around some host rock breccias）and stibnite-bearing calcite veins,respectively.The early-stage quartz and late-stage calcite in the hydrothermal period were selected to investigate fluid inclusions.Two types of widely developed fluid inclusion,H2O and CO2-H2O types,were identified under petrographic observation.The homogenization temperature and salinity of fluid inclusions ranged 113-266 ℃ and 0.8-12.0 wt.% NaCl_（eqv.）, respectively.Gaseous constituents in fluid inclusions were dominated by CO2 as identified by Laser Raman analysis.The characteristics of middle-to-low homogenization temperature,low salinity and high CO2 content indicate the ore-forming fluid may be of metamorphic origin.In consideration of the regional tectonic evolution,we conclude that the Xingziyan stibnite deposit,is an orogenic-type stibnite mineral system formed in the tectonic setting of the Indosinian-Yanshanian intracontinental strik-slip faulting.