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Arsenian pyrite formation: Solid-State diffusion or dissolution-reprecipitation replacement?

Xia, F.ORCID: 0000-0002-4950-3640, Brugger, J. and Pring, A. (2009) Arsenian pyrite formation: Solid-State diffusion or dissolution-reprecipitation replacement? In: 10th Biennial SGA Meeting of the Society for Geology Applied to Mineral Deposits, 17 - 20 August, Townsville, Australia pp. 700-702.


The formation of arsenian pyrite has been studied experimentally by hydrothermal reactions of either pyrite or pyrrhotite with arsenic-bearing fluids. Both pyrite and pyrrhotite were transformed to arsenian pyrite retaining the overall morphology of the starting grains but distinct kinetic and textural features were observed. Pyrite was transformed to dense arsenian pyrite with diffused arsenic distribution at the phase boundary; the transformation rate increases with increasing temperature, suggesting that the incorporation of As was controlled by solid-state diffusion processes. By contrast, pyrrhotite was transformed to a mixture of porous arsenian pyrite and arsenian marcasite with zonation textures; the newly formed arsenian pyrite/marcasite was separated from the unreacted pyrrhotite by gaps of tens of microns. Also, the transformation rate decreases with increasing temperature. These are typical characteristics of pseudomorphic coupled dissolution-reprecipitation replacement reactions. Elemental distribution revealed a negative correlation between S and As distributions, suggesting the substitution of As for S during arsenian pyrite formation. Therefore, arsenian pyrite can form by dissolution-reprecipitation during pyrite crystallization from a solution or by later solid-state diffusion of arsenic into the pyrite structure. The textures formed are similar to natural examples, suggesting that the same mechanisms may dominate in the formation of natural arsenian pyrites.

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