南秦岭柞水-山阳矿集区小河口矽卡岩型铜矿床矿物化学及其成矿意义  

Mineral chemistry of the Xiaohekou skarn copper deposit in the Zhashui-Shanyang ore cluster area,South Qinling and its metallogenic significance

作　　者：熊潇[1] 朱赖民[1] 张国伟[1] 杨文强[1] 郑俊[1] 姜航[1] 刘凯 郭延辉 XIONG Xiao;ZHU LaiMin;ZHANG GuoWei;YANG WenQiang;ZHENG Jun;JIANG Hang;LIU Kai;GUO YanHui(State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China;No. 713 Team of Northwest Mining and Geological Exploration Bureau for Nonferrous Metals, Shangluo 726000, China)

机构地区：[1]西北大学地质学系,大陆动力学国家重点实验室,西安710069 [2]西北有色地质勘查局713总队,商洛726000

出　　处：《岩石学报》2019年第8期2597-2614,共18页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41730426、41803039、41421002、41272092);中国博士后科学基金(2018M643712);西北大学大陆动力学国家重点实验室科技部专项基金联合资助

摘　　要：秦岭造山带燕山期斑岩-矽卡岩型铜矿床因过去发现的数量有限,限制了对区内铜矿床成矿机制的深入研究。小河口铜矿床是南秦岭柞水-山阳矿集区内的典型矽卡岩型铜矿床,矿体产于燕山期花岗闪长玢岩与泥盆系桐峪寺组地层接触处的矽卡岩带内。成矿作用划分为4个阶段:Ⅰ干矽卡岩阶段、Ⅱ湿矽卡岩-氧化物阶段、Ⅲ石英-硫化物阶段和Ⅳ碳酸盐-石英阶段。本文在对该矿床矽卡岩矿物(石榴子石和辉石)和金属矿物(磁铁矿和硫化物)详细的岩(矿)相学观察基础上,针对这些矿物进行系统的电子探针成分分析,来示踪矽卡岩的成因和形成环境,讨论成矿元素的沉淀富集过程。研究表明,小河口铜矿床为典型的接触交代成因钙质矽卡岩型矿床。干矽卡岩矿化阶段从早到晚依次形成钙铝榴石(Adr24-31Gr68-74)、钙铝榴石组分-钙铁榴石组分交替系列(Adr26-68Gr31-72)和透辉石(Di73-91Hd8-24)-纯钙铁榴石(Adr68-100Gr0-30)。伴随着岩浆结晶分异,初始岩浆-热液流体与灰岩发生接触交代作用首先形成无环带钙铝榴石(Grt-a)矽卡岩,此时成岩环境为低氧逸度、酸性还原环境,不利于矽卡岩铁、铜矿化的形成;成矿流体不断从岩浆中出溶并发生多次沸腾,引起残留热液的氧化还原状态发生周期性变化,成矿热液由酸性逐渐向弱碱性演化,进而导致Fe3+和Al3+活度的变化,在振荡的物理化学环境中形成了钙铝榴石-钙铁榴石组分交替生长的宽环带石榴子石(Grt-c)矽卡岩;随着岩浆演化和流体作用的扩大,成矿体系处于较稳定的碱性和高氧逸度环境,Fe和Al的过饱和程度此消彼长,形成了透辉石-密集振荡环带钙铁榴石(Grt-b和Grt-d)矽卡岩。成矿流体演化进入湿矽卡岩-氧化物阶段后,富含挥发分的热液活动起主导作用,沸腾作用将H+和CO2分离进入气相,导致流体体系碱性和氧逸度程度进一步升高,进而形成磁铁�Due to the few discoveries of Yanshanian porphyry-skarn copper deposits in the Qinling Orogen,the in-depth study on the ore-forming mechanism of copper deposits in the area is limited. The Xiaohekou copper deposit is one of the few typical skarn-type and commercial deposits that have been mined in the Zhashui-Shanyang ore cluster area of the eastern part of South Qinling. Orebodies mainly developed in the skarn in the contact zones between the Yanshanian corcovadite and Devonian Tongyusi Formation. Four mineralization stages of the deposit are identified as follows:(Ⅰ) an anhydrous skarn stage,(Ⅱ) a hydrous skarn-oxide stage,(Ⅲ) a quartz-polymetallic sulfide stage,and(Ⅳ) a carbonate-quartz stage. Based on the detailed petrography( ore mineralogy) observations of the skarn( garnet and pyroxene) and metallic minerals( magnetite and sulfides) in the deposit,here we present integrated electron microprobe data of these minerals for the first time to constrain the genesis and formation environment of the skarn and discuss the precipitation and enrichment process of metallogenic elements. The Xiaohekou Cu deposit is a typical contact-metasomatic calcic skarn deposit. From early to late anhydrous skarn stage,grossularite( Adr24-31Gr68-74),grossularite-andradite alternation series( Adr26-68Gr31-72) and diopside( Di73-91Hd8-24)-pure andradite( Adr68-100Gr0-30) were formed in order. Accompanied by magma crystal fractionation,contact metasomatism occurred between the initial magma-hydrothermal fluid and limestone firstly forming the unzoned grossularite( Grt-a) skarn,and the diagenetic environment was low oxygen fugacity,acidic,and reduced,which is not avail to forming skarn iron and copper mineralization.The ore-forming fluids constantly dissolved from the magma,and coupled with repeated boiling of hydrothermal fluids caused the redox state of residual fluids change periodically,thereby inducing the activities of Fe3+ and Al3+ change to form the grossularite-andradite alternation series( Grt-c) with wide zones in an

关 键 词：小河口矽卡岩型铜矿床 石榴子石 辉石 金属矿物 物理化学条件 成矿流体演化 

分 类 号：P575.1[天文地球—矿物学] P595[天文地球—地质学]