广西天峨坪金矿区金银次生晕异常分布地质意义与金银表生地球化学性质差异分析

Different Distribution of Silver and Gold Secondary Halo in the Tian’eping Gold Ore Field,Guangxi and the Different Geochemical Features of Gold and Silver in Supergene Setting

广西天峨坪金矿区多被土壤覆盖,区内局部出露轻变质粉砂岩及碳酸盐岩。为了圈定深部金矿体及了解金银表生地球化学行为,系统分析了区内土壤、原生晕及半风化原生晕金银元素含量。天峨坪金矿异常区金银次生晕异常分离,银次生晕异常中心分布于矿区中北部地势较高地区,而金次生晕异常中心却分布于矿区中南部较低洼地区,Au/Ag比从原生晕、半风化原生晕至全风化土壤逐渐降低。根据金银在不同风化程度岩石中的比值变化,结合金银在碳酸盐岩出露区地表流体中金比银更易形成金硫络合物迁移,提出在碳酸盐岩出露区地表中至弱碱性流体中金比银更易发生迁移,银次生晕异常中心指示深部金矿体。后经工程验证发现Ag的次生晕异常中心对应深部金矿体,而金异常中心偏离深部矿体。成果表明,碳酸盐岩出露区金银表生地球化学行为有差异,热带亚热带植被覆盖区次生晕找金过程中,不但要注意金的次生晕异常,也要注意银的次生晕异常。

Most area of the Tian eping gold ore filed was covered by soil and vegetation,metamorphic siltstone and some carbonate outcrop locally.Gold and silver concentration of primary halo, semi-weathering primary halo and soil was analyzed. It is found surprisingly that secondary halo anomalies of gold and silver are separatedfrom each other, the centers of goldsecondary halo anomaly occurs at thelow-lying area in the south of the Tian eping gold ore field and the silver s at the higher ground in the north of the Tian eping gold ore field and that the Au/Ag ratios decrease progressively from primary halo, semi-weathering primary halo, and to soil.Based on the Au/Ag ratios decreasing with the weathering intensity, together with that gold more easy to form sulfur complex compound than silver in the neutral to weakly alkaline weathering fluids which formed in an area where carbonate outcrop, it is proposed that gold is more easy to be dissolved and mobilized than silver in weakly alkaline weathering fluids and that the center of silver secondary halo anomaly should locate blind gold ore bodies.The conclusion was confirmed by drilling, which a gold ore body of about 30 m in thickness was met underlying directly the center of silver secondary halo anomaly. The results suggest that gold and silver is characterized by slightly different geochemical features in supergene environment where carbonate outcrop and more attention must be paid to silver second halo anomaly in gold ore prospecting in an area where carbonate out crop.