dariush esmaeily

The Tash bauxite mine is located approximately 6 km northeast of Tash village and 40 km northwest of Shahroud city in Semnan Province with coordinates of 36° 32′ N to 36° 37′ N and 54° 41′ E to 54° 48′ E. The actions of the orogenic phase of the former Cimmerian as well as the chemical and physical factors have caused the erosion of the basalts in the Shemshak sedimentary basin, which has resulted in the simultaneous deposition of the Shemshak molasses and bauxite in the Tash area. According to some geological evidence and the location of Elias rule, bauxites in the vicinity of Shemshak Formation shales, it is concluded that the clay minerals have played an important role in forming the bauxite deposits in this area. The results showed that the basalts were formed from the alkaline magma and then altered to clay minerals. The remaining immobile elements such as aluminum and residual iron formed the Tash bauxite deposit. The investigation of thin sections designates that the studied ore contains ooidal, plitomorphic, allogeneic pizolite, coloform, and compressive dissolution texture, which indicates the autochthonous origin. Pyrite, chalcopyrite, goethite, and hematite were also recognized. The mineralogical study, performed by the X-Ray diffraction method, led to the identification of minerals of anatase, boehmite, diaspore, chamosite, kaolinite, quartz, and hematite. Analysis of ore samples by the X-Ray fluorescence method and calculation of aggregation coefficient of trace elements and geochemical indicators along with geological evidence revealed the source rock could be from the mafic type.

Anomaly 21A, as a part of Bafq iron-apatite ore metallogenic district, is located in Central Iran, and encompasses wide spectrume of igneous, sedimentary and metamorphic rocks. The igneous rocks that show narrow geochemical variations and dominantly plot in the monzonite to monzodiorite fields, are plotted in the calc-alkaline and high-K calc-alkaline affinities. Geochemical data are characterized by enrichment LILE and LREE as compare to HFSE and HREE, respectively, and depletions in Nb-Ta-Ti imply the mantle-derived melts modified by subduction components. The isotopic signatures of Anomaly 21A samples, e.g., (87Sr/86Sr)i, εNd(t)=, imply the dominant mantle signature. Their initial Pb isotopic composition of study rocks are 18.87 to 20.32 for (206Pb/204Pb), 15.72 to 15.84 for (207Pb/204Pb), and 40.74 to 42.32 for (208Pb/204Pb). The isotopic modellings show less than 4% incorporation of melt-derived subducted sediment into the mantle wedge or variable degrees of contamination by upper continental crust. We suggest partial melting of a sub-arc mantle melt that has been metasomatized by slab-derived sediments and interacted with continental crust en-route the shallower surface as the premise of the geodynamic of Central Iran.

Sr-Nd-Pb isotopes and whole-rock geochemical analyses were carried out on plutonic rocks of the Chadormalu district to constrain the magmatic history of the Cadomian orogeny of the northern Gondwana margin during Late Precambrian–Early Paleozoic times. Despite the similarities in the geochemical data, i.e., calc-alkaline affinity, enrichment in large ion lithophile elements (e.g., Rb, Ba, K, and Cs), and depletion in high field strength elements, e.g., Nb, Ta, P, Ti, and rare earth element patterns, bulk rock Sr-Nd isotope data rull out the co-magmatic nature of investigated basic (gabbro) and felsic (granite) magmas. Sr-Nd isotopic data (e.g., ɛNd(t)= -3.6 to +1.8) along with rather high (207Pb/206Pb)t attest to the crust-dominant, and mantle-derived melts for the granitoids and gabbros, respectively. The investigated zircons yielded the older ages for the gabbroic samples. The extensional tectonic regime is followed by slab retreat or delamination brought flare-up of the oldest arc-related igneous rocks and interacted with Cadomian basement to form the investigated granitoid melts. The gabbroic rocks show geochemical and isotopic disruption and elevation of L-MREE/HREE ratios on the chondrite-normalized rare earth element (REE) patterns; interpreting the evidences of mantle heterogeneity and interaction with Paleoproterozoic basement.

