مجله بلور شناسی و کانی شناسی ایران
سال بیست و یکم شماره 3 (پیاپی 53، پاییز 1392)

Significance of chromite, as the unique source for chromium, a metal with key role in industry, has inspired many geologists to investigate its genesis and natural distribution as an important contribution to its exploration in many parts of the world. To do this, geochemistry of chromite, which is considered to be the reflection of the nature of its parent magma and the geotectonic setting in which it is generated, is extensively used by many researchers. To reveal the nature of chromite’s parent magma, its chemical composition is used as a petrogenetic indicator. In this regard many authors have classified chromite deposits as either high-Al (Al2O3 0 25 wt %) or high-Cr (Cr2O3 0 45 to 60 wt %) and have demonstrated that Al-rich chromites are generated from tholiitic and Cr-rich ones from Mg-rich boninitic magmas, two melts generated in distinct and different geotectonic setting. In this study on the basis of geochemistry of chromite samples from three nearby mining districts in Sabzevar Ophiolite Range, in the North-East of Iran, the nature of chromite parent magma and its geotectonic setting is investigated. Chromite samples are analyzed by EPMA method. The layered chromitite bodies, embedded in serpenitnized dunite, are displayed to belong to high-Cr deposits. Considering high Cr# (86-88), moderate Mg# (44-51), low TiO2 content (0.1 0.2 wt %) and other geochemical features of chromite, the parent magma dominantly accords with a high Mg# boninitic melt. According to the results of the previous works and petrography, geochemistry (especially Cr#, Mg#, Fe+3 and TiO2 contents) and field observations represented in this work, the chromitites must be generated in a suprasubduction zone setting. Sea floor hydrothermal processes have probably caused especially, the Mg# not to be as high as expected.

The polymeric compound, {(C10H9N2)[Mn(C7H3NO4)2].(C10H8N2).6H2O}n, was prepared by the reaction of manganese (II) nitrate with pyridine-2,3-dicarboxylic acid, (py-2,3-dcH2) and 4,4'-bipyridine (4,4'-bipy) in a 1:2:4 molar ratio. The crystal system of the complex is monoclinic with space group P21/n and four molecules per unit cell. The unit cell parameters are: a = 22.2099(15) Å, b = 6.6599(4) Å, c = 23.5921(16) Å and 9 = 104.014(3)°. The final R value was 0.04 based on 8960 reflections. The central atom is attached to two (py-2,3-dc)2– ligands through their N and O atoms in a planar square arrangement and two O atoms from bridging carboxylate groups, forming polymeric chains. So, the anionic complex features six-coordinate Mn (III) with a distorted octahedral geometry. In the crystal structure, a wide range of non-covalent interactions consisting of hydrogen bonding (of the types O>H···O, O>H···N and C>H···O), ion pairing, and @–@ (centroid-centroid distances of 3.607 and 3.721 Å), C>H···@ (with H···@ distance of 2.941 Å) and C=O···@ (with O···@ distances of 2.943, 3.702 and 3.743 Å) stacking interactions stabilize the supramolecular structure.

Panah Kuh skarn is located about 50 km northwest of Taft City in Yazd province. The intrusion of Panah- Kuh stock with granodiorite-quartz diorite composition into the limestone Jamal Formation has led to the skarnification in this area. Field and mineralogical observations show that Panah-Kuh skarn included two endoskarn and exoskarn zones. Exoskarn is calcic type and magnesian skarn which formed in contact with the marbles whereas endoskarn formed with restrict development into intrusion. Dominated minerals are garnet (andradite) and pyroxene (diopside-hedenbergite) in the calcic skarn and forsterite, diopside, serpentine and talc in the magnesian skarn. At least two paragenetic stages of skarn formation have been recognized. The early skarn formation (stage I) was dominated by anhydrous minerals such as pyroxene and garnet in the calcic skarn and forsterite and diopside, in the magnesian skarn. According to mineral assemblages which formed at this stage, it can be concluded that the temperature range was less than 500 0C. The hydrous skarn assemblage such as serpentine and talc (stage II) replaced early-formed skarn assemblages. The mineralogy and geochemical characters of Panah-Kuh skarn is consistent with deposition under oxidized conditions, formation at shallow crustal levels and similar to those of Fe bearing skarn system. 

