高台沟硼矿地质地球化学及成因分析

GEOLOGY AND GEOCHEMISTY OF THE GAOTAIGOU BORON DEPOSIT IN SOUTHERN JILIN,CHINA

高台沟硼矿位于吉南集安地区,含硼岩系普遍经受中-高级区域变质作用,区域上含矿镁质岩石类型划分为镁橄榄岩大理岩混合型和大理岩型两种矿化类型,高台沟硼矿属于镁橄榄岩大理岩混合型硼矿。含矿层岩石为灰绿色和黄绿色蛇纹岩,顶部岩石为金云母、透辉、滑石岩或金云透辉大理岩,向下为金云蛇纹岩或金云白云石大理岩,与蛇纹岩成渐变关系。蛇纹岩原岩为菱镁矿大理岩和镁橄榄岩,蛇纹石化镁橄榄岩中以产出硼镁铁矿为主,蛇纹石化大理岩中主要产出硼镁石。矿石化学成分反映,B_2O_3品位变化与MgO含量正相关,高品位硼矿石MgO含量均在40%以上。硼矿石稀土总量较低,小于22.03×10^(-6),轻重稀土略有分异,不同的负铕异常,明显的铈正异常。矿石中除B外,F也明显富集,其次是Cl、Rb、Sn、Th、U高于地幔岩石,而Ti、V、Cr、Co、Ni、Ga、Ba等则亏损,而硼镁铁矿的Co、Sn、U热液元素明显高于硼镁石矿石。矿床成因属于变质热液交代富镁质岩石形成的矿床,硼酸热液交代富镁岩石及磁铁矿形成硼镁石和硼镁铁矿,也可以是硼酸热液与铁镁溶液混合形成硼镁石和硼镁铁矿。

A boron-beaing rock series at the Gaotaigou boron deposit located in the Ji＇an district of southern Jinlin has undergone extensive meso- or high-degree regional metamorphism. Regionally, B-bearing magnesian rock can be divided into two mineralized types： mixed forsterite and marble; and marble type; the Gaotaigou boron deposit belongs to the former. Ore-bearing rock layers are grayish green and fresh green serpentinite, with phlogopite, diopside, talc or pholoptie diopside marble on the footwall and phogopite serpentinite or phogopite dolomitic marble as footwall. The both are of gradual contact with the serpentinite. Source rock of the serpentinite is magnesite marble and forsterite; ludwigite occurs mostly in serpentinized forsterite while szaibelyite in serpentinized marble. Chemical compositions of the ores reflect that B203 concentration varies positively with MgO content. High-grade boron ore contains more than 40% of MgO, with less REE content less than 22.03×10^-6. There is slight differentiation between LREE and HREE, with various negative Eu anomly and distinct Ce anomly. Besides boron, fluorine is also enriched in the ores; and the contents of C1, Rb, Sn, Th and U are also higher than those in the mantle rock. Although Ti, V, Cr, Co, N, Ga and Ba are depleted in the ores, the thermal elements such as Co, Sn and U in ludwigite ore are distinctly higher than those in the szaibelyite ores. The deposit was formed by metamorphic hydrothermal replacement of Mg-rich rock, with either boracic acid fluid replacing Mg-rich rocks or mixture of boracic acid and Fe-Mg solution to form szaibelyite and ludwigite.