Iranian Journal of Crystallography and Mineralogy
Year:2007 | Volume:14 | Issue:2|Papers Count:21

Ophiolitic complex of Sahneh could be considered as part of ophiolite sequences in the Zagros Suture Zone.This complex is a part of  3000 km belt, which is started from Syria after crossing south Turkey and Zagros leading to Oman. The studied ophiolitic complex is curvature in shape which is situated in south of Sahneh. No complete ophiolite sequence were seen in this complex. In general, the present lithology of the area consists of harzburgitic peridotites, isotrope and mylonitic gabbros, and small outcrop of plagiogranite sequence. Ultramafic rocks consist mainly of harzburgite, dunite, lherzolite, websterite, and mafic rocks are composed of pegmatoidic gabbro, olivine gabbro, mylonitic gabbros and isotrope gabbros. On the bases of major elements diagrams and spider diagrams, this complex could be resulted from a P-type ocean floor tholeiitic basalt (P or E MORB). Geochemical and petrological evidence showed that parent magma were high Mg sub-alkaline in type. Tholeiitic nature of magma are responsible for the formation of oceanic crust, and their position on to the mid oceanic ridge field. The P-type nature of magma indicated that the old-ridge were formed during a high spreading sea floor conditions. Geochemical and petrological evidence showing that parent magma were picritic in composition and may resulted from high melting ratio of the upper mantle.

It is very important to identify the source of sediment yield in a drainage basin for any practical soil conservation program. Clay minerals in litological units can be used as an indicator for prediction of soil erosion. Marl and marly-limestone of Neogen red beds, Hezardarreh Formation and Quaternary alluvium, are exposed in the Lateshure watershed. 21 samples from surface soils of different lithologic units and alluvium sediments were collected. These samples were analyzed by XRD for identification of different types of clay minerals (montmoriolit, cholorite, illite and kaolinite) as well as their amounts was semi-quantitatively determined. Cluster analysis showed that the clay minerals can differentiate surface soils from Neogen red beds and alluvium sediments. Based on F test in this study, montmoriolit and illite can be used as an indicator for prediction of the source of soil.

The conglomerates of Sangestan Formation (Lower Cretaceous) have been metamorphosed in the vicinity of the leucogranitoid rocks of the Shir-Kuh batholith and have created the mineral assemblage of garnet- epidote-quartz-calcite-pyrite in the contact halo. Following the contact metamorphism, hydrothermal alteration (pyrite formation and silicification) has likely occurred. Based on the trace element contents of the garnets, the skarn in the contact halo is Cu-Pb-Zn bearing calcic skarn type. The above mentioned minerals, apparently, indicate that there is a genetic relationship between intrusions related Cu-mineralization and the skarnification in the study area.

The effect of SPEX mechanichal milling on a mixture of Al-SiC composites has been investigated. Results of XRD, SEM and cumulative size distribution analysis show that the size of crystallites is decreased as milling time increases to 12 hours, while lattice strains are increased.Meanwhile the crytallite size increases with increasing milling time between 12 and 24 hours, but the lattice strains decreas. In addition, average particle size of the composite decreses at initial 6 hours but increases for longer milling times. SEM and TEM micrographs of the productions indicate homogeneous distribution of 50 nm size SiC particles into Al matrix, where the homogeneity increases with increasing milling time.  

Chahar-Gonbad copper mine, in Kerman province, has mainly formed as veins with low reserves and medium grade. Mineralization is mainly occured as chalcopyrite, pyrite, rare galena and sphalerite. Sericitic, argillic and propylitic alterations have been identified in this are deposit. This alteration occurred in the thermal range of about 350oC. In this research, the morphology of pyrite crystals is used for determination of the thermal range of mineralization. It is possible that the pyrite form in a mineralization zone shows the state of thermal range during mineralizaton. Based on this assumptian, the needle crystals are formed in temperatures below or equal to 250oC, abundant grooves while with increasing temperature to 450oC the cubic crystals with abundant grooves and a few octahedral surfaces are formed. Investigations of collected pyrite crystals from alteration zones of this ore deposit show that the cubic types with abundant pyritohedron surfaces are common and crystals with high density with groove surfaces are seen with smooth surfaces crystals. Therefore it is interpreted that pyrites have formed in the thermal range between 250 to 450oC. According to the temperature range for alteration (mean 350oC), it seems copper that the mineralization have occurred between 350 to 450oC.

The soil properties are function of mineral type, characteristics of pore fluid, microstructure of soil, and environmental conditions. Scanning electron microscope (SEM) can be used as a tool for a direct study of soil microstructure. In addition, one of the methods for evaluation of heavy metal contaminated clayey soils is related to the application of SEM. In this paper, a method for homogeneous sample preparation for SEM micrograph from clayey soil suspension is presented. Due to the importance of the application of undisturbed samples for SEM study, different methods of sample preparation including; peeling, fracturing, and resin application for contaminated soils are investigated. Sample of illite and kaolinite were laboratory contaminated with different concentrations of lead nitrate as a source of heavy metals. After achieving equilibrium, samples were exposed to the resin. Then, different sample preparation methods were applied for those contaminated illite and kaolinite. Finally, micrographs of samples were taken by scanning electron microscope. The impact of sample preparation method on the quality of SEM images in these clay minerals and in the presence of Pb ions is investigated. The prepared SEM pictures are compared with untreated samples as well. The results indicate that the exposure of samples to resin has a noticeable impact on the quality of SEM micrographs of contaminated clay minerals.

