投稿时间：2022-07-21
修订日期：2022-10-11
网络发布日期：2023-01-07
中文摘要:福建泰宁李家坊金矿床位于武夷山成矿带中段，为闽西北何宝山矿田内新发现的一个中型金矿床，成因类型尚未明确。磁铁矿是该矿床中常见的氧化物，文章应用磁铁矿微量元素特征对李家坊金矿床成矿过程与成因类型进行约束。基于野外地质踏勘和钻孔岩芯编录，结合室内详细的岩相学观察，依据磁铁矿的结构和矿物共生组合，文章将其分为4种类型（Mt1a、Mt1b、Mt2和Mt3）。其中，Mt1a位于铜金矿脉边缘，呈板柱状，与绿泥石共生； Mt1b位于铜金矿脉边缘，呈自形-半自形粒状，与绿泥石-赤铁矿共生； Mt2位于铜金矿脉中，呈脉状产出，穿插早阶段的石英-黄铁矿脉，与绿泥石-绿帘石共生； Mt3位于铜金矿脉中，呈半自形-他形粒状，与绿帘石-赤铁矿共生，被后阶段黄铜矿包裹、交代。金主要以自然金和银金矿的形式赋存于Mt3中。原位微区分析结果表明，李家坊金矿不同类型磁铁矿均属于热液型磁铁矿。此外，从Mt1a型到Mt3型磁铁矿，w（Ti）呈逐渐降低的趋势，指示热液流体逐渐向低温条件演化； w（V）表现出先降低后升高再降低的变化规律，暗示热液流体的氧逸度有明显波动，但总体呈升高趋势。磁铁矿的显微结构和化学组成具矽卡岩型矿化特征，是判断矿床成因类型的证据。其中，Mt3型磁铁矿与Au矿化密切相关，其矿物组合与微量元素特征可指示金在低温高氧逸度的环境下沉淀。
Abstract:The Lijiafang gold deposit is located in the Hebaoshan district in the Middle of the Wuyi Metallogenic Belt in Northwest Fujian. It is medium-sized gold deposit newly discovered and the type of deposit is obscure. Magnetite is a common oxide mineral in the deposit. The characteristics of trace elements in magnetite are applied to restrict the mineralization process and genetic type of Lijiafang gold deposit. This paper divided the magnetite of this deposit into four different types (Mt1a、Mt1b、Mt2 and Mt3) according to its structure and mineral assemblage. The plate-columnar Mt1a type magnetite grains coexist with chlorite on the edge of the copper and gold veins, whereas the euhedral-subhedral granular Mt1b type magnetite grains is intergrown with chlorite and hematite on the edge of the copper and gold veins. The euhedral granular Mt2 type magnetite grains is symbiosis with chlorite and epidote located in a copper and gold vein and occurs as veins, whereas the subhedral-anhedral granular Mt3 type magnetite grains is intergrown with epidote and hematite and contains native gold and electrum located in a copper and gold vein. The results of in-situ microanalysis show that different types of magnetite in Lijiafang gold deposit belong to hydrothermal magnetite. In addition, the content of Ti showed a decreasing trend, indicating that hydrothermal fluids gradually evolved to low temperature conditions and the content of V showed a change rule of first decreasing, then increasing and then decreasing, suggesting that the oxygen fugacity of hydrothermal fluid had obvious fluctuations, but it showed an overall upward trend. Microscopic structure and chemical composition of magnetite have the characteristics of skarn, which can be used to provide evidence for genetic types of deposits. Among them, the Mt3 magnetite is closely related to Au mineralization and the mineral assemblage and trace element characteristics can be used to indicate the precipitation of gold in low temperature and high oxygen fugacity environment.
keywords:geochemistry magnetite mineral chemistry fluid evolution genetic type Lijiafang gold deposit
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基金项目:本文得到国家自然科学基金项目（编号：41672035）资助
引用文本：
陈娟,赵骏峰,刘文元,邢波,肖政,周小深,卢林.2022.福建李家坊金矿床磁铁矿成因及其对金矿化过程的指示[J].矿床地质,41(6):1142~1163CHEN Juan,ZHAO JunFeng,LIU WenYuan,XING Bo,XIAO Zhen,ZHOU XiaoShen,LU Lin.2022.Genesis of magnetite and its implication of gold mineralization process in Lijiafang gold deposit, Fujian[J].Mineral Deposits41(6):1142~1163
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