Hydrogen,oxygen and sulfur isotope geochemical characteristics of Taoxikeng tungsten deposit in Chongyi County,Southern Jiangxi Province
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δ34S
Magmatic water
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On the basis of ore-forming periods and stages of the Dachang ore field, the pH and $$f_{0_2 } $$ conditions and the S isotopic systematics during ore formation have been thcrmodynamically treated in this paper. Calculations show a progressively decreased pH, an increased oxidation regime and an intensified activity of sulfur from the early to the late stage. Owing to the unreliability of inferring the S source from δ34Smin, $$\delta ^{34} S_{\Sigma _S } $$ has been calculated using the Ohmoto’s model. Results indicate that the δ34 min frequency distribution is more concentrated than that of δ34Smin and the peak value shifts to negative region by 2.5%. The sulfur in the whole ore field seems to be of multiple source, i.e., different deposits have their own S sources. But the S isotopic composition pertaining to each stage is nearly constant, suggesting that the ore-forming system be open to sulfur and the supply of sulfur be sufficient. The conclusions deduced from calculations are supported by many lines of geological evidence.
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Jinshachang Pb-Zn deposit,located in Yunnan province and the northwest of Sichuan-Yunnan-Guizhou(SYG) Pb-Zn-Ag multi-metal mineralization area,is mainly hosted in the Upper Neoproterozoic carbonate rocks of Dengying Group.The ore minerals mainly contain sphalerite and galena,and the gangue minerals mainly contain barite,fluorite and quartz.The δ34S values of sphalerite minerals are in the range between 3.6‰ and 13.4‰ with an average value of 5.7‰.The δ34S values of galena range from 6.0‰ to 9.0‰ with an average value of 7.1‰.Two δ34S values of barite are 34.8‰ and 34.5‰ and consistent with that of sulfate from the Lower Cambrian stratum,indicating that the sulfur of barite were derived from this stratum.Because the homogenization temperatures of fluid inclusions exceed the suitable temperature for bacterial sulfate reduction,therefore this process is not an efficient path for the production of reduced sulfur in this district.If sulfides were derived from the Cambrian stratum due to thermochemical sulfate reduction,sulfides in this deposit should preserve a minimum δ34S value of 14‰ which exceeding that of sulfide from Jinshachang deposit.Therefore,this process is not the only source of reduced sulfur.Considered the fact that the ore district is surrounded by basalts and δ34S values of sulfide related to magmatic activities are relatively low,the reduced sulfur of sulfide may be derived from magmatic activities.The δ34S values of sphalerite are higher than that of coexisting galena,indicating that sulfur isotopic composition in ore-forming fluid had partly reached equilibrium.The equilibrium temperatures calculated by using the δ34S values of surfur-bearing mineral pairs are consistent well with the homogenization temperature of fluid inclusions.
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Sulfide Minerals
Gangue
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The features of the ore-forming fluid and the origin of the metallogenic material in the Dalucao REE deposit of Panxi rift were studied by means of H,O and C isotope analyses. The δ 13 C values of the bastnaesite change narrowly from -8.1‰ to -8.0‰ ,while the δD values vary from -89‰ to -79‰. The δD, δ 18 O and δ 13 C of the quartz-fluid inclusions in the orebody are -87‰,+6.0‰ and -8.4‰,whereas he δD and δ 18 O of the fluorite-fluid inclusions in the orebody are -99‰ and -11.6‰,respectively. The study shows that the ore-forming fluid was a mixture of magmatic water and meteoric water. The carbon isotopic features suggest that the carbon in the bastnaesite was derived from the mantle,while the carbon in fluorite-fluid inclusions of the orebody came from a mixed carbon source.
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Magmatic water
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The Giant Huize Zn-Pb Deposit is well-known for its large scale, high grade and many associated byproduct trace elements. These characteristics imply that it maybe formed in a special background. In this paper, we report the sulfur isotope compositions of primary ores and the REE concentrations of gangue mineral calcites. Combining with the C, H, O, Pb isotope compositions and chronology data, we discuss the source of ore-forming fluid. The primary sulfides are enriched in heavy sulfur and the values of δ 34S are concentrated in the range of 13‰ to 17‰. δ 34S pyrite δ 34S sphalerite δ 34S galena indicates that sulfur isotopes in ore-forming fluid have reached equilibrium. That the values of δ 34S of sulfides are close to that of sulfates in the ore field suggests that sulfur in ore-forming fluid mainly came from sulfate reduction and thermochemical sulfate reduction (TSR) maybe the most possible reduction mechanism. The REE contents of gangue mineral calcites are higher than those of carbonate strata of different ages but lower than those of non-carbonate strata and the Emeishan Basalt in this region. The REE patterns and related REE parameters of gangue mineral calcites are different from those of the strata and the Emeishan Basalt. Further discussion shows that the ore-forming fluid is a kind of mixed fluid coming from the crust and the mantle. Mantle fluids produced in the Emeishan Basalt activities (including fluid derived from mantle degassing and magma degassing) took part in forming the ore-forming fluid.
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Gangue
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Ore genesis
δ18O
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The Sakaerde copper deposit is a mesothermal-epithermal deposit. The δ13CPDB values of quartz and calcite samples in the deposit vary in a narrow range of-17.3‰~-0.7‰. The δ18OSMOW values range from 16.2‰ to 22.4‰, their corresponding δ 18OH2 O values are between 6.9‰ and 12.5‰, and the δD values of fluid inclusions vary from-73.8‰ to-52.4‰. These data imply that the ore-forming fluids of the ore deposit were mainly derived from the heated formation water mixed with a small amount of magmatic water and metamorphic water. The carbon in ore-forming fluids mainly came from formation water or atmosphere precipitation, with the addition of some deep magmatic water at the late stage. The δ34S values range from 0.2‰ to 6.1‰, implying that the sulfur in ore fluids mainly came from the magma or the upper mantle.
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Magmatic water
Mesothermal
Isotope Geochemistry
Ore genesis
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