黑龙江省三矿沟矽卡岩型铁铜矿床成矿作用研究

Skarn deposits are the main sources of the high-grade iron and copper ores in China, and have been the subject of numerous studies and intense exploration activity over the centuries. However, the ore-forming material source of skarn deposits remains controversial, which restricts the development of the metallogenic theory of skarn deposits. In recent years, the development of new analytical techniques has provided new methods and ideas for the research of ore-forming material source. The Sankuanggou Fe-Cu deposit is located in the Duobaoshan metallogenic belt in the northern Great Hingan Range, Heilongjiang province. It is the most representative skarn Fe-Cu-Au deposit in the metallogenic belt, making it a perfect window to understand the skarn metallogenic system of this area. However, the mineralogical characteristics, the source of ore-forming material and the metallogenic mechanism are poorly understood. In this proposal, we will carry out systematic mineralogical studies to reveal the mineralization process and metallogenic mechanism of skarn deposits from microcosmic angle especially by LA-ICP-MS in situ trace elements analysis of garnet and magnetite. Combined with fluid inclusions study, we attempt to determine the mineralization temperature and ore-forming fluid properties. Then, we aim to trace the ore-metal sources using Fe isotope signatures. We aim to reveal the ore-forming material source of skarn deposits through a variety of means from multi angle, and set up the metallogenic model of the Sankuanggou Fe-Cu deposit. This work will help to promote the development of the metallogenic theory of skarn deposits, and provide a theoretical basis for the skarn deposit exploration in the northern Great Hingan Range.

矽卡岩型矿床是我国富铁矿石和富铜矿石的主要来源，长久以来受学术界和矿业界高度重视。然而其成矿物质来源颇具争议，制约了矽卡岩型矿床成矿理论的发展。近年来，分析测试技术的发展为揭示矽卡岩型矿床成矿物质来源这一难题提供了新的研究手段和分析思路。三矿沟铁铜矿床位于大兴安岭北段多宝山矿集区内，作为区内最典型的矽卡岩型铁铜金矿床，是认识该区矽卡岩成矿系统的窗口。但其矿物学特征、成矿物质来源和成矿机理研究均较薄弱。本项目拟展开系统的矿物学研究，重点进行石榴子石和磁铁矿的LA-ICP-MS原位微量元素分析，从微观角度揭示矽卡岩矿床的成矿过程及成矿机理；利用流体包裹体地球化学反演成矿流体性质与来源，通过Fe同位素示踪成矿物质的来源；本项目旨在通过多种手段从多角度揭示矽卡岩型矿床的成矿物质来源，建立成矿模式，促进矽卡岩型矿床成矿理论的发展，为大兴安岭北段矽卡岩型矿床的勘查提供理论依据。

三矿沟铁铜矿床位于大兴安岭北段多宝山矿集区，作为区内最典型的矽卡岩型铁铜金矿床，是认识该区矽卡岩成矿系统的窗口。矿体产于燕山期花岗闪长岩与奥陶系多宝山组大理岩接触带的的矽卡岩内。根据矿物共生组合及交代关系，其热液成矿过程可分为矽卡岩阶段、退矽卡岩阶段和石英硫化物阶段。电子探针分析表明，三矿沟铁铜矿床发育钙质矽卡岩矿物组合，其石榴子石主要为钙铝榴石和钙铁榴石，辉石为透辉石-钙铁辉石系列。LA-ICP-MS微量元素分析结果显示，钙铝榴石富集重稀土元素，具有显著的Eu负异常，钙铁榴石富集轻稀土元素，Eu随样品不同呈微弱负异常至显著正异常，暗示其形成于不同的氧化还原环境。流体包裹体研究及H-O同位素研究表明，三矿沟成矿流体为高温、高盐度的岩浆热液，后期有大气降水的加入。Fe同位素研究表明，成矿物质主要来自于成矿岩体花岗闪长岩，在流体出溶及后期流体演化过程中发生了Fe同位素的分馏。矽卡岩阶段成矿流体具有高温、弱酸性、高氧逸度的特征；退矽卡岩阶段流体温度降低，pH升高，形成大量铁氧化物；石英-硫化物阶段流体温度、氧逸度降低，金属硫化物沉淀。