小秦岭大湖金钼矿床地质特征及成矿流体  

Geological Characteristics and Ore-forming Fluids of the Dahu Au-Mo Deposit in Xiaoqinling Gold Field

作　　者：郭云成 刘家军[2,3] 尹超[2,3] 郭梦需 GUO Yuncheng;LIU Jiajun;YIN Chao;GUO Mengxu(Yantai Center of Coastal Zone Geological Survey,China Geological Survey,Yantai,Shandong 264000,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质调查局烟台海岸带地质调查中心,山东烟台264000 [2]中国地质大学(北京)地球科学与资源学院,北京100083 [3]中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处：《现代地质》2021年第6期1536-1550,共15页Geoscience

基　　金：国家自然科学基金重大研究计划重点项目(92062219);国家自然科学基金重点项目(41730426);中国地质调查局项目“胶西北地区金矿资源勘查”(DD20208006)。

摘　　要：小秦岭地区位于华北克拉通南缘,赋存许多大型-超大型的金矿床,大湖金钼矿床位于小秦岭北矿带。大湖金钼矿床成矿具有多期多阶段特点,包括热液期和表生期,根据矿脉穿切关系、矿石的矿物组成以及结构、构造研究,热液期分为4个成矿阶段,即石英-钾长石-辉钼矿阶段(Ⅰ)、石英-黄铁矿-自然金阶段(Ⅱ)、石英-多金属硫化物-自然金阶段(Ⅲ)和石英-碳酸盐阶段(Ⅳ)。流体包裹体岩相学、激光拉曼成分分析和冷热台测温结果表明,大湖金钼矿的初始成矿流体属H_(2)O-CO_(2)-NaCl体系,包裹体分为三种类型,即CO_(2)-H_(2)O型包裹体(C型)、水溶液型包裹体(W型)和纯CO_(2)型包裹体(PC型)。成矿Ⅰ、Ⅱ、Ⅲ和Ⅳ阶段包裹体均一温度范围分别为275.3~350.0℃、260.0~312.7℃、245.3~287.6℃和237~251℃,流体盐度范围为5.2%~16.7%,密度为0.777~1.108 g/cm^(3),为中-高温、中-低盐度、低密度流体,与变质流体特征一致。均一温度从Ⅰ阶段→Ⅳ阶段呈逐渐下降趋势,盐度从Ⅰ阶段→Ⅲ阶段逐渐降低,Ⅳ阶段沸腾作用使流体中的气体组分逸出,导致剩余流体的浓缩盐度增高。流体成矿压力范围为58.0~196.3 MPa,对应成矿深度范围为3.0~7.1 km。矿区普遍存在的围岩蚀变表明水岩反应强烈,氢同位素δD为-90‰~-44‰,成矿流体氧同位素δ^(18)O_(水)范围为2.1‰~5.9‰,属于变质热液范围;在δ^(18)O_(水)-δD组成图解投图中落在变质水范围左下侧,Ⅱ、Ⅲ阶段样品的δ^(18)O_(水)较Ⅰ阶段整体左移,表明高温变质流体与围岩(斜长角闪岩等变质岩)发生水岩反应,导致同位素互换平衡。大湖金钼矿床受区域近东西向断裂构造控制,属典型的断控脉状矿床,成矿流体以变质水为主,矿床主要特征与典型的造山型金矿特征相符。The Xiaoqinling district,located on the southern margin of the North China Craton,is the second largest gold province in China.The Dahu is a typical Au⁃Mo deposit on the northern margin of the Xiaoqinling terrane,and is hosted by migmatitic granites and biotite⁃plagioclase gneiss of the Taihua supergroup metamorphic complex.According to crosscutting relationships and mineral assemblages,the hydrothermal ore⁃forming process can be divided into four stages,including quartz⁃K⁃feldspar⁃molybdenite assemblage(Ⅰ),quartz⁃pyrite⁃molybdenite assemblage(Ⅱ),quartz⁃pyrite⁃polymetallic sulfide assemblage(Ⅲ),and quartz⁃calcite assemblage(Ⅳ).Petrographic,fluid inclusion microthermometric and micro⁃Raman spectroscopic analyses reveal three types of fluid inclusions in quartz,i.e.,CO_(2)⁃H_(2)O(C⁃type),H_(2)O⁃solution(W⁃type),and pure CO_(2)(PC⁃type).StageⅠquartz mainly contains C⁃type,PC⁃type,and W⁃type inclusions.Homogenization temperatures of C⁃type inclusions vary from 275.3 to 350.0℃with salinity of 6.3%to 14.7%,and haveδ^(18)O_(water)values from 4.6‰to 5.9‰andδD values from-82‰to-63‰.StageⅡquartz mainly contains C⁃type inclusions with small amounts of PC⁃type and W⁃type inclusions.Their C⁃type inclusions homogenized at 260.0 to 312.7℃,lower than that of stageⅠ.The fluid salinities vary from 2.2%to 17.5%.The fluids haveδ^(18)O_(water)values from 3.0‰to 4.5‰andδD values from-90‰to-50‰.Maximum trapping pressure estimated from the CO_(2)⁃H_(2)O inclusions are 196 MPa for stageⅡ,corresponding to 7.1 km depth.The ore⁃forming fluid is characterized by meso⁃to hypothermal,CO_(2)⁃rich and low salinity,resembling typical metamorphic fluids.Hydrogen⁃oxygen isotope signatures indicate that the fluids were originated from metamorphic devolatilization.The reactions of metamorphic fluid with the wallrocks may have led to the isotope exchange.Therefore,the Dahu Au⁃Mo deposit is best classified to be an orogenic⁃type gold deposit.

关 键 词：小秦岭 大湖金钼矿床 流体包裹体 氢氧同位素 造山型金矿床 

分 类 号：P618.51[天文地球—矿床学]