Geology, fluid inclusions and S，Pb isotopic geochemistry of the Chitudian Pb-Zn deposit in Luanchuan, Henan Province

Abstract：Numerous Pb-Zn ore veins were recently found in Luanchuan area, southwestern Henan Province. These veins host enormously huge resources of Pb and Zn. The Chitudian ore deposit is one of these newly-discovered Pb-Zn deposits. Its Pb-Zn ore veins are controlled mainly by WNW-trending fractures. Apart from Pb-Zn ore veins, skarn with Pb-Zn mineralization was also discovered recently in the ore deposit, but the economic value is lower than that of the ore veins. Considering that weak Mo mineralization occurs in skarn close to the intrusion in the ore deposit, the authors put forward a mineralization zoning: Mo mineralization in skarn occurs close to the intrusion, Pb-Zn polymetallic mineralization in skarn occurs away from the intrusion, and Pb-Zn mineralization in veins is controlled by fractures much more distant but is around the periphery of the intrusion. Petrography, microthermometry and laser Raman spectrometry of primary fluid inclusions show abundant content of CO2 in the ore-forming fluid, immiscible separation of CO2 and H2O, and homogenization temperatures in a range of 290℃-340℃ during lead-zinc mineralization. δ34S of sulfides from the Chitudian lead-zinc ore deposit vary between -0.32‰ and 8.30‰ (averagely 4.01‰), and show a bimodal distribution with one peak consistent with the peaks of porphyry Mo-W deposits (2‰ to 4‰) and the other peak shifting the heavy δ34S values to the values close to S content of strata (12.43‰ to 18.63‰), which may indicate that the S of lead-zinc ore veins have two main sources: a magmatic source and a stratatigraphic source. In addition, a pair of paragenetic sphalerite and galena from an ore vein gives a high sulfur isotope equilibrium temperature of 388.29℃. The Pb isotopic compositions of the Chitudian lead-zinc ore deposit are scattered in a relatively small range (206Pb／204Pb=17.005- l7.953，207Pb／204Pb=15.414-15.587，208Pb／204Pb=37.948-39.036), which accords mainly with the zone defined by Yanshannian porphyry, suggesting that the metals might have been mainly derived from Yanshannian porphyry intrusions, and partialy from the strata. In conclusion, it is reasonable to hold that the Chitudian Pb-Zn deposit is genetically related to Yanshannian porphyry and the Pb-Zn ore veins are of magmatic hydrothermal filling-metasomatic genesis.