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    Influence of lead ions in sulfide flotation — The application of laser-ionization mass spectrometry
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    Keywords:
    Sulfide Minerals
    Lead sulfide
    Zinc sulfide
    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.
    δ34S
    Sulfide Minerals
    Gangue
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    Abstract Native arsenic is an occasional ore mineral in some hydrothermal base metal deposits. Its rarity (compared to pyrite, arsenopyrite, galena, sphalerite, or chalcopyrite, for example) is surprising, as arsenic is a common constituent of upper crustal fluids. Hence, the conditions of formation must be quite special to precipitate native arsenic. An ideal location to investigate the formation of native As and to explore the parameters constraining its crystallization is the Michael vein near Lahr, Schwarzwald, southwest (SW) Germany. Here, galena, sphalerite, and native arsenic are the most abundant ore minerals. The two important ore stages comprise (1) galena-barite and (2) sphalerite-native arsenic-quartz, the latter with a general mineral succession of pyrite → sphalerite ± jordanite-gratonite solid solution → galena → native As. The native arsenic-bearing mineralization formed by cooling of an at least 130 °C hot saline fluid accompanied by a reduction due to the admixing of a sulfide-bearing fluid. Thermodynamic calculations reveal that for the formation of native arsenic, reduced conditions in combination with very low concentrations of the transition metals Fe, Co, and Ni, as well as low sulfide concentrations, are essential. “Typical” hydrothermal fluids do not fulfill these criteria, as they typically can contain significant amounts of Fe and sulfide. This results in the formation of arsenides, sulfarsenides, or As-bearing sulfides instead of native arsenic. Very minor amounts of pyrite, sulfarsenides, and arsenides record the very low concentrations of Fe, Co, and Ni present in the ore-forming fluid. High concentrations of aqueous Zn and Pb lead to early saturation of sphalerite and galena that promoted native arsenic precipitation by decreasing the availability of sulfide and hence suppressing realgar formation. Interestingly, native arsenic in the Michael vein acted as a trap for uranium during supergene weathering processes. Infiltrating oxidizing, U+VI-bearing fluids from the host lithologies reacted under ambient conditions with galena and native arsenic, forming a variety of U+VI (±Pb)-bearing arsenates such as hügelite, hallimondite, zeunerite, heinrichite, or novacekite together with U-free minerals like mimetite or anglesite. Some parts of the vein were enriched to U concentrations of up to 1 wt% by this supergene process. Reduced (hypogene) uranium phases like uraninite were never observed.
    Arsenopyrite
    Sulfide Minerals
    Supergene (geology)
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