广东长坑-富湾金银矿床微量元素及稀土元素地球化学

DISCUSSION ON GEOCHEMISTRY OF TRACE AND RARE EARTH ELEMENTS IN THE CHANGKENG-FUWAN GOLD-SILVER DEPOSIT, GUANGDONG

金银矿体位于同一矿田并共存在同一个构造破碎蚀变带内 ,严格地受控于下石炭统梓门桥组 (C1 z)和上三叠统小坪组 (T3x)之间的滑覆构造破碎带 ,这一构造带也是 C1 z和 T3x间的平行不整合界面。围岩蚀变以硅化、粘土化和硫化物化为主。本文通过对金、银矿矿石及围岩的微量元素组成特征的分析 ,认为金、银矿物质来源是不同的 :金可能来源于矿区周围的下石炭统梓门桥组地层 ,银则来源于粤西地区广泛分布的中 -新元古代地层 (云开杂岩和震旦系 )。在对金、银矿体和围岩稀土元素地球化学研究的基础上 ,推断金、银成矿作用和围岩蚀变作用皆属热液交代作用的结果 。

The Changkeng Fuwan large scale gold and super large silver deposits were explored in the Sanshui Mesozoic Cenozoic sedimentary basin (about 50 km southwest Guangzhou) in 1990s. Gold and silver orebodies occurred in the same field and yielded in one brecciated zone. The interformational tectonic belt directly controlled the orebodies and was located between the strata of Zimenqiao Fm. (C 1z) of Lower Carboniferous and Xiaoping Fm. (T 3x) of Upper Triassic. It was also the unconformable contact boundary of Lower Carboniferous and Upper Triassic. The silicification, clayization and sulfidization were the main alteration for the host rocks. On the basis of analysing the trace element geochemistry for the gold and silver orebodies and their host rocks, and also the background values of Au and Ag in the regional strata, the paper concludes that the sources of Au are quite different from the Ag. Probably Au came from the stratum of Zimenqiao Fm., and Ag was supplied by the regional Mesoproterozoic and Neoproterozoic strata such as Yunkai Complex or Sinian. According to the REE content of orebodies and host rocks and its chondrite normalized distribution charts, the paper predicts that the mineralization or silicification was resulted from the hydrothermal replacement and not related to the hot water sedimentation.