尼日尔阿泽里克铀矿床蚀变及地球化学特征——对成矿物质来源的约束

Features of alteration and geochemistry of Azelik uranium deposit of Niger:Restraint to source of metallogenetic materials

为揭示尼日尔阿泽里克铀矿床成矿物质来源,文章研究了其蚀变特征、稀土元素特征、流体包裹体特征、方解石胶结物碳和氧同位素特征、沥青铀矿氧同位素特征等。阿泽里克铀矿床发育灰绿色还原蚀变、方沸石化、酸性火山玻璃脱玻化、碳酸盐化、黄铁矿化、重晶石化等。矿化砂岩稀土元素 Eu 强正异常。流体包裹体气体成分为 H2+N2+CO2组合。方解石胶结物的δ^13CV-PDB值为-7.45‰^-6.65‰,δ^18OV-SMOW值为-0.74‰~1.26‰。沥青铀矿的δ^18OV-SMOW值为-1.30‰^-0.8‰。灰绿色还原蚀变岩石呈灰绿色是因为绿泥石矿物充填粒间孔隙和包裹颗粒表面。矿化砂岩的 Eu 强正异常揭示有来自深部的强还原性流体参与成矿。H2为强还原物质,来自深部,可为铀成矿提供还原剂。矿化砂岩方解石胶结物碳同位素显示成矿流体有深部流体的作用,可能有地幔物质的加入;氧同位素显示成矿流体有表生流体的作用。沥青铀矿氧同位素值显示成矿流体受表生大气水作用影响。酸性火山物质方沸石化和酸性火山玻璃脱玻化为铀成矿提供铀。成矿流体为表生氧化性流体与深部的还原性流体的混合。总之,地层、阿伊尔花岗岩和火山物质可能为铀成矿提供了铀。

To reveal the source of metallogenetic material in the Azelik uranium deposit, the paper studied its features of alteration, REE geochemistry, fluid inclusion, C-O isotope of calcite cement and O isotope of pitchblende. Alterations are gray green reduction, analcimization, devitrification of acidic volcanic glass, carbonatization, pyritization, chalcopyrite, baritization, et al. The genesis of gray green of reduction is chloritization. Analcimization and of acidic volcanics and devitrification of acidic volcanic glass provided uranium for mineralization. Positive anomaly of Eu from mineralized sandstone reveals that reductive fluid from the deep was involved into mineralizing. Gaseous compositions of fluid inclusions are H2, N2 and CO2, which present the character of gaseous compose from the deepth, and H2 is a type of strong reductive agent which provided reductive material for mineralization. Isotopic of C from calcite cement of mineralized sandstone shows that fluid from the deep was involved which maybe contains material from the mantle. Isotopic of O from calcite cement of mineralized sandstone and pitchblende show that hypergene meteorological fluid was involved. Metallogenetic fluid is the mixture of reductive fluid from the deep and oxidized fluid from the hypergene. Uranium is provided by stratum and the A?r granite mass and vitroclastic tuffs may provide uranium for mineralization.