H-O-C-S isotopic compositions of ore-forming fluids in Daping gold deposit in Ailaoshan gold belt, Yunan Province, China.

Daping is one of the largest Cenozoic orogenic type gold deposits in Ailaoshan gold belt. Gold ores in the Doping may be divided into two types; (1) Late Proterozoic diorite hosted; (2) Maludong Formation of Middle Devonian (D(2)m) limestone hosted. In this study, H-O-C-S isotopic compositions of fluid inclusions, hydrothermal carbonate minerals and sulphides from the Daping auriferous quartz veins were analysed, and the results show that: In the diorite hosted gold ores, the delta O-18(H2O) and delta D are 2.39 parts per thousand similar to 7.59 parts per thousand and -85 parts per thousand similar to -60 parts per thousand, the delta C-13 of hydrothermal carbonate minerals are -4.7 parts per thousand similar to -4.6 parts per thousand, delta S-34 of pyrite and galena are -2.8 parts per thousand similar to 7.6 parts per thousand (average 3.1 parts per thousand) and 0.2 parts per thousand similar to 6.3 parts per thousand (average 2.0 parts per thousand), respectively, while in the Middle Devonian (D(2)m) limestone hosted gold ores, the delta O-18(H2O) and delta D are 4.36 parts per thousand similar to 6.82 parts per thousand and -75 parts per thousand similar to -67 parts per thousand,delta C-13 of hydrothermal carbonate minerals are -7.6 parts per thousand similar to -0.5 parts per thousand,delta S-34 of pyrite are 2.2 parts per thousand similar to 10.2 parts per thousand (average 6.5 parts per thousand), respectively, suggesting that stable isotopic compositions of ore-forming fluids in the two different type gold ores are nearly the same. Both of their ore-forming fluids and materials might have derived from same source; Lower crust and upper mantle. Daping is a typical ductile shear zone controlled mesothermal gold deposit, crust-mantle interaction occurred at the early of Himalayan Orogen), might have played an important role in its mineralization. At about 33Ma ago, the middle and lower crust in the Daping area suffered high temperature and high pressure metamorphism because of ductile deformation and upwelling upper mantle magmas. The ore-forming fluids enriched in CO2, which were generated by granulitization and firing of the upwelling upper mantle magma, were transported to the middle to upper crust along the ductile shear zone, and finally precipitated auriferous sulfide-quartz veins in the brittle structures in diorite batholith or D(2)m limestone because of declined temperature and pressure and subsequent boiling. Lithologic characters of wall rocks is not an important controlling factors in mineralization of Daping gold mine.