Minor and trace elements in pyrite and marcasite from the Sarnak low-sulfidation gold deposit, SE Bulgaria. Part 1
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Abstract:
Here we present statistical and geochemical data on 12 minor and trace elements from pyrite- and marcasite-bearing samples from drillhole cores in the Sarnak (also known as Surnak) gold deposit. The data were obtained by SEM-EDX and single-spot LA-ICP-MS analyses in marcasite and different pyrite zones – core, mantle, and rim.Keywords:
Marcasite
Sulfidation
The Upper Freeport Coal (UFC) of west-central Pennsylvania is separated into upper, middle, and lower facies on the basis of distinctive mineral and maceral assemblages. Microscopic examination of these facies revealed two distinct types of pyrite occurrence: (1) finely disseminated framboids and well-formed crystals; and (2) coarser, irregularly shaped pyrite (with minor marcasite) that in part replaces the coal macerals. Both pyrite concentration (wt.%) and pyrite /delta//sup 34/S values are strongly correlated with pyrite morphology. The lower facies of the UFC contains /approx/1.9% pyrite of type 1 that has /delta//sup 34/S values of /approx/1 /per thousand/. The upper facies contains /approx/4.3% pyrite (+marcasite) of type 2 that has /delta//sup 34/S values of /approx/10 /per thousand/. Both pyrite types were deposited prior to significant compaction, from H/sub 2/S produced during bacterial sulfate reduction. The difference in the /delta//sup 34/S values of the two pyrite types reflects either different sulfate sources or reduction of a greater proportion of the sulfate available during formation of the coarser pyrite. The depositional and diagenetic setting of the UFC is entirely nonmarine, yet the high pyrite content of the upper facies is equivalent to that of many high-sulfur coals that were influenced by marine waters duringmore » early diagenesis. However, marine-influenced coals that were the site of extensive bacterial sulfate reduction have organic sulfur contents of several percent, compared to uniformly low organic sulfur contents of /approx/0.6% in the UFC. The low organic sulfur content of the UFC most likely reflects the different chemistry of the fresh water diagenetic conditions.« less
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Single phase pyrite has been successfully prepared via the reaction of FeSO 4 ·7H 2 O, S and Na 2 S·9H 2 O using hydrothermal method. The X-ray powder diffraction measurements confirm the formation of iron disulfides in the pH range of 1-12. Marcasite is formed at pH<4, the marcasite contents in the final products increasing with decreasing pH; when the pH is higher than 4, the final product is single phase pyrite. Scanning electron microscope (SEM) images reveal that both the pH and temperatures have significant effects on the size and morphology of final products. Pyrite micro-nanocubes of 200-400nm in length were synthesized at pH=9. Detailed information of the experimental results are analyzed in the results and discussion part.
Marcasite
Powder Diffraction
Hydrothermal Synthesis
Morphology
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We first describe the structures of FeS2-marcasite and FeS2-pyrite, and the way in which they are related. It is then explained how this relationship can successfully account for several phenomena: pyrite- marcasite intergrowths, the reported anisotropy of (nominally cubic, and therefore isotropic) FeS2-pyrite, stacking and deformation faults in pyrite parallel to {100}, and the observed structure of the pararammelsbergite polymorph of NiAs2.
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The electronic structures of pyrite,marcasite and pyrrhotite were calculated using the first-principles method which was based on the density functional theory(DFT),and the relationship between the electronic structure and floatability of the three sulfurous iron minerals was discussed.The calculation results show that pyrite is a direct band-gap semiconductor,and marcasite is an indirect band-gap semiconductor,while pyrrhotite is a conductor.The density of state analysis reveals that pyrite and marcasite are in low spin state,while pyrrhotite is in spin-polarized state.In addition,the calculation of the frontier orbital indicates that the oxidized order of the three sulfurous iron minerals from easy to difficult is as follows: pyrrhotite,marcasite,pyrite,and the floatability order of the three sulfurous iron minerals from easy to difficult using xanthate as a collector is as follows: marcasite,pyrite,pyrrhotite.The interaction between the three sulfurous iron minerals and oxygen,and the floatability of the three sulfurous iron minerals collected by xanthate can be well explained by the calculation results.
