Economic Geology
Mohammad Ali Rajabzadeh; Mohammad Amini
Abstract
This is the first report on the presence of podiform chromititeLenses associated with the Marivan ophiolite. These ore deposits with granular massive fabric are hosted by dunite and harzburgite occurred in south Marivan city. Chemistry of chromian spinel in the chromite Lenses indicated that Cr# for ...
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This is the first report on the presence of podiform chromititeLenses associated with the Marivan ophiolite. These ore deposits with granular massive fabric are hosted by dunite and harzburgite occurred in south Marivan city. Chemistry of chromian spinel in the chromite Lenses indicated that Cr# for two ore occurrences is high (0.85) with very low TiO2, but for the other ore occurrence is lower (0.67) with higher TiO2 (0.05). The finding shows that the chromite ore Lenses and consequently their host ophiolite were developed in two different geotectonical settings. Geochemical data indicated that some of the studied ore deposits occurred during the opening of oceanic crust in a Mid Oceanic Ridge setting from a tholeiitic magma while the others were fractionated form a boninitic melt in a Supra Subduction Zone. Formation of these ore Lenses and the host rocks occurred in response to the very fast divergence and then convergence of Neo-Tethys oceanic crust. A wide range of gabbros including coarse-grained gabbro, melagabbro and microgabbro host ilmenite, magnetite and titanite in three regions at the northwest of Kamyaran (Yakhtekhan village), the east of Sarvabad (Mianeh village) and the south of Marivan (Dragashikhan-Vyseh villages). Ilmenite is found in all the three regions, but magnetite and titanite are only found in the east of Sarvabad. Plagioclase (andesine-labradorite) and diopside, the main rock-forming minerals with minor augite, olivine and amphibole are the minerals of the host rocks. The chemical composition of the ilmenites showed that the average concentration of TiO2 increases from Kamyaran (43.19 wt.%) to Sarvabad (46.09 wt.%) and then to Marivan (47.42 wt.%). These minerals occur as interstitial fine to medium grains (up to 1.5 mm) and often in the amoeboid, anhedral and to a lesser extent as subhedral forms. Based on textural and mineral chemistry evidence, mineralization of titanium occurred as the result of magma oxidation. The oxidation of magma resulted in the formation of iron-titanium immiscible liquid droplets, following the plagioclase crystallization.
M. SoltaniNezhad; H. Ahmadi Pour; A. Moradian; B. Zaboli Sarvtamin
Abstract
The Hadji-Abad ultramafic complex is located at the north of Hormozgan province and represents a part of Orzuieh-Dowlat Abad colouredmelange in the northern edge of Zagros thrust. The complex contains harzburgites, lherzolites, dunites and chromitites. Harzburgite is the dominant rock type. Evidence ...
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The Hadji-Abad ultramafic complex is located at the north of Hormozgan province and represents a part of Orzuieh-Dowlat Abad colouredmelange in the northern edge of Zagros thrust. The complex contains harzburgites, lherzolites, dunites and chromitites. Harzburgite is the dominant rock type. Evidence such as lobateboundaries, elongation of chromianspinels and pyroxenes, evidence for incongruent melting of orthopyroxenes and exsolution lamellae of clinopyroxenes show that the studied peridotites, experienced high temperature deformation in the upper mantle, and then emplaced in the crust. Different amounts and various shapes of chromite grains occur in all of the studied lithological units. In the harzburgites and lherzolites, disseminated brown chromites are seen as either euhedral isolated crystals or anhedral interstitial ones which crystallized between the other minerals. In the dunites, chromites appear as disseminated black euhedral and subhedral crystal grains which formed within or at the boundaries of olivine grains. In the high grade chromitites, the coarse black euhedralchromites show smooth and triple junction boundaries with cumulative textures, while in the low grade types, disseminated euhedralchromites set in a silicate matrix. Chemical analysis of disseminated chromites in the studied rocks show that maximum amounts of Cr# belong to those exist in the high grade chromitites (80-84) and the minimum are for those in the lherzolites (45-52). Tectonic discrimination diagrams reveal that chemical compositions of chrome spinels from the harzburgites and lherzolites are similar to those exist in the suprasubduction zone mantle peridotites. The host rocks as a part of ophiolites in this environment, suffered 15 to 20% partial melting. Disseminated chrome spinels from the dunite and also the chromitites have been crystallized from boninitic type melts in the same tectonic setting. These evidence show that probably, Hadji-Abad peridotites and their host ophiolitemelange belong to suprasubduction zone upper mantle and the evolutions related to this environment such as melt-peridotite reaction and partial melting have been recorded in their mineral chemistry and textures.
