Iranian Journal of Crystallography and Mineralogy
Year:2012 | Volume:20 | Issue:2|Papers Count:17

The present study investigates the shape preferred orientation (SPO) and crystal preferred orientation (CPO) of quartz crystals using electron backscatter diffraction (EBSD) in andalusite-cordierite schist from the Ythan Valley, Aberdeen shire, in the Scottish Dalradian block. Quartz crystals in the matrix and andalusite pophyroblasts have inequant to slightly equant shapes. Quartz crystals show weak SPO in the matrix and andalusite pophyroblasts, which are sub-parallel to each other. The weak SPO in quartz crystals of the studied sample can be related to (1) Grain boundary migration of quartz crystals and (2) non-quartz crystals (e.g. mica) at junction of quartz crystals. Also, quartz crystals show random CPO in the matrix and inclusion. The lack of CPO of quartz crystals in the matrix can be explained by (i) absence, or low amounts of strain in the rock that is experienced only low temperature and pressure and (ii) diffusion creep. The random crystallographic orientation of quartz inclusions may confirm non-selective orientations of the matrix quartz crystals by andalusite pophyroblast during growth.

Tang-e-Hana skarn is located at part of the Zagros ophiolitic sequence, and then it is considered as a part of the Zagros structural province. According to the current study, this skarn is classified in 4 main groups: 1- Wollastonite skarn 2- Augite wollastonite skarn 3- Grossular wollastonite skarn 4- Andradite titanite augite wollastonite skarn. Geochemical characteristics indicate that Tang-e-hana skarn is lies in the calcic skarn domain. In addition, percentage of TiO2 in the fourth type of these skarns (bearing titanite) reaches 4%. This fact is important for concentration of REE and other trace elements in titanite. The field and mineralogical evidence illustrated that the studied skarns are endoskarns. These evidences include a high percentage of calc-silicate and non-metallic minerals and in contrast a low percentage of metallic minerals. Therefor, Tang-e-hana skarn is important for its non-metallic minerals such as wollastonite and garnet. The study of mineral paragenetic sequence and the variation diagrams of %TiO2 and %Al2O3 per %CaO suggested that wollastonite skarn is formed at the early stage and andradite –titanite – augite - wollastonite skarn at the late stage of skarnification.

Galali orebody is located in Sanandaj-Sirjan zone in west of Iran in the Karamkhani slops in Almogholagh mountains. The main ore is magnetite association with hematite, goethite, secondary limonite, malachite and pyrite. This orebody is located on north Galali fault, mineralization is made by fault movements in this orebody. Three types of ores have been seen in the Galali orebody as below: Type I: this ore is made of compact, high density and high grad magnetite. Fine grain, subhedral to unhedral pyrite has found in this type as minor mineral. Pyrite is dispersed in magnetite. Type II: this ore type are made of silicates, oxides and sulfides, this phase is injected in the type I minerals. Type III: the hydrothermal goethite is the third type of ore in the Galali orebody. Skarn, epydotization, dolomitization and some argilic veins are alteration haloes around the orebody. Evaporatic origin is recognized for sulphur isotopes in this study.

The Argash antimony ore deposit is located at south of Neyshabour and the eastern part of the Sabzevar zone. This deposit occurs within a sequence of Eocene-Oligocene volcanic intrusion rocks. The mineralization occurs as open space filling, taking place as irregular veins, veinlets and hydrothermal breccias. The mineralogy of the veins is comparatively simple. The primary antimony-bearing mineral is stibnite. Other sulfides have been found in association with stibnite are pyrite, chalcopyrite and sphalerite. Quartz, illite, adularia, chlorite, epidote and kaolinite are the main hydrothermalg gangue minerals occurring around the veins. Hydrothermal alteration is zoned around the veins and consists of three major types including silicification within the immediate veins, argillic alteration enveloping the veins, and propylitic alteration distal to the veins. The intensity of silicification and argillic alteration decreases with depth and away from the veins. The evaluation of the geochemical data set based on multivariate statistical analyses indicates positive correlation between Zn, Ag, As and Sb and the same distribution pattern of these elements in the boreholes. The mineralogical, alteration and geochemical characteristics of the studied area and comparison with epithermal ore deposits indicate that the Arghash quartz-antimony veins represent an epithermal system of the lowsulfidation type. This data suggests that boiling and cooling were the main ore deposition processes in the area.

