Iranian Journal of Crystallography and Mineralogy
Year:2010 | Volume:18 | Issue:2|Papers Count:19

The Maherabad gold-rich porphyry copper prospect area is located in the eastern part of Lut block, east of Iran. This is the first porphyry Cu-Au prospecting area which is discovered in eastern Iran. Fifteen mineralization-related intrusive rocks range (Middle Eocene 39 Ma) in composition from diorite to monzonite have been distinguished. Monzonitic porphyries had major role in Cu-Au mineralization. The ore-bearing porphyries are I-type, metaluminous, high-K calc-alkaline to shoshonite intrusive rocks which were formed in island arc setting. These rocks are characterized by average of SiO2> 59 wt %, Al2O3 > 15 wt %, MgO< 2 wt %, Na2O> 3 wt %, Sr> 870 ppm, Y< 18 ppm, Yb< 1.90 ppm, Sr/Y> 55, moderate LREE, relatively low HREE and enrichment LILE (Sr, Cs, Rb, K and Ba) relative to HFSE (Nb, Ta, Ti, Hf and Zr). They are chemically similar to some adakites, but their chemical signatures differ in some ways from normal adakites, including higher K2O contents and K2O/Na2O ratios and lower Mg#, (La/Yb)N, (Ce/Yb)N and eNd in Maherabad rocks. Maherabad intrusive rocks are the first K-rich adakites that can be related with subduction zone. Partial melting of mantle hybridized by hydrous, silica-rich slab-derived melts or/and input of enriched mantle-derived ultra-potassic magmas during or prior to the formation and migration of adakitic melts could be explain their high K2O contents and K2O/Na2O ratios. Low Mg# values and relatively low MgO, Cr and Ni contents imply limited interaction between adakite-like magma and mantle wedge peridotite. The initial 87Sr/86Sr and (143Nd/144Nd)i was recalculated to an age of 39 Ma (unpublished data). Initial 87Sr/86Sr ratios for hornblende monzonite porphyry are 0.7047-0.7048. The (143Nd/144Nd)i isotope composition are 0.512694-0.512713. Initial eNd isotope values 1.45-1.81. These values could be considered as representative of oceanic slab-derived magmas. Source modeling indicates that high-degree of partial melting (relatively up to 50%) of a basaltic garnet-bearing (lower than 10%) amphibolite to amphibolite lacking plagioclase as a residual or source mineral can explain most of the moderate to low Y and Yb contents, low (La/Yb)N, high Sr/Y ratios and lack of negative anomaly of Eu in the rocks of the district. The geochemical signature of the adakites within the granitoid rocks represents a characteristic guide for further exploration for copper porphyry-type ore deposit in Eastern Iran.

The study area is a part of so-called Sanandaj-Sirjan zone or Zagros imbricate zone of the Zagros Orogen, Iran. The Hamedan region comprises a metamorphic sequence of low- to high-grade regional and contact metamorphic rocks intruded by mafic, intermediate and felsic plutonic bodies. The sequence comprises pelitic, psammitic, mafic, calc-pelitic and calc-silicate rocks.  Pelitic rocks are the most abundant rocks in the region which are mostly composed of slates, phyllites, mica schists, garnet-mica schists, garnet-andalusite-(±sillimanite/±kyanite) schists, garnet-staurolite schists, mica hornfelses, garnet hornfelses, garnet-andalusite-(± fibrolite) hornfelses, cordierite-(±andalusite) hornfelses, cordierite-K-feldspar hornfelses and sillimanite-K-feldspar hornfelses. Several interlayers of amphibolites and amphibole schists alternate with pelitic rocks in the sequence. Various types of Al2SiO5-bearing silicic veins occur in the region.  Isotope characteristics indicate metamorphic origin for some of them.  In this study, we have defined three different generations of kyanite according to their various geological characteristics, including: (1) metamorphic (randomly distributed and commonly co-existed with sillimanite/andalusite), (2) stress-(shear)-induced (pseudomorphs of kyanite after andalusite in the shear zones) and (3) late-stage (hydrothermal or metasomatic) kyanites.  The quartz-kyanite veins/pods are late structures that are created by interactions with wall rocks. Circulating Al- and Si-rich fluids may be responsible for formation of these veins/pods.

