Abstract:

The Pulang copper deposit is located in the eastern part of Diqing Tibetan Autonomous Prefecture in northwest Yunnan. It occurs in the Late Triassic quartz diorite porphyry quartz diorite porphyry granite diorite porphyry complex. Due to the extremely weak research on the ore-bearing fluids in the northern mining section of the first mining area of the Pulang porphyry copper deposit, the understanding of the ore-forming system has been restricted.This article conducts petrographic observations, uniform temperature tests, and laser Raman probe composition analysis on fluid inclusions of ore bearing quartz fluids in the northern part(line 20-44) of the first mining area of the mining area. The results show that the ore bearing quartz veins in the northern part of the first mining area of the Pulang copper deposit are widely developed with gas-liquid two-phase inclusions and three-phase inclusions containing daughter crystals. The types of daughter crystals mainly include rock salt, potassium salt, calcite, chalcopyrite, etc. Fluid inclusions have two types: high salinity and medium low salinity. The uniform temperature range of high salinity fluid inclusions is 243-418 ℃, with an average of 338 ℃, a uniform pressure range of 1008-1552 MPa, and an average of 1178 MPa; The salinity is 30.1%-49.7%, with an average of 36.6%; The density ranges is 0.89-1.16 g/cm³, with an average of 1.02 g/cm³; The uniform temperature range of medium low salinity is 317-438 ℃, with an average of 392 ℃; The uniform pressure range is 370-559 MPa, with an average of 464 MPa. The salinity is 5.7%-13.0%, with an average of 9.3%; The density ranges is 0.55-0.77 g/cm³, with an average of 0.66 g/cm³. Based on analysis, it is believed that the ore-forming fluid in the northern part of the first mining area of the Pulang Copper Mine did not experience significant boiling, indicating that the area is not the ore-forming center. The laser Raman spectroscopy show that the gas phase composition of the inclusion contains CH₄, H₂O, and SO₂, indicating that the early ore-forming fluids may have been in a reducing environment. The decrease in temperature and pressure of high salinity medium density fluids, as well as the mixing effect of magmatic fluids, jointly led to the formation of vein like and disseminated mineralization in the northern area of the first mining area of the Pulang copper mine.

Key words: porphyry copper deposit, quartz, fluid inclusion, ore-forming fluid, Pulang, nothwestern Yunnan