The study area is located at 130 km northwest of Nehbandan in South of Khorasan and is a part of the rectangular Chahvak (Dehsalm). Dacite, rhiodacite, andesite, rhyolite, tuff and lithic tuff with Eocene age are recognized in the study area. According to mineralogy, mentioned rocks include plagioclase, quartz, pyroxene, amphibole, biotite and alkaline feldspar. Plagioclase consists of zonal structure and amphiboles include a burned rim that this phenomenon is a sign of high temperature magma. Based on chemical classification, studied rocks are andesite, truckyandesite, andesitic basalt, rhyolite, dacite and rhiodacite. According to the petrologic graphs, the studied rock magmatic series have a nature ultraptasic calc-alkaline, Also by using from the separator graphs of tectonic setting, mentioned volcanic rocks have been located in subduction zones. Negative anomaly of elements P, Nb and Ti and positive anomaly of Pb and K in these rocks indicate the similarity of chemical properties of these rocks with volcanic arcs magmatism.

Hornblende biotite bearing tonalite from the west of Dehnow comprises of quartz, calcic plagioclase (andesine-labradorite), garnet (mostly almandine), biotite (annite to siderophyllite), calcic amphibole (mainly ferrohornblende) and accessory minerals of chlorite, epidote, calcite and ilmenite. According to thermo barometry of amphibole, plagioclase as well as the chemistry of garnet that shows CaO content of about 4.91-5.48 wt% and MnO content of about 1.89-2.40 wt%, the garnet in tonalite has crystallized in the temperature and pressure range of 696 to 950°C and 6.4 to 12 kbar, respectively, and which is in a greater depth than that of amphibole and plagioclase.

Hasht-Sar Kaleybar mafic, ultramafic and syenitic dykes are surrounded by Majid Abad Formation, Palaeocene age, volcanic deposits. The suite is restricted within the Horand, Mahmud Abad and Mokhtekan thrust and reverse faults. Clinopyroxenites, the oldest unit of the suite, have tholeiitic volcanic arc character and have some similarities with tectonite layer of oceanic crust, like Group A pyroxenites of the Ronda massif, Spain. The surrounding gabbro is the calc-alkaline part of volcanic arc. Clinopyroxenes composition of the two above units, is comparable with oceanic post-cumulates. Quartz and nephelin syenitic dykes, the youngest unit, crop out interior of the mafic-ultramafic rocks. Shoshonitic, I-type and post-collisional affinities of the dykes determined by geochemical studies. Considering the geological position, the Hasht-Sar plutonic suite is probably related to the Secondary Palaeo-Tethys subduction events.

The study of Microprobe Analyses in different tourmaline bearing unites in Boroujerd area, for example, quartz tourmaline veins in Nezamabad quartz diorites, Aplitepegmatite tourmaline bearing Ghalesamorkhan, Gijali and Kabotarlan granodiorites, pegmatite veins in Kolahjob schist and nodular tourmaline in Dehgah and Astaneh show that most tourmalines in Boroujerd area are schorlite. Needle like Ghalae Samorkhan and some samples from Kolahjob-Gijali are foitite. Euhedral and none zoning, high Fe/Fe+Mg, low X site vacancy and high Al amount in more of tourmaline are reasons of magmatic source. The occurrence of tourmaline in peraluminous granite Dehgah and Astaneh is evidence of enriched B magma source. Therefor, the studied area tourmalines depend of granitic source and originate of hydrothermal fluid to magmatic source.