Tourmaline is present as alteration and mineralization at Maherabad and Khopik Cu-Au prospecting areas, Najmabad Sn-W-Au prospecting areas, Hired Au-Sn prospecting area, and within Gheshlagh pegmatite dikes. Based on X-ray diffraction graphs, Maherabad, Gheshlagh and Hired tourmaline are schorl, but Najmabad and Khopik are dravite type. Based on chemical composition, all of tourmalines belong to alkali group. The Mg/(Mg+Fe) ratio in Gheshlagh tourmaline is 0.21-0.29, in Hired is 0.32-0.47 and in Maherabad is 0.44-0.5 and in Najmabad and Khopik are Mg/(Mg+Fe)= 0.55-0.82. Khopik tourmaline contains considerably higher Mg (1.9-2.3) compared with the Maherabad (Mg = 1.4-1.9). The average TiO2 content of Maherabad tourmaline is 0.35 and Khopik is 0.19. At Khopik, deeper portion of the porphyry Cu-Au is exposed. Najmabad tourmaline contains the highest Mg (Mg= 2.2) and Gheshlagh the lowest Mg (Mg=0.5-0.7) and highest Fe (Fe= 1.9-2.3). Najmabad tourmaline contains the highest TiO2 (0.48%) and other tourmaline contains less than 0.3 % TiO2. In general, there is a reverse correlation between CaO and Na2O. Gheshlagh has the lowest CaO and highest Na2O. The CaO and Na2O content of tourmaline from Hired are very variable.

Post-Eocene volcanic rocks of Alborz tectonic zone located in the NE of Qazvin, composed of rhyolite, trchydacite, trachyandesite, andesite, trachybasalt and basalt with porphyritic textures, pyroclastic rocks and volcanic red breccia which are settled alternatively on Eocene pyroclastics and tuffs. The volcanic rocks are enriched in LIL and depleted in HFS elements which may indicate a calc-alkaline volcanic arc. However negative Ti and Nb anomalies as well as enrichment in LILE implied in generation of these rocks by a low grade partial melting of an enriched mantle on a subduction zone. The presence of a negative Ba anomaly in rhyolitic to andesitic rocks is a common characteristic for the upper continental crust and is a typical feature for high-K suite which reveals the role of upper crust contamination.

Structural analysis of the High Zagros Zone and southwestern rim of the Sanandaj-Sirjan Zone in the Chaharmahal-va-Bakhtyari area resulted in recognition of a thrust system comprises the Ben, Hafshejan, Farsan, Kuhrang and Bazoft thrust sheets from NE to SW. In this study, quartz and calcite microstructures as well as fluid inclusions have been utilized to inspect deformation conditions of the thrust sheets. Microstructural study of quartz grains from the Ben and Hafshejan thrust sheets and their basal thrust zone show evidence of ductile deformation that demonstrate the deformation temperature from 250o to 350oC for the sheets. Geothermometry study of the sheets using calcite mechanical twins also reveals temperature of 250oC for the sheets. Fluid inclusions study on quartz veins from these thrust sheets display homogenization temperature up to 220oC for primary inclusions. This geothermometry survey demonstrates that physical conditions of deformation do not change significantly but increases gradually from the southwestern rim of the Sanandaj-Sirjan Zone toward High Zagros Zone. Based on present data, the area between the Ben and Hafshejan thrust sheets where is considered as the internal part of the Zagros orogen, display characteristics of a transitional zone. Therefore, the Farsan thrust sheet or the Main Zagros Reverse Fault which is known as the margin between the Arabian Plate and Central Iran do not pose this character. The boundary between the Sanandaj-Sirjan Zone as the internal part and the High Zagros Zone as the external part of the Zagros orogene is not abrupt and occurs across a transitional zone comprises a thrust system where basement is also partially involved.

Misho granitoid pluton is exposed at the North Western part of the Misho Mountains and at the South Western part of the Marand compresional depression. The minerals in the rocks of this pluton include unhedral to sub – hedral quartz, K – feldspar both as microcline with tartan twinning and  sub - hedral to unhedral orthoclase, two generations of biotite and zircon, subhedral to euhedral plagioclase (oligoclase - albite), magmatic epidote, titanite and apatite. One generation of zircon and biotite show restitic characteristics. The samples show distinct textures indicating the effect of pressure during crystallization (such as myrmekitic textures, slight alignment of mica, fragments of microcline in orthoclase). The samples exhibit syn-collisional, displaced and S-type geochemical features and the pluton is exposed in an area which is tectonically very faulted. The relative age of the pluton is Paleozoic. The source material for this pluton was a mixture of Meta – greywacke and metapelite. Field relations, mineralogy, geochemistry, existence of mica – rich enclaves and horse – shoe shape of the pluton all suggest a rapid ascent due to dyking and fracture distribution as the main mechanism for melt transport and formation of two generation of zircon and biotite. Therefore diapirism had negligible rule in emplacement and characteristics of misho granitoid.

The Zaroo Cu-skarn is located NW of Yazd province, within the Cenozoic magmatic belt of Central Iran. The widespread rocks in the region are Eocene age volcanic with granitoids intrusives. The Cretaceous limestones in western parts of West Zaroo are hosted by skarn – marble mineralization. The skarns are distal type and are characterized by assemblage: Clinopyroxene, garnet, ilvaite, vezovianite, termolite, epidote, chalcopyrite, magnetite, calcite and quartz. The paragenetic relationships of these minerals have revealed a polygenetic nature of skarn assemblage reveal a polygenetic nature. Black crystals and masses of ilvaite have a close association with hedenbergite clinopyroxene and andradite garnet zone, likely as replacement bodieds. The formation of ilvaite is related to following reactions: Andradite + Fe (OH)2 + CO2 = ilvaite + magnetite + quartz + calcite + H2 Hedenbergite + magnetite + Fe (OH)2 = ilvaite The early skarn minerals are formed at 550 oC and the decomposition of early minerals to formation of final hydrous assemblages started below 470 oC in fO2.

Chlorite group minerals have a wide range of chemical compositions which reflect the physicochemical conditions of their crystallization. The solid solution (cationic substitution) model in crystal lattice of chlorite were satisfactorily used in estimation of its formation temperature in different geologic environments such as ore deposits, low-degree metamorphism, hydrothermal alteration and diagenesis by some researchers. In present research, the chlorite geothermometry method was used in the estimation of temperature of hydrothermal alteration and massive sulfide mineralization in the Qezildash area, northwest of Khoy city. In this work, at first, petrographic and mineralogical (XRD) studies were carried out on the samples taken from surface and borehole drilling cores. Eleven chlorite crystal grains which belong to different parts of hydrothermal system were selected and analyzed by electron microprobe equipment. Structural formulate were calculated on the basis of 14 oxygens. Chlorites have significant compositional variations and atomic solid solutions which reflect their formation temperatures. Chlorites from different parts of orebody and unmineralized altered rocks gave temperatures of formation of 318 to 368oC, and 202-210oC respectively. High-temperature chlorites have smaller Si contents than chlorites formed at low- temperatures.

Amphibolitic rocks are the main part of the north of Khoy metamorphic complex. Petrographicaly these rocks are normal amphibolite, muscovite amphibolite, biotite amphibolite, garnet amphibolite and pyroxene amphibolite. The protolith of these rocks is mainly igneous. These rocks belong to tholeiitic and calc-alkaline series and Ocean Floor Basalt and Arc tectonic setting. These two distinctive tectonic setting clearly are distinguishable in REE and spider diagrams as samples from Oceanic Floor Basalt are steeper and enriched LREE than those from Arc samples. Considering the fact that Sialic Back Arc Basins can show MORB and Arc characters together, therefore probably amphibolitic rocks of study area generated in this tectonic setting.

Aitamir Formation (Albian–Cenomanian) crops out in the Kopet-Dagh basin in north-east Iran.This formation is mainly composed of sandstone, shale, siltstone, and several shellbeds. One of the major components in all of the siliciclastic facies is glaucony. They are autochthonus and parautochthonus types which have formed in suitable physico-chemical conditions and replaced quartz, chert, feldspar, mica and carbonate cement. Nonselective replacement, poorly sorted, along with phosphate, fish teeth and morphological shrinkage are major evidences of autochthonus glaucony. These glauconies are pale green nascent, evolved and highly evolved. Glaucony within marine deposits (suitable host rock), associate with bioturbation, presence of pellets of nascent glaucony and debris of sparse glaucony within the matrix forms of greenhalo are others evidences of autochthonus glauconites. Characteristics of paraautochtonus glaucony, including: ooidal rims around rounded peletic glauconites, well sorted glauconys, presence of glauconites within cross lamination and low fractures in peletics glauconites due to local reworking into in early transgressive surface.

Bafgh Mishdovan ore body is located in the Central Iranian zone and is recognized as potential of the sillimanite group minerals. In this region, the outcrops of the different formations can be observed which mainly consist of the Precambrian metamorphic rocks. Silimanite group minerals are existed in the schistic rocks. The area is located in a tectonized zone and subjected to regional metamorphism then intruded by igneous plutonic rocks. The study area has 95 km2 coverage and according to quality and grade of sillimanite group minerals can be divided to four different mineral zones. Primary exploration activities have been carried out by digging of the trenches and test pits. Samples were taken systematically from outcrops, trenches and test pits. In order to recognize of the ore body (via mineralogy studies), some samples were sent to the laboratory for thin section studies and also XRD and XRF analysis. Based on these investigations, it is verified that the refractory minerals are consisted of sillimanite and kyanite and rarely andalusite. Based on the hosted rocks type and their metamorphic stages, thin section studies and XRD analysis, the phase transition of the primary and alusite into sillimanite and kyanite due to the high temperature-contact metamorphism can be justified. Also regarding the XRD analysis, only one sample contains some kyanites, so it seems that ore bodies is low grade and beneficiation of this industrial  minerals face many difficulties or may not be feasible.

Weathering of K-bearing minerals as the major source of potassium in soils is of special importance under K deficient conditions. Many studies have been carried out on the effect of plant types and microorganisms on the transformation of micaeous minerals and their potassium release. However, there is no information on the effect of organic matter on mineralogical changes in micaceous minerals. The objective of this study was to investigate the effect of organic matter on transformation of muscovite (a dioctahedral mica) and phlogopite (a trioctahedral mica) in the rhizosphere of alfalfa. A pot experiment was carried out in a completely randomized design with factorial combination and three replicates. The growth medium was a mixture of quartz sand, micaceous mineral (muscovite or phlogopite) and organic matter (0, 0.5 and 1 %). During 120 days of cultivation, plants were irrigated with either complete or K-free nutrient solution and distilled water as needed. At the end of cultivation, plants were harvested and their K uptake was measured by flame photometer following the dry ash extraction. Also, the mica particles and their weathering products in each pot were separated from the quartz sand and their clay fraction analyzed using x-ray diffraction (XRD). The results showed a significant increase of total K uptake occurred in pots containing trioctahedral mica (phlogopite) and organic matter as compared to those with no organic matter amendment, under both nutrient solution treatments. XRD data clearly showed the transformation of phlogopite under both nutrient solution treatments, but no XRD detectable transformation of muscovite was recognized. Organic matter amendment seems to have created considerable mineralogical changes in clay sized phlogopite. Root activities and organic matter decomposition appear to have increased the acidity of rhizosphere which, in turn, facilitated the K release from trioctahedral mica (phlogopite) and induced the transformation of phlogopite to vermiculite and a minor quantity of smectite and chlorite. In conclusion, the effect of organic matter on mineralogical changes greatly depends on the type of micaceous mineral.

In this work yttrium iron garnet (Y3Fe5O12 or YIG) nanoparticles have been prepared by sol-gel method, raw materials were dissolved in citric acid and warmed up and stirred to form a gel. Synthesized nanoparticles were characterized, using X-ray diffraction (XRD), FT-IR and TG-DTA methods. Magnetic properties of the nanoparticles were measured, using vibrating sample magnetometer (VSM) and Faraday balance (M-T curve). XRD patterns showed that calcining temperature is far below than that is related to the bulk sample prepared by conventional ceramic technique. From the result of VSM and Faraday balance it was found that the saturation magnetization and Curie temperature of nanoparticles are lower than those related to the bulk sample. The decrease of saturation magnetization and Curie temperature were discussed based on core-shell model and super exchange interaction, respectively.

In this paper Sb2O3 nanoparticles are synthesized by solution method. The effect of these nanoparticles on the Bi-2223 superconductor properties has been investigated. The critical temperature, critical current density and activation energy were measured by the standard four-probe method. Magnetic properties of the samples were measured by using the AC magnetic susceptibility. The microstructure and morphology of samples have been studied by X-ray diffraction, scanning electron microscope and energy dispersive X-ray. The results of X-ray diffraction patterns show that the low amount of Sb2O3 and long annealing time enhance the fraction of Bi -2223 phase. Also the results show that the Sb2O3 nanoparticles do not change the phases and critical temperature of Bi-2223 superconductor, but by increasing the amount of Sb2O3 nanoparticles, the critical current density and the activation energy of the samples increase.

In this work, substituted lanthanum manganites with calcium and strontium, La 0.7Ca0.3-x SrxMnO3 (x = 0, 0.1, 0.2, 0.3), were prepared by a high-energy ball milling method and their microstructure and magnetotransport properties were studied. The raw materials were Mn2O3, La2O3, CaO and SrO, mixed in the stoichiometric ratio to obtain these manganites. The mechanical activation process was performed at room temperature in a SPEX 8000 mixer/mill. X-ray diffraction was used to determine the phase transformation as a function of the milling time. The XRD results showed that after up to 10 h of milling process, using a charge ratio of ball to powder of 10:1, crystallite powder with an orthorhombic structure (S.G. Pbnm) was formed for all compounds. Mean crystallites size of the samples obtained from the XRD patterns and TEM micrograph are about 20 nm. Magneto-resistivity of the disc shape samples was measured using four point probe technique, in the temperature ranging from 77 to 300 K in presence of an external magnetic field up to 1.5 T. Maximum metal-insulator transition temperature is 190 K for La0.7 Ca0.3 MnO3. In this compound the maximum magnetoresistivity factor is 38%, in magnetic field of 1.5 T and temperature of 190 K.