Geochemical studies of the Pinavand Fluorite Mines indicates that fluorite has been deposited from a high salinity, typically low temperature and Mg-rich fluid in two stages: Based on geothermometrical data, at the first stage fluorites were formed at relatively high temperature (85-235Co) and accompanied by host rock replacement (in the form of epigenetic dolomitization). The second stage of fluorite mineralization has occurred at low temperature (65-115oC) and has formed lodes and vein-likes along the breccia and fault zones. However, the salinity was relatively invariable (15-23 wt% NaCl), suggesting salinity of fluorite-forming fluid was the same at all occurrences. By studying of REE patterns and regarding to some ratios of HREE to LREE, it could be observed that the first stage of fluorites was enriched in LREE revealing mineralization has occurred in early stage of crystallization .In contrast, the second stage of fluorites containing high proportion of HREE were deposited in the last stages of crystallization event. Based on the calculated (Yb/La), (Yb/Ca), (Tb/La) and (Tb/Ca) ratios, two mechanisms could be proposed: assimilation (replacement) for the first type fluorites and remobilization (rejuvinilization) for fluorites of the second stage.

The Jajarm Bauxite deposit 16 kilometers E-W trending and overlis, the Karstic dolomite rocks of the Elika Formation. The study of texture and different phases has been carry out in order to understand the degree of crashing, particles size, condition of formation, degree of crystallization, porosity, distribution of constituent elements and beneficiation for the propose of digestion and potential of physical beneficiation. The phase analysis indicates that the Jajarm Bauxite is typical diasporic bauxite accompanied with Kaolinite, hematite and anatase. Hard bauxite is the high quality bauxite with Al2O3>50% and SiO2< 9%. Mineral chemistry shows that out of 58% of Al2O3, 54.39% constituting diaspore structure, 1.6% is in kaolinite and 0.94% in topaz. Where as out of 5.78% SiO2, 3.72% occurring in kaolinite structure, 1.5% as free and inactive quartz and the rest of it is located in topaz structure. The Jajarm bauxite shows a politomorphic, micro granular texture with several secondary textural elements. The size of main minerals component are generally below 10 micron, with homogeneous matrix. Kaolinite minerals forms stacks of very thin (<0.1 micron) crystal platelets. In addition, in a very hard bauxite, separation between the crystal grains and the matrix can not be done because of similar hardness for both with closely packed space filling and in consequence of the missing defined borderlines of the grains. Based on the above studies, the Jajarm bauxite can be enriched neither by grain analysis nor by the magnetic separation. Laboratory study shows, only it can be improve by water treatment.

The study area is located in the Dehaj-Sarduyeh belt in Kerman province. This belt forms the south eastern part of the Central Iranian Volcanic Belt. Enhanced Thematic Mapper plus (ETM+) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data have been used for this study. Different image processing techniques such as false color composite, band ratioing and principal component analysis are used for recognizing the alteration zones related to the copper mineralisation. The aim of this investigation is to compare ETM+ and ASTER data and finding out their capabilities to recognize the altered and iron oxide bearing areas. This investigation showed that ETM+ data due to its blue region spectral band can enhance the iron oxide rich areas much better than ASTER data. ASTER data due to its various spectral bands in the short wave infrared is more capable of enhancing clay bearing areas.

The samples studied through this research were collected from active black smokers located in the mid-oceanic ridge from a depth of 2276m by a sea-born ship “Academician Mstislav Keldysh” (2002), in its 47th research mission. The collected samples were studied by microscopic, microprobe and X-ray analysis (Debye-sherer). These samples were in the form of narrow pipes with zoned structure, which included the following zones from the core to the margin: isocobanite, Chalcopyrite, Bornite and cupper sulfide zones. For the first time, it has been observed that tetragonal phase within the cupper-sulfide zone in recent sulfide, deposits. Tetragonal phase of Cu2S, which is an unstable form of chalcocite, is stable only at high pressures (more than 0.8 Kb) and temperatures higher than 102 oC. The tetragonal form of Cu2S in one of the studied samples was associated with Chalcocite-Djurleite mixture and in another studied sample was associated with chalcocite-Bornite mixture. Its average chemical composition was also determined as Cu2.02S. It is likely that the emergence of this unstable phase in young hydrothermal deposits, which are formed at 250-350 oC, is not odd but after hydrothermal activity and temperature reduction it is changed to more stable phases. Evaluation of older black smokers showed no trace of tetragonal phase.

