S-and Pb-isotopic Tracing On Uragen Super-large Zn-Pb Deposit,Western Tianshan

The Uragen Zinc-Lead deposit is located in the northwest of Kashi sag in western Tarim Basin,Western Tianshan,this deposit contains more than 8 million tons of zinc and lead metal reserves.Ore-forming process needs more than 1.15×106m3 H2S and huge amount of metal,the way of ore sulfur generation and the source of huge amount of metal and sulfur are the key to figure out the genesis of deposit.In this paper,S-Pb isotopes of the sulfide ore,sulfate,surrounding rock and the old basement strata was carried out in Uragen Zinc-Lead deposit.In addition,some ores with similar bacterial action were observered in detail by field emission scanning electron microscope(FESEM)and energy dispersive spectrometer(EDS)analysis,and trace the formation mechanism of ore sulfur and origin of the massive metal,provide a new reference for the deposit genesis.The value of ore sulfide ?34S of the Uragen deposit is-27.9‰ to 15.0‰ and the sulfate ?34S varies from 10.84‰ to 18.76‰.S,which is mainly originated from the sulfate,is mainly derived from the bacterial sulfate reduction(BSR)and thermochemical sulfate reduction(TSR).Before mineralization or under the condition of low metallogenic temperature,sulfate reduces bacteria by deacidizing the sulfate in stratum,forms numerous nanometer spherical sphalerite,calcite and filamentous mineralized extracellular polymeric substances(EPS)and micron spherical siderite,which are the products of the action of in-situ bacteria of bacteria activity named biological minerals.Both the discovery of these phenomenas and sulfide sulfur isotope value further confirmed the mechanism of in-situ bacterial of ore sulfur acting.When temperature is higher than that becteria needs to survive,TSR plays a crucial role in the generation of S.Organic matter in Basin fluid reacts with the massive dissolved sulfate SO42-in Uragen mining area,which generates large amounts of reduced sulfur.In addition,the thermal cracking of sulfur-containing organic matter also provides a part of the sulfur required for Uragen deposit.Among the Pb isotopes of ore sulfide,clastic rock,carbonate rock and old basement strata in Uragen Zinc-Lead deposit,the Pb isotopes of sulfide and clastic rock stratum are not only especially similar but also presenting a distinct linear relationship,however,that from the sulfide,carbonate rock and old basement rock differ greatly without siginificant linear relationship,which indicates that the ore-forming material comes from clastic rock stratum.The study of REE of clastic rock in Uragen mining area denotes that the source of clastic rock is felsic rock.From the regional distributions,numerous felsic rocks have been found in the Southern Tianshan,which are mainly formed in the Paleozoic era,especially at the end of late Paleozoic.Since the Mesozoic era,felsic rocks in the high altitude of Southern Tianshan suffer constant weathering,denudation,finally transporting to the low-lying Kashi sag and diagenesis.Under the action of tectonic stress,the late fluid extracts the ore-forming metal in the stratum and eventually leads to the formation of Uragen Zinc-Lead deposit.Comparing with SEDEX,MVT,SST and Jinding type Pb-Zn deposit,the genesis of the deposit is termed as the SST type Pb-Zn deposit.