Pyrite/pyrrhotite/magnetite

Wood, S.A., Crerar, D.A. and Borcsik, M.P. (1987) Solubility of the assemblage pyrite-pyrrhotite-magnetite-sphalerite-galena-gold-stibnite-bismuthinite-argentite-molybdenite in H20-NaCl-C02 solutions from 200°C to 350°C. Econ. Geol, 82, 1864-1887. 

The H2S concentration of hydrothermal solution is plotted in Fig. 2.33. Based on these data, we can estimate the temperature of hydrothermal solution buffered by alteration mineral assemblages such as anhydrite-pyrite-calcite-magnetite and pyrite-pyrrhotite-magnetite for Okinawa fluids. 

Table 7.1 Comparison of the yields of carbon-containing compounds obtained from an atmosphere of CH4, NH3, H2O and H2 using spark discharges with those obtained under hydrothermal conditions from a mixture of HCN, HCHO and NH3 at 423 K and 10 atm in the presence of pyrite-pyrrhotite-magnetite redox buffer (Holm and Andersson, 1995)...

Fig. 13.6 The highest-temperature end-member fluids in black smokers have compositions that are close to equilibrium with pyrite-pyrrhotite-magnetite (A). Somewhat more oxidized fluids may result from equilibrium with an assemblage of epidote-plagioclase-epidote-quartz-magnetite-anhydrite-pyrite (PEQMAP buffer B). As a result of this buffer assemblage, the end-member hydro-thermal fluids have a narrow range of aH S and aH (modified after Seyfried et al. 1999).

Probably the simplest use of fo minerM buffers is to include the buffer assemblage as part of the total system being studied. For example, the assemblage pyrite + pyrrhotite + magnetite fixes /oj at any T and P by the reaction... 

Figure 7.25 Log/02 vs pH diagram for sulphur species showing the stability fields of pyrite, pyrrhotite, magnetite and hematite. The boundaries are for ji = 1.0, and molalides for totaJ sulphur = 0,01, JC " 0.1, Na" = 0.9, Ca " — 0.01. The contours show deviations of 6 ShjS from at 250 C under equilibrium conditions (after Ohmoto and Rye, 1979).

Magnetite is common in Pb-Zn-Mn and Cu deposits but has not been reported in Au-Ag deposits. It commonly coexists with other iron minerals such as hematite, pyrite, pyrrhotite, siderite, and chlorite and also occurs in both the main stage of sulfide mineralization and in the late stage of mineralization. 

The /co2 values could be estimated based on FeCOa content of carbonates coexisting with iron minerals (pyrite, hematite, magnetite, pyrrhotite) and minerals containing... 

For example, assuming anhydrite-magnetite-calcite-pyrite-pyrrhotite buffers redox in sub-seafloor reaction zones and a pressure of 500 bars, dissolved H2Saq concentrations of 21 °N EPR fluid indicate a temperature of 370-385°C. However, the estimated temperatures are higher than those of the measurement. This difference could be explained by adiabatic ascension and probably conductive heat loss during ascension of hydrothermal solution from deeper parts where chemical compositions of hydrothermal solutions are buffered by these assemblages. 

Fig. 2.33. H2Saq concentration.s as a function of temperature for hot spring fluids at midocean ridges as a function of redox. Assuming AMPC (anhydrite-magnetite-pyrite-calcite) and PPM (pyrite-pyrrhotite) buffers redox in sub-seafloor reaction zones and a pressure of 500 bars, dissolved H2Saq concentrations indicate temperatures of approximately 370-385°C. Solid star Okinawa. (Modified after Seyfried and Ding, 1995.)...

The silicate facies is of a black finely laminated type, consisting mainly of magnetite with up to 15 vol. % grunerite and up to 5% carbonaceous matter. The facies is found in layers up to a few dm thick. Common to the silicate facies is the scarcity of quartz and the complete absence of carbonates. The sulphide facies of Isua consists of up to 60 vol. % sulphides (pyrite, pyrrhotite) together with grunerite or actinolite and magnetite (Appel, 1980) 118). 

