Geology and S-Pb isotope geochemistry of the Hatu gold deposit in West Junggar,NW China:Insights into ore genesis and metal source

The Hatu gold deposit is the largest historical gold producer of the West Junggar,western China,with an Au reserve of about 62 t.The orebodies were controlled by NE-,EW-,and NW-trending subsidiary faults associated with the Anqi fault.This deposit exhibits characteristics typical of a fault-controlled lode system,and the orebodies consist of auriferous quartz veins and altered wall rocks within Early Carboniferous volcano-sedimentary rocks.Three stages of mineralization have been identified in the Hatu gold deposit:the early pyrite-albite-quartz stage,the middle polymetallic sulfides-ankerite-quartz stage,and late quartz-calcite stage.The sulfur isotopic values of pyrite and arsenopyrite vary in a narrow range from-0.8‰to1.3‰and an average of 0.4‰,the near-zeroδ~(34)S values implicate the thorough homogenization of the sulfur isotopes during the metamorphic dehydration of the Early Carboniferous volcano-sedimentary rocks.Lead isotopic results of pyrite and arsenopyrite(^(206)Pb/^(204)Pb=17.889-18.447,^(207)Pb/^(204)Pb=15.492-15.571,^(208)Pb/^(204)Pb=37.802-38.113)are clustered between orogenic and mantle/upper crust lines,indicating that the lead was mainly sourced from the hostrocks within the Early Carboniferous Tailegula Formation.The characteristics of S and Pb isotopes suggest that the ore-forming metals of the Hatu orogenic gold deposit are of metamorphogenic origin,associated with the continental collision between the Yili-Kazakhstan and Siberian plates during the Late Carboniferous.

Fluid Geochemistry and Metallogenesis of the Hatu Gold Deposit in the Junggar Basin, Xinjiang

The Hatu large gold deposit is located on the western margin of the Junggar basin, Xinjiang. Its mineralization is characterized by auriferous quartz veins and Au-bearing altered fracturing zones. Studies on mineralogy, inclusions and decrepitation temperature indicate that the gold deposit was formed by overlapping of two kinds of fluid of different origins, instead of gradual evolution of a single fluid. The auriferous quartz veins are related to magmatism-originated fluid, but the Au-bearing altered fracturing zones to deep-derived fluid. Bonanzas in quartz veins were formed and localized at overlapping positions of two types of fluid under intensive compression.

新疆哈图金矿原生晕特征及深部预测

在对哈图金矿地下450~1 000 m深处盲矿体及围岩系统取样和成矿指示元素含量分析基础上,计算获得该矿原生晕轴向分带序列(自上而下):(Au、Pb、Ag、Cu、Zn)—(Hg)—(As、Mo、Sb、W)—(Ni)—(Bi)。结合指示元素含量衬度图形及前人资料,确定了原生晕的前缘晕元素组合:Hg、As、Sb,尾晕元素组合:W、Ni、Bi,近矿指示元素组合:Pb、Ag、Cu、Zn。根据指示元素的组合及分布,发现已知矿体的下部以尾晕元素组合为主,虽有前缘晕元素Sb与As的异常,但规模和强度较小,且前缘晕元素组合与尾晕元素组合的累乘比较低,预示深部可能仍有隐伏矿体,但规模不大。

新疆哈图金矿地球化学原生晕的深部找矿意义

哈图金矿是新疆目前开采规模和产量最大的金矿床。利用矿区中东段的坑探工程和矿区西段钻探工程,开展了原生晕地球化学测量,中东段坑探工程中11个中段共采集矿体及围岩样品159件,西段钻探岩芯等间距取样54件,测试元素为Hg、Au、Ni、Pb、As、Sb、Cu、W、Zn、Ag、Mo、Bi共12项。通过研究,查明哈图金矿前缘晕为Hg-As-Sb,近矿元素为Ag-Cu-Zn-Mo,尾晕元素为W-Bi-Ni;中东段矿体原生晕轴向分带序列为Au、Pb-Hg-As、Ag-W-Sb、Bi-Zn、Cu、Ni、Mo;西段分带序列为Bi、Zn、Hg-Pb-Sb-Cu-W、As-Ag、Ni-Mo-Au。西段原生晕出现"反分带"与"头尾晕共存"现象,受雁列式含矿构造尖灭再现的影响,原生晕存在叠加结构,垂向上地球化学参数波动明显,结合区域地质矿产资料推断,矿区西段深处找矿潜力大于中东段。

新疆哈图金矿成矿地球化学特征

文章分析了哈图金矿成矿元素与共(伴)生元素的种类和含量以及矿脉中的石英流体包裹体特征,结果显示:含矿石英脉中发育含CO_2的三相(V_(CO_2)+L_(CO_2)+L_(H_2O))包裹体以及富液相和富气相的气液两相包裹体,均一温度为198?C～329?C,盐度0.7%～3.51%NaClwt%,成矿热液属于中低温、低盐度流体,其温度、压力随流体向上运移而明显降低.矿石中石英氧同位素δ^(18)OV-SMOW值为20.3‰～21.0‰,对应矿液中水的δ^(18)O值为8.6‰～14.8‰,具有变质水和岩浆水的混合特征.根据矿床地质特征、成矿条件及CCA多元统计结果,认为成矿元素和共(伴)生元素按地球化学活性依次析出,形成了由下而上的尾晕元素组合→近矿元素组合→前缘晕元素组合的分带序列.

新疆哈图金矿成矿流体组分与同位素地球化学特征分析

哈图金矿床位于新疆西准噶尔地区南部,是哈图金矿带中重要的金矿床之一。通过对金矿石英脉样品中的石英开展流体包裹体成分分析,结合矿石样品中的毒砂和黄铁矿的硫同位素以及方解石中的碳、氧同位素特征,分析可知:包裹体气相成分以H2O为主,CO2和N2含量次之。液相成分中阳离子以Na^+、Ca^2+为主,阴离子以Cl^-和SO24^-为主,成矿流体属SO24^--Cl^--Na^+-Ca^2+型。从早阶段至晚阶段,H2O含量增加,CO2及Na^+、Cl^-等离子含量降低。硫化物中硫同位素组成为-2.9‰^+0.8‰,集中在0±3‰范围,成矿物质的硫来自岩浆流体或赋矿围岩。方解石中的碳、氧同位素组成中δ13 CPDB值为-11.4‰^-9.2‰,δ18 OSMOW值为+8.5‰^+17.4‰,认为成矿流体属大气降水和岩浆水混合流体。哈图金矿与穆龙套型金矿有相似的含矿地层和成矿时间,因此可以考虑哈图地区寻找穆龙套型金矿的可能性。