E Khazaei; M.H Mahmudy Gharaie; A Mahboubi; J Taheri
Abstract
The studied section in SW Kashmar located in Tabas block of central Iran sedimentary - structural zone. According to field observations and petrography, two sets of siliciclastic and carbonate facies were distinguished. Three lithofacies were identified based on the field parameters such as lithology, ...
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The studied section in SW Kashmar located in Tabas block of central Iran sedimentary - structural zone. According to field observations and petrography, two sets of siliciclastic and carbonate facies were distinguished. Three lithofacies were identified based on the field parameters such as lithology, geometry, sedimentary structures, layering surfaces and bedding contacts. Three lithofacies including conglomerate (Gcm, Gp), Sandstone (St, Sr, Sh, Sl, Sm), muddy (Fl), four petrofacies (polymictic orthoconglomerate 1 and 2, arkosic wacke, and subarkose as well as four microfacies associations of open marine, shoal, lagoon, tidal flat were identified based on microscopic features such as grain type, grain size and texture. Based on finning upward Bouma cycles, erosional surface and greywacke composition, siliciclastic sediments of upper part of the Shirgesht Formation are deposited in turbidity conditions. Present of hummocky stratification, finning upward cycles with shellbeds at the base of units revealed that carbonate rocks of lower part of the Niur Formation are deposited in a shallow ramp storm - dominated. The regional tectonic, expansion of glaciers and melting led to environmental changes during Upper Ordovician – Early Silurian transition in the studied region.
S. R. Moussavi-Harami; Y. Nasiri; A. Mahboubi; A. Bayetgoll
Abstract
Amiran Formation (Paleocene) in Lorestan, folded Zagros zone, contains a diverse and exceptionally well preserved ichnofauna. A quantitative study of trace fossil in the Paleocene deep-marine clastic systems, this Formation, shows that they are powerful discriminators of submarine fan and related environments. ...
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Amiran Formation (Paleocene) in Lorestan, folded Zagros zone, contains a diverse and exceptionally well preserved ichnofauna. A quantitative study of trace fossil in the Paleocene deep-marine clastic systems, this Formation, shows that they are powerful discriminators of submarine fan and related environments. The host lithologies are conglomerates, sandstones, siltstones and mudstones. These sediments are interpreted to be deposits in upper to lower-fan palaeoenvironment. Channel deposits consist of thick-bedd turbidite and interchannel deposits are interpreted to be deposited by unconfined debris flows and high concentration turbidity currents. The ichnofauna with high diversity is most frequently, and best, preserved within the Tcde interval of turbidities, which are interpreted as interchannel deposits, produced by low concentration turbidity flows. On the basis of trace fossil diversity, ichnotaxonomic composition, ethology, and morphologic complexity, trace fossils assemblage were grouped into pre-depositional or post-depositional forms. The predepositional assemblage is rich in graphoglyptids and grazing trails, and feeding structures. The ichnodiversity, ethology, and morphologic complexity of the predepositional association are indicative of the Nereites ichnofacies. The postdepositional association essentially consists of dwelling and feeding traces. The post-depositional association includes elements of the Skolithos ichnofacies. Overall characteristics of trace fossils suggest that from the proximal to the distal environment of Amiran Formation, proportions of domichnia trace-fossil assemblages decreases while agrichnia, fodinichnia and pascichnia increases.
M. Maanijou; I. Rasa; D. Lentz
Abstract
Chehelkureh copper deposit is located in Kuh-e-Lunka area, 120 km NW of Zahedan (SE of Iran). The host rocks of mineralization are intercalated Eocene turbiditic greywackes, siltstones, and shales (flysch). They are folded with N-S trend and the eastern limb of this fold has ...
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Chehelkureh copper deposit is located in Kuh-e-Lunka area, 120 km NW of Zahedan (SE of Iran). The host rocks of mineralization are intercalated Eocene turbiditic greywackes, siltstones, and shales (flysch). They are folded with N-S trend and the eastern limb of this fold has been drag folded. Several stocks and dykes of granodiorite to quartz monzodiorite and granite compositions intruded the turbidites, converting them locally to hornfels. These intrusions are oriented parallel to the major NW-SE fault set. The Chehelkureh ore field comprises numerous irregular lenses and veins. The ore field extends for 1500m in N23°W direction, and is displaced by late brittle faults striking roughly E-W. The fault and fracture filling ores include quartz, dolomite, ankerite, siderite, calcite, and lesser amounts of pyrrhotite, arsenopyrite, pyrite, chalcopyrite, sphalerite, galena, Se-rich galena, marcasite, molybdenite, ilmenite, and rutile. Assay data from 39 drill holes show high contents of base metals, with an average of 1.48% Cu, 1.77% Zn, 0.85% Pb (4.1% Cu+Zn+Pb), and silver (average 22 ppm in 45 samples). The ores are not so enriched in gold (0.14 ppm on average in 45 samples).
A composite sample of least-altered greywackes and shales (host rocks) is used for comparison with mineralized samples. Mass-balance calculations were carried out to quantify chemical changes resulting from different alteration episodes. With the low solubility and low variance of Al (Al2O3) in moderately altered sedimentary country rocks compared with many other immobile trace components, Al2O3 is used as an immobile component for mass-balance calculations. There is a net mass increase in Fe2O3T, and MgO and a net mass decrease in Na2O, CaO, K2O, and SiO2 with chloritization. Carbonatization shows Fe2O3T, and MgO enrichment and SiO2 and Na2O depletion, implying that ankerite, siderite and dolomite are predominant phases. SiO2 is enriched in silicified samples and depleted in other alteration types. There is no mass change in Cu, Pb and Zn with kaolinization, but these elements are enriched in other alteration types. Hg is enriched in all alteration types except kaolinization, which may even show a slight depletion. Samples from gossan with silicification showed an increase in SiO2, Fe2O3T, Cu, Pb, Hg, and Zn and a decrease in MgO, Na2O, CaO, and K2O. Some trace and major elements have high variance in different alterations and are more complicated to interpret, such as P2O5, MnO, Ni, Co, and Rb.
The REE contents of the composite host rock sample are enriched in the LREE relative to the HREE and moderately depleted in Eu and Ho. As a whole, samples with kaolinization and carbonatization (ankerite and siderite) have been enriched in REE contents and other wallrock alteration, including chloritization, dolomitization, kaolinization, minor sericitization, and silicification, are depleted in REE. SEM-EDS evidence indicates that enrichment of REE-bearing phosphates, such as monazite, occurred with carbonatization and kaolinization assemblages.