S.H Ghetmiri; S.M.A Aleyasin
Abstract
Surveying the uptake of metal substances by plants has a very important role in mineral exploration, but biogeochemical exploration has not been paid much attention in Iran. The aim of current study was surveying vegetative species of Khajeh-jamali mineral area to evaluate the probability of biogeochemical ...
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Surveying the uptake of metal substances by plants has a very important role in mineral exploration, but biogeochemical exploration has not been paid much attention in Iran. The aim of current study was surveying vegetative species of Khajeh-jamali mineral area to evaluate the probability of biogeochemical exploration of chromite and to evaluate the uptake of Iron, Copper, Lead and Nickel in the floral plants providing biological absorption coefficient (BAC). Also it aimed to evaluate the reliability of comparing metal uptake of the plants with control groups as an assisting method of exploration. The area is located on the Zagros thrust zone belong to the Alps ophiolitic band. Rock units of this area are mainly composed of rocks from Neyriz ophiolite assemblage, which are mostly of Harzburgite and Dunite types with chromite as the major mineral. The concentrations of metal substances in this area are assessed in previous studies.To study six substances of Chrome, Nickel, Iron, Cupper, Lead, and Zinc, in five herbal species including Amygdalus carduchorum ,Pistacia atlantica, Ebenus stellata, Asragalus sp. and Rheum ribes, twenty five samples (5 from each species) were collected in the study area and five samples (one for each species) were collected from an area outside of the region as control. The samples were analyzed by ICP-OES method. The resultant data was statistically analyzed using One-way Anova and T-test. BAC was in “low” or “very low” range for all the five plant species. The results showed that Rheum Ribes could be useful in Nickle exploration and Ebenus stellata for Lead exploration. This study suggests future biogeochemical investigations of areas with flora having undefined or low BAC to consider comparison of plants’ substance uptake with controls as an assisting method.
M.R Shayestehfar; M Mohammadi; A Rezaei; H Ranjbar
Abstract
With detection of the magnetic minerals along with the chromite, it is possible to prospect the chromite deposits. Chromite has no magnetic properties but from the genetic aspects, there is a close relation between chromite and magnetite. With this respect and the magnetic differences of chromite minerals ...
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With detection of the magnetic minerals along with the chromite, it is possible to prospect the chromite deposits. Chromite has no magnetic properties but from the genetic aspects, there is a close relation between chromite and magnetite. With this respect and the magnetic differences of chromite minerals with the country rocks, the effort was to prospect the chromite mineralization of 1: 50000 Abdasht sheet by the use of air born geophysical data. In the study of the geophysical air born of the area, the observed magnetic piles in the area has been investigated by using of the digital filters of reduce to pole, first and second derivations, analytical signals and upwards continuation on the map of the magnetic field of the total intensity. With the study of these maps and compare them with the area, especially ophiolite and ultramafic bodies and chromite-included areas have been studied and the final results are compared with the magnetic pattern and with respect to the maps of the vertical derivation and upwards continuation, 25 areas for the detailed exploration and field sampling area suggested in the entire sheet of the Abdasht.
H.R. Vatanpour; A. Khakzad; M. Ghaderi
Abstract
Sabzevar ophiolitic belt is located in the northwest of Iran, north of Sabzevar. The current study is carried out for the first time in Iran with an exploration approach in the western part of the belt. Study of Platinum Group Elements (PGE) is of high importance for determining the genesis and economic ...
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Sabzevar ophiolitic belt is located in the northwest of Iran, north of Sabzevar. The current study is carried out for the first time in Iran with an exploration approach in the western part of the belt. Study of Platinum Group Elements (PGE) is of high importance for determining the genesis and economic evaluation of chromite deposits specifically in ophiolitic complexes. Chondrite-normalized PGE patterns of the chromitites related to ophiolites have a negative slope suggesting that during initial stages of magma crystallization, chromite preferentially removed compatible PGE from the magma. These patterns in the Sabzevar chromitites imply that these rocks are related to ophiolitic complexes (Alpine type). Chromite ore bodies which exhibit a relatively high incompatible/compatible element (Pd/Ir, Cu/Ni) ratios are derived from a more evolved magma with a lower fractional melting degree and do not seem to be of economic importance; this ratio in Al-rich chromites is higher than that of Cr-rich type. Pd/Ir ratio in Sabzevar chromitites on the average is less than 1, similar to many important chromite ore bodies related to ophiolitic complexes throughout the world. This ratio being low, as well as high chromium number (Cr/Cr+Al>0.60) suggests that this complex can be considered to contain a significant potential for economic and metallurgical chromite. Furthermore, the complex does not contain chromitites of uniform composition in chalcophile elements. PGE patterns of peridotites in the study area also show that these units in upper parts of the Gaft area are similar to ultramafic cumulates of oceanic crust, while in lower parts of Faroumad area related to mantle sequences.
