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Ehya F.,Islamic Azad University at Behbahan | Lotfi M.,Geological Survey of Iran | Rasa I.,Shahid Beheshti University
Journal of Asian Earth Sciences | Year: 2010

The Emarat deposit, with a total proved reserve of 10 Mt ore grading 6% Zn and 2.26% Pb, is one of the largest Zn-Pb deposits in the Malayer-Esfahan belt. The mineralization is stratabound and restricted to Early Cretaceous limestones and dolomites. The ore consists mainly of sphalerite and galena with small amounts of pyrite, chalcopyrite, calcite, quartz, and dolomite. Textural evidence shows that the ore has replaced the host rocks and thus is epigenetic. Sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from Cretaceous seawater through thermochemical sulfate reduction. Sulfur isotope compositions of four apparently coprecipitated sphalerite-galena pairs suggest their precipitation was under equilibrium conditions. The sulfur isotopic fractionation observed for the sphalerite-galena pairs corresponds to formation temperatures between 77 °C and 168 °C, which agree with homogenization temperatures of fluid inclusions. Lead-isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high 238U/204Pb and 232Th/204Pb ratios. Ages derived from the Pb-isotope model give meaningless ages, ranging from Early Carboniferous to future. It is probable that the Pb-isotope model ages that point to an earlier origin than the Early Cretaceous host rocks are derived from older reservoirs in the underlying Carboniferous or Jurassic units, either from the host rocks or from earlier-formed ore deposits within these units. This research and other available data show that the Emarat Zn-Pb deposit has many important features of Mississippi Valley-type (MVT) lead-zinc deposits and thus we argue that it is an MVT-type ore deposit. © 2009 Elsevier Ltd. All rights reserved. Source

Fluorite vein mineralization occurs mainly in slates and phyllites of Lower Jurassic Shemshak Formation and scarcely in Triassic limestones in Bozijan, which is situated at the west of Mahallat city in the Markazi Province of Iran. The ore consists mainly of fluorite, quartz, calcite, and iron oxides. The subordinate components are galena, pyrite, manganese oxides, and malachite. Local wall-rock alterations include argilization and silicification. The nature of the mineralization and ore-host rock relationships indicate an epigenetic mode of formation for fluorite mineralization. Fluid inclusions in early fluorites and quartz consist of aqueous and aqueous-carbonic inclusions, thereby showing that during deposition of bulk fluorites, two immiscible fluids are involved: aqueous and carbonic. The aqueous fluid is a mixture of two low- and high-salinity (<15 and >26.24wt.% NaCl equivalent) H 2O-NaCl-(CaCl 2-KCl-MgCl 2) brines, as is evidenced by T h-salinity plots. The aqueous inclusions are homogenized at temperatures between 152.5 and 312°C. The aqueous-carbonic inclusions exhibit salinity and homogenization temperature in ranges between 22.04 and 24.26wt.% NaCl equivalent and between 253 and 390.5°C, respectively. Fluid inclusions in late fluorites show the fluorites were precipitated from a colder (102.4-175°C) and less saline (15.96-24.45wt.% NaCl equivalent) fluid than the early fluorites. Rare earth element (REE) analysis in fluorites revealed extremely low values in ranges between 2.87 and 34.39. ppm for early fluorites and between 1.91 and 6.4. ppm for late fluorites, thus indicating that fluorites had been derived from a sedimentary environment. However, Tb/Ca and Y/Ho ratios invariably suggest a hydrothermal origin for Bozijan fluorites. The Ce/Yb ratios and chondrite-normalized patterns revealed that the fluorites (early as well as late ones) are enriched in LREE (light rare earth element) relative to HREE (heavy rare earth element). This indicates that REE leaching from source rocks and fluid migration occurred under high-temperature and low-pH conditions. The enigmatic LREE-enriched late fluorites suggest that deposition of fluorites in Bozijan did not occur during a long-lived episode of mineralization. Europium represents positive as well as negative anomalies that have been probably caused by fluorite precipitation from mixing two fluids possessing opposite Eu anomalies. The Ce/Ce * ratios portray persistent negative Ce anomalies, thus indicating reducing conditions in the hydrothermal fluids. In the (La/Yb)n-Eu/Eu * diagram, data points do not overlap with the fields represented by fluorite-bearing Au-Ag deposits from elsewhere, thus indicating a very low potential for precious-metal mineralization in the studied area. This interpretation is well in line with the low contents of precious metals in the Bozijan deposit, thus suggesting that REE geochemistry is a reliable tool for exploring precious metals in fluorite deposits. The Bozijan deposit is classified here as an "unconformity-related fluorite deposit." According to a conceptual model, mineralization occurred when the ascending hypersaline brines mixed with the less saline connate fluids in sediments of Triassic and predominantly Jurassic ages. The less saline connate brines were assumed to be the fluoride-bearing solutions, as suggested by the high F contents of the rocks containing them and REE patterns. © 2011 Elsevier B.V. Source

Ehya F.,Islamic Azad University at Behbahan
Mineralogy and Petrology | Year: 2012