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Troilite
Mordenite
Xanthate
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The occurrence of sphalerite in pyrite-marcasite lenses in Indiana coal was reported. The sphalerite crystals (1 mm to 1 cm in diameter) were found filling interstices between the larger granules of pyrite-marcasite. Nodules of sphalerite-pyrite-marcasite occur most abundantly in the lower few centimeters of shale above the coal bed and in between the shale and coal. The author estimates that these lenses contain approximately 27% sphalerite.
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Marcasite
Iron sulfide
Sulfide Minerals
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Samples of coal from the eastern part of the Upper Silesian Coal Basin, between Jaworzno and Libiąż, were collected from test boreholes and underground excavations in the Janina Coal Mine, southwest Poland. The No. 111-119 hard coal seams are in the upper part of the Cracow Sandstone Series (the Libiąż Beds, Westphalian D). Macroscopically, iron sulfides (pyrite and marcasite) found in hard coal seams are usually in vein and impregnation forms. On the basis of microscopic observations, the following forms of iron sulfides occurrence in the studied coal were observed: framboidal pyrite, euhedral crystals, skeletal and massive vein forms, or pocket-like (impregnation) forms. On the basis of SEM-EDS analysis and X-ray diffraction it can be stated that the iron sulfides observed in coal are a mixture of pyrite and marcasite. WDS analysis in the micro area revealed the chemical composition of sulfides. The iron sulfides contain admixtures of Pb, Hg, Zn, Cu, Au, Ag, Sb, Co, and Ni. There was no As and Cd found in the examined minerals. It has been shown that the tested iron sulfides do not include significant admixtures. There is only a slight enrichment in lead in the vein forms of sulfides. In addition to the iron sulfides, individual inclusions of galena and sphalerite within the pyrite and marcasite have been observed.
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Iron sulfide
Sulfide Minerals
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Iron sulfide
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The massive sulfide ores of the Pobeda hydrothermal fields are grouped into five main mineral microfacies: (1) isocubanite-pyrite, (2) pyrite-wurtzite-isocubanite, (3) pyrite with minor isocubanite and wurtzite-sphalerite microinclusions, (4) pyrite-rich with framboidal pyrite, and (5) marcasite-pyrite. This sequence reflects the transition from feeder zone facies to seafloor diffuser facies. Spongy, framboidal, and fine-grained pyrite varieties replaced pyrrhotite, greigite, and mackinawite “precursors”. The later coarse and fine banding oscillatory-zoned pyrite and marcasite crystals are overgrown or replaced by unzoned subhedral and euhedral pyrite. In the microfacies range, the amount of isocubanite, wurtzite, unzoned euhedral pyrite decreases versus an increasing portion of framboidal, fine-grained, and spongy pyrite and also marcasite and its colloform and radial varieties. The trace element characteristics of massive sulfides of Pobeda seafloor massive sulfide (SMS) deposit are subdivided into four associations: (1) high temperature—Cu, Se, Te, Bi, Co, and Ni; (2) mid temperature—Zn, As, Sb, and Sn; (3) low temperature—Pb, Sb, Ag, Bi, Au, Tl, and Mn; and (4) seawater—U, V, Mo, and Ni. The high contents of Cu, Co, Se, Bi, Te, and values of Co/Ni ratios decrease in the range from unzoned euhedral pyrite to oscillatory-zoned and framboidal pyrite, as well as to colloform and crystalline marcasite. The trend of Co/Ni values indicates a change from hydrothermal to hydrothermal-diagenetic crystallization of the pyrite. The concentrations of Zn, As, Sb, Pb, Ag, and Tl, as commonly observed in pyrite formed from mid- and low-temperature fluids, decline with increasing crystal size of pyrite and marcasite. Coarse oscillatory-zoned pyrite crystals contain elevated Mn compared to unzoned euhedral varieties. Framboidal pyrite hosts maximum concentrations of Mo, U, and V probably derived from ocean water mixed with hydrothermal fluids. In the Pobeda SMS deposit, the position of microfacies changes from the black smoker feeder zone at the base of the ore body, to seafloor marcasite-pyrite from diffuser fragments in sulfide breccias. We suggest that the temperatures of mineralization decreased in the same direction and determined the zonal character of deposit.
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