The rhyolitic flows and sills in the extremity of Ghal'eh-chay river (East of Ajabshir, East Azerbaidjan) are exposed in the Lalun sandstone deposits. Compositionally, these rocks are rhyolite and are composed of euhedral quartz phenocrystals and subhedral perthitic orthoclases in a glassy to fine grained matrix containing quartz, k-feldspar and minor sodic plagioclases. There are not any ferromagnesian mineral except traces of decomposed and altered biotites. These rocks are highly differentiated and hololeucocratic in color and belong to the A-type series and the parental magma has calc-alkaline to shoshonitic characteristics. The REE distribution pattern in these rocks has a gentle negative slope and gives remarkable negative Eu anomaly. Negative Ba, Eu and P anomalies and non-depleted HREE pattern as well as relatively flat HREE distribution pattern show the emplacement of these bodies in a tensional within-plate regim related to initial movements of Caledonian epirogenic phase in continental crust.

The chemical composition of amphiboles from granitoid rocks of Selijerd and Neshveh plutons in NW Saveh, Central Iran, are studied for petrogenetic purpuses, tectonomagmatic features and geotermobarometery of these plutons. The chemical composition of these amphiboles falls in the calcic amphibole group and is actinolite to magnasio-hornblende. They are assosiated with the active continental margin subduction-related zone and formed in relatively high oxygen fugacity. Based on the geotermobarometeric methods, amphiboles from these plutons formed in temperatures ranging from 700 to 750 ° C and low pressures ranging from 0.3 to 1.2 kilobars equivalent to a depth of approximately 1 to 4.5 km, respectively.

Garnet is the most abundant calc-silicate mineral in the Darreh Zereshk skarns, and occurs as grained euhedral, to massive anhedral, isotropic to anisotropic crystals and display concentric and sector zoning or no zoning. Based on mineralogical investigations and paragenetic relations, garnet formed during progrademetasomatic stage of skarn formation. Geochemically they display two different patterns, i.e: (1) LREE-enriched and HREE-depleted, with strong positive Eu anomaly and (2) HREE-enriched and LREE-depleted with small Eu anomalies characteristic of andraditic and grassuleritic garnets, respectively. Electron probe micro analyzer (EPMA) identifies the garnets from Darreh Zerreshk skarn as grossular–andradite (grandite) solid solution series, with a less contents of spessartine and pyrope components. This is significant of a composition similar to Cu, Fe and Au skarn.

Pirkuh region is a part of western Alborz. The outcrops in this region are mostly Paleogene volcanosedimentary successions which are crossed by several intrusives. Some of these intrusives have monzogabbroic, monzonitic and granitic compositions with granular or porphyritic textures. Pronounced harmony among REE patterns of these rocks like more enrichment of LREE than HREE, flat pattern of HREE, negative EU anomaly, steep LREE and smooth MREE slopes, all certify common origin for them. Metaluminous character, existence of normative diopside, presence of clinopyroxene as major mafic mineral in all groups (even in granitic rocks) with biotite, lack of  mica-rich metamorphic enclaves, high relative Na2O content, Al, Ga and Y behaviors, K2O/MgO weight ratio, SiO2 weight percent variation ranges, low K2O/Na2O ratio, enrichment of LREE to HREE all are suggestive of I nature for these intrusives, and  Zr behavior against SiO2  (increasing in intermediate and decreasing in more felsic rocks) are representative of Zr-undersaturated original magma because of high temperature. Therefore Pirkuh region intrusives are set as high temperature I type granite category (similar behavior of Ba, Ce and Y confirm this claim). The REE pattern and position of Pirkuh intrusive data on discrimination diagrams shows that they belong to a continental arc (VAG) setting

The study area is located in North-East of Lut block, and in Basiran Geological Quadrangle Map (1:100000).Tertiary intrusive-subvolcanic rocks intruded Paleocene limestone and formed skarn and Iron mineralization. Petographic studies show that rocks are Hbl-diorite porphyry, Hbl-qtz- diorite porphyry, Px- diorite porphyry, Hbl-px- diorite porphyry, Hbl-diorite and Bt-diorite. These rocks are subalkaline, meta-aluminous and based on magnetic susceptibility and geochemical features; they belong to magnetite series and I-type granitoids. Enrichment of samples in LREE and depletion in HREE and small negative Eu anomalies imply continental margin volcanic arc metaluminus I-type magmatism. Depletion in HREE probably is due to garnet in source. On the tectonic discrimination diagrams, all samples fall within the volcanic arc granite. Different geochemical diagrams show correlation between Bishe granitoids and intrusions associated with Iron skarns.

