Mechanisms of pyrite and marcasite formation from solution: 3. Hydrothermal processes
- Pennsylvania State Univ., University Park (United States)
The formation of pyrite and marcasite from solutions between 100 and 300C has been examined experimentally, and the solubility product for the initial precipitate upon mixing of Fe{sup 2+} and H{sub 2}S solutions has been determined. Below 300C, pyrite and marcasite form via an FeS precursor. The precursor phase is crystalline, nearly stoichiometric FeS with a solubility product of 10{sup 2.9{plus minus}0.2} (K = a{sub Fe{sup 2+}}a{sub H{sub 2}S}/(a{sub H+}){sup 2}). It reacts progressively to mackinawite, hexagonal pyrrhotite, and/or greigite before forming pyrite or marcasite. In the presence of elemental sulfur, thiosulfate, or polysulfides, the rate of reaction is extremely fast (minutes at 150C). Without these sulfur species and only hydrogen sulfide or bisulfide present, the conversion rate drops significantly (1 h at 300C). In the absence of any aqueous sulfur source, the conversion proceeds at an indetectably slow rate. Because the rate of direct FeS{sub 2} nucleation is insignificant in (slightly) acidic solutions below 300C, most pyrite and marcasite in hydrothermal ores form via the conversion of an FeS precursor.
- OSTI ID:
- 5035619
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 55:12; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Reactions forming pyrite and marcasite from solution: 1. Nucleation of FeS sub 2 below 100C
Related Subjects
58 GEOSCIENCES
MARCASITE
HYDROTHERMAL SYNTHESIS
PYRITE
CHEMICAL REACTION KINETICS
HYDROGEN SULFIDES
HYDROTHERMAL SYSTEMS
NUCLEATION
PRECIPITATION
SOLUBILITY
CHALCOGENIDES
GEOTHERMAL SYSTEMS
HYDROGEN COMPOUNDS
KINETICS
MINERALS
REACTION KINETICS
SEPARATION PROCESSES
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
SYNTHESIS
152003* - Geothermal Data & Theory- Rock-Water-Gas Interactions
580000 - Geosciences