滇西云县坝子街铜矿床黄铜矿地球化学特征及地质意义

Geochemical Characteristics and Geological Significance of Chalcopyrite from the Bazijie Copper Deposit,Yunxian County,Western Yunnan Province

摘要

南澜沧江构造带作为三江成矿带的重要组成部分,区内矿产资源丰富.滇西云县坝子街铜矿床作为该区代表性矿床之一,迄今尚未开展系统研究.以该矿床为研究对象,采用Electron Microprobe Analysis(EPMA)和 LA-ICP-MS 测试技术对该矿床的黄铜矿进行主量、微量元素测试,并探讨其矿床成因.结果表明:坝子街铜矿床矿体主要赋存于上三叠统小定西组玄武岩中,其成矿过程可划分为浅成低温热液期及表生氧化期;坝子街铜矿床黄铜矿中Cu、Fe、S元素组成较为稳定,铁、铜元素的总物质的量与硫元素质量的比值(w(Fe+Cu)/w(S))平均值为1.822,黄铜矿中铜、铁总物质的量与硫物质的量的摩尔比(n(Cu+Fe)/n(S))平均值为0.98,均低于黄铜矿标准值,表明坝子街铜矿床可能形成于中温-中低温环境;坝子街铜矿床黄铜矿中相对富集Ag、Pb、Sb、As等低温成矿元素,Ag主要以矿物包裹体形式存在,而Pb则以纳米级微粒形式赋存于黄铜矿中;结合地质特征及黄铜矿地球化学特征,可认为坝子街铜矿床属浅成低温热液矿床.

Abstract

The South Lancangjiang Tectonic Belt is an important part of the Sanjiang Metallogenic Belt with abundant mineral resources.As one of the typical deposits in this region,the Bazijie copper deposit in Yun County,western Yunnan,has not been systematically studied so far.Taking this deposit as the research object,electron probe microanalysis (EPMA) and LA-ICP-MS were adopted to determine the major and trace elements of chalcopyrite,and the genesis of the deposit was further discussed.The results show that:the ore bodies of the Bazijie copper deposit are mainly hosted in the basalt of the Xiaodingxi formation of the Upper Triassic.The mineralization process can be divided into two stages:the epithermal hydrothermal stage and the supergene oxidation stage;The chalcopyrite in the Bazijie copper deposit has a relatively stable composition of Cu,Fe,and S elements.The average value of w(Fe+Cu)/w(S) is 1.822,and the average value of n(Cu+Fe)/n(S) is 0.98,both of which are lower than the standard values for chalcopyrite.This suggests that the Bazijie copper deposit likely formed in a medium-temperature to medium-low-temperature environment; The chalcopyrite in the Bazijie copper deposit is relatively enriched in low-temperature ore-forming elements such as Ag,Pb,Sb,and As.Ag is primarily present in the form of mineral inclusions,while Pb is hosted in the chalcopyrite as nanoscale Particles,Combined with the geological characteristics and geochemical signatures of chalcopyrite,the Bazijie copper deposit is classified as an epithermal lowsulfidation hydrothermal deposit.

关键词

元素地球化学 / 元素赋存状态 / 矿床成因 / 黄铜矿 / 坝子街铜矿床 / 滇西

Key words

elemental geochemistry / elemental occurrence phase / deposit genesis / chalcopyrite / Bazijie copper deposit / Western Yunnan

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基金资助

国家自然科学基金项目(42462014)

云南省基础研究专项-重点项目(202401AS070063)

西藏科技厅重点研发计划(XZ202501ZY0140)

云南省万人计划青年拔尖人才专项(YNWR-QNBJ-2018-093)

昆明理工大学重点学科建设项目(14078384)