The Surk ophiolitic melange is located at the south west of central Iran and along the Naein-Dehshir-Baft ophiolitic belt. In petro logical sequence, peridotites are nominated the undermost part of rock unit, and then gabbros and volcanic rocks are at the following ranks respectively. The predominant peridotitet of this ophiolitic melange is harzburgite. Lherzolite that is the primitive mantle rock consists of olivine, orthopyroxene, clinopyroxene as major minerals and chromian spinel and amphibole (pargasite) as accessory mineral. Petro graphical characteristics and mineral chemistry of these peridotites show the lithology evaluation from lherzolite to harzburgite and dunite ultimately. The average SiO2 and Na2O content of volcanic rocks in the ophiolitic melange are 70 and 5 weight percent respectively. Petro graphical investigations and also classification of these volcanics based on major and trace elements and norm calculations show that these rocks are dacite. REE/chondrite normalized diagrams of these volcanic rocks show horizontal to positively sloping patterns, LREEs are lower than HREEs and their La/Yb ratio is lesser than 1, suggest tholeitic nature of their parent magma. Moreover, Hf/Zr, U and Pb contant of these rocks is higher than the content in the Primitive mantle but the Sr, Ti and Y contant is lower. These differences can be caused by melt migration of subducted oceanic lithosphere on mantle peridotites. By melt/rock reactions clinopyroxene dissolution, incongruent melting of orthopyroxene, formation of replacive olivines and SiO2 increasing in ascending melt will occur. All these characteristics propose that the Surk ophiolitic melange is a Harzburgite Ophiolitic Type (HOT) which is formed at the supra-subduction (back-arc basin) zone.

Mahour polymetal deposit located west of Nehbandan, east-central Iran, formed in hypabyssal acid rocks. Mineralization occurs along a three-km-long vein. Three zones have observed in the ore, downward: 1) leached zone marked by malachite, azurite, hematite, goethite and limonite, 2) supergene zone characterized by bornite, covellite, and chalcocite, and 3) Hypogene zone containing magnetite, chalcopyrite, pyrite, galena, and sphalerite. The significant alterations are silicic, sericitic, and propylithic. Gangue minerals are mainly composed of quartz and calcite. The textures vary from replacement and open-space filling to brecciate. Fluid inclusion study of three samples of sphalerite is indicative of temperature variation of the ore-forming fluids between 194oC and 292oC. Considering the measured icemelting temperature (Tm ice), the salinity is estimated to be between 11.7 and 23 equivalent weight of NaCl (wt%). Mineralogical and fluid inclusion evidence such as texture and structure of mineralization, vein mineralization, mineral para genesis, gangue minerals, wall-rock alteration, homogenization temperature and salinity and trapped fluids, and depth of mineralization, all suggest that the Mahour deposit is a vein-type epithermal to mesothermal deposit.

Uranium becomes soluble and mobile under oxidizing conditions in aqueous environment, and presence of complexing agents with uranium increase this mobility. Existence of such conditions in ground waters of Ayrakan and Cheshmeh Shotori areas has led to oxidation, solubility and mobility of uranium minerals. Hydro geochemical study of uranium in the study areas reveals the presence of bicarbonate ion, as the complexing agent with uranium (UO2 (CO3) 22-) and icreasing factor of uranium mobility in ground waters. Calculating the uranium mineral's saturation index also indicates the super saturation of water samples in pitchblende. The positive saturation index of pitchblende expresses the proper water flow rate to steady-state equilibrium with probable uranium mineralization in depth and indicates that the permeability of ground waters by porous flow has provided the enough time for their contact with hidden uranium mineralization (uranium ore deposit). As a result of this contact and because of the presence of carbonate complexes, solubility and mobility of uranium has increased. Hydro geochemical studies, high activity of water and soil samples and all the above evidences indicate the possibility of existence of hidden uranium mineralization in depth and the distance between Ayrakan and the Cheshmeh Shotori areas.