The Gol-e-Gohar iron deposit in the Sanandaj-Sirjan zone of south-western Iran comprises six majorore bodies. The largest deposit is Gol-e-Gohar No. 3 (Gohar-Zamin) with about 643 Mt @ 53.1% Fe.Magnetite is formed in massive and brecciated shapes. Gol-e-Gohar magnetite contains Mg, Ca, and Siup to the percent range, V and Ti in the 100s ppm level, and low Cr, Co, Ni in the tens of ppm range,typical of Kiruna mineralization (especially Bafq mining district). But Chador-Malu magnetite is formedat a higher temperature than Gol-e-Gohar magnetite, therefore, hydrothermal high-T nature (magmatic ore-forming fluids), which are related to felsic magmatism (host meta-granites), and both of them are attributed to the Early Paleozoic. The oxygen isotope composition of magnetite is 4.9 ± 0.7‰ δ18 O (n = 9) and the iron isotope composition is 0.49 ± 0.05‰ δ56 Fe (n =17). These data suggest that the magnetite ore formed from a magmatic- hydrothermal (high-T) fluid in equilibrium with a granitic source. The Gol-e-Gohar iron ore district shows several similarities to the Bafq mining district, located about 400 km to the north, and seems to be a disrupted member of theKashmar-Kerman arc. Finally, according to the mentioned evidence and comparison of Gol-e-Gohar iron deposit with global samples, the genesis of mineralization in this deposit is most similar to Kiruna- type (Kiruna-type magnetite ± apatite mineralization).

Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve texture, two generation of fresh and altered plagioclase, reaction rim, corrosion and rounding of phenocrysts. Major and trace element diagrams show, although crystal differentiation was effective in the evolution of the study rocks, the scatter and unusual trends, which are observed in some diagrams in comparing with fractionation trend, reflect magma mixing and contamination were also important during magma generation. Inconsonance and high variations in Sr concentrations together with binary diagrams of Nb/Y-Nb and Rb-Zr/Rb reveal magma mixing role in the evolution of Neshveh volcanic rocks. Considering the above facts, we can conclude that magma mixing and magmatic differentiation were the important processes in formation of the Neshveh volcanic rocks. As well as, the incorporation of new magmatic pulse(s) with differentiation magma is the most effective mechanism for the evolution of volcanic rocks from the study area.

Andesitic and andesitic-basaltic lavas are widespread over most of the ground surface of the Gurgur area altered mostly by the hydrothermal solutions. The main rock forming minerals in these rocks are plagioclase, pyroxene and olivine affected by the hydrothermal solutions. The altered rocks do contain minerals including calcite, sericite and chlorite. Given the results obtained and the mineral chemistry studies, the clinopyroxenes formed in the area are, chemically, calkalkaline and of diopside-augite type formed in subvolcanic to near surface levels contemporaneous with magma ascending. Plagioclase minerals show zoning textures and lie within the two andesine and albite-oligoclase fields. These units, in terms of total rock chemistry, are classified as the calk-alkaline volcanic rocks formed in the continental arcs. On the other hand, on the trace elements chondrite-normalized diagrams and enriched mantle-normalized multi- element diagrams, the LREE enrichment relative to the HREE is observed. The LILE (i.e. Rb, K and Th) and the LREE (e.g. La, Ce and Nd) show an enrichment in comparison to the HFSE (Zr, Hf, Nb, Yb, Y and Sm). Given the Nd/Th (1.42-1.15), Zr/Nb (12.27-21.22), Ba/La (18.64-29.77) as well as LILE enrichment associated with depletion in Nb, Ta and Ti, an environment related to the subduction zones can be proposed for the area under study. Moreover, the similarity between the REE distribution pattern and the incompatible elements point to the genetic relationship between these rocks. Finally, on the base of the obtained data, it can be concluded that the volcanic rocks in the Gurgur Mountain were likely formed during the extended magmatism of the Urumieh-Dokhtar in the Cenozoic.

