粤东北嵩溪银-锑矿有机质中银的异常富集及其矿床勘探意义

运用电子探针测定了粤东北嵩溪黑色页岩型Ag-Sb矿床岩石中海相镜质体和固体沥青两种不同类型有机质中银的含量。矿区有机质中银含量的变化在100×10^-6～350×10^-6范围内,是原岩石中银含量的几十至上百倍。有机质中银的平均值也高出该矿床工业开采矿石品位的数倍之多,具有显著的银异常富集特征。本项研究认为有机质中银的异常值主要来源于嵩溪黑色页岩矿源层的原岩和含矿流体。在沉积成岩和后期热液改造过程中,有机质能够通过化学络合作用和还原作用捕获矿源层中岩石和含银流体中的成矿元素银,并使之进一步富集(或沉淀)在固体沥青中;据此建议矿区中沥青的分布和沥青中银矿化的特征可作为矿床勘探中一种新的找矿标志。

SILVER ANOMALOUS ENRICHMENT IN ORGANIC MATTERS OF SONGXI SHALE-HOSTED Ag-Sb DEPOSIT IN NE GUANGDONG AND ITS SIGNIFICANCE FOR ORE EXPLORATION

The silver content of individual organic matters in host rocks of the Songxi shale hosted Ag-b deposit in northeastern Guangdong, South China, has been directly determined using electron microprobe technique. The silver contents in the two types of organic matters both marine vitrinite and solid bitumen vary in the range of 100×10^-6～350×10^-6, which are general higher from tens of times up to hundreds of times than those of host rocks in the ore deposit. The average silver content in organic matters is still several times higher than tenor of silver for industrious exploitation of the ore deposit. It is quite obvious that the organic matters of host rocks in the ore district are characteristics of silver anomalous enrichment. The result of this study indicates that the silver anomalies in organic matters derived from both host rocks and silver-bearing fluid of the Songxi black shale ore source. In the course of sedimentation and later hydrothermal-reworking mineralization, organic matters could be able to link elemental silver from source rocks and silver-bearing fluid through the formation of organic silver complexes and reduction, so that silver could further enrich (or precipitate) within the solid bitumen. Quantitative assessment in this study suggests that the distribution of solid bitumen in the ore district may be considered as an ore indication for mineral exploration.