The study area is located in the southern part of Qorveh granitoid complex. Investigation of textural and mineral chemistry evidence in granitoid host with composition of granodiorite, granite, qtz-monzonite, and mafic micro granular enclave (MME) with composition of qtz-diorite to meladiorite, are focused in this paper. Microscopic study and data of microprobe analyses in host and enclave rocks reveal disequilibrium textures and compositional (such as, tabular plagioclase with inclusions, sieved, zoned and resorbed plagioclases, needles of apatite, overgrowth of felspars and zoned amphiboles) in the granitoid host and mafic micro granular enclave. Because of agreement between the textural and mineralogical evidence, we accept the Elburg theory that globules (drops) of mafic magma and host granitoid rock have mixed and effective process in formation of enclave is a simple mechanical magma mixing (magma mingling), ceased by mafic magma stopping in a felsic magma chamber. This fact is linked to geochemical conditions and tectonic setting of the complex in Sanandaj-Sirjan Zone, as a remained zone of subduction setting.

Intrusion of granodioritic bodies into the lime stones of Ghorveh area led to the formation of calc-silicate marbles and various types of skarns. These skarns consist essentially of calcite, clinopyroxene, garnet, wolastonite, vesuvianite and epidote. Based on geochemical studies, garnets were identified as grossular and anderadite. The clinopyroxene found in the skarns is diopside. With respect to mineral assemblages identified in the skarns and using various calibrations of garnet-clinopyroxene geothermometery, the temperature of skarns is estimated to be in the range of 450 to 587oC corresponding to hornblende hornfels to lower field of pyroxene hornfels facies.

In this paper, in order to investigation the effect of calcination temperature on the structural and magnetic properties of cobalt nanoparticles, samples have been prepared by Coprecipitation method at different calcination temperature. Cobalt nanoparticles have been prepared by Co-precipitation method at room temperature using hydrazine as reducing in ethanol hydrazine alkaline environment. This agent reduces cobalt salts to Cobalt nanoparticles in FCC and HCP phases. Phase analysis and investigation of Structural properties of the samples using X-ray diffraction patterns (XRD) confirm the formation of hexagonal phases of Co nanoparticles. Transmission electron microscopy (TEM) was used for determining the size and shape morphology of nanoparticles. Magnetic properties of these nanoparticles have been investigated using a Vibrating sample magnetometer (VSM). The results indicate that these nanoparticles are ferromagnetic at room temperature. In addition, in this paper Co nanoparticles coated with silica shell have been prepared by the wet chemical method. TEM images showed the cobalt core with average diameter of 17-20 nm coated by a silica shell with thickness of 5-7nm. Hysteresis Loop of these Co nanoparticles coated by silica shell illustrates 16.9 emu/gr for saturation magnetization at 10000 (Oe), which is much less than that of Cobalt nanoparticles.

Nanostructure Forsterite powder was prepared by Sol-gel method and its microstructure was studied at a number of annealing temperatures using Rietveld structure and microstructure refinements. It was found that Sol-gel method used in this experiment does not produce pure Mg2SiO4 nano powder. Instead the product is a mixture of Mg2SiO4 and MgO phases with approximate weight fractions of 75% and 25%, respectively. X-ray diffraction line broadening analysis revealed the crystallite shape is nearly spherical with the volume weighted average size of 20–50 nm in the annealing temperature range of 800–1100 oC. More investigations considering anisotropic line broadening confirmed the crystallite size and lattice strain are hkl dependent, but the anisotropy of strain is more pronounced.

In this work, barium zirconate nanoparticles were prepared by sol gel technique in four different conditions. In these conditions zirconium n-propoxide (Zr (OPrn) 4) was used as the source of zirconium. Also barium hydroxide (Ba (OH)2.8H2O) and barium acetate (Ba (CH3COO) 2) were used as the source of barium. Water and isopropyl alcohol were used as the solvents. The samples were characterized by SEM and XRD. The optimum preparation condition was chosen considering the production time, the sintering temperature, homogeneity and the particle size of obtained nanoparticles. In optimum condition, the BaZrO3 nanoparticles were produced at 100oC with about 80 nm in size.