Depositional environment and origin of the Lilaozhuang Neoarchean BIF-hosted iron–magnesite deposit on the southern margin of the North China Craton
Depositional environment and origin of the Lilaozhuang Neoarchean BIF-hosted iron–magnesite deposit on the southern margin of the North China Craton
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DOI：
10.1007/s00531-016-1384-2
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发表时间：
2017-07
影响因子：
2.3
通讯作者：
Hua Huang;Lianchang Zhang;S. Fabre;Changle Wang;M. Zhai
中科院分区：
文献类型：
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作者：
Hua Huang;Lianchang Zhang;S. Fabre;Changle Wang;M. Zhai
新太古代李老庄铁镁矿床位于华北克拉通南缘安徽霍丘条带状铁组（BIF）矿带中部。霍丘BIF是该区唯一同时发育石英型、硅酸盐型和碳酸盐型磁铁矿的BIF。李老庄矿床以磁铁矿中富镁碳酸盐（菱镁矿）为特征。含矿铁矿主要为硅酸盐型和碳酸盐型，少量石英型，以带状、块状构造为主，浸染状构造为辅。菱镁矿呈晶体状亮白色，呈块状结构。铁矿和菱镁矿矿石的Y/Ho比值和REY模式与海水相似，而Eu呈正异常，为海底热液混合的标志。这些特征表明，李老庄矿床铁、镁的成矿物质主要来自海底热液与海水的混合作用。两个矿石均未出现负Ce异常，说明矿床形成于缺氧环境。C-O同位素组成表明，菱镁矿经低角闪岩相变质和后期热液蚀变改造而成。综合分析认为，李老庄铁矿和菱镁矿形成于陆缘封闭海盆，受后期复杂地质作用的影响。
The Neoarchean Lilaozhuang iron–magnesite deposit is located in the middle of the Huoqiu banded iron formation (BIF) ore belt in Anhui Province on the southern margin of the North China Craton. The Huoqiu BIF is the unique one that simultaneously develops quartz-type, silicate-type, and carbonate-type magnetite in the region. The Lilaozhuang deposit is characterized by magnesium-rich carbonate (magnesite) in magnetite ores. The BIF-hosted iron ores include mainly of silicate type and carbonate type, with a small amount of quartz type, which chiefly exhibit banded and massive structure, with minor disseminated structure. The magnesite ores occur as crystal-like bright white and exhibits massive structure. The Y/Ho ratio and REY pattern of both iron and magnesite ores are similar to that of seawater, while Eu shows positive anomaly, which is the sign of seafloor hydrothermal mixture. These features suggest that ore-forming materials of iron and magnesium in the Lilaozhuang deposit are mainly from the mixture of seafloor hydrothermal and seawater. Both ores do not exhibit negative Ce anomaly, which indicates that the deposit was formed in an environment showing a lack of oxygen. C–O isotopic compositions indicate that magnesite ore has been reformed by metamorphism of low amphibolite facies and later hydrothermal alteration. Based on the comprehensive analysis, authors suggest that iron and magnesite ores in the Lilaozhuang deposits formed in a confined sea basin on continental margin and was influenced by later complex geological processes.