Three intrusive granitoid bodies from northwest Saveh, central Iran, are embedded in volcanic sedimentary rocks of the Eocene, forming isolated small outcrops: Khalkhab quartz monzodioritic units (SiO2: ~52-57 wt %) to the northwest, Neshveh granodioritic units (SiO2: ~62-71 wt %) to the northeast, and Selijerd granodioritic units (SiO2: ~63 69 wt %) to the southeast. The Khalkhab unit is composed of quartz monzogabbro and quartz monzodiorite with medium- to coarse grained textures. The Neshveh unit is composed mainly of granodiorite with subordinate granite of medium grain size and a porphyritic texture with plagioclase megacryst. The Selijerd unit ranges from granodiorite to tonalite with a medium- to coarse-grained granophyric texture. The rocks studied display a relatively high Na2O content,with a molecular A/CNK ratio less than 1.1, Na2O/ K2O ratio of ~2.06 and calc-alkaline affinity. They contain modal clinopyroxene, hornblende, magnetite and titanite, suggesting I-type characteristics for these rocks and formation in an active continental margin. Isotopic data (87Sr/86Sr39Ma= 0.704536-0.704860; ε(Nd)39Ma= 2.2-3.9) from northwest Saveh intrusive rocks are plotted to the left of bulk silicate Earth. These ratios, together with geochemical data, suggest that the parent magmas of the rocks studied might be generated by crystal fractionation of arc basalts in crustal magma chambers, coupled with some lower crustal assimilation prior to silica enrichment, to form quartz monzogabbros. Consequently, granodiorites formed dominantly by crystal fractionation from evolved parental magmas that ascended into the upper crustal magma chambers.

Biotite samples from different units of Boroujerd Granitoid Complex (BGC) of the Sanandaj-Sirjan Zone, western Iran, have been analyzed by electron microprobe for major elements. Biotite analyses from three units of quartzdiorite, granodiorite and monzogranite of BGC have their own distinct non-overlapping compositional fields in the annite – siderophyllite – phlogopite – eastonite quadrilateral (ASPE), reflecting their host rock compositions. Biotite from each rock unit has an increasing trend of Al contents at almost fixed Fe/(Fe+Mg) values. In quartzdiorite it shows an approximately constant range of Fe (Fe+Mg) with a low to moderate Al content from 2.5 to 3 atoms per formula unit (apfu). Biotite from granodiorite exhibits a fairly wide range of Al values reaching up to 3.32 apfu, at Fe/(Fe+Mg) from 0.6 to 0.7, whereas biotite from monzogranite have a relatively narrow range of Fe/(Fe+Mg) and total Al values of limited range of 3.1 to 3.3 apfu. Biotite compositions from these two latter units considered to be derived entirely from crustal material, characterized by a remarkable increase in total Al at relatively high Fe contents. Biotite samples of quartzdiorites define a distinct and non-overlapping trend from those of granidiorites and monzogranites and hence interpreted to be derived from a parental magma with different composition. Calculation of log(XMg/XFe) ranges from -0.09 to -0.0 and most of samples from quartzdiorite fall within weakly and moderately contaminated I-type field of log(XF/XOH) versus lo (XMg/XFe) diagram, whereas the other two units, containing biotites with log(XMg/ XFe)< -0.21, classified as strongly contaminated reduced I-type. Oxygen fugacity (log ƒO2) of -15.4 to -17.5 bars and ƒH2O of 200 to 560 bars were calculated for quartzdiorite. Likewise, log (ƒO2) of –17.66 bars and water fugacity (ƒH2O) of 400 and 700 bars were also calculated for granodiorite and monzogranites respectively. In the FeO*–MgO–Al2O3 biotite discrimination diagram, biotite compositions from BGC are distributed between the calc-alkaline and peraluminous fields, i.e., biotite from the qaurtzdioritic rocks fall principally in the calc-alkaline field, whereas those from the granodioritic and monzogranitic units plot almost exclusively in the peraluminous field consistent with their host rock nature