Iranian Journal of Crystallography and Mineralogy
Year:2009 | Volume:17 | Issue:1|Papers Count:12

The Muteh gold district is located about 70 km northeast of Golpaygan within Sanandaj-Sirjan metamorphic zone of Zagros Structural Belt. Geological studies show that the area had been under poly - phase metamorphism. Gold mineralization occurs in metamorphic complex which consists mainly of green schists, meta-volcanics, and gneisses. Shear zones are the host of gold mineralization, and intense alterations occur along the normal faults. Gold par agenesis minerals include pyrite, chalcopyrite, pyrrhotite and secondary minerals. There is three generation of pyrites. This contribution is aimed to improve our knowledge of understanding the source of the ore-bearing fluids in this area. In this regard, fifteen samples were selected for hydrogen, oxygen and sulfur isotope studies. The mean values of 12.4% and-42% for d18O, and dD isotopes with the mean value of 7.75% of calculated fractionation factors for d18OH2O from quartz veins indicate that metamorphic host rocks are the most important source for the fluids and gold mineralization in the Muteh area. Gold mineralization is closely associated with intense hydrothermal alteration along the ductile shear zones. However, our observation shows that the characteristics of the gold mineralization in the study area are also similar to that of other hydrothermal with magmatic origin. Five available sulfur isotope (d34S) data are highly variable (+2.2, 6.6, 9.1, 13.9, and 16.9%) even from the same type of hosted rocks. The isotope data, suggest that the source of sulphurs were not homogenous. Based on sulfur isotope compositions at Muteh gold district, it can be concluded that several different sources or processes could account for the sulphide fluids. The d34S values in the studied area demonstrate that source of sulphides are mainly derived from the metamorphism fluids though hydrothermal fluids related to magmatic activities.

Two types of rodingitization (static and dynamic) are observed in the rodingites of the ophiolite north of Nain. Two stages have been occurred in the formation of static rodingites. At the initial stage, epidote, prehnite and hydrogrossular have crystallized respectively at the expense of plagioclase, with the increase of Calcium content rodingite forming fluid. In the advanced stage, xonotlite at the expense of plagioclase, and Mg–chlorite, tremolite and secondary diopside, at the expense of pyroxene, have formed simultaneously with an increase of Si content of rodingite forming fluid. The high content of vein xonotlite, in the dynamic rodingites, shows that the CaO/SiO2 ratio in the fluid is first close to one, but with time, it reduces to less than one and prehnite and pectolite have crystallized. In the dynamic rodingites, due to the low variations of rock–forming fluids, the mineralogy of dynamic rodingites do not vary much. In contrast, the mineralogy of static rodingites display variation, indicating the changing in composition of rock–forming fluids.

Eocene volcanic rocks in south of Asad Abad (north-east of Koohpayeh, Isfahan Province) experienced very low-grade metamorphism (hydrothermal metamorphism), resulting in prehnite, malachite, azurite, zeolite, quartz and calcite crystallization in cavities and fractures. Chlorite (brunsvigite) and amphibole (ferro-actinolite) appear on secondary phases. Augite and labradorite are two main minerals based on electron microprobe analyses and petrography evidence. Composition of minerals in these volcanic rocks and xenoliths are similar. Field and microscopic evidence show that an alternation of acidic and basic magmatism has occurred in the study area. Very low-grade metamorphic minerals formed in neutral to slightly alkaline PH, low CO2, at temperature of 200-400oC and pressure lower than 3 Kbars. Based on calculations, clinopyroxene and plagioclase phenocrysts in basaltstic magma in the study area have formed at temperature of 1100oC and pressure of 3.17 Kbars corresponding to a depth of 11 Km. Chemistry of volcanic minerals and open space fillings minerals is close, both are rich in Ca, Si and Al and relatively poor in Fe, Na, K and Mn. This shows that the volcanites chemistry had important role in composition of metamorphic minerals. On the basis of the geochemical studies and tectonic setting patterns, these rocks are volcanic arc basalts. These basalts belong to the calc-alkaline magmatic series.

Saghand playa is located about 150 km northeast of Yazd in central Iran. In order to study brine evolution and effect of brine origin on mineralogical distribution and hydro chemical characteristics of evaporate minerals for exploration, 21 samples were collected from different parts of this playa. The samples were analyzed using the XRD to determine mineralogical characteristics of the brine. Normalized XRF results were led to establish elemental analysis of the samples. Results were compared with data of Great Saline Lake, the Death Valley and the Great Salt pan in North the America. Cation and anion variations in the Saghand playa brine, hydro chemically and physic chemically are similar to the Great Saline Lake the brine type is Na-K-Mg-Cl-SO4 as alkaline meteoric brine.Mineralogically, halite, gypsum and bazanite are the most frequent evaporite minerals in this playa which suggest higher Concentration in of Saghand playa brine in comparison with the other mentioned playa.

