地学前缘 ›› 2019, Vol. 26 ›› Issue (5): 146-162.DOI: 10.13745/j.esf.sf.2019.8.3

• 矿床地质地球化学 • 上一篇    下一篇

西秦岭左家庄金矿成因研究：来自黄铁矿微量元素及多元同位素地球化学的制约

马健，吕新彪，但荣飞，朱丁云，卢飞，袁波，殷新   

  1. 1. 东华理工大学 核资源与环境国家重点实验室, 江西 南昌 330013
    2. 东华理工大学 地球科学学院, 江西 南昌 330013
    3. 中国地质大学(武汉) 地质调查研究院, 湖北 武汉 430074
    4. 中陕核工业集团 211大队有限公司, 陕西 西安 710024
  • 收稿日期:2018-06-19 修回日期:2019-01-12 出版日期:2019-09-28 发布日期:2019-09-28
  • 通讯作者: 吕新彪(1962—)，男，博士，教授，博士生导师，主要从事矿床学研究。
  • 作者简介:马健(1990—)，男，博士研究生，讲师，从事秦岭造山带金成矿过程及成因研究。E-mail：jian.ma@cug.edu.cn
  • 基金资助:
    国家自然科学基金项目(41902076)；陕西省地勘基金项目(61201304171)；中陕核工业集团211大队有限公司项目(ZHS211KY2016001)

Ore genesis of the Zuojiazhuang gold deposit in the West Qinling Orogen: constraints from pyrite trace elements and multi-isotope analyses

MA Jian,LÜ Xinbiao,DAN Rongfei,ZHU Dingyun,LU Fei,YUAN Bo,YIN Xin   

  1. 1. State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, China
    2. School of Earth Sciences, East China University of Technology, Nanchang 330013, China
    3. Institute of Geological Survey, China University of Geosciences(Wuhan), Wuhan 430074, China
    4. Number 211 Geological Brigade of Sino Shaanxi Nuclear Industry Group, Xi'an 710024, China
  • Received:2018-06-19 Revised:2019-01-12 Online:2019-09-28 Published:2019-09-28
  • Supported by:
     

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摘要： 左家庄金矿位于西秦岭凤太盆地西北部，金矿体赋存在印支早期何家庄岩体的东西向剪切破碎带内。矿石类型以石英硫化物脉型为主，与西秦岭地区沉积岩控矿为主的特征有显著的差别。流体包裹体测温及成分分析表明，左家庄金矿成矿流体具有含CO2、中低温(122~305 ℃)、低盐度(1.2%~11.8% NaCleq)、浅成(约2.4 km)热液的特征。H-O同位素组成(δDH2O集中在-88.8‰~-81.1‰；δ18OH2O在-0.4‰~+7.6‰)显示成矿初始流体以变质水为主，随着流体向上运移不排除有岩浆水和大气降水的加入。Pb同位素组成显示成矿物质来源于浅部上地壳及造山带内；S同位素组成集中(11.4‰~13.4‰)，与凤太盆地内泥盆系沉积岩控金矿相似，且与全球范围内泥盆系控矿造山型金矿组成吻合，反映出泥盆系地层为成矿提供了硫源；热液期黄铁矿原位微量元素分析显示左家庄金矿成矿流体富集Au、As、Cu、Sb、Ag、Pb、Bi等元素，该元素组合与前人分析凤太盆地内泥盆系地层(尤其是中、上泥盆统界面)富集元素特征一致。上述分析一致表明泥盆系地层是左家庄金矿成矿物质来源理想场所。多元同位素对比分析表明，左家庄金矿与凤太盆地内其他金矿在成矿流体及成矿物质来源上具有统一性，但是在矿化形式上有显著区别，其差异可能与二者赋矿围岩性质不同有关。成矿流体沿断裂向上运移过程中，当遇到上泥盆统渗透性较高的千枚岩时发生水岩反应，形成以微细浸染状矿化为主的金矿；当碰到岩体内脆性剪切破碎带时，由于压力释放，流体沸腾，导致矿质迅速沉淀在张性破碎带内，形成石英硫化物脉型左家庄金矿。通过与典型造山型金矿成矿特征对比分析，认为左家庄金矿可划归为浅成造山型金矿床。

 

关键词: 西秦岭, 金矿, 黄铁矿, 同位素, 微量元素

Abstract: The Zuojiazhuang gold deposit is located in the northwestern part of the Devonian Feng-Tai basin in the West Qinling Orogen. Gold ore bodies are mainly hosted in the EW striking shear zone in the Hejiazhuang pluton (247 Ma). The quartz-sulfide ore (lode gold), as micro-disseminated gold hosted in the Devonian sediments, is quite different from other gold deposits in the basin. Fluid inclusion study indicated that the ore fluid in the Zuojiazhuang gold deposit can be characterized as a middle-low temperature (122 – 305 ℃), low salinity (1.2% – 11.8% NaCleq) and epizonal (2.4 km) CO2-NaCl fluid system. Hydrogen-O isotope analysis (δDH2O=-88.8‰-81.1‰；δ18OH2O=-0.4‰+7.6‰) shows that the ore fluid is metamorphic fluid at origin, with magmatic and meteoric water mixing during upward movements. Lead isotope distribution indicates the metal source came from shallow upper crust and orogene belt. Sulfur isotopic composition was concentrated between 11.4‰ and 13.4‰, which is in agreement with sedimentary-hosted gold deposit in the basin and Devonian orogenic gold deposit around the world. In-situ trace elemental analysis of auriferous pyrite shows that the ore fluid was enriched in Au, As, Cu, Sb, Ag, Pb, Bi, etc. Moreover, similar trace elemental enrichment in the Devonian sediments in the Feng-Tai basin, especially at the boundary of Middle to Upper Devonian, has been widely reported. Therefore, we hypothesize that the Devonian sediments could be the reasonable metal source for the Zuojiazhuang deposit. The mechanism of gold deposition in the Zuojiazhuang deposit could be attributed to the sharp decrease of fluid pressure and subsequent fluid boiling, which caused rapid precipitation of minerals inside the tensile fracture zone to form the lode gold deposit. The Zuojiazhuang deposit may be defined as epizonal orogenic gold deposit as it is compared with typical orogenic gold around the world.

Key words: West Qinling Orogen, gold deposit, pyrite, isotopes, trace elements

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