Loess/soil sequences have been proven to be excellent paleoclimate indicators. Large areas of northern Iran are covered by loess deposits which provide a good condition to carry out research on paleoclimate, paleosols and discontinuities. The objectives of this research were to identify clay minerals of soil-loess sequences, to determine the role of climate change in clay mineral transformation and to estimate the relative ages of soil development based on archaeological information. Samples were analyzed by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results showed that kaolinite, illite, quarts and feldspar were dominant in the fine clay, coarse clay and silt fractions. The type and the quantity of clay minerals in soils are highly correlated with parent material. Semiquantitative estimation indicated that different clay minerals are quantitatively different in the profiles. This may be due to different weathering rates caused by cool/dry and wet/warm periods. A high degree of chlorite to smectite transformation was observed in deep soil horizon (130–170 cm) where a developed horizon was buried. Differences between soil layers development were confirmed by comparison of oxalate and dithionite extractable Fe.

The La0.75Sr0.2Mn1-xCoxO3 (0≤X≤1) Manganite-Cobaltites are synthesized by sol-gel method and their structural, electrical and magnetic properties are studied. After calcination over 800 oC, all compounds were crystallized in the perovskite rhombohedral structure (R`3, Space group). Due to nonstochiometery, some traces of the La2O3 phase were appeared in final samples. Resistivity measurements of the samples between 77 and 328 K revealed that resistivity at first decreased and then increased by increasing cobalt content. Also, magnetoresistance results in presence of external fields up to 1.5 T exhibit negative magnetoresistance in all samples. The colossal magneroresistance effect has been observed in all samples except the samples without Mn. Variation of the resistivity and magnetoresistance of the samples with Co content are described based on three following mechanisms: spin scattering, charge compensation and distortion of metal–oxygen-metal bonds. Magnetoresistance behavior of the samples are evaluated based on (1) increased of the double exchange interaction, (2) increased probability of inter-grain tunneling of the carriers, and (3) decreased scattering of carriers from magnetic fluctuations  mechanism in the presence of applied field.

Metamorphic rocks of the Hamadan region  have experienced regional and also contact metamorphism (due to intrusion of gabbro, diorite and granitic bodies), therefore, their mineral assemblages have formed in multiple stages. Evidence of regional metamorphism (M) and contact metamorphisms at the contact of gabbros (M'1) and porphyroid granites (M'2) are separatable, hower At the contact of hololeucocratic granites a very local contact metamorphism (M'3) have occurred (from a few decimeter up to a few meters, due to small size of these bodies). Minerals such as micas, garnet, staurolite, cordierite, andalusite, kyanite and sillimanite are usually produced by several reactions, and participated in other reactions to form  other minerals. The relationship between mineral growth to deformational events have been found at several stages (i.e. pre-tectonic, syn-tectonic and post-tectonic minerals are common in metamorphic rocks of the region.) Pegmatites and silicic veins have played essential role in some metamorphic reactions as sources for heat and fluids, so that some metamorphic minerals are common near these veins and disappear far from the veins. Considering observed mineral assemblages in metamorphic rocks of the region, regional metamorphism can be correlated with low to moderate P/high T Buchan type metamorphism. In final stages of metamorphism, high T minerals such as cordierite experienced retrograde reactions or pseudomorphed and higher pressure minerals such as kyanite have been more stable.

yttrium bismuth garnet (YBG) and its doped systems were prepared by citrate gel process. The condition and process of pure phase formation were confirmed by X-ray diffi'action . The studies of homogeneity and particle size of prepared garnet were done by FTIR spectroscopy and SEM. The DTA study of YBG shows that the single phase state and particle size of YBG change with the amount of doped Mo as well as depend to the heating time.

Study of lamproites from Leucite Hills, Wyoming, indicates that the isotopic compositions of some specimens have been modified due to the alteration and/or the presence of secondary carbonate impurities within the whole rocks. Leachate test shows that while phlogopite lamproites are not affected by secondary processes, the transitional madupitic lamproites from Middle Table Mountain and one madupitic lamproite from Pilot Butte localities are most affected by the mentioned processes. Comparing the Sr and Nd isotopic compositions of sedimentary enclaves with those of lamproites also pinpoints affected samples. Based on such observation, mineral grains from a number of samples were separated and analysed for Sr and Nd isotopic compositions. The analysis of clinopyroxene, apatite and perovskite from the Leucite Hills lamproites provides the most reliable mean for determining the isotopic composition of the affected samples. It also shows that the the whole rock samples from Middle Table Mountain are not representative of their parental melts and that the transitional madupitic lamproites should be classified as madupitic lamproites. Variation of isotopic ratios on Nd vs Sr isotopic diagram suggests that the madupitic lamproites have originated from a mantle source that was geochemically different from that of the phlogopite lamproites.

In this study we attempt to distinguish the relationship between the altered chromites and non-altered ones by X-ray diffraction. For the purpose of this study, an assemblage of altered/non-altered and deformed/non-deformed ophiolitic chromites has been collected and analyzied. Sharp and doubled peaks are resulted from non-altered and altered samples respectively. By using XRD studies, the parameter "a" from chromite grains has been calculated and the composition of same samples, obtaining from microprobe analysis, has given a chart that is useful for semi-qualitative recalculation of chromites composition.