陕西大西沟喷流沉积型菱铁矿矿床地质特征及矿床成因  

Geological characteristics and origin of Daxigou SEDEX siderite deposit in Shaanxi Province

作　　者：詹涵钰 李占轲[2] 武文辉 李建威[2,3] ZHAN HanYu;LI ZhanKe;WU WenHui;LI JianWei(Sichuan Geological Survey, Chengdu 610081, Sichuan, China;Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, Hubei, China;State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, Hubei, China)

机构地区：[1]四川省地质调查院,四川成都610081 [2]中国地质大学资源学院,湖北武汉430074 [3]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《矿床地质》2019年第1期1-20,共20页Mineral Deposits

基　　金：国家自然科学基金项目(编号:41325007;41402066;91514303)的资助

摘　　要：陕西大西沟铁矿床位于秦岭造山带山-柞盆地西北部,与银洞子大型银铅矿床毗邻。矿体主要赋存在泥盆系青石垭组中上段,容矿岩石为一套海相复理石碎屑岩和碳酸盐岩建造。矿床的金属矿物主要有菱铁矿、磁铁矿、黄铁矿,其次为黄铜矿、磁黄铁矿等;非金属矿物主要是重晶石、石英、铁白云石,其次为方解石、绢云母、绿泥石、黑云母、斜长石、钠长石、堇青石等,局部地段由于表生氧化和次生富集作用而形成针铁矿、赤铁矿、蓝辉铜矿等。与矿化有关的围岩蚀变较弱,主要有硅化、绢云母化、绿泥石化和碳酸盐化。基于野外地质观察、矿物共生组合和矿石结构构造的系统研究,将大西沟铁矿床的形成划分为3期6阶段,分别是:①喷流沉积期:硅质岩-黄铁矿-菱铁矿阶段(Ⅰ)、重晶石-磁铁矿阶段(Ⅱ);②热液改造期:堇青石-黄铁矿-磁铁矿阶段(Ⅲ)、石英-碳酸盐阶段(Ⅳ)、碳酸盐-硫化物-磁铁矿阶段(Ⅴ);③表生氧化期(Ⅵ)。流体包裹体显微测温结果表明,喷流沉积期Ⅰ阶段菱铁矿完全均一温度和盐度w(NaCl_(eq))峰值区间分别为230～270℃和13%～14.5%,Ⅱ阶段重晶石中流体包裹体的完全均一温度和盐度w(NaCl_(eq))峰值区间分别为220～290℃和9%～13%;热液改造期Ⅳ阶段菱铁矿和石英中气液两相包裹体均一温度峰值区间为240～300℃,盐度w(NaCl_(eq))为2.6%～15.7%;热液改造期Ⅴ阶段菱铁矿与石英中流体包裹体,除大量气液两相包裹体外,还发育有含子矿物多相包裹体,其中,气液两相包裹体均一温度峰值区间为290～340℃,盐度w(NaCl_(eq))为5.1%～13.4%,含子矿物多相包裹体均一温度峰值区间为380～440℃,盐度w(NaCl_(eq))为40.6%～59.7%。含子晶流体包裹体可能是流体不混溶或/和高盐度流体加入的反映。矿区内不同产状碳酸盐矿物的C、O同位素组成比较均一,δ^(13)C_(PDB)值集中在-3.58‰～-1.15‰�The Daxigou iron deposit is located in the northwest of Shan-Zha Basin in the Qinling Orogen, adjacent to the Yindongzi Ag-Pb deposit. The orebodies are hosted in the upper section of Devonian Qingshiya Group, which is a set of flysch clastic-carbonate sedimentary formations of marine facies. The metallic minerals consist mainly of siderite, magnetite, pyrite, and chalcopyrite with minor pyrrhotite, hematite, goethite, and digenite. The non-metallic minerals are dominated by barite, quartz, and ankerite, with a little calcite, sericite, chlorite, biotite, plagioclase, albite, and cordierite. Supergene oxidation has formed some iron and copper supergene minerals, such as goethite, hematite, and digenite. Wall rock alteration associated with mineralization is weakly developed, and is mostly characterized by silicification, sericitization, chloritization, and carbonatization. On the basis of a systematic study of field geological features, mineral paragenesis, ore texture and structure, the mineralization process can be divided into six stages: SEDEX period: the silicolite-pyrite-siderite stage (Ⅰ) and the barite-magnetite stage (Ⅱ);hydrothermal alteration period: the cordierite-pyrite-magnetite stage (Ⅲ), the quartz-carbonate stage (Ⅳ) and the carbonate-sulfide-magnetite stage (Ⅴ), and supergene period (Ⅵ). Fluid inclusion study shows that the temperature and salinity w(NaCleq) of siderite from stage Ⅰ focus on 230~270℃ and 13%~14.5%, respectively;the temperature and salinity w(NaCleq) of barite from stage 2 are mainly distributed in 220~290℃ and 9%~13%, respectively. The fluid inclusions in siderite and quartz from stage Ⅳ in hydrothermal alteration period mostly are gas-liquid two-phase inclusions, with the temperature and salinity w(NaCleq) distributed in 240~300℃ and 2.6%~15.7%, respectively. The siderite and quartz from stage Ⅴ have many gas-liquid two-phase inclusions and polyphase inclusions containing daughter minerals. The temperature of gas-liquid two-phase inclusions ranges from 2

关 键 词：地质学 菱铁矿 流体包裹体 C、O同位素 成矿流体 大西沟 

分 类 号：P618.31[天文地球—矿床学]