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豫西熊耳山矿集区九仗沟金矿床黄铁矿微量元素、硫同位素组成及地质意义

Trace element and sulfur isotope composition of pyrite from Jiuzhanggou Gold Deposit, Xiong’ershan Ore Concentration Area, western Henan, and its geological significance

  • 摘要: 黄铁矿是金矿床中最主要的载金矿物,其微量元素组成和硫同位素特征记录了成矿元素赋存状态、成矿条件等关键信息,也是判别矿床成因类型的重要指标。豫西熊耳山矿集区内的九仗沟金矿床为典型构造蚀变岩型金矿床,其矿床成因研究对区域找矿具有重要意义。以成矿阶段黄铁矿为研究对象,系统开展原位微量元素组成研究,并结合闪锌矿开展原位硫同位素分析。结果表明:①在微量元素赋存状态方面,Co、Ni主要以类质同象替代Fe进入黄铁矿晶格;Cu、Pb、Zn多呈显微矿物包裹体形式存在,Au与As、Sb、Ag正相关,并以固溶体形式赋存于富As黄铁矿中,暗示As、Sb可作为有效找矿指示元素;②黄铁矿w(Co)/w(Ni)值为0.03~309.78,平均值为3.26,结合w(Co)−w(Ni)−w(As)图解,指示矿床成因类型为岩浆热液型,但成矿流体中有显著大气降水混入;③黄铁矿δ34S值为−15.25 ‰~−4.14‰,闪锌矿δ34S值为−16.79 ‰~−13.99 ‰,δ34S峰值出现在−14.50 ‰左右,反映成矿过程中硫同位素发生强烈分馏。九仗沟金矿床成矿物质主要来源于地壳浅部,深部岩浆热液在上升过程中与大气降水混合并萃取围岩成矿物质,最终在有利构造部位沉淀成矿。

     

    Abstract: Pyrite is the dominant gold-bearing mineral in gold deposits. Its trace element composition and sulfur isotopic signature not only record critical information such as the occurrence state of metallogenic elements and metallogenic conditions, but also serve as key indicators for determining the genetic type of ore deposits. Located in the Xiong’ershan Ore Concentration Area of western Henan, the Jiuzhanggou Gold Deposit is a typical structurally controlled alteration-type gold deposit. Research on its genesis is therefore essential for regional prospecting. By taking pyrites formed in different metallogenic stages as the research objects, the in-situ trace element composition was systematically studied, combined with in-situ sulfur isotope analysis of sphalerite. The results show that in terms of the occurrence of trace elements, Co and Ni enter the pyrite lattice mainly by isomorphous substitution for Fe, while Cu, Pb and Zn occur largely as microscopic mineral inclusions. Au displays positive correlations with As, Sb and Ag, and occurs as a solid solution within As-rich pyrite, implying that As and Sb can serve as effective prospecting elements. The w(Co)/w(Ni) ratio in pyrite ranges from 0.03 to 309.78, with a mean value of 3.26. Combined with the w(Co)−w(Ni)−w(As) diagram, the ratio indicates a magmatic-hydrothermal origin, but the metallogenic fluid is significantly diluted by meteoric water. Pyrite yields δ34S values ranging from −15.25 ‰ to −4.14 ‰, while the values of sphalerite range from −16.79 ‰ to −13.99 ‰. The δ34S values exhibit a peak at −14.5 ‰, reflecting strong sulfur-isotope fractionation during mineralization. The metallogenic materials of the Jiuzhanggou Gold Deposit are derived predominantly from the shallow crust. Deep-seated magmatic hydrothermal fluids ascend, mix with meteoric water, leach metals from the wall rocks, and finally precipitate gold in favorable structural sites to form the deposit.

     

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