GEOCHEMISTRY
Year:2014 | Volume:3 | Issue:3|Papers Count:8

In Sahand area, northern part of Urmia-Dokhtar Magmatic Arc (UDMA) there are some high silica adakitic domes with rhyolite, dacite, trachy-dacite, trachy-andesite and andesite composition belonging to Late Eocene-Pliocene, the Eocene volcano-sedimentary series and in some cases the Oligocene-Miocene sedimentary rocks. They enclose some fragments of these rocks as xenoliths. The most abundant minerals in these rocks are plagioclase and amph-ibole with various textures such as felsitic porphyric, microlitic porphyric, sieve, flowage and glomeroporphyric. The parent magma of these rocks is calc-alkaline and per-aluminous in nature which is characteristics of the arc volcanism. These rocks fell in to the field of high-silica adakites (HAS) in classification diagrams. Enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depletion in heavy rare earth elements (HREEs) are obvious in their MORB, primitive mantle and chondrite-normalized spider diagrams. Strong depletion in HFSEs including Nb, Ti and P which is signature of arc volcanism, can be observed in these rocks. According to the petrogenetic diagrams, the parent magma of the rocks studied was generated by partial melting of an eclogitic or garnet amphibolitic source derived from metamorphism of the Neotethyan subducted oceanic slab underbeneath the Central Iranian zone. Also, the magma has been subjected to assimilation, fractional crystallization (AFC) and crustal contamination during ascend to higher levels and emplacement. The presence of the corrosion and chemical disequilibrium of the phenocrysts and their sieve textures in these rocks support the occurrence of these processes.

The study area is located in NE of Sarab in the East Azarbaijan province. Based on tectonic zonation this area is situated in the Alborz-Azarbaijan subzone of Central Iran zone. According to field studies, above mentioned volcanic rocks are the youngest edifice in the area and composed of trachy-andesite cones and lava flows with porphyritic texture. As well as petrographic studies indicate that they have porