Iranian Journal of Crystallography and Mineralogy
Year:2011 | Volume:18 | Issue:4|Papers Count:16

Biotite, the dominant ferromagnesian mineral in granitoid rocks, can be used to discriminate tectonic setting, magma types and magnetite- ilmenite series. In this study, we analyzed biotite with an electron microprobe (wavelength dispersion) from different granitoids. Intrusive rocks from Maherabad porphyry Cu-Au prospecting are meta-aluminous. Biotite from Maherabad are Mg-rich type and the ratio of Fe/ (Fe+Mg) is 0.286-0.309. Maherabad biotite compositions fall in the field of (sub-alkaline) calc-alkaline orogenic suites. Based on High TiO2 and low Al2O3 in biotites, Maherabad also belongs to magnetite series. Intrusive rocks from Najmabad, Dehnow, Gheshlagh and Khajehmourad (NDGK) are classified as belonging to the ilmenite-series of reduced S-type granitoids. Biotite from NDGK areas are Fe-rich and the Fe/ (Fe+Mg) ratio in Najmabad is 0.491-0.511, in Dehnow-Kuhsangi 0.583-0.675, Gheshlagh 0.56-0.58, and Khajehmourad 0.705-0.720. respectively NDGK biotite compositions fall in the field of peraluminous granite (P) suites (S-type). Based on low TiO2 and high Al2O3 in biotites, Najmabad, Dehnow and Gheshlagh biotite belong to ilmenite series.

The study area is a part of the Sanandaj- Sirjan metamorphic belt. The Hamadan metamorphic rocks can be divided into three groups including regional metamorphic rocks, contact metamorphic rocks and migmatites. Garnet crystals are usually common in all of the metamorphic rocks (except for slates and phyllites) and in the igneous rocks (i.e. aplite, pegmatite and monzogranite). These garnets, from point of morphological view, can be divided into three groups: special rhombic dodecahedron form, special trapezohedron form and composite forms that made up of particular dodecahedron form, mature composite forms and particular trapezohedron form. Particular dodecahedron forms are common in these rocks: garnet amphibole schists, seldom in garnet mica schists, rarely in mesosome of migmatites and in garnet mica hornfelses. Garnets in aplites and pegmatites have special trapezohedron form. Garnet crystals in other rocks of the study area have composite forms. The important factor, which is effective in changing these crystal forms, is chemical composition. With increasing of Mn/Ca and (Mn+Mg)/Ca ratio, garnet crystal forms change from dodecahedron to trapezohedron.

There are metabasite exposures inside ophiolitic belt of northwest Sabzevar that metamorphosed under high pressure granulite facies. On the basis of mineralogical paragenesis, reactional textures between different mineralogical assemblages, textural and mineralogical relations between inclusion and porphyroblast and stability fields of different mineralogical assemblages, five stages of evolution of metamorphism is distinguished. These stages consist of prograde metamorphic stage (M1), peak metamorphic stage (M2), garnet kelyphitisation as the formation of Pl+Am symplectite and corona (M3), partial or quite replacement of garnet by Am+Chl+Ep assemblage (M4) and the occurrence of Prh-Zl veins. The thermobarometric data of these stages represent a clock-wise P-T path. This path is consistent with the collision of the Iranian micro-continent with the Alborz block and later erosion and uplifting.

The Javaherdasht gabbros cropped out in the northern part of the Alborz Mountains in east of Guilan Province. According to geochemical, petrographical and field studies, they are divided into two types of gabbros including non-layered and layered gabbros, and layered gabbros. Regarding the mineralogy, the first group gabbros include plagioclase, clinopyroxene, olivine and biotite as primary phases accompanying magnetite and titanomagnetite. The second groups of layered gabbros unlike the first group gabbros have no primary biotite and titanomagnetite. From the geochemical view of point, the first group have high contents of alkali oxides (Na2O+K2O), TiO2 and Fe2O3 total in comparision to the second-group gabbros. Compared with the first group gabbros, the second group layered gabbros have high contents of Mg# and compatible elements (Ni, Cr and Co). Our studies show that the first group gabbros have a clear elemental equilibrium with lower crust rocks and have been contaminated with them. Geochemical studies of major and trace elements show that they originated from the parental magma of the first group gabbros from a MORB mantle source with spinel facies. The second group gabbros show sign of relation to the melting which is originated from MORB mantle source with garnet facies. Studing the propotions of incompatible elements and patterns of incompatible elements of Javaherdasht basalts show that the first group gabbros are related to the Javaherdasht basalts and have similar petrogenetic relationships and similar geodynamic setting.

Moshirabad granitoid body is located, as part of intrusive bodies, in Sanandaj-Sirjans zone and crops out elongated with east-west trend. Based on field observation as well as mineralogical characteristics, this suite consists of three main units, diorites, granodiorites and granites, followed by minor gabbros. Mineralogical and geochemical studies show that rocks of this suite are I-type, calc- alkaline and from the point of view of saturation degree of aluminum (ASI) are metaluminous to weakly aluminous. Variation diagrams trends of major and trace elements indicate a continuous compositional range and comagmatic origin for these rocks. Trends of compatible-incompatible elements indicate the important role of fractional crystallization in the genesis of these rocks. Depletion in Ta, Nb, P and Ti and enrichment in Ce, K, Th, Rb and Ba are obvious in the spider diagrams of these samples. The enrichment in LILE and depletion in HFSE reveal the I-type metaluminous magmatism of volcanic arcs (VAG). The low ratios of Al2O3/(FeOtotal+MgO+TiO2) and (Na2O+K2O) /(FeO+MgO+TiO2) and the geochemical evidences of rare earth elements and trace elements show that the origin of initial magma is from the lower crust that created in a margin of convergent plate. Discrimination diagrams for tectonic setting also indicate the intrusion of this granitoid into the volcanic arc related to an active continental margin setting, so that with regard to geological history of this area, it can be attributed to subduction of Neo-Tethyan oceanic crust below Central Iran.

Dahaneh Qaleh exploration prospect is located about 300 km south west of Mashhad and is belong to the Taknar structural unit. This unit is separated from Sabzevar structural unit with Taknar fault in the north and Darouneh fault in the south, is the separator of this unite from Lut structural unit. Before the operation field, ASTER sensor data processing introduces Hematitic, Chloritic, Epidotic, Sericitic and Silicification alteration zones in the study area. Field work observations and optical microscopy confirm the remote sensing results. Geological formation of the area is consists of metamorphic rocks and low grade metamorphed subvolcanic granitoid rocks with porphyry texture. The origin of granitoid rocks is calk-alkaline, peraluminous to metaluminous magma that is leading to the formation I-type granitoid rocks in the area. The tectonic setting of the rocks is subduction zone. Stream sediment geochemical analysis shows Au, Ag, Cu, Pb, Zn anomalies in secondary halos. Maxzimum value of Au is (12.3ppb), Ag (97ppb), Cu (87.28ppm), Pb (88.94ppm), Zn (160.3ppm). On The base of field studies, petrography and mineralography investigations recognized two mineralization systems in the area: 1-Taknar VMS mineralization sysrem and 2-Copper Porphyry mineralization system (monzonite model).

The Dehno Granites are located 20 Km northeast of Aligudarz. They are one of the four separated plutonic masses, exposed in the Sanandaj – Sirjan Zone. These rocks are composed of granodiorite and tonalite covered by granite arens. The main minerals of these rocks are quartz, plagioclase, biotite, muscovite and accessory minerals such as sphene, apatite, epidote, zircon, rutile and opaques. By using equation of change percentage (%change= [(RW-RP)/RP] 100), the changes of the elements content in the weathered and fresh rocks were determined and compared. According to this equation, the Si, Al, Na, K, P, Ba, Rb, Zr, Ta, Fe3+, Nb, Y and U concentrations are decreased whereas Mg is increased. Fe2+, Sr and Ca show various trends in the weathered samples compare to the parent rocks. The elements such as Hf, Y and Ta display the least changes in different depths. The chondrite – normalized REE's show decreasing trend indicating that the LREE's content in comparison to HREE's are enriched and concentrated in the weathering products rather than in fresh rocks. This may be due to surface absorption of clay minerals. In the weathered samples, Eu and Ce show depletion and slightly positive anomaly respectively. Depletion in Eu is likely caused by alteration of feldspars.

To investigate the characteristics of Paleozoic magmatism in Central Iran, the volcanic rocks from some area like Abyane, Zefreh, Bagherabad and Dalmeh have been studied and have been compared to another area like Jahagh and Polekhavand. The volcanic horizon occurred as lava flows with massive and pillow structures and intermittent with several sediments layers such as sandstones and carbonates. Geochemical investigations and some diagrams show the transitional nature (tholeiitic to alkaline) of magma and show that it is formed within inter continental rift. This situation related to the tensional movements in Central Iran in Paleozoic. Carboniferous intrusives in Late Devonian of Zefreh and Bagherabad all are evidences of the existence of pulses movement’s rhythms of push and pull, especially in Dalme area in Iranian crustal plate. In worldwide scale, these movements are comparable with Hercynian Orogeny.

Heris intrusive body has cut Kahar Formation and has been covered by Permian basal sediments, non-conformably. The composition of this body is granite- alkali granite with metaluminous to weak peraluminous nature. The strong negative anomaly of Eu in REE diagram indicates the presence of plagioclase in the source area or differentiation of it during evolution of the magma. Negative anomaly of Ba and enrichment of Rb and Th relative to Ta and Nb is an indicator of crustal origin. These granites are within-plate and A-type granites, which have been formed by partial melting of tonalitic- granodioritic source in extensional setting. Zircon U-Pb dating yields 306±34 Ma for crystallization of these rocks. This age is consistent with primary extensions of rifting in Arabian- Iranian platform.

The studied area located in south and south western Arak town and are the part of Sanadaj-Sirjan Zone. The plutonic rocks in Astaneh and Boroujerd areas are quartz diorite, granodiorite and monzogranite. In addition to plutonic rocks, subvolcanic rocks of rhyodacite composition are present in Astaneh area. In general, in these areass mineral assemblage is the same in different units. The common minerals are amphibole, biotite, plagioclase and alkali feldspar, but mineral concentration is different in studied areas. Geological, petrographic and geochemical characteristics in these areas show that magma is calc-alkaline, high- medium K and metaluminous to peraluminous composition. Relationships of place, time, similar geochemistry and isotopic characteristics indicate that granites in two areas have cogenetic and same source nature. The most possible source for granitoid rocks in two areas are partial melting of lower crust amphibolites and sediments that occur in extended Boroujerd and small pluton in Astaneh area.

Bacterial and Archeae colonies in marine sediment play important role in methane production and precipitation of authigenic minerals such as pyrite in the Nankai sedimentary basin in south east of Japan. Authigenic pyrite precipitates in anerobic condition, whithout light and in suitablet medium by sulfate-reducing bacteria (SRB). These bacteria are mezophile and heterotroph. pH and Eh of medium play important role in growth of these microorganisms and precipitation of authigenic pyrite in laboratory condition while chemical composition of materials in medium and organic material in Nankai sediments have important role as chemical factors in precipitation of pyrite too. Organic matrix (extracellular polymeric substances [EPS]) that covers bacterial cells also plays important role in electron arrival (resulted by sulfate reduction) into the cell of SRBs. In fact, the Fe+2 in the pore water of sediments react with EPS. The iron in the EPS may serve as an electron shuttle or conductor for conveying electrons from the oxidative half-reaction of metal sulfides to the electron transport system in the plasma membrane. Organic matrix forms biofilm in sediments. The results indicates formation of authigenic pyrite by Geobacteria Sulphate-Reducer in biofilms within the sediments of the Nankai basin.

Shape or habit of crystal is controlled by physicochemical conditions of crystallization, thus quantitative measurements of crystal shape can reveal aspects of crystallization environment. In this paper, based on statistical calculations, numerical modeling software and microscopic observations. various methods of quantitative measurement of the shape of crystal have used More than 3200 plagioclase crystals in 9 thin sections of the two groups of rocks including basaltic andesite and quartz diorite were processed. Study area is located about 120 Km southeast of Birjand. The results of calculated crystals aspect ratio (Short: Intermedite: Long or S: I: L) have showed that both groups have tabular habit (I »L), but tabulation amount in the first group is to be more (I, L>2). Analysis demonstrates that microlites in the first group were formed under conditions with high undercooling, fast growth rate and environment with high advection (relative movement between the crystal and growing medium) and the high mechanical movement of magma and high chemical potential gradient had significant role on ctystal shapes. In the second group, contrastingly, low growth rate and high diffusion rate were established. Also, textural coarsening process was affected on shift of crystal shapes from tabular to more equant forms and reduction of aspect ratio with increment of maximum length of crystals.

Miserite, as a type of calcium potasium silicate mineral, was characterized by J.D. Scott at 1975 in the form of a chain silicate structure according to (k1.29 0.21) [Ca5.51 M3+0.49](Si6 (O,OH)15)(Si2O7) (F,OH)2 0.29H2O Formula. The primary cell parameters and the positioning of all atoms in the cell were characterized by scott and he also denoted that in this structure, some impurities such as, Y+3,Ce3+,… were substituted by Ca2+ as solid solution. Beal were synthesized this composition in 1999 by glass ceramic route and reported 235 MPa, 3.5 MPa.m1.2 as bending strength an fracture toughness values of the products. In this research, the syntheses of miserite based compositions by glass ceramic rout were investigated. The results of DTA and XRD study showed that the synthesis of this composition is possible just by using of some additives such as Ce3+. Also it is denoted that using of other additives such as Al2O3 and Be2O3 beside Ce3+ can promote the formation of miserite as major phase. The microstructure of this composition obtained as interlocked rods with 1 micron diameter and more than 20 micron length. Also it is dented that this structure can enhance the mechanical properties at the samples.

Plio-Quaternary volcanic eruptions in southeast of Nehbandan are composed of basic rocks, overlying the Late Cretaceous flysch-type and younger alluvium deposits. Petrographically, these rocks are basalt, basaltic andesite and andesite. These lavas are characterized by porphyritic, microlitic-porphyry, trachytic and glomeropophyritic textures. They contain plagioclase, clinopyroxene (augite), olivine and amphibole (hornblende) phenocrysts and fine-grained plagioclase-clinopyroxene microlite in groundmass. Geochemically, these rocks are calc-alkaline and represented by 47.8 - 57 wt. %. SiO2 and about 17 wt. % Al2O3. In chondrite-normalized REE diagram, these rocks show enrichment in LREEs and depletion in HREEs. In primitive-mantle normalized trace elements diagram, they are characterized by Nb (and P, Ti, Zr) negative anomalies and positive anomalies in Pb, K, Ba and Sr. These chemical characteristics of Nehbandan Plio-Quaternary lavas associated with high LILE/HFSE and LREE/HREE ratios are consistent with derivation from a subduction environment. Y/Zr ratio of these rocks is similar to that of continental arc lavas. Discrimination tectono-magmatic diagrams suggest an active continental margin for the formation of Nehbandan Plio-Quaternary lavas.

In northwest of Marand northern part of Urumieh Dokhtar Magmatic Arc (UDMA) a set of volcanic rocks crop out with composition of andesite, dacite, and sodic, potassic and ultrapotassic alkaline basalts with Upper Miocene until Plio-Quaternary in age. This paper report the andesitic and dacitic lavas erupted within pyroclastic rocks. These rocks have porphyritic texture and consist of plagioclase, hornblende, pyroxene and a minor biotite phonocrysts. Based on geochemical study, these rocks have SiO2 in rang of 57.5-65.2, high Al2O3 (14.5-16.2) and Sr (557-1185), high Sr/Y (30.7-84.46), La/Yb (13.27-67.36) ratios, and low Y (11.2-20.2) that show adakitic characteristic for the parent magmas. On the base of geochemical characters, these rocks are high- SiO2 adakites which is considered to represent subducted basaltic slab-melts that have reacted with peridotite during ascent through mantle wedge. Also these samples are enriched in LILEs and LREEs and are depleted in some HFSEs like Ta, Nb, and Ti. Intensive fractionated pattern of REEs and low quantities of HREEs and Y may prove existence of garnet or amphibole in the residua of melt. High Sr and negative anomalies of Ta, Nb, and Ti may be resulted from lack of plagioclase and having iron and titanium oxides in the residua phase. Breaking of oceanic slab during subduction and melting of this slab product adakitic magmatism in NW of Marand. High Mg#, Cr, and Ni in rocks indicate metasomatism of melt with mantle wedge. High Ba, Rb, and K2O contents of studied rocks indicate assimilation of magma with crust during rising of magma.

Hassan Abad Au-Sb prospect area is located in north of Khorasan Razavi Province about 45 km souht of Neyshabour. Volcanic rocks (rhyolite, rhyodacite, trachyandesite and andesitic-basalt) and sub-volcanic intrusive (Eocene-Oligocene) such as biotite diorite porphyry, biotite hornblende diorite porphyry, hornblende monzonite porphyry, biotite micogranite, micogranodiorite, and granodiorite were identified in the study area. Alteration zones which are mapped in the surface and sub-surface are: 1- argillic zone, 2- sericite-quartz-pyrite zone, 3- carbonate zone, 4- propylitic zone, and 5- silicified zone. Vein type mineralization is dominate with minor veinlets, breccia and disseminated. Eight exploratory holes were drilled in the exploration area. In this research, IP/RS pseudo section in profiles 0, 150W and 300W were interpreted using drilled core observation and studies. Profile 0 has a chargeability anomaly greater than 25 milli second in the south eastern part of Gold- Antimony vein which is smaller than 150W and is at greater depth. In profile 150W, chargeability anomaly reach to greater than 50 millisecond with northeast-southwest trend and is highest in the center of the vein and is dissected by a fault. Chargeability anomaly extends towards northwest of the main Gold-Antimony vein and is observed as three small discontinuous anomaly in profile 300W. High chargeability anomaly and its extension in all three pseudo sections confirm the presence of conductive sulfide and correlates with the results of observed mineralization on the drilled cores. Increase in electrical resistivity in profile 150W is related to subvolcanic intrusive body of quartz monzodiorite porphyry which is observed on drilled cores and appears to be younger than granite. Observed mylonite in drilled core and dissection of chargeability anomaly infer a fault which mylonite the quartz monzonite sub-volcanic body before the creation of mineralization. Detailed surface and sub-surface geological, alteration and mineralization studies correlate well with IP/RS anomalies and confirm them. Thus it can be predicted that in the north eastern portion of profile P150W where no mineralization is observed in the surface but it well extend at depth and two drill cores at 200 and 440 meter distance on the north are proposed.