Relationship between Se/S and sulfur isotope ratios of hydrothermal sulfide minerals |
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| Authors: | M Yamamoto |
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| Institution: | (1) Department of Earth Sciences, Faculty of Science, Okayama University, 700 Okayama, Japan |
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| Abstract: | The pH and fO
2 dependences of the Se2–]/S2–] ratio in chloride solutions at 100°, 200° and 300°C are predicted thermodynamically. Under the high fO
2 conditions where sulfate species are dominant in solution, the Se2–]/S2–] ratio always increases with increasing pH and/or fO
2. Under the low fO
2 conditions where sulfide species are dominant in solution, the pH and fO
2 dependences of the Se2–]/S2–] ratio are seriously affected by the presence of native selenium. With native selenium present, the Se2–]/S2–] ratio decreases with increasing fO
2, but almost independent of pH in geologically important pH regions. When native selenium is absent, the Se2–]/S2–] ratio is solely a function of pH and independent of fO
2. Combining the above with the pH and fO
2 dependences of  34S value of aqueous sulfur species, we discuss the possible influences of the pH and fO
2 of ore-forming solutions on the relationship between the Se/S ratio and 34S value of hydrothermal sulfide minerals. The results are applied to some Japanese sulfide ore deposits. |
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| Keywords: | |
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