Devolatilization equilibria in graphite-pyrite-pyrrhotite bearing pelites with application to magma-pelite interaction |
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Authors: | Simon R Poulson Hiroshi Ohmoto |
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Institution: | (1) Department of Geosciences, The Pennsylvania State University, 16802 University Park, PA, USA |
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Abstract: | The proportions of species in a C-O-H-S fluid in equilibrium with graphite, pyrite and pyrrhotite were calculated for a range of pressure, temperature and
conditions, using the equilibrium constants and mass balance method, for ideal and non-ideal mixing in the fluid. Under typical metamorphic conditions, H2O, CO2, CH4 and H2S are the principal fluid species with H2S favored by higher temperatures, lower pressures and lower
conditions. The dominance of H2S in the fluid at high temperatures leads to values of
becoming significantly less than 1, and causes hydrous minerals to dehydrate at lower temperatures than the case when
. The production of H2S-bearing fluids provides a mechanism for the selective transfer of sulfur from a graphite-pyrite-pyrrhotite bearing pelite into a pluton via a fluid phase, without requiring wholesale melting and assimilation of rocks. Such a process is feasible if a magma is intruded by stoping, which allows a significant volume of pelite country rock to be raised rapidly to temperatures approaching that of the magma. H2S-bearing fluids produced from graphite-pyrite-pyrrhotite pelites (due either to magmatic intrusion or regional metamorphism) may also mobilize ore-forming metals as sulfide complexes. |
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