湖北白果园银钒矿床中银的成岩富集机制探讨

A PRELIMINARY DISCUSSION ON SILVER ENRICHMENT MECHANISM IN THE DIAGENETIC PROCESS OF THE BAIGUOYUAN SILVER VANADIUM DEPOSIT,HUBEI PROVINCE

通过对白果园银钒矿床中不同形态和不同期次含银黄铁矿的研究，发现富银矿体在空间上与含银量高的黄铁矿密切相关，反映在时间上，趋向于成岩晚期富集。本文从热水沉积成矿的观点出发，结合流体包裹体的研究和含银黄铁矿的演化特点，探讨了银在不同成岩阶段所处的物理化学环境及其迁移富集条件。

The Baiguoyuan silver vanadium deposit is of balck shale type rarely seen both in China and abroad,with pyrite in the ore bed serving as the main carrier mineral.Based on studying pyrite of different shapes and stages, the authors have found that the enrichment of silver was intimately related to pyrite of diagenetic stage. Spatially,the grade of silver is obviously conditioned by the content of silver high pyrite (spear shaped,spherical and cubic pyrite) in the ore bed;temporally,the migration and enrichment of silver were consistent with the evolution of pyrite of the diagenetic stage.(1) The sedimentary and syngenetic period:in a hot water environment, silver was scattered in sediments together with the deposition of colloidal pyrite and carbonaceous siliceous pelitic sediments.(2) The early diagenetic period:under a certain temperature and pressure condition ( t =165℃±, p =550×10 5￣580×10 5Pa),connate water evolved into hot brine solution characterized by low oxygen fugacity ( f O 2 ≈10 -46 49￣-47.7 ×10 5Pa),slightly acid nature (pH≈4.29￣4.40) and rich activated ions (Na +,Ca 2+ ,Cl -,SO 2- 4etc.),which caused the mobilization and migration of silver in the form of AgCl 2 -.(3) The late diagenetic stage:The drop in temperature ( t <152℃),the increase in sulfur fugacity,the rising of alkalinity and the intensification of reduction resulted in the decomposition of silver complex,and the silver was concentrated in pyrite formed at the late diagenetic stage,thus exhibiting the macroscopic unity of the rich silver orebody and the silver bearing pyrite bed.