The Sulfur Isotopic Geochemical Characteristics And Its Metallogeny Significance Of The Yunnan Jinding Lead-Zinc Deposit

The Jinding Zn-Pb deposit, located in Northwest Yunnan, China, is the largest Pb-Zn deposit in China, and also the youngest and only continental sediment-hosted super-large Pb-Zn deposit in the world. The Jinding Pb-Zn deposit is one of the seventeen super-large deposits reserve more than 1000×104t in the world. Its genesis differs from the well-known major types of sediment-hosted Zn–Pb deposits, like MVT, SEDEX and SST. Since the Jinding deposit is a super-large one which approximately needed 317×104m3 H2 S in the process of mineralization, revealing the origin and forming mechanism of reduced Sulfur is important for the mineralization study. According to previous studies, the δ34SV-CDT of Sulfur in the sulfides of the Jingding deposits is between-1.7‰ to-30.4‰, the δ34SV-CDT values of gypsum is from +12‰ to +16‰, the δ34SV-CDT values of celestite vary from +6‰ to +26‰, and the sulfur isotope fractionation has a larger value, possibly suggesting the reduced sulfur of Jinding Zn-Pb deposit mainly formed by bacterial sulfate reduction(BSR) and thermo-chemical sulfate reduction(TSR). Most of the sulfur originated from the hydrogen sulfides reduced by Triassic gypsum rock, the halosalt minerals probably from the Triassic marine stratum, and the SO42- of celestite mainly from dissolved gypsum.Based on field observation, samples collection and sulfur isotope analysis for sulphide and bitumen on each ore block possibly suggest:(1)The Jinding deposit has an ideal environment for BSR,(2)the δ34SCDT values of sulfides in Jinding deposit is between-32‰~0‰, containing two peak values. Most metallic sulfides can be divied into two groups, one group of δ34SCDT values is concentrated at-8‰~0‰, another group is concentrated at-32‰~-10‰. This suggests that the reduced sulfur of the Jinding Zn-Pb deposit mainly formed by bacterial sulfate reduction(BSR) and thermo-chemical sulfate reduction(TSR),(3)the sulfide ores from different ore blocks and in different ore-forming stages have different δ34S values. Overall, the sulfide ores from the western area of the deposit and formed in the early-main ore-forming stage have lower δ34S values, possibly suggesting maximum sulfur isotopic fractionation through BSR. Relatively the the sulfide ores originated from the eastern area of the deposit and formed in the late ore-forming stage have higher δ34S values, which are interpreted to be possibly related to the BSR and TSR.(4)All of these phenomena indicates that the reduced sulfur of Jinding deposit is mainly formed by sulfate reduction and took place in Jinding dome, ranther than transported from other place,(5)the δ34S values of organic matters were distributed dispersedly, and its δ34S values vary from-26‰ to-4‰. This result revealed that sulfur-containing organic thermal cracking(TDS) might be another source for the reduced sulfur apart from the BSR and TSR. The organic matters contributed to provided a portion of reduced sulfur and catalyze the BSR occur in the process of mineralization.