Iranian Journal of Crystallography and Mineralogy
Year:2010 | Volume:18 | Issue:1|Papers Count:15

Some Fe and Fe-Mn deposits are found within sedimentary pelagic rocks and radiolarian cherts of the Khoy ophiolite. Mn-Fe mineralizations in Safo area north of Chalderan City are examples of them. In Safo area, deposition of manganese occurred as lense-like orebodies in different horizons within pelagic rocks. They are strati form and have syn-sedimentary origin. Mineralogically, braunite, pyrolusite, bixbyite, and hematite are the main minerals present in ore and calcite, quartz and barite are principal gangue minerals.The banded, massive and disseminated textures are seen in ore bodies. Geochemical and geological evidence indicates that deposition of ore minerals took place from submarine hydrothermal solutions (exhalative) on the neotethyan oceanic basin during late Cretaceous time. The Mn/Fe ratios in this deposit are highly variable and ranges from 1.35 to 31.7 with an average of 8. This mean ratio is many times higher than that of mid-ocean metalliferous sediments. The high ratio of Mn/Fe and Si/Al, very low content of trace metals specially Co, Ni and Cu, low values of Y and Ce, and high values of SiO2, Mn, Fe, Ba and Sr provide good evidence for Mn enrichment by exhalative hydrothermal fluids and also for insignificant contribution of hydro genetic processes in formation of this deposit. The study of correlation coefficients among different oxides and elements show that there are no meaningful relationships among Cu, Co and Ni in exhalative hydrothermal solutions rich in Si, Mn and Fe.

In this research, a thermodynamic model used to describe the growth of ZnSxSe1-x single crystals by chemical vapor transport technique with iodine as the transporting agent. The optimum growth condition in the ZnSxSe1-x-I2 system has been predicted theoretically based on partial of different components. Some experiments were carried out for growing ZnS0.5Se0.5 crystals by the chemical vapor transport method using iodine as a transporting agent in the closed ampoule under various conditions. The experimental results showed that the ZnSxSe1-x single crystals, which have been grown with growth parameters close to the theoretically predicted optimum growth conditions, have better quality in comparison with crystals grown under other conditions.

Lower Paleozoic metabasites of south Chah Palang are located in north of the Yazd block in Central Iran with limited distribution and are associated with Doshakh metamorphites. Metabasites divided in to two portions: metavolcanics, and metagabbro, amphibolite and metadiabase masses. Metavolcanic with basaltic composition are presented by foliation and vesicles filled by calcite. Amphibole, plagioclase and biotite are essential rock forming minerals. Actinolite, chlorite, epidote, calcite and albite are index minerals of greenschist facies that found in melanocratic groundmass of metabasites. On the basis of amphibole barometries at pressure of 8kbar, equilibrium temperatures for magnesio-hornblende in amphibolites and for ferro-hornblendes and ferrotschermac-hornblendes in metadiabase are 622 and 659-94oC, respectively. Biotite thermometry indicate crystallisation temperature, 648-665oC for metavolcanic biotites and 585–596oC for biotites of metadiabasic dykes. Petrography and chemistry of minerals reveal alkaline nature of magmatism and polymetamorphism. These metabasites at the first metamorphosed in amphibolite facies and then in greenschist facies.

The study area is located south of Nehbandan, in southern Khorasan Province. There are three mineralization zones with three veins in this area which number two is antimony rich and has anomaly for Au and Hg. This zone is composed of silica-carbonate with stibnite, pyrite, chalcopyrite and Fe-hydroxide. The textures of veins are open space filling, brecciate and colloidal. Mineralization occurred in Paleocene buff color conglomerate in deep seated faults. The basal part of conglomerate is composed of flysch type sediments and blocks of ophiolitic melange. Mineralization fault zones have NW-SE trend. Young volcanic activity occurred as dacite and andesite composition. Based on field evidences, microscopic studies and analytical data, the mineralization occurred in an epithermal system. Chemical analysis show high anomalies for Sb, Au and Hg in these zones. The grades for Au vary between 1.2 to 472 ppb, for Sb 14ppm to 32.48% and for Hg 150 ppm to 1.8%.

The Mississippi Valley Type Pb-Zn ore deposits of northern Semnan could be classified as 1) Eram Series in north-west of Shahmirzad and 2) Shahmirzad Series in south and east of Shahmirzad. The host rocks of these mineralizations are Cretaceous carbonates and fawlts have a major role in controlling hypo gene ore formation. Age, mineralogy and structural evidences of both series show a resemblance similarity in hypo gene ore but there are a lot of differences in carbonate host rock of two series. Petrographic investigations indicate that the host rock of Eram mineralizations precipitated in deep-sea impermeable facies without any dolomitization. While the host rock of Shahmirzad ore deposits exhibit shallow permeable facies and widespread dolomitization. In the Cretaceous carbonate sequence of north-west Shahmirzad, impermeable facies and lack of dolomitization had prevented fluid circulations imply from insignificant lead (<5ppm) and zinc (<20ppm) concentration in the sequence. On the other hand, the impermeability may be had prevented supergene processes in north-western deposits. In addition, oxygen and carbon isotope data show low effects of ore fluids with no any effects of diagenetic fluids on host rock of Eram deposits. Existence of shallow facies, permeability and dolomitization in south and east of Shahmirzad facilitate circulation of fluids in host rock causing Pb-Zn mineralization, consequent supergene mineralizations and raised mean concentration of lead (132 ppm) and zinc (98 ppm) in host rock. This study indicates the significance of epigenetic process and insignificance of carbonate rocks in Pb-Zn mineralization in Eram series. It seems that structure has a major role in all mineralization series.

Taknar mining district is located about 28 Km northwest of Bardaskan in the central part of Taknar zone. Taknar Zone is surrounded by Rivash fault in the north and Dorouneh fault to the south. At least 30 percent of Taknar Formation (Ordovician age) is made up of submarine volcanic rocks. Geological evidence indicates that Taknar Zone displaced from another place to present location. Major structural features which are identified included: right lateral strike slip, left lateral strike slip, overturned and reverse faults. Several intrusive rocks were identified within Taknar mining area. Based on the effect of regional metamorphism, intrusive rocks were classified into two major groups: 1- Mid-Late Paleozoic and 2- after Paleozoic. Mid-late Paleozoic is mainly composed of granite, granodiorite and diorite. Based on Al-index, they consist mainly of per-aluminous and minor sub-aluminous, and mid to high in potassium content. Tectonic setting are includes intraplate granite (WPG) and minor volcanic are (VAG). Based on REE content and (La/Yb) N=9.75-2.15 magma originated from continental crust. Based on magnetic susceptibility, all of them belong to ilmenite series. After Paleozoic intrusive rocks are mainly granite, trondhjemite and quartz monzonite. Except trondhjemite, they are per-aluminous, and the potassium content is mid to high. Spider diagram show enrichment in K, Rb, Ba and Ce and depletion in Sr, Nb, P and Ti. Based on REE content and (La/Yb)N=6.47-4.87 magma originated from continental.

Finite crystallite size and strain in polycrystalline material led to broadening of the diffraction lines. By analyzing this broadening, it is possible to extract information on the microstructure of crystalline material. In this research, we obtained the microstructure of nanocrystalline CeO2 sample using synchrotron diffraction data, applying the whole powder pattern fitting and Williamson-Hall techniques. The volume weighted average crystallite size and the root-mean-square strain both averaged over all reflections found to be 225A and 6×10-5 respectively. In another attempt a model of lognormal size distribution of spherical crystallite has been used and the average volume weighted crystallite sizes of 234 A and average area weighted size of 168A have been determined, respectively.

The (Bi2Te3)0.96(Bi2Se3)0.04 is an n-type thermoelectric semiconductor for using in thermoelectric cooling systems. Single crystal of this composition was grown by Zone Melting Method and thermoelectric power (a 2 s) along the crystal growth where a is the See beck coefficient and s is the electrical conductivity was measured. In this measurement a gradient along length of the prepared crystalline ingot was observed. The structures were characterized by XRD system. The obtained results for compositional variation (Bi2Se3 distribution function) were in good agreement with tentative value of the thermoelectric power measured along the crystal growth. The experimental processes were analytically simulated. Simulation of the growth confirms that, Bi2Se3 concentration of Bi2Te3-Bi2Se3 quasi binary solid solution system was eminent.

Astaneh granitoid intrusion is located in southwest of Arak city that is part of Sanandaj-Sirjan zone.  This intrusive mass alterated under influence of hydrothermal fluids and so propylitic alteration is one of the most important types of alterations in this granitoid. Epidote, sphene, prehnite and quartz are important minerals in this alterated rocks. The weight percent of pistacist in epidote is about 24 so this base epidote origin if saussuritization of plagioclase took place. On the bases of Al and Fe in structural formula of sphene, these minerals are secondary in origin and forms during the alteration processes. Prehnites have low enrichment of iron so formed in low temperature and oxygen fugacity. Normalization of altered rocks to parent rock is indicator of depletion of REE and this depletion increased from propylitic to phyllic alteration. The variations of major oxides relative to immobile oxides of Al2O3 are indicative of increasing of Na2O in all zones except phyllic zone that it is reason of reduce plagioclase basicity. CaO increasing in propylitic zone and finally MgO is only depleted oxide in all alteration zones.

In order to investigate the alteration products of rhyolitic tuffs under alkaline hydrothermal condition, samples of acidic pyroclastic rocks from Darabad area (N-E Tehran) were selected. Rock samples were examined under petrographic microscope, X-Ray powder diffraction, X-Ray Fluorescence and were eventually powdered and mixed with Na+ and K+ bearing solutions in hydrothermal autoclaves. The effect of changes in temperature, time and concentration of cations in solution, alteration of aforementioned tuffs have been studied. The solutions with 1.25-7.5 mol/lit cation concentrations from KOH and NaCl salt have been prepared and used in hydrothermal experiments in 100 °C and 150 °C. The results revealed that in alteration of rhyolitic tuffs, in presence of KOH and NaCl solutions, with increasing temperature, concentration of Na+ and pH, the quality of quartz decreases and the quality of albite increases (sodic alteration). At 150 °C  and high concentration of Na+ and K+ (7.5 mol/lit), quartz dissolves completly, albite changes to orthoclase with cationic exchange of Na+ by K+ (potassic alteration) and forms hydroxy sodalite (zeolitic alteration). XRD studies proposed cubic system with unit cell dimensions of a0=b0=c0=8.8760 A for hydroxy sodalite.

Palygorskite is a widely distributed clay mineral that is commonly found in soils and sediments of arid regions, particularly in the Middle East. This study aimed to determine the distribution of palygorskite in major parent materials of soils developed on central Iranian Tertiary sediments. Based on field observations and geologic maps, 12 geological formations with Tertiary age were sampled and analyzed for mineralogical composition using x-ray diffraction (XRD) and transmission and scanning electron microscopy (TEM and SEM). Results showed that sediments of Miocene and Pliocene ages had the highest amount of palygorskite in the study area. In contrast, no trace of palygorskite was found in samples of Paleocene, Eocene and Oligocene ages. Smectites were highly associated with palygorskite. Stability diagrams for smectite-palygorskite system in Tertiary sediments of different ages showed that geochemical conditions were not conductive for pakygorskite formation during the Late Oligocene. Occurrence of palygorskite in the Tertiary sediments of Central Iran suggests that the most possible source of this mineral in soils of the study area, and probably those of other areas with similar conditions, is the inheritance from parent materials. It seems that the geochemical conditions of the Tethys Sea became gradually suitable for palygorskite formation in the Tertiary sediments of central Iran. Today's arid environment prevailing in central, eastern and southern Iran has led to the stability of palygorskite in soils developed on Tertiary sediments.

Metamorphic sequences have been examined from contact aureole of Mashhad granite. According to field evidences and textural features, contact aureole of Mashhad granite belongs to contact facies series of type 2b. Therefore, a pressure range from 3.5 to 4.5 Kbar and a contact temperature of around 600oC is estimated for the formation of this aureole.

The S-type granitoidic batholith of Shir-Kuh consists of three main granodioritic, monzogranitic and leucogranitic units. The separation of restite crystals from the primary melt, followed by the fractional crystallization, appears to have been an effective differentiation process in the batholith. Small biotite assemblages with higher XMg relative to host flaky biotites, surmicaceous enclaves, the biotite cored by sillimanite, the calcic cores of plagioclase, refractory metasedimentary enclaves and cordierite containing less than 0.5 wt% Na2O are the main putative restites which are widespread in more mafic rocks of the batholith. In addition, inherited zircons, monazite and apatite, which are enclosed in biotite, would be considered as restite. Geochemical criteria emphasis the petrographic evidences. Accordingly, the anatexis of upper crust is likely to have been mainly controlled by biotite breakdown.

Mineralogical and geochemical investigations indicate two general stages of skarnification i.e, prograde and retrograde stages in the Mohammad-Abad district, south west of Yazd province. Metasomatic skarn (Prograde stage) occurred with precipitation of anhydrous calc-silicate mineral assemblages (andradite and diopside-hedenbergite) within the temperature ranges of 470 to 550oC. During the retrograde stage (<470oC) considerable amounts of anhydrous calc-silicates were altered and replaced by a series of hydrous calc-silicates (epidote, tremolite–actinolite). Finally, both anhydrous and hydrous calc-silicates were altered to fine aggregates of chlorite, calcite, quartz and clay minerals at temperatures lower than 300 oC. The absence of wollastonite among the calc-silicate assemblages may suggest that andradite and hedenbergite were crystallized from metasomatizing fluids at lower than 550 oC in the Mohammad-Abad skarn. The presence of intergrowth texture and non-replacive crystal boundaries between garnets and pyroxenes suggest that they were formed contemporaneously within the temperature and fO2 ranges of 430–550oC and 10-26–10-23, respectively. Andradite converted to quartz, calcite and magnetite below 470 oC and fO2=10-24–10-21. Since, both magnetite and pyrite along with quartz and calcite are present in mineral assemblages of sub-stage III, it can be reasoned that the metasomatizing fluids probably had an approximate fS2 10-6.5 and a temperature of about 430 oC.