Geochemical characteristics of ore-forming fluids and genesis of Hongshan copper deposit in northwestern Yunnan Province.

The Hongshan copper deposit is a large porphyry-skarn type polymetallic deposit in northwestern Yunnan Province. It occurred in quartz diorite porphyry of Indo-Chinese Period and quartz monzonite porphyry of Yanshanian Period as well as their neighbouring wall rocks. The formation of it experienced superimposition of mutiphases/stages hydrothermal mineralization. Comprehensive study on petrography, microthermometry and carbon-hydrogen-oxygen isotope of fluid inclusions showed that the ore-forming fluids of early metallogenic stages are of medium to high temperature,high salinity NaCl-H2O type solutions and mainly came from arc magmatism of Indo-Chinese Period, they were responsible for the formation of skarn type mineralization. The ore-forming fluids of later metallogenic stages are of medium to high temperature, high salinity NaCl-CO2-H2O type solutions and mainly came from the buried granitic magmatism of post orogenic extension environment, and they played important role in the formation of porphyry type Cu, Mo and relevant Pb, Zn mineralization. So the Hongshan copper deposit is of superimposed poyphyry-skarn type deposit that originated from the metallogenic superimposition of two phases of magmatic hydrothermal fluids.