Kaolinite is non-sensitive, low swelling clay with high chemical resistance and high workability. It is commonly found as a major fraction of clay liner in waste disposal sites. These clay liners are usually exposed to different concentrations of heavy metals. Even though there are several researches focusing on the interaction process of kaolinite and heavy metal contaminations, there are only few researches have been conducted to evaluate the influence of pore fluid properties on the microstructure of clayey soils. Therefore, the aim of this research is to investigate the impact of kaolinite and heavy metal interactions on the microstructure of kaolinite. For this purpose, kaolinite soil were laboratory contaminated with different concentrations of lead and zinc nitrates. Then, with performance of a series of physical and microstructural analysis, the change on the behaviour of contaminated kaolinite is assessed. The result of atterberg limits tests as physical experiment shows that with an increase on the concentration of heavy metal contamination, a decrease on the liquid limit happens. Furthermore, in the presence of high concentrations of zinc and lead ions, due to the formation of flocculated structure and retention of water in macro pores of soil, the rate of reduction on the liquid limit decreases. The results of SEM micrograph and the variations on the intensity of the XRD peaks confirm the noticeable change on the microstructure of kaolinite.

The Astaneh granitoid massif is located about 40 km to Arak city, central Iran, is a part of Sanandaj-Sirjan structural Zone. These intrusive rocks which are mainly composed of grnodioritic rocks, widely affected under hydrothermal alteration. The alteration zones, on the basis of field studies and mineralogy as well as the study of the REE behavior, are investigated in this paper. Eight alteration zones including phyllic (sericitic) with quartz, sericite and pyrite, chloritic with quartz, sericite and chlorite, propylitic with chlorite, epidot, calcite and albite, argillic with clay minerals (chlorite and illite), silicic with abundant quartz, albitic with albite, chlorite and quartz, hematitisation with hematite, Fe-carbonates (ankerite and siderite) and tourmalinisation with tourmaline (dravite) are identified. The results demonstrate notable differences in the REE behavior in the different alteration zones. Accordingly, comparison with the fresh rocks, in the phyllic (sericitic) alteration, LREE are enriched, but HREE, except Yb which enriched, unchanged. Also in chloritic alteration zone, LREEs are depleted, but HREEs represent different behaviors. In the argillic and propylitic alteration zones, all REE are depleted, but compared with HREE, the LREE represent more depletion. In the silicic and hematitisation alteration zones, compared with HREE, the LREE are enriched. Finally, in the albitic and tourmalinisation alteration zones all REE are depleted. These features indicate that the behavior of REE in the hydrothermal alteration zones of the Astaneh granitoid rocks is mainly controlled by PH, availability of complexing ions in the fluid as well as the presence of secondary phases as host REE minerals.

The Kamar-Mehdi fluorite deposit is located 100 km southwest of Tabas in Tabas Block, Central Iran. There are five strata bound orebodies in the area exposing in carbonate rocks of Shotori Formation. The oldest unit is Shotori Formation dolomite of Triassic age that is emplaced in the core of Kamar-Mehdi Anticline. Folding direction in the area is N-S and normal faults with W-E direction have caused some dislocations. Based on field and microscopic evidences, three types of mineralization are identified: 1- Early Diagenetic mineralization which is observed as disseminated in fenestral porosity in Shotori Formation dolomicrites, 2- Late Diagenetic mineralization that occurs as open space filling in vein and veinlets and open spaces of Shotori Formation. 3- Vein mineralization which occurs along with normal faults in the study area. Fluid inclusions studies of late diagenetic mineralization and vein mineralization show that the fluids in the late diagenetic mineralization have salinities between 15 and 26 wt% NaCl equivalent and homogenization temperatures of 150-270oC. Fluid inclusions of the vein mineralization have salinities between 3.4 and 20.2 wt% NaCl equivalent and homogenization temperatures of 140-237 oC. The present study, with consideration on the late diagenetic mineralization and comparing it with vein type fluid inclusions, shows that the diagenetic fluid inclusions have higher salinities and homogenization temperatures. All the evidences show that mineralization at Kamar-Mehdi fluorite deposit is related to Shotori Formation and it is regarded as a fluorite-rich Mississipy Valley Type deposit.

Clinoptiloite transforms to phillipsite under hydrothermal conditions in the presence of alkaline fluids. The effect of Na+ and K+ concentrations, temperature and time are the variable parameters in the present study. Alkaline solutions of KOH and NaCl were used in concentrations of 1.25 up to 7.5mol/lit at temperatures of 100 and 150oC. Results of this study show that phillipsite has been synthesized at 100 and 150oC and high concentration of K+ at the expense of clinoptilolite dissolution. With increasing K+ content of the fluids and reaction time, the amount of phillipsite increases drastically.  Powder X-ray diffraction study has revealed a monoclinic (pseudo-orthorhombic) symmetry with the unit-cell parameters as follows for phillipsite: a: 10.104 A, b: 14.305 A, c: 14.618 A , b: 91.401o.

In this article, we have employed GSAS software to do Reitveld profile refinement on XRD patterns from H-Tc superconductor powder YBa2-xKxCu3O7-y (0<x,y<1) samples. Increasing the Potassium doping content of the sample, x, causes some changes in the XRD patterns such as creating new peaks and also deteriorating of goodness of the refinement, c2. On the other hand, substituting of K instead of Ba led to oxygen depletion and also lowering the Ba (K) plane position along the Z direction (||c). The structural phase ratio of tetragonal to orthorhombic increased and it means that the superconductivity exist even in samples with dominant tetragonal phase.

On the basis of petrographic observations and electron microprobe analyses data set on major and minor minerals from ultramafic- mafic rock suite with komatiitic to picritic-tholeiitic affinity, East of Fariman, we have investigated some of the petro logical features of their parental magmas and condition of minerals crystallization. Major minerals in ultramafic rocks show various disequilibrium textures, including elongated hopper olivines with sharp tips, and spray to acicular, skeletal and hopper elongated pyroxenes, while in mafic rocks disequilibrium textures are dendritic pyroxene-plagioclase intergrowth. Such textures must have been produced by rapid growth of crystals due to undercooling of a previously superheated melt. High Fo contents of olivines is necessary the equilibrium of these crystals in a hot melt with high MgO content. On the basis of maximum Fo content of an olivine crystal in a komatiitic sample, we have estimated MgO percent and temperature of parent melt as much as 23.74% and 1470oC -1535 oC respectively. High TiO2 contents of pyroxene and spinel crystals indicate that their host magma must have been originated from a fertile mantle source, similar to OIB and /or LIP sources, indicating the probable role of a mantle plume in petro genesis of these rocks.

In this paper, a new method for mineral boundary detection is proposed using a model prepared in ArcGIS Model Builder tool. Required data for this method are gray scale images taken from petrographic thin sections. The images are captured in 19 numbers through 90o polarizers and lambda plate rotation with 5o intervals while the microscope table is fixed. Mineral boundaries are detected using the ArcGIS software by comparison of colour intensity amongst the adjacent minerals in sequential images. The presented method is fast and accurate to detect favorite grain boundaries from thin sections, and is able to create a powerful database containing grain shape characteristics. Petrographic study on four rock samples demonstrates that the results of grain boundary detection by the model without operator intervention, are more than 80 percent correlated with manual boundary detection method.

The Southern Caspian Sea ophiolite complex (SCO) is one of the Late Cretaceous discontinuous oceanic lithosphere remnants in northern Iran. These complex is almost a complete sequence from bottom to top, ultramafic cumulates, layered gabbros, isotropic gabbros, dike complex and basaltic lavas which is covered by Late Cretaceous (Companion- maaestirchtian) pelagic limestone. Crustal ultramafic cumulative rocks are mainly composed of dunite, wehrlite, olivine clinopyroxenite and clinopyroxenite. The crystallization order in the ultramafic rocks is: olivine (with high Mg# in clinopyroxene) + clinopyroxene (cumulus and with high Mg#) + olivine (intercumulus and with low Mg#). The mineral chemistry of the ultramafic cumulates of the Southern Caspian Sea ophiolite (SCO) is not consistent with crystal–liquid fractionation of primitive mid oceanic ridge basalts at low pressures. The presence of highly magnesian clinopyroxene (Mg#=81-90), homogenous composition of clinopyroxene, absence of zoning in clinopyroxene together with the absence of plagioclase, as early fractionating phases, indicate medium- to high-pressure (up to 10 kbar) crystal fractionation of primary basaltic melts. Mineralogical and geochemical data suggest that the ultramafic cumulates are distinct from rocks in mid oceanic ridge ophiolites. Mineral composition of clinopyroxene show that the ultramafic rocks of Southern Caspian Sea ophiolite, were formed from the basaltic magma in an island arc/suprasubduction zone tectonic setting.