粤中茶山银金多金属矿床地质特征及形成时代

Geological characteristics and forming age of Chashan silver-gold-bearing polymetallic deposit in central Guangdong Province, P. R. China

茶山银金多金属矿床位于三水盆地西南缘矿化富集区南端，矿化主要成脉状产于泥盆系冒子峰组粉砂岩及晚白垩系砂砾岩中。矿床包裹体类型复杂，有纯液体包裹体、气体包裹体、气液比变化较大（ 5％～ >50％）的包裹体等。成矿均一温度为 160～ 270℃。矿化石英脉 Rb含量变化大，在 1.871～ 11.22μ g/g之间 , Sr含量在 2.628～ 3.548μ g/g之间 , 87Rb/86Sr为 1.959～ 11.61, 87Sr/86Sr为 0.723 19～ 0.748 49，矿化石英 Rb-Sr等时线年龄 (189± 6)Ma， MSWD为 1.17, (87Sr/86Sr)i为 0.717 2± 0.000 3。据等时线年龄、矿化特征及相关地质背景等资料，认为该矿床发生过两期矿化，首期矿化发生在燕山期，晚期矿化发生在晚白垩世到早第三世之间。矿床主要是改造作用形成的。

Chashan silver-gold-bearing polymetallic deposit, located in southern domain of southwestern mineralization region of Sanshui Basin, occurred as veins and veinlet filled in the fractures in Devonian siltstone, Cretaceous conglomerate and sandstone. The main metallic minerals involve galena, sphalerite, and pyrite, with minor chalcopyrite and chalcocite, and trace gold and silver minerals. The nonmetallic minerals include quartz, calcite and sericite, with minor chlorite. The homogeneous temperature of quartz fluid inclusion is in the range of from 160℃ to 270℃ . The 87Rb/86Sr and 87Sr/86Sr ratios of quartz from vein mineralization filled the fractures in Devonian siltstone are in the range of 1.959～ 11.61 and 0.723 19～ 0.748 49, respectively. In 87Sr/86Sr-87Rb/86Sr diagram, isotope compositions of 5 quartz samples define an isochron age of (189± 6) Ma, an initial strontium isotope ratio of 0.717 2± 0.000 3, and a MSWD of 1.17. Based on the Rb-Sr isochrone age, together with mineralization characteristics, which filled in the late Cretaceous conglomerate and sandstone, as well as the regional geological tectono-magmatic evolution in Sanshui basin, it is concluded that the Chashan silver-gold-bearing polymetallic deposit is formed by two-stage mineralization processes. The first stage occurred during (189± 6) Ma and the second between late Cretaceous and Eogene period. Chashan polymetallic deposit owes its origin to reworking mineralization processes.