Clean Kentucky Coal and Clean Kentucky Coal with Sulfur-Containing Additives. In Figure 14 are presented values tor the clean Kentucky coal with synthesis gas, and clean Kentucky coal with additives containing sulfur. The additives were present in amounts calculated to contain the same relative amount of sulfur. All of the autoclave times were one hour. The point for clean Kentucky coal (which still contains some pyrite and some magnetite (as an artifact of the cleaning process) in about a 2 1 mole ratio) and the point for thiophene lie on the pyrite-pyrrhotite equilbrium line. The... 

A zonal sequence of opaque minerals is also found. Pyrite is found in zones (1) and (2). Very tiny amounts of pyrrhotite coexisting with pyrite are found in zone (1). Magnetite is common in zone (3) but this mineral is thought to be original. 

Figure 1.96. Log /oj-pH diagram constructed for temperature = 200°C, ionic strength = 1, ES = 10 m, and EC = 10 m. Solid line represents aqueous sulfur and carbon species boundaries which are loci of equal molalities. Dashed lines represent the stability boundaries for some minerals. Ad adularia. Bn bomite, Cp chalcopyrite, Ht hematite, Ka kaolinite, Mt magnetite, Po pyrrhotite, Py pyrite, Se sericite. Heavy dashed lines (1), (2), and (3) are iso-activity lines for ZnCOs component in carbonate in equilibrium with sphalerite (1) 4 co3=0-1- (2) 4 ,co3=0-01- (3) 4 co3 =0-001 (Shikazono, 1977b).

Figure 1.196. /oj-pH ranges for hot-spring-type deposits and low sulfidation-type deposits. Temperature = 250°C, ES = 0.01 mol/kg H2O, ionic strength = 1. Ka kaolinite, Al alunite, SI liquid sulfur, Kf K-feldspar, Hm hematite, Mt magnetite, Py pyrite, Po pyrrhotite. Bn bomite, Cp chalcopyrite. 

Fig. 2.44. logaoi-pH range.s for Kuroko ore fluid.s and midoceanic ridge hydrothermal. solution. I Kuroko 2 Axial Explorer 3 2I°N, Southern Juan de Fuca 4 2I°N, Endeavour 5 Guaymas. Temperature = 250°C, ESr (total reduced sulfur concentration) = 6.6 x 10 m. HM hematite, MT magnetite, PY pyrite, PO pyrrhotite. Dotted line Au solubility (ppm) (Shikazono, 1988). 

The redox properties of these systems are vitally important for possible abiotic chemical syntheses the main minerals present in young basalt ocean basins, at depths between 300 and 1,300 m, are pyrite (FeS2), pyrrhotite (FeS) and magnetite (Fe3C>4) (the PPM system). 

This is one of the oldest operations in the world. The mine and plant are located in the southern part of Norway. This ore can be classified as an ilmenorutile, with ilmenite and magnetite as the valuable minerals. The gangue consists mainly of feldspar, hypersthene and biotite. The secondary minerals present in this ore include pyrite, olivine and pyrrhotite. 

Natarajan, K. A., Riemer, S. C., Iwasaki, I., 1984. Influence of pyrrhotite on the corrosive wear of grinding balls in magnetite ore grinding. Inter. J. Miner. Process, 13(1) 73-81 Nesbitt, H. W., Bancroft, G. M., Pratt, A. R., Scaini, M. J., 1998. Sulfur and iron surface states on fractured pyrite surfaces. American Mineralogist, 83 1067 - 1076 Neeraj, K. M., 2000. Kinetic studies of sulphide mineral oxidition and xanthate adsorption. Doctor thesis of Virginia Polytechnic Institute and State University. A Bell Howell Company UMI dissertation Services... 

Several minerals have been identified in polished thin sections of various rock types including massive sulphide, gossan, intermediate crystal-lapilli tuff, and felsic ash tuff (Fig. 2). These minerals include apatite, monazite, zircon, allanite, titanite, xenotime, magnetite, cassiterite, cobaltite-gersdorffite, rutile, ilmenite, goethite, sphalerite, galena, arsenopyrite, chalcopyrite, pyrite, and pyrrhotite. These minerals range in size from 20 pm to 250 pm and represent potential Indicator minerals. 

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