黔西南丫他金矿矿化过程中元素迁移特征研究

Elements' migration during ore-forming process, Yata gold deposit, Southwestern Guizhou, China

关键词:  元素迁移  成矿过程  Isocon图解法  丫他金矿  右江盆地

Key words:  elements migration  mineralization process  Isocon graphic method  Yata gold deposit  Youjiang basin

摘要:

黔西南册亨县丫他金矿是扬子地块西南缘右江盆地中的重要卡林型金矿之一，产于三叠系巨厚的裂陷槽盆相复理石建造碎屑岩相区中。矿体受控于褶皱断裂带，其形态、规模、产状受高角度断裂带控制。根据典型矿物蚀变组合，可划分三个成矿阶段：铁白云石-黄铁矿阶段、白云石-黄铁矿-似碧玉岩-多金属矿物阶段以及毒砂-雌雄黄-方解石-石英阶段。本文为探究丫他金矿成矿过程中元素的迁移特征，通过采集不同矿化程度的样品，采用Isocon图解法对元素质量平衡进行了定量计算，结果显示在成矿作用过程中，伴随着持续的SiO₂含量升高以及CaO含量的降低，指示硅化与去碳酸盐化与成矿关系密切；K₂O和TFe₂O₃含量虽有变化但过程中有所波动，表现为载金矿物黄铁矿与黏土矿物的沉淀；TiO₂和Al₂O₃含量在各个阶段岩石中变化不大，且显示出较高的平均值。与金矿化密切相关的微量元素是As、Sb、W、Hg、Ag、Cu、Zn、Tl，随着成矿流体通过与围岩的相互作用成矿过程中发生迁移，在金以Au（HS）⁰或是Au（HS）^2-络合物形式进入含砷黄铁矿晶格中的同时沉淀黄铜矿、闪锌矿、硫砷锑汞矿等其他金属矿物。

Abstract:

Located at Youjiang basin, southwest margin of Yangtze block, the Yata gold deposit is a Carlin-type gold deposit hosted by a series of Triassic thick basin-face flysch formation and controlled by the high angle thrust-fault system. Based on detailed study of relationship of ore minerals and alteration, the ore-forming process of Yata gold deposit can be divided into three stages, including the Fe-dolomite-pyrite stage, the dolomite-pyrite-jasperoid-polymetallic minerals stage, and the asenopyrite-orpiment-realgar-calcite-quartz stage. In order to figure out the elements’ migration during ore-forming process, we have collected samples with different degrees of mineralization and conducted mass balance quantitative calculation using Isocon graphic method. The results show that mineralization is companied by clear increase of SiO₂ content and decrease of CaO content, which represents the existence of ore-related silification and decarbenation. The contents of K₂O and TFe₂O₃ change with slight fluctuation, suggesting the deposition of gold-bearing pyrite and clay minerals. The average contents of TiO₂ and Al₂O₃ are stable and relatively high in different stages. As, Sb, W, Hg, Ag, Cu, Zn, and Tl have showed intimate relationship in mineralization while trace elements migrate between host rock and ore-fluid during fluid-host rock reaction, polymetallic minerals e.g. chalcopyrite, sphalerite, routhierite are deposited while gold entered the crystal framework of As-pyrite as Au(HS)⁰ or Au(HS)^2-.