南秦岭大桥超大型金矿早成矿阶段黄铁矿Re-Os同位素年龄及其地质意义  

Re‑Os dating of pyrite from early ore stage of the Daqiao superlarge gold deposit in South Qinling and its geologic significance

作　　者：赵洪葆 何甘地 牛鹏飞 吴保祥 何进忠[1] Zhao Hongbao;He Gandi;Niu Pengfei;Wu Baoxiang;He Jinzhong(Geological Survey of Gansu Province,Lanzhou 730000;Northwest Institute of Eco‑Environment and Resources,CAS,Lanzhou 730000)

机构地区：[1]甘肃省地质调查院,兰州730000 [2]中国科学院西北生态环境资源研究院,兰州730000

出　　处：《地质科学》2025年第2期594-606,共13页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：中国地质调查局项目(编号:12120114050001,121201004000150017-35);甘肃省自然资源厅科技创新项目(编号:202231)资助。

摘　　要：南秦岭大桥超大型金矿早成矿阶段的成矿年龄一直以具偶然蚀变矿化的花岗闪长岩脉推定,对该年龄和相关物质来源的研究,可以为深化矿床成因研究提供依据。南秦岭大桥超大型金矿矿床成矿期次依次为沉积变质期、热液成矿期和表生氧化期,热液成矿期包括早、主和晚3个成矿阶段。本研究借助在1440m中段71勘探线采准巷道采集到的矿石样品,经过样品甄别、筛选、单矿物挑选和实验测试,获得了5件理想的热液成矿期早成矿阶段样品,测得黄铁矿Re-Os同位素等时线年龄221±7.6 Ma(2σ),初始锇同位素组成(^(187)Os/^(188)Os)为0.215±0.033(MSWD=0.85)。结合花岗闪长岩脉成岩年龄判断,大桥金矿早成矿阶段在误差范围内涵盖矿区印支晚期花岗闪长岩成岩年龄(232.8~203.8 Ma)的早期;含金黄铁矿的世代可能与花岗闪长岩的不等间隔脉冲式侵入期后热液活动相对应。根据Os同位素初始值,Au与Os的亲铁性,地幔流体形成过程中Au的不相容性,含金地幔流体形成过程,以及区域成矿构造背景,判定幔源流体是成矿流体和金的重要来源。同时,黄铁矿硫同位素较宽的变化范围,以及前人对基底白龙江群黑色岩系的认识指示不能排除基底变质流体对金成矿的贡献。Since the ore‑forming age of early ore stage of Daqiao superlarge gold deposit in South Qinling has ever been deduced from the accidentally gold‑mineralized granodiorite dykes,this paper reports the study results of the ore‑forming age and related ore material sources,so as to provide a light for deepening research of genesis of the deposit.The previous studies showed us that the ore‑forming process experienced sedimentary and metamorphic period,hydrothermal ore‑forming period,and hypergene oxidized period,in which the hydrothermal ore‑forming period was composed of early ore stage,main ore stage,and late ore stage.In this study,from ore samples taken from developing workings in No.71 exploration line of stage 1440 m of the deposit,an ideal early ore stage of five samples and their Re‑Os isochron of pyrite of 221±7.6 Ma(2s),together with an initial osmium isotope composition of 0.215±0.033(MSWD=0.85),were obtained by using of sample identification,single mineral selection,test,and data analysis.Combining the Re‑Os isochron age with the emplacement ages of granodiorites,we thought that the early ore stage of the gold deposit covered early period of diagenetic age(232.8~203.8 Ma)of Late Indosinian granodiorites within the error range in the mining area.The generations of gold‑bearing pyrite could correspond to postmagmatic hydrothermal activities related to irregularly pulse emplacement of the granodiorites.From the initial osmium isotope composition,Au and Os as siderophile elements,incompatibility of Au in the exsolution process of mantle fluid,generating process of gold‑bearing mantle fluid,and regional tectonic background,we judged that the mantle fluid is one of important sources of gold and ore‑forming fluid besides the basement.The wide variation of sulfur isotopic composition of pyrite,and previous knowledge about black rock series of Bailongjiang Group suggest the contribution of metamorphic fluid in basement shouldnt be excluded.

关 键 词：超大型金矿 幔源流体 花岗闪长岩脉 印支晚期 南秦岭 

分 类 号：P597[天文地球—地球化学] P611[天文地球—地质学]