HELIUM AND ARGON ISOTOPIC GEOCHEMISTRY OF JINDING SUPERLARGE PB-ZN DEPOSIT

The study results of He and Ar isotopes from fluid inclusions in pyrit es formed during mineralization stage of Jinding superlarge Pb-Zn depo sit in west Yunnan, China are reported. The data show that the Ar-40/A r-36 and He-3/ He-4 ratios of fluid inclusions are respectively in the range of 301.7-385.7 and 0.03-0.06Ra, suggesting the ore-forming flui d is a kind of air saturated meteoric groundwater. On the basis of res earch on coupled relationships among He, Ar, S and Pb isotopes, the ev olution history of ore-forming fluid of the deposit can be summarized as (i) air saturated meteogenic groundwater infiltrated down and was h eated--> (ii) leached S, C and radiogenic He, Ar from the basinal stra ta --> (iii) leached Pb and Zn from mantle-derived igneous rocks locat ed in the bottom of the basin--> (iv) ore-forming fluid ascended and f ormed the deposit. Due to this process, the isotope signatures of crus tal radiogenic He, atmospheric Ar (with partial radiogenic Ar-40), cru stal S and mantle-derived Ph remained in the ore-forming fluid.