Algal-Bacterial Fabrics of Ores and Their Genetic Implications in the Longtang Lead-Zinc Deposit at Yanbian, Sichuan

摘要

The Longtang Pb-Zn deposit occurs in the Upper Sinian Guanyinyan Formation. The host rocks include sandy shale, cherty limestone and dolomitic limestone. The deposit is a typical one of thallogen origin. The mineral assemblage in the ore is made up of sphalerite, galena, pyrite, enargite, tennantite, seligmannite, asphalt, etc. The ore-forming process is possessed of multi-episode and multi-stage characters. Generally, sphalerites exhibit algal stromatolitic, bacterial and algal colloidal textures, providing evidence for the direct involvement of algae and bacteria in mineralization of ore-forming elements during sedimentary diagenesis. This is the first transmigration of ore-forming elements. However, pyrite embracing bacteria and galena replacing/filling trichomes are typical organic textures, which are related to organic carbon and bitumen that can adsorb or reduce ore-forming elements. This is an indirect process of organic mineralization, i.e., the second transmigration of ore-forming elements. δ~(34)S values are all greater than 5 per thousand, indicating the dominance of the heavy sulfur isotopes. The ore-forming temperature deduced from fluid inclusions ranges from 100℃ to 150℃±. All this goes to show that the Longtang Pb-Zn deposit is of thallogen origin.