Gabbroic pluton of Bagham is located in southeastern Ardestan and has intruded into Eocene volacanic rocks. The study area is a part of Central Iranian zone and Urumieh-Dokhtar magmatic belt. Clinopyroxene, plagioclase and amphibole are main minerals in the pluton. Mineral chemistry studies show that clinopyroxenes are augite and are plotted in almost medium pressure field. The clinopyroxene composition yields the crystallization temperatures that range from 840°C to 920°C. In tectonic setting diagrams, clinopyroxenes is plotted in orogenic field and related to magmatic arc. Amphiboles plot in the field of calcic amphiboles and are magnesiohornblende. Tectono-magmatic study indicates a sub alkaline nature for the pluton. The coexisting amphibole-clinopyroxene geothermometer shows the temperatures range from 730 to 790 °C. Plagioclases are only felsic mineral in the gabbros. The mineral chemistry of plagioclases shows bytonite (core), labradorite - andesine (rim) and albite (results of saussuritization) fields.

Khunik area is located in eastern Iran, about 106 km south of Birjand. Preliminary prospecting in the area, using ASTER mineral mapping (SAM) for locating possible alteration zone in the area provided satisfactory results when checked with field observation. The area comprises outcrops of Paleocene to Eocene volcanics, which was intruded telescopically by several subvolcanic intermediate bodies. Alteration is related to some of these units. The main alteration types are propylitic, argillic and sericitic. Mineralization observed at the surface as disseminated and hydrothermal breccia. Maximum amount for distribution of gold, silver and arsenic are in places within stream sediments where upstreams alteration zone of  propylitic, argillic-silicified and hydrothermal breccia are located. The range of variation for elements in the lithogeochemistry samples are as follows: Au from 2 to 46000 ppb, Ag from 40 to 9080 ppb, As from 7 to 134 ppm, Cu from 21 to 601 ppm, Pb from 4 to 1485 ppm. The highest Au and Ag anomalies are associated with hornblende monzodiorite porphyry and monzonite porphyry. Type of the mineralization, as disseminated and associated with hydrothermal breccia, the extent of alteration and its relation with lithology and structural geology indicate the presence of an epithermal gold deposit.

The electrogeochemical method is a new exploration technique with a foundation of electrochemistry. The method has ability to detect hidden ore deposits which have been covered with overburden placers and topsoil. Although this technique is unique and powerful, no attempt was made in our country to apply this new method practically so far. In this method an artificial DC electrical current has been injected into the topsoil over hidden ore deposit which causes ionization, ion concentration and migration towards an especially designed cathode. The anode is an steel electrode while the cathode is made from graphite which has been fixed in a semi-permeable container full of acid. Then the DC current will be injected into the cover soil. After some time (at least several hours), due to ionization of metallic orebodies and electrochemical processes, metallic ions will be migrated towards cathode and will be concentrated in acidic electrolyte. Using AAS or ICP analytical methods the metallic ions will be analyzed in the acid. Before applying the technique in the field, the ability of the method was evaluated with different ore and soil situation and conditions in the laboratory scale. According to our findings, the factors such as depth of mineralization, soil moisture, the amperage and voltage of injected current, injection time and acid concentration as electrolyte are the most important factors influencing the method. The optimum amperage and time injection have been identified as 500 mA and 8 hours, respectively.

In this study, a series of copper substituted in nickel–zinc ferrite nanoparticles with composition of Ni0.3Zn0.7-xCuxFe2O4 (where x = 0.1 - 0.6 by step 0.1) were synthesized by sol-gel method. The effect of Cu substitution on phase formation and crystal structure of sample were investigated by X-Ray diffraction (XRD), Thermogravimetry (TG), Differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Moreover the room saturation magnetization of samples was studied by Vibration sample magnetometer (VSM). Hysteresis loops measurements exhibited an increase in the saturation magnetization value (Ms) up to sample with x = 0.3 followed by a linearly decrease. The increases in the coercivety (Hc) with increase in copper content is attributed to the bigger magneto crystalline anisotropy of  Cu2+ ions compared with Zn2+ ions.

Boznein vein-type has penetrated in the porphyric rhyolite-hosted and along a single northeast-trending reverse fault. Microscopic studies and electron microprobe data, show the presence of a variety of Mn minerals such as spessartine, rhodochrosite, bixbyite, hausmannite, braunite, pyrolusite, psilomelane, cryptomelane, manganite and mangano-calcite in the Mn deposit as well as braunite, pyrolusite, psilomelane, calcite, mangano-calcite and rhodochrosite in volcanoclastic sub-unit of Fe-Mn-carbonate-bearing tuff (E6vct). The mineralogical characteristics of workshop No. 1 along with its higher topography indicate that it has experienced more intense supergene activity. Field evidence, mineralogical studies and electron microprobe analyses on carbonate volcanoclastic unit (E6py & E6t) confirm genetic relationships between Mn deposit and sedimentary-volcanic sequences. It is thus concluded that hydrothermal fluids leached manganese and carbonates from the volcanoclastic rocks and then upon reaching favorable conditions, deposited these minerals along major and main faults in the region.