The Bijgan barite deposit, which is located northeast of Delijan in Markazi Province of Iran, occurs as a small lenticular body at the uppermost part of an Eocene volcano-sedimentary rock unit. The presence of fossiliferous and carbonaceous strata suggests that the host rocks were deposited in a quiet marine sedimentary environment. Barite, calcite, iron oxides and carbonaceous clay materials are found as massive patches as well as thin layers in the deposit. Barite is marked by very low concentrations of Sr (1-2%) and total amounts of rare earth elements (REEs) (6.25-17.39 ppm). Chondrite-normalized REE patterns of barite indicate a fractionation of light REEs (LREEs) from La to Sm, similar to those for barite of different origins from elsewhere. The La CN/Lu CN ratios and chondrite-normalized REE patterns reveal that barite in the Bijgan deposit is enriched in LREE relative to heavy rare earth elements (HREEs). The similarity between the Ce/La ratios in the barite samples and those found in deep-sea barite supports a marine origin for barite. Lanthanum and Gd exhibit positive anomalies, which are common features of marine chemical sediments. Cerium shows a negative anomaly in most samples that was inherited from the negative Ce anomaly of hydrothermal fluid that mixed with seawater at the time of barite precipitation. The δ 18O values of barites show a narrow range of 9.1-11.4‰, which is close to or slightly lower than that of contemporaneous seawater at the end of the Eocene. This suggests a contribution of oxygen from seawater in the barite-forming solution. The δ 34S values of barites (9. 5-15. 3‰) are lower than that of contemporaneous seawater, which suggests a contribution of magmatic sulfur to the ore-forming solution. The oxygen and sulfur isotope ratios indicate that submarine hydrothermal vent fluids are a good analog for solutions that precipitated barite, due to similarities in the isotopic composition of the sulfates. The available data including tectonic setting, host rock characteristics, REE geochemistry, and oxygen and sulfur isotopic compositions support a submarine hydrothermal origin for the Bijgan barite deposit. At the seafloor, barite deposition occurred where ascending Ba-bearing hydrothermal fluids encountered seawater. Sulfate was derived from the sulfate-bearing marine waters, and, to a lesser extent, by oxidized H 2S, which was derived from magmatic hydrothermal fluids. © 2011 Springer-Verlag. Source

Askari M.,Behbahan Higher Educational Complex | Taghizadeh M.,Islamic Azad University at Behbahan
European Journal of Scientific Research | Year: 2011

One of the emerging technologies that being investigated as an alternative to CMOS VLSI is Quantum-Dot Cellular Automata (QCA). Its advantages such as faster speed, smaller size, and lower energy consumption are very good-looking. Unlike conventional digital circuits in which information is transferred using electrical current, QCA transfers information by propagate a polarization state. This paper proposes a detailed design analysis of combinational and sequential logic circuits for quantum-dot cellular automata. The aim is to maximize the circuit density and focus on a layout that is minimal in its use of cells. Source

Lead and zinc mineralization occurs in dolostones of the Middle Devonian Sibzar Formation at Ozbak-Kuh, which is located 150 km north of Tabas city in East Central Iran. The ore is composed of galena, sphalerite and calcite, with subordinate dolomite and bitumen. Wall-rock alterations include carbonate recrystallization and dolomitization. Microscopic studies reveal that the host rock is replaced by galena and sphalerite. The Pb-Zn mineralization is epigenetic and stratabound. The δ13C values of hydrothermal calcite samples fall in the narrow range between -0.3‰ and 0.8‰. The δ18O values in calcite display a wider range, between -14.5‰ and -11.9‰. The δ13C and δ18O values overlap with the oxygen and carbon isotopic compositions of Paleozoic seawater, indicating the possible important participation of Paleozoic seawater in the ore-forming fluid. The δ18O signature corresponds to a spread in temperature of about 70 °C in the ore-bearing fluid. The δ13C values indicate that the organic materials within the host rocks did not contribute significantly in the hydrothermal fluid. The δ34S values of galena and sphalerite samples occupy the ranges of 12.2‰-16.0‰ and 12.1-16.8‰, respectively. These values reveal that the seawater sulfate is the most probable source of sulfur. The reduced sulfur was most likely supplied through thermochemical sulfate reduction. The sulfur isotope ratios of co-precipitated sphalerite-galena pairs suggest that deposition of the sulfide minerals took place under chemical disequilibrium conditions. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the galena samples represent average values of 18.08, 15.66, and 38.50, respectively. These ratios indicate that galena Pb likely originated from an orogenic source in which supracrustal rocks with high 238U/204Pb and 232Th/204Pb ratios are dominant. The average lead isotope model age portrays Cambrian age. This model age is not coeval with the host rocks, which are of middle Devonian age. It is probable that the pre-Middle Devonian model age shows the derivation of Pb from older sources either from host rocks of Cambrian age or from deposits previously formed in these rock units. The Pb isotopic composition of galena accords with the occurrence of an orogenic activity from Late Neoproterozoic to Lower Cambrian in Central Iran. The proposed genetic model considers the fact that mineralization formed in fractured and brecciated host rocks along shear zones and faults from metal-bearing connate waters that were discharged due to deformational dewatering of sediments. © 2013 Springer-Verlag Wien. Source

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