Replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 °C: An experimental study of reaction textures and mechanisms
-
Gujie Qian
Abstract
The transformation of pyrrhotite to Fe disulfide (pyrite and/or marcasite) under hydrothermal conditions was studied experimentally by probing the effects of temperature (up to 220 °C, vaporsaturated pressures), ΣS(-II) concentrations, pH, and availability of oxygen on reaction progress and on the resulting textures.
The pyrrhotite to Fe disulfide reaction proceeded by a dissolution-reprecipitation mechanism under all conditions. Marcasite and pyrite formed under both oxic and anaerobic conditions, which is inconsistent with the traditionally assumed polysulfide route for FeS2 formation (oxidants required for polysulfide formation). The nature of the products was controlled by the level of supersaturation of the solution with respect to Fe disulfide minerals. Marcasite formed preferentially at low pH or S(-II)-deficient solutions (saturation index << 1000), while pyrite was the main product at saturation indices >1000.
Different textures were obtained for the replacement of pyrrhotite by either pyrite or marcasite. Pyrite formation proceeded by direct replacement of pyrrhotite and, simultaneously, by overgrowth from solution. The pyrite crystals were >10 μm in size and randomly oriented. In comparison, marcasite crystals were <1 μm in size, and no significant overgrowth was observed. At pH21°C <3, the marcasite nanocrystals showed the well-known crystallographic relationship with pyrrhotite, but at pH21°C 3.96, the marcasite crystallites were randomly oriented. These experimental results confirm that the preservation of the crystallographic orientation is not a distinguishing feature between dissolution-reprecipitation and solid-state reactions. The different textures among pyrite and marcasite reflect the dominance of crystal growth (pyrite) vs. nucleation (marcasite) as a precipitation mechanism.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- In situ stress-strain measurements in a deformation-DIA apparatus at P-T conditions of the upper part of the mantle transition zone
- Element diffusion rates in lunar granulitic breccias: Evidence for contact metamorphism on the Moon
- The crystal structure of franckeite, Pb21.7Sn9.3Fe4.0Sb8.1S56.9
- Ammonium vermiculite in schists from the Betic Cordillera (Spain)
- Natrolite is not a “soda-stone” anymore: Structural study of alkali (Li+), alkaline-earth (Ca2+, Sr2+, Ba2+) and heavy metal (Cd2+, Pb2+, Ag+) cation-exchanged natrolites
- Analysis of hydrogen in olivine by SIMS: Evaluation of standards and protocol
- New accurate elastic parameters for the forsterite-fayalite solid solution
- In-situ mid/far micro-FTIR spectroscopy to trace pressure-induced phase transitions in strontium feldspar and wadsleyite
- Structural study of the coherent dehydration of wadsleyite
- An atomic force microscopy study of diamond dissolution features: The effect of H2O and CO2 in the fluid on diamond morphology
- Unraveling the stacking structure in tubular halloysite using a new TEM with computer-assisted minimal-dose system
- High-pressure structural behavior of α-Fe2O3 studied by single-crystal X-ray diffraction and synchrotron radiation up to 25 GPa
- The IR vibrational properties of six members of the garnet family: A quantum mechanical ab initio study
- On the presence of OH defects in the zircon-type phosphate mineral xenotime, (Y,REE)PO4
- Cesium and strontium incorporation into zeolite-type phases during homogeneous nucleation from caustic solutions
- Electrical conductivity of albite at high temperatures and high pressures
- Crystal-chemical and structural characterization of fluorapatites in ejecta from Somma-Vesuvius volcanic complex
- In situ ion-microprobe determination of trace element partition coefficients for hornblende, plagioclase, orthopyroxene, and apatite in equilibrium with natural rhyolitic glass, Little Glass Mountain Rhyolite, California
- In situ FTIR investigations at varying temperatures on hydrous components in rutile
- Methods to analyze metastable and microparticulate hydrated and hydrous iron sulfate minerals
- Crystal chemistry of Ti-rich ferriallanite-(Ce) from Cape Ashizuri, Shikoku Island, Japan
- Replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 °C: An experimental study of reaction textures and mechanisms
- Argandite, Mn7(VO4)2(OH)8, the V analogue of allactite from the metamorphosed Mn ores at Pipji, Turtmann Valley, Switzerland
- Murchisite, Cr5S6, a new mineral from the Murchison meteorite
Articles in the same Issue
- In situ stress-strain measurements in a deformation-DIA apparatus at P-T conditions of the upper part of the mantle transition zone
- Element diffusion rates in lunar granulitic breccias: Evidence for contact metamorphism on the Moon
- The crystal structure of franckeite, Pb21.7Sn9.3Fe4.0Sb8.1S56.9
- Ammonium vermiculite in schists from the Betic Cordillera (Spain)
- Natrolite is not a “soda-stone” anymore: Structural study of alkali (Li+), alkaline-earth (Ca2+, Sr2+, Ba2+) and heavy metal (Cd2+, Pb2+, Ag+) cation-exchanged natrolites
- Analysis of hydrogen in olivine by SIMS: Evaluation of standards and protocol
- New accurate elastic parameters for the forsterite-fayalite solid solution
- In-situ mid/far micro-FTIR spectroscopy to trace pressure-induced phase transitions in strontium feldspar and wadsleyite
- Structural study of the coherent dehydration of wadsleyite
- An atomic force microscopy study of diamond dissolution features: The effect of H2O and CO2 in the fluid on diamond morphology
- Unraveling the stacking structure in tubular halloysite using a new TEM with computer-assisted minimal-dose system
- High-pressure structural behavior of α-Fe2O3 studied by single-crystal X-ray diffraction and synchrotron radiation up to 25 GPa
- The IR vibrational properties of six members of the garnet family: A quantum mechanical ab initio study
- On the presence of OH defects in the zircon-type phosphate mineral xenotime, (Y,REE)PO4
- Cesium and strontium incorporation into zeolite-type phases during homogeneous nucleation from caustic solutions
- Electrical conductivity of albite at high temperatures and high pressures
- Crystal-chemical and structural characterization of fluorapatites in ejecta from Somma-Vesuvius volcanic complex
- In situ ion-microprobe determination of trace element partition coefficients for hornblende, plagioclase, orthopyroxene, and apatite in equilibrium with natural rhyolitic glass, Little Glass Mountain Rhyolite, California
- In situ FTIR investigations at varying temperatures on hydrous components in rutile
- Methods to analyze metastable and microparticulate hydrated and hydrous iron sulfate minerals
- Crystal chemistry of Ti-rich ferriallanite-(Ce) from Cape Ashizuri, Shikoku Island, Japan
- Replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 °C: An experimental study of reaction textures and mechanisms
- Argandite, Mn7(VO4)2(OH)8, the V analogue of allactite from the metamorphosed Mn ores at Pipji, Turtmann Valley, Switzerland
- Murchisite, Cr5S6, a new mineral from the Murchison meteorite