The Chah ruii area in southwest of Nehbandan contains two types of tourmaline pegmatites. Type one (type CH) pegmatites are found in the granitoid body and type two (type D) pegmatites in metamorphic rocks around the granitoid. Based on petrography and electron microprobe analyses these tourmalines show schorl- dravite, and located in alkali groups and have high Al contents and deprotonation-substitution and alkali- substitution. The spider and REE diagrams in tourmaline indicate that both groups have similar patterns but the  rate of trace elements are different, and the reason for  more rate of trace elements in tourmaline CH type are setting in granitoid rocks. Then, based on analytical studies, it appears that tourmalines form by interaction of postmagmatic/ residual or hydrothermal fluids related to Chah ruii granitic magma with Deh Salm metamorphic rocks. Temprature variations in formation of mineral types in the pegmatites are very important.

Amphibolites are one of the major rock units in the Posht-e-Badam ophiolite that are formed by metamorphism of basalts. There are tow types of amphibolite in the Posht -e- Badam ophiolite: 1) amphibolites with intermediate plagioclase (first type), amphibole, plagioclase, quartz, sphene, ilmenite, apatite, sericite and epidote, 2) amphibolites with high content of anorthite (second type), amphibole, plagioclase, quartz, and muscovite, with mior amounts of garnet, ilmenite, sphene, prehnite, chlorite and leucoxene. Amphibole barometry and amphibole - plagioclase thermobarometry conclude 6.16 to 7.79 kbar and 650 to 738 ◦c (amphibolites facies) for the first type of amphibolites and 4.47 to 9.31 kbar and 930 to 1566 ◦c (granulite and higher P - T codition) for the second type. The proposed high temperature for the second type of amphibolites can attributes to the prehnitization of some plagioclases (M1) before metamorphism of the amphibolite facies (M2). High anorthite plagioclases are formed by metamorphism of prehnite. Presence of prehnite, chlorite, epidote, sericite and leucoxene indicates occurrence of a retrograde metamorphism in the greenschist facies (M3) which follows the amphibolites facies metamorphism. It can be concluded that this Paleozoic ophiolite has suffered three phases of metamorphism M1 (EarlyCimmerian), M2 (Middle Cimmerian) and M3 (LateCimmerian) in the Mesozoic.

SnO2 nanotubes have been synthesized via sol-gel template method using alumina membrane. Synthesis parameters, such as sol preparation conditions, the required time of immersion and annealing conditions, were optimized to obtain the SnO2 nanotubes with well defined composition. Transmission electron microscopy (TEM) and X-ray diffraction techniques have been used to investigate the structure and morphology of SnO2 nanotubes. TEM image showed that the nanotubes have been obtained. The diameter of the obtained nanotubes were approximately 200 nm, were consistent by the pore size of alumina template. The optical transmittance and absorption spectra show that the nanotubes are semi-transparent against visible spectra whereas they absorb the ultraviolet waves. The optical bandgap were measured (3.56 eV) very close to that of the bulk materials.

The studied shear zone is located in E-Qorveh (Kurdistan). The rocks of this zone are granite and granodiorite in composition. In present paper, deformed rocks, protomylonites and mylonites, are investigated in Sangin-Abad, Koh-e-Gazgaz and Poloserkan areas. Petrographic studies show that evidence of tectonic activities are such as myrmekite, recrystallized and slide alkali feldspars, fractured plagioclases, dynamic quartzes, perthitic orthoclase, feldspar crystals with enriched rim from alkalis (mantled texture) with Or 91.19 - 91.54. Comparing geochemical data of whole-rocks and primary rock (protolith) reveal that there are varieties in abundances of main elements such as increasing of CaO، MnO، TiO2 & P2O5 in protomylointes and mylonites. Also, quartz-rich veins and plagioclases altered have observed in the zone. These examples are interpreted to present activities of hydrothermal fluids and open system. The Feldspars are sodic-potsic and sodic in composition in Sangin-Abad & Koh-e-Gazgaz, and Poloserkan. Overall, relationship field, microstructural, textural, geochemical and mineral chemistry characteristics confirm role of the shear zone for formation of these features.  Many of researchers have approved relationship between forming of microstructures with stress/ strain and hydrothermal fluids. The studied biotite crystals with content of (∑FeO + MnO ≈ 13.4-42.21) are neoform. They may be occurred by post-magmatic fluids of the Qorveh granitoid batholith. Formation temperature of biotites is ~550 to ~750 ºC which corresponds to this deformation temperature.