摘要
马场金矿床位于北祁连造山带东段的宁夏西华山地区,是区内已发现的规模最大的金矿床,然而关于该矿床的成因研究比较薄弱,且岩浆活动是否参与金成矿尚无共识。为详细了解马场金矿床成因,本文对含金煌斑岩和矿石开展了锆石U-Pb年代学、石英流体包裹体和C-H-O-S同位素研究。结果表明:马场金矿成矿热液期可划分为3个成矿阶段,从早到晚依次为黄铁矿-石英阶段(Ⅰ阶段)、黄铁矿-绢云母-石英阶段(Ⅱ阶段)和石英-黄铜矿硫化物阶段(Ⅲ阶段),其中Ⅲ阶段为主成矿阶段。不同成矿阶段的流体包裹体有4种类型,分别是富液两相包裹体(Ⅰa型)、纯液相包裹体(Ⅱ型)、含CH4两相包裹体(Ⅳ型)和含CO_(2)三相包裹体(Ⅲa型)。显微测温结果显示,成矿流体的完全均一温度为218~345℃,峰值集中在280~300℃,盐度(w(NaCl))为1.40%~12.73%,密度为0.77~0.93 g/cm^(3),平均压力为60×10~5 Pa,成矿深度为2.0~6.7 km,为中温、低盐度、低密度的富CO_(2)、含CH4的H2O-NaCl-CO_(2)体系。热液期石英δD值为-95.5‰~-75.2‰,δ^(18)OV-SMOW值为+13.8‰~+16.7‰;方解石的δ^(13)CV-PDB值为-6.28‰~-2.55‰,指示成矿流体为岩浆水、变质水和大气降水组成的混合流体。S同位素结果显示,成矿物质为以岩浆为主的混合来源,地层对金矿的贡献次之。与金矿关系密切的煌斑岩锆石U-Pb年龄为433 Ma,暗示金矿成矿时代为早志留世。综合北祁连构造岩浆演化,认为马场金矿形成与原特提斯洋俯冲及随后的俯冲板片断离诱发的弧后伸展构造环境有关,为造山型金矿床。
The Machang gold deposit,located in the eastern part of the North Qilian orogen,is the largest gold deposit discovered in the Xihuashan area of Ningxia.However,the genesis of the deposit is still unclearly,and there is also no consensus on whether magmatic activity is involved in the gold mineralization.In this study,zircon U-Pb age of lamprophyre dyke,quartz fluid inclusions,and C-H-O-S isotope data of quartz,calcite and sulfide in the Machang gold deposit were carried out to determine the ore genesis.The results show that the metallogenic process of the Machang gold deposit can be divided into three stages:the pyrite-quartz stage(Ⅰ),pyrite-sericite-quartz stage(Ⅱ),and quartz-chalcocite sulfide stage(Ⅲ)from early to late,and the StageⅢis the main mining stage.There are four types of fluid inclusions in different metallogenic stages,which are liquid-rich two-phase inclusions(Ⅰa),pure liquid phase inclusions(Ⅱ),CH4-bearing two-phase inclusions(Ⅳ),and CO_(2)-bearing three-phase inclusions(Ⅲa).Microthermometric results show that the complete homogenization temperature of the ore-forming fluid is between 218-345℃,with a peak concentration between 280-300℃,salinity between 1.40%-12.73%NaCl equiv,density of 0.77-0.93 g/cm^(3),average pressure of 60×10^(5) Pa,and the mining depth is 2.0-6.7 km,forming a medium-temperature,low-salinity,low-density CO_(2)-rich,CH4-containing H2O-NaCl-CO_(2) system.TheδD values of hydrothermal quartz range from-95.5‰to-75.2‰,andδ^(18)OV-SMOW values range from+13.8‰to+16.7‰,theδ^(13)CV-PDB values of calcite range from-6.28‰to-2.55‰,indicating that the ore-forming fluid is a mixed fluid composed of magmatic water,metamorphic water,and atmospheric precipitation.The S isotope results show that the source of ore-forming materials is a mixed source mainly of magmatic origin,with a secondary contribution from the strata.The zircon U-Pb age of the lamprophyre closely associated with the gold deposit is 433 Ma,suggesting that the gold mineralization age is the early Silurian.Combined with the tectonic and magmatic evolution of the North Qilian orogen,it is believed that the formation of the Machang gold deposit is related to the subduction of the Proto-Tethys Ocean and the subsequent detachment of the subduction slab,which induced the post-collisional extensional tectonic environment in the back-arc.The Machang gold deposit is classified as an orogenic gold deposit.
作者
海连富
母彩霞
梅超
陶瑞
赵少卿
HAI Lianfu;MU Caixia;MEI Chao;TAO Rui;ZHAO Shaoqing(Mineral Geological Survey Institute of Ningxia Hui Autonomous Region(Institute of Mineral Geology of Ningxia Hui Autonomous Region),Yinchuan 750021,China;Geological Bureau of Ningxia Hui Autonomous Region,Yinchuan 750021,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China;Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University),Ministry of Education,Changsha 410083,China;School of Geosciences,Yangtze University,Wuhan 430100,China)
出处
《中国有色金属学报》
北大核心
2025年第5期1799-1820,共22页
The Chinese Journal of Nonferrous Metals
基金
地质过程与矿产资源国家重点实验室科技部专项经费(GPMR202439)
有色金属成矿预测与地质环境监测教育部重点实验室(中南大学)开放基金资助项目(2024YSJS08)
宁夏回族自治区重点研发计划项目(2021BEG03003,2024BEH04016)
宁夏回族自治区自然科学基金项目(2021AAC03447)。
