安徽铜陵冬瓜山铜（金）矿床层状矿体的成因——热液锆石U-Pb年代学和原位硫同位素制约

The major stratiform orebody of the Dongguashan copper (gold) deposit contains one Mt Cu metal, and has important economic value. The genesis of the stratiform orebody has been perplexing people for a long time. At present, there are three kinds of understanding on the genesis of the stratiform orebody: magmatic hydrothermal genesis, exhalative sedimentary genesis, and the overprinting genesis of the first two kinds. With the needs of deep and peripheral mineral exploration, it is urgent to determine the genesis of the stratiform orebody. Based on the detailed geological field investigation and microscopic observation, two aspects of researches are to be carried out in this project: (1) hydrothermal zircon age are to be determined by LA-ICP-MS U-Pb dating to reveal the metallogenic age of stratiform orebody; and (2) the comparative in-situ sulfur isotopic analysis on different types of pyrite and chalcopyrite by Nano-SIMS and the trace element analysis on pyrite are to be performed to trace the ore-forming material source of stratiform orebody and discuss its ore-forming environment and process. Combined with the previous research and comprehensive analysis, this project is aimed at discussing the genesis of the stratiform orebody in the Dongguashan copper (gold) deposit. This work will not only contribute to understanding the genesis and formation mechanism of the stratiform orebody correctly, but also provide scientific basis for the mineral exploration in depth and margin at the Dongguashan copper (gold) deposit, meanwhile providing an example for the study of similar deposits.

冬瓜山铜（金）矿床层状主矿体铜资源量达近百万吨，具有重要的经济价值，其成因长期困扰着人们，目前有岩浆热液、海底喷流和前两种复合叠加成矿三种认识。随着深部和外围找矿勘查的需要，亟待破解这一难题。本项目拟在详细的地质调查和矿相学观察的基础上，着重开展以下2方面的研究：（1）采用LA-ICP-MS锆石U-Pb定年技术，测定层状矿体中热液锆石的U-Pb年龄，揭示其形成时代；（2）采用纳米二次离子质谱（Nano-SIMS）测试技术，对比分析不同类型矿体、不同类型矿石中黄铁矿、黄铜矿的原位S同位素组成，结合黄铁矿等硫化物的微量元素成分特征，示踪层状矿体成矿物质来源，探讨其成矿环境和成矿作用过程。结合前期研究基础及前人研究成果，探讨冬瓜山铜（金）矿床层状矿体的成因。此项研究，不仅有助于正确认识该层状矿体的成因及形成机制，也可为找矿勘查提供科学依据，同时为类似矿床的研究提供范例。

冬瓜山铜（金）矿床是铜陵矿集区的重要组成部分，层状矿体是该矿床的主矿体，赋存于中上石炭统黄龙组-船山组碳酸盐岩地层层位中。关于该矿床层状矿体的成因长期存在争议，争议的焦点在于层状矿体的成矿时代和成矿物质来源没有明确的定论。鉴于此，本项目重点开展了冬瓜山铜（金）矿床层状矿体的成矿物质来源及成矿时代研究。单矿物和原位S同位素组成均落入岩浆硫范围内，表明冬瓜山铜（金）矿床层状矿体的成矿物质主要来源于岩浆源。H-O同位素结果显示，冬瓜山铜（金）矿床层状矿体的成矿流体主要为岩浆水。流体包裹体研究结果显示，流体不混溶作用是冬瓜山铜（金）矿床形成的主要机制。年代学结果显示，冬瓜山铜（金）矿床层状矿体热液锆石U-Pb年龄为134±1Ma、辉钼矿Re-Os年龄为132.3±2.8Ma、石榴子石U-Pb年龄为133.7±0.7Ma，表明冬瓜山铜（金）矿床形成时代为燕山期。微量元素分析结果表明，冬瓜山铜（金）矿床层状矿体和纹层状矿体中的黄铁矿（Py I，Py II）和磁黄铁矿（Po I，Po II）富集Cu、Co、Au和Se，亏损As、Pb和Zn，Py I、Py II、Po I和Po II的 Co/Ni比值分别为4.37−56.38、0.43−226.00、1.55−14.45和1.02−1.36，与岩浆热液成因的黄铁矿和磁黄铁矿特征一致。综合以上分析，认为冬瓜山铜（金）矿床层状矿体的形成与燕山期岩浆侵入活动有密切的成因联系，为受层间虚脱空间控制的层控矽卡岩型矿床，不存在海西期喷流沉积成矿作用。