A Abedini
Abstract
The Basir-Abad area (northeast of Ahar, East-Azarbaidjan province) is a part of the Cenozoic Ahar-Arasbaran magmatic belt in northwest of Iran. Intrusion of granitic and granodioritic igneous rocks of Oligocene age into the Eocene volcanic rocks (andesite, trachy-andesite, andesi-basalt and basalt) resulted ...
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The Basir-Abad area (northeast of Ahar, East-Azarbaidjan province) is a part of the Cenozoic Ahar-Arasbaran magmatic belt in northwest of Iran. Intrusion of granitic and granodioritic igneous rocks of Oligocene age into the Eocene volcanic rocks (andesite, trachy-andesite, andesi-basalt and basalt) resulted in occurrence of metallic mineralization along with development of widespread alteration zones in this area. Mineralogical studies indicate that these alteration zones include silicic (quartz), intermediate and advanced argillic (kaolinite, smectite, quartz and alunite), and propylitic (chlorite, epidote, albite and calcite). Hypogene ores within veins and veinlets of silicic alteration zone contain pyrite, chalcopyrite and galena accompanied by covellite, copper-carbonate minerals (malachite and azurite) and iron-oxides and- hydroxides (goethite, limonite and hematite) of supergene origin. The distribution patterns of REEs normalized to chondrite display differentiation and enrichment of LREEs relative to HREEs and occurrence of variant negative Eu anomalies in all alteration zones. Mass balance calculations of elements, using isocon method, indicate that during development and evolution of the silicic and the intermediate argillic alteration zones, REEs experienced enrichment in the former and depletion in the latter. Furthermore, development of advanced argillic and propylitic alteration zones was accompanied by enrichment of LREEs and selective depletion of HREEs. Further investigation revealed that occurrence of negative Eu anomaly (0.20-0.23) in silicic alteration zone is related to abundance of chloride ions, increase of oxygen fugacity of hydrothermal system and highly acidic nature of the fluid. The results obtained from geochemical studies (mass balance calculations, changes in values of Eu and Ce anomalies and ratios of REEs) suggest that changes of pH, temperature, oxygen fugacity, difference in abundance and type of complexing ions in solution, fluid/rock ratio, and presence of minerals such as kaolinite, goethite, smectite, hematite and alunite played important role in differentiation, mobilization and distribution of lanthanides in the studied alteration system.
Sh Fatahi; A.A Calagari; A Abedini
Abstract
Neyestanak bentonite deposit is located in northwest of Naeen, Isfehan province. This deposit is an alteration product of Oligocene tuff breccias. Mineralogical considerations of this deposit show that montmorillonite, kaolinite, and quartz are the principal minerals which are accompanied by lesser amounts ...
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Neyestanak bentonite deposit is located in northwest of Naeen, Isfehan province. This deposit is an alteration product of Oligocene tuff breccias. Mineralogical considerations of this deposit show that montmorillonite, kaolinite, and quartz are the principal minerals which are accompanied by lesser amounts of anorthite, calcite, chlorite, illite, albite, dolomite, microcline, orthoclase, sanidine, and halite. Mineral chemistry investigations testify to the similarity of this deposit with Wyoming-type bentonite deposits. Geochemical studies reveal that bentonitization of tuff breccias at Neyestanak is accompanied by depletion of Ba, Co, Zn, Y, Ni, Sr, Au, Ca, Fe, Mg, Mn, P, Ti, and Na, enrichment of Si, Th, As, Hf, Nb, and U, and leaching-fixation of K, Pb, Cs, Rb, Zr, and Cu. Geochemical analyses make clear that variation of Eu and Ce anomalies in this deposit were controlled by the degree of alteration of feldspars and oxidation potential of the environment, respectively. By considering the results obtained from this study, it seems that factors such as differences in degree of alteration intensity of parent materials, physico-chemical conditions of the environment, adsorption, incorporation in crystal structure, access to complexing ligands, and differences in degree of resistance of the primary minerals against alteration played prominent role in mobilization, distribution, and concentration of elements in this deposit.
Sh Fatahi; A.A Calagari; A Abedini; H Bagheri
Abstract
Chahreeseh bentonite deposit is located at ~55 km northeast of Isfahan, structural zone of Central Iran. This deposit has layered and massive form and includes six discrete outcrops. The field observations showed that the ores are genetically related to Oligo-Miocene tuff breccia. The mineralogical studies ...
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Chahreeseh bentonite deposit is located at ~55 km northeast of Isfahan, structural zone of Central Iran. This deposit has layered and massive form and includes six discrete outcrops. The field observations showed that the ores are genetically related to Oligo-Miocene tuff breccia. The mineralogical studies testified to the presence of minerals such as montmorillonite, saponite, beidellite, cristobalite, anorthite, calcite, dolomite, albite, vermiculite, actinolite, pyrophyllite, quartz, sanidine nontronite, orthoclase, microcline, tridymite, and hematite in rock-forming quantities in the bentonitic samples. Based on the minerals chemistry considerations, the Chahreeseh bentonite deposit can be classified as the Wyoming type. The results of mass change calculations (with assumption of Hf as low-mobile index element) show that progression of bentonitization process at Chahreeseh was accompanied by depletion of elements like Al, Fe, K, Ti, Mn, P, Ba, Co, Zn, Cs, Rb, Y, Zr, Ni, Sr, and Cu, enrichment of U, and leaching-fixation of elements such as Na, Mg, Ca, and Si. The geochemical interpretations revealed that variations of Eu negative anomaly (0.27-0.90) and weak negative to weak positive anomalies of Ce (0.97-1.22) at Chahreeseh have been controlled by the degree of feldspar alteration and changes in the rate of oxidation potential of the environment, respectively. By considering the results obtained from field relations, mineralogy and geochemistry, it seems factors such as physico-chemical conditions of alteration environment, absorption mechanism, difference in degree of alteration intensity of parent materials, the degree of access to fluoride, chloride, and sulfate ligands, incorporation in crystal structure, ionic exchange, physical concentration, and the presence in resistant mineral phases played significant roles in distribution and concentration of elements in this deposit, respectively.
