Abstract:

The Beiya goldpolymetallic deposit is one of the typical deposits related to the alkalirich intrusion of the Cenozoic period in western Yunnan. This paper studies the fluid inclusions from quartz vein, quartz porphyroblast of alkalirich porphyry and calcite vein in the mining area. We investigated their types, temperatures, salinities, densities, pressures, the analytical data of liquids and gases, and the results of Laser Raman Microprobe Analysis. Based on above study, we made further discussions on the characteristics and sources of fluids. The research shows that the ore forming fluids are of NaClH2O types; the homogenization temperatures range from 132 ℃ to 550 ℃(individual is more than 550 ℃); the salinities are in the range of 19%611% (NaCleq). There exist three types of fluids, namely, the high temperature and high salinity fluids; the mediumhigh temperature and high salinity fluids; the mediumlow temperature and low salinity fluids. The fluidinclusion observations and microthermometric data suggest that the high salinity fluids were not produced by aqueous fluid immiscibility or boiling; they were directly formed in the magma chamber owing to the evolution of intermediateacidic magma, or from a shallow crystallized melt at the final stage. The high salinity fluid inclusions containing daughter minerals especially chalcopyrite have been found in the blocks of Hongnitang and Nadaping, indicating that these inclusions were formed from magmatic fluids before the incursion of meteoric water and magmatic water. The evidences from this study imply that the alkalirich intrusion has the great potential for forming porphyry deposit and the further research should be concentrated on the porphyry type of goldcopper deposit in Beiya.

Key words:  fluid inclusion; chalcopyrite; magmatic hydrothermal fluids; alkalirich porphyry; Beiya in Western Yunnan