Other
Scientific paper
Dec 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55.3491s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 55, Issue 12, pp.3491-3504
Other
16
Scientific paper
The formation of pyrite and marcasite from solutions between 100 and 300°C has been examined experimentally, and the solubility product for the initial precipitate upon mixing of Fe 2+ and H 2 S solutions has been determined. Below 300°C, pyrite and marcasite form via an FeS precursor. The precursor phase is crystalline, nearly stoichiometric FeS with a solubility product of 10 2.9±0.2 ( K = a Fe 2 + a H 2 S /( a H + ) 2 ). It reacts progressively to mackinawite, hexagonal pyrrhotite, and/orgreigite before forming pyrite or marcasite. In the presence of elemental sulfur, thiosulfate, or polysulfides, the rate of reaction is extremely fast (minutes at 150°C). Without these sulfur species and only hydrogen sulfide or bisulfide present, the conversion rate drops significantly ( 1 h at 300°C). In the absence of any aqueous sulfur source, the conversion proceeds at an indetectably slow rate. Because the rate of direct FeS 2 nucleation is insignificant in (slightly) acidic solutions below 300°C, most pyrite and marcasite in hydrothermal ores form via the conversion of an FeS precursor.
Barnes Hubert L.
Schoonen Martin A. A.
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