Iranian Journal of Crystallography and Mineralogy
Year:2003 | Volume:11 | Issue:2|Papers Count:9

The ABS2 sulphides (A=Cu, or Ag), B=As, Sb, Bi) are a naturally occurring group of minerals, typically found in polymetallic vein deposits. Behind chemically simple, the minerals have a complex structure and undergo several temperature/composition phase transitions. In this study, synchrotron radiation is used to collect Ag, As, Bi, Cu, Cd, Hg and Sb K-edge EXAFS data from a series of synthetic sulphosalts. EXAFS are used to characterize and determine the local structure behavior. Analysis of the spectra has provided direct evidence about the coordination environment, the structural and electronic environments of major and minor cations within the substituted phases. In this study, M (metal or semimetal)-S bond distances of emplectite, chalcosibite, miargyrite and smithite minerals were determined by EXAFS and XANES methods.

Titanium silicate-2 (TS-2) is synthesized in the presence of different amounts of methylamine. The as-synthesized samples were characterized using IR, DRS UV and SEM techniques. The effect of hydrogen fluoride and methylamine on the synthesis is studied. Results showed that the TS-2 crystallinity and titanium content in the framework increase with addition of both hydrogen fluoride and methylamine to the gel mixture, respectively. It seems that the methylamine plays an important role to promote formation of Si-O-Ti oligomeric species. But, hydrogen fluoride improves the crystallinity of the product via increasing the solubilities of the oligomers in the gel.

Razdar ultramafic–mafic complex is located in south of Kerman province and contains ultramafic (dunite with chromitite, lherzolite, wehrlite, websterite and olivine websterite) and mafic (gabbro) rocks. The most important minerals in this complex are olivine, chromospinel, orthopyroxene, clinopyroxene, plagioclase and amphibole. Mineralogical studies indicate that chemical composition of these minerals from lower to upper parts of Razdar complex has distinctive variation. That is, with variation of rocks from ultramafic to mafic, Mg-contents in ferromagnesian minerals decrease and the minerals become more mafic. Comparision of chemical composition of major minerals in Razdar with other ultramafic association in the world reveals that ultramafic part of Razdar complex likely belongs to upper mantle that has been emplaced in present position by major faults.

Amphiboles are one of the major minerals in metabasic rocks in greenshist to upper amphibolite facies. Amphiboles have variable chemical composition; therefore, various elements with different ionic charge and radius can intering into their structure that occupy special mineralogical sites. There are some elements in amphiboles which are sensitive to the changes of pressure and temperature. The important elements from this point of views are Al, Na, Ti and Ca. Once that pressure and temperature of metamorphism is determined, the type of metamorphism can be distinguished. On this basis, we studied metabasic rocks of north and northwest of khoy township in north-west (NW) Iran. Geothermobarometry estimation indicates that amphiboles have crystallized at temperatures between 550OC and 680OC and pressures between 4.5 and 7 kbars. Therefore, metamorphism in the Khoy area was low to medium grade. 

The Qopi bauxitic horizon is located west of Miandoab, in West-Azarbaidjan province, NW of Iran. It lies along the boundary of Ruteh (middle-upper Permian) and Elika (lower Triassic) Formations. This horizon includes four distinct lithologic facies such as (1) bauxitic iron ore, (2) ferruginous bauxite, (3) Fe-rich bauxite, and (4) Fe-rich clayey bauxite. Microscopic examinations showed various textures including pelitomorphic, fluidal, colloform, pseudo-breccia, and pseudo-porphyry within the horizon, suggesting an authigenic origin. Based upon field evidence and geochemical data, the fine-grained diabase in the area may be the probable parent rock from which the bauxite layers developed. The results of calculations of mass changes showed that elements such as Na, K, Mg, P, Si, and Ca were depleted, and Fe, Al, and Ti were enriched during bauxitization processes. According to field observations, microscopic examinations, and geochemical investigations, Eh variations (from reducing to oxidizing) and suitable pH (6-8) of descending meteoric waters were the prime factors controlling the formation of Qopi bauxite layers. In addition, the enrichment pattern of immobile elements and field evidence indicate that the Qopi bauxitic horizon may be classified as Mediterranean karst bauxite.

The structural properties of HoBa2Cu3O7-d high Tc superconductor by XRD, SEM and EDX, resistively, critical electrical current density and oxygen content measurement have ben studied. The HoBa2Cu3O7-d sample of is prepared by solid state reaction, with two different thermal conditions. The XRD results have shown the formation of pure phase of HoBa2Cu3O7-d . The oxygen content measurement for two samples by Iodometric titration gives 6.76+0.9 and 7.0+0.09. The measurement of critical current density measurement for two samples has shown that between Jc and Jco the potential versus current has exponential behavior (V-aIB). Also measuring Jc near transition temperature gives lower critical current density than measuring it far from the transition temperature. The critical current density of the sample with lower oxygen content is lower than in other samples. The SEM results showed that by increasing the oxygen content and slow cooling, the grains growth of sample increase.

Fire clay of the Kabutarkuh deposit, located about 50km southeast of Gonabad (Khorasan Province), was analyzed for its mineralogical and chemical compositions. Kaolinite, pyrophilite, quartz, dickite, gypsum, illite and alunite are the dominant minerals, and a minor phase of hematite is also present. Geochemical data show that the whole rock sample is mainly composed of SiO2, Al2O3 and K2O. Chemical results and petrographical studies give an indication of andesite-latite parent rock, which has been altered under the influence of hydrothermal fluids. The chondrite-normalized rare earth element (REE) patterns show enrichment in the Light REEs. The LREE/HREE ratio of upper layer is higher than the lower ones, which indicates mobility of HREE toward the depth. Generally, REE, trace elements and major elements patterns show evidence of intense alteration and weathering processes related to kaolinization. The high measured values of EC and Low measured values of PH are due to solubility of alunite and gypsum minerals.

The Mehdi Abad zinc-lead deposit, which is located in central Iran, is one of the largest zinc deposits of the region. The orebody consists of primary sulphide as well as supergene non-sulphide ore. The deposit comprises a main sulphide/nonsulphide orebody below a valley floor and of the so-called Calamine Mine (exclusively non-sulphides), on the flank of a mountain, separated by faults from the fonner. The non-sulphide ore of the Calamine Mine is hosted within Cretaceous (Albian) strata of the regional Abkou Formation, and occurs as a matrix of fault- and karst breccias. .ore minerals are composed of hemimorphite, hydrozincite, smithsonite, goethite, as well as small amounts of mimetite, hetaerolite, and sauconite. Texturally, hemimorphite occurs as two different types. Type-l displays sub- to anhedral shapes and is commonly associated with goethite and/or hydrozincite. This type-l hemimorphite is commonly altered and partly dissolved to relict box work textures on a microscopic scale. Type-2 hemimorphite is euhedral and has grown in fractures and open spaces of the host rock and in breccias. At least three different stages are proposed for the genesis of the hemimorphite mineralisation: (i) formation of type-l hemimorphite from supergene ore fluids, (ii) the partial dissolution and alteration of type-l hemimorphite to hydrozincite, probably accompanied by the precipitation of goethite due to a change in Eh-pH conditions, and fmally (iii) the precipitation of type-2 hemimorphite within fractures and open spaces.