Jurassic and Triassic coals and organic matter-rich shales of the Tabas Basin, Iran, were investigated with respect to their thermal maturation and petrographic composition. The Triassic coals of the Parvadeh coal field range in vitrinite reflectance between 1.17% and 1.37% and the Jurassic coals of the Mazino coal field between 2.08% and 2.29% VRr. Maceral analysis revealed a predominance of vitrinite in all samples, with slightly higher percentages of inertinite in the Jurassic samples. Rock–Eval analyses confirm the presence of type III kerogen in the Triassic coals, while the Jurassic coals contain strongly carbonized residual kerogen. The range of sulfur contents for coals from the Parvadeh coal field (0.37% to 4.64%) and Mazino coal field (0.45% to 2.92%) is related to the effect of marine water in peat. The studied samples are characterized by the predominance of short- over long-chained n-alkanes. The relatively high Pr/Ph ratios indicate predominance of terrestrial organic matter whereas Pr/n-C17 and Ph/n-C18 ratios prove oxic conditions during deposition. In addition, the DBT/Phen ratio shows that these coals formed in fluvial/deltaic environments. Molecular geochemical parameters such as carbon preference index (CPI, 0.99–1.04), methyl phenanthrene index (MPI, 1.20–1.60), methyl naphthalene ratio (MNR, 1.61–3.45), and ethyl naphthalene ratio (ENR, 4–6.78) confirm the high maturity of the samples. Burial and thermal history reconstruction indicates necessity of an erosional thickness of about 4000 m in the Parvadeh area. Towards the Mazino area, a higher basal heat flow up to 80 mW m−2 is assumed for the Paleogene leading to higher maturities.
The Komshecheh barite-fluorite deposit is the product of epigenetic hydrothermal mineralization in dolomitized limestone of Middle Triassic age. The deposit is structurally and lithologically controlled and occurs predominantly as bedded stratabound replacement sheets, although the veins and solution-collapse breccias constitute important modes of occurrence. Brecciation, dolomitization, silicification and mineralization are interrelated. Post-Eocene intrusions and NW-SE and NE-SW trending faults are important ore controls. The ore mineralogy is simple and consists of barite and fluorite with very minor galena, pyrite, chalcopyrite, malachite and azurite. Sulfides are extremely rare in the deposit. At least two episodes of deposition have been identified: an early stage of fluorite precipitation and a later barite-fluorite mineralization event with spatial and temporal variations in salinity and temperature. Thermometric investigations indicate that homogenization temperatures (TH) for primary and pseudosecondary fluid inclusions in the fluorite range from 89 to 244°C with a mode at 150°C, whereas those for primary fluid inclusions in barite range from 119 to 323°C with two modes at 150 and 250°C. Evidence for boiling is seen during barite deposition. The mean salinities measured are 12 and 10 equivalent weight percent NaCl for fluids in fluorite and barite, respectively. Hydrocarbons in the inclusions hosted by fluorite samples were also detected. Chemical analyses of fluids extracted from inclusions in fluorite and barite show compositions dominated by Na, Ca and Mg ionic species. Barite shows δ 34 S values between 22.6 and 26.7 per mil. The comparatively narrow spread in δ 34 S values suggests very uniform environmental conditions throughout the mineralization field. Consideration of these data in their geologic context favors a basinal source for the ore- forming fluids which have been significantly affected by heating during intrusive emplacement. The deposition of barite and fluorite resulted from physicochemical changes in Ba-F-rich hydrothermal brines during mixing with sulfate-rich formational water and wall rock interaction.
The Qatruyeh iron deposits, located on the eastern border of the NW-SE trending Sanandaj-Sirjan metamorphic zone, southwest of Iran, are hosted by a late Proterozoic to early Paleozoic sequence dominated by metamorphosed carbonate rocks. The magnetite ores occurred as layered to massive bodies, with lesser amounts of disseminated magnetite and hematite-bearing veins. Textural evidences, along with geochemical analyses of the high field strengths (HFSEs), large ion lithophiles (LILEs), and rare earth elements (REEs), indicate that the main mineralization stage occurred as low-grade layered magnetite ores due to high-temperature hydrothermal fluids accompanied by Na-Ca alteration. Most of the main ore-stage minerals precipitated from an aqueous-carbonic fluid (3.5–15 wt.% NaCl equiv.) at temperatures ranging between 300° and 410°C during fluid mixing process, CO 2 effervescence, cooling, and increasing of pH. Low-temperature hydrothermal activity subsequently produced hematite ores associated with propylitic alteration. The metacarbonate host rocks are LILE-depleted and HFSE-enriched due to metasomatic alteration.
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