GEOLOGICAL CHARACTERISTICS OF JINBA GOLD DEPOSIT IN SOUTHEAST YUNNAN

Jinba gold deposit of ultramicro-grained type, located in the southeast of Yunnan Province, includes more than 30 ore bodies, which are grouped into 6 ore belts trending NE and 350~2000 m in length. The ore bodies are in lens, sub-stratiform or moniliform. The Zhesang anticlinorium controls the distribution of ore belts. The faults provide migratary channels for ore solution. The secondary sturctures control the location and occurrence of ore bodies. The host strata are mainly Upper Permain (containing 5 ore belts), with also Middle and Lower Triassic. The wall rocks are pelitic siltstone, siltstone, silty tuff, tuff, argillaceous dolomite, spilite, diabase dyke, ets. The mineralization types cover altered rock of fractured formation, altered rock of fractured dyke, and quartz vein. The wallrock alteration involves pyritization, arsenopyritization, silicification and carbonation. The oxidized and primary ores may be lithologically classified into tuffaceous ore, silty/silty-argillic ore, argillaceous dolomite ore, diabase ore and spilite ore. The Au grades of ore range from 0.5×10^-6 to 15.9×10^-6. The metallic minerals in primary ore are pyrite, arsenopyrite and chalcopyrite; while in oxidized ore, are limonite and scorodite. The gangue minerals depend on the types of wall rocks. Chemically, the content of SiO₂ in the ore is lower than that in primary rocks; while Fe₂O₃ + FeO is higher. The ore is rich in K and poor in Na. The trace elements such as Au, Ag, As, Sb and Cu are more in the ore than in the primary rock. The ores are in pelitic, fine-clastic, tuffaceous, diabasic, granular crystalline and rim-zonal textures, and cataclastic, breccia, disseminated, nodular and honeycomb structures. The gold is hosted in limonite, arsenopyrite and chalcopyrite as micro-inclusions.