Sulfur, lead and helium isotopic compositions of sulfide minerals from the Dachang Sn-polymetallic ore district in South China: implication for ore genesis |
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Authors: | K-D Zhao S-Y Jiang P Ni H-F Ling Y-H Jiang |
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Affiliation: | (1) State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, Jiangsu Province, P.R. China |
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Abstract: | Summary The Dachang Sn-polymetallic ore district is one of the largest tin producing districts in China. Its origin has long been
in dispute between magmatic-hydrothermal replacement and submarine exhalative-hydrothermal origin. The Dachang ore district
comprises several types of ore deposits, including the Lamo magmatogenic skarn deposit near a granite intrusion, the Changpo-Tongkeng
bedded and vein-type sulfide deposit, and the Gaofeng massive sulfide deposit. Sulfide minerals from the Lamo skarn ores show
δ34S values in the range between −3 and +4‰ with a mean close to zero, suggesting a major magmatic sulfur source that likely
was the intrusive Longxianggai granite. Sulfide minerals from the Gaofeng massive ores show higher δ34S values between +5 and +12‰, whereas sulfide minerals from the Changpo-Tongkeng bedded ores display lighter δ34S values between −7 and −0.2‰. The difference in the sulfur isotope ranges in the two deposits can be interpreted by different
degrees of inorganic thermochemcial reduction of marine sulfate using a one-step batch separation fractionation model. Sulfur
isotopic compositions from the vein-type ores at Changpo-Tongkeng vary widely from −8 to +4‰, but most of the data cluster
around −2.9‰, which is close to that of bedded ores (−3.6‰). The sulfur in vein-type ores might be derived from bedded ores
or it represents a mixture of magmatic- and sedimentary-derived sulfur. Pb isotopic compositions of sulfide minerals in the
Dachang ore district reveal a difference between massive and bedded ores, with the massive ores displaying more radiogenic
Pb isotope ratios. Correlations of 206Pb/204Pb and 207Pb/204Pb or 208Pb/204Pb for the massive and bedded ores are interpreted as two-component mixing of Pb leached from sedimentary host rocks and from
deep-seated Precambrian basement rocks composed of metamorphosed volcano-sedimentary rocks. Pb isotopic compositions of sulfide
minerals from vein-type ores overlap with those of bedded sulfides. Similar to the sulfur, the lead in vein-type ores might
be derived from bedded ores. Skarn ores at Lamo show very limited variations in Pb isotopic compositions, which may reflect
a major magmatic-hydrothermal lead source. Helium isotope data of fluid inclusions trapped in sulfides indicate that He in
the massive and bedded ores has a different origin than He in fluorite of granite-related veins. The 3He/4He ratios of 1.2–2.9 Ra of fluid inclusions from sulfides at Gaofeng and Changpo-Tongkeng imply a contribution of mantle-derived
fluids. Overall our data support a submarine exhalative-hydrothermal origin for the massive and bedded ore types at Dachang.
Supplementary material to this paper is available in electronic form at
Appendix available as electronic supplementary material |
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