机构地区：[1]中国地质大学(北京)地球科学与资源学院/地质过程与矿产资源国家重点实验室/深时数字地球前沿科学中心,北京100083 [2]甘肃省地质矿产勘查开发局第三地质矿产勘查院,甘肃兰州730050 [3]甘肃省金属贵金属矿产资源勘查与综合利用工程技术研究中心,甘肃兰州730050
出 处：《地学前缘》2023年第6期371-390,共20页Earth Science Frontiers
基 金：国家自然科学基金项目(42072087,42111530124);中国地质大学(北京)深时数字地球前沿科学中心项目(2652023001);高等学校学科创新引智计划项目(BP0719021);矿床地球化学国家重点实验室开放研究项目(202202);北京市科技新星计划课题(Z201100006820097)。
摘 要：西秦岭造山带在晚三叠世期间由华北板块和华南板块碰撞拼合而成。其地质演化历史复杂,岩浆活动频繁,矿产资源丰富,区内累计探明黄金储量大于1 200 t。然而,金矿床成因还存在卡林型、造山型、岩浆热液型和与侵入体相关等多种观点。完肯金矿床金资源量约3.5 t,位于西秦岭造山带西南段,赋存于下三叠统隆务河组浅变质沉积岩中,矿体主要受近EW和NW-SE向断裂控制,主要发育浸染状和细脉网脉状矿化,是区域内典型金矿床,也是理想的研究对象。本文通过开展岩石学、矿相学和载金硫化物地球化学研究,拟查明金的赋存状态,并探讨其矿床成因。研究表明完肯金矿床成矿作用可以分为3个阶段:成矿早阶段为黄铁矿(Py1)-石英-绢云母-绿泥石阶段;成矿主阶段为黄铁矿(Py2)-毒砂-石英-绢云母-绿泥石阶段;成矿晚阶段为石英-方解石-闪锌矿-方铅矿-辉锑矿阶段。电子探针分析数据(已检出的样品)显示黄铁矿金的含量(质量分数)为0.11%~0.24%,毒砂和闪锌矿金的含量分别为0.11%~0.28%和0.16%~0.37%。黄铁矿、毒砂样品中的金含量大多低于检测限,闪锌矿样品中金含量相对较高,70%的测点金含量高于0.15%,表明Au在硫化物中分布不均匀。黄铁矿Au/As值为0.007~0.20,均大于0.004,且在扫描电镜下未观察到自然金,表明完肯金矿床金主要以纳米级金颗粒或晶格金的形式赋存。此外,黄铁矿和毒砂中Fe-As、S-As的负相关关系揭示,Au主要是通过进入富As的八面体Fe结构位和化学吸附的方式进入载金硫化物。黄铁矿的Fe含量为45.41%~46.26%,S含量为51.48%~52.79%,其Fe/S(原子个数比)大于0.875,表明其为变质热液成因黄铁矿。成矿主阶段毒砂As含量为42.80%~46.52%,晚阶段闪锌矿Fe、Zn含量分别为1.77%~2.57%和63.75%~64.82%。进而,通过毒砂和闪锌矿温度计估算出成矿主阶段温度大致为(385±40)℃,硫逸度lgf(S2)为-7.55±1.45,成�The West Qinling Orogen,formed as a result of Late Triassic collision between the North and South China Blocks,has undergone complex geological evolution and multi-episodic magmatic activities.It has abundant ore resources,including over 1200 tons of gold by estimation.The genesis of the gold deposits is still debatable,with possibilities including Carlin-type,orogenic,magmatic hydrothermal,and intrusion-related.The Wanken gold deposit in the southwest contains~3.5 tons of proven gold,hosted in metasedimentary rock of the Lower Triassic Longwuhe Formation.Typical of the region,the gold deposit is structurally controlled by EW and NW-SE trending faults,and mainly exhibits disseminated vein mineralization styles.This study investigates the gold occurrences in the Wanken gold deposit and its genesis through petrological and mineralogical analyses,combined with geochemical analysis of gold-bearing sulfides.Three mineralization stages are delineated:pyrite(Py1)-quartz-sericite-chlorite(Stage I),pyrite(Py2)-arsenopyrite-quartz-sericite-chlorite(Stage II),and quartz-calcite-sphalerite-galena-stibnite(Stage III).According to electron microprobe analysis,the gold content(wt%)is mostly below detection limits in pyrite(0.11%-0.24%)and arsenopyrite(0.11%-0.28%),but relatively high in sphalerite(0.16%-0.37%),with 70%sites above 0.15%,indicating a heterogeneous distribution of Au in sulfides.The Au/As ratio of pyrite(0.007-0.20)is generally greater than 0.004,and there is no evidence of native gold,indicating gold mainly occurs as Au nanoparticles or nanocrystals.A negative correlation between Fe and As or between S and As in As-rich pyrite and arsenopyrite reveals that Au enters sulfide lattice through substitution into octahedral Fe(II)sites,or through chemical adsorption.The Fe(45.41%-46.26%)and S(51.48%-52.79%)contents in pyrite correspond to a Fe/S ratio of greater than 0.875,indicating a metamorphic-hydrothermal origin.Arsenopyrite from the main metallogenic epoch contains 42.80%-46.52%arsenic,and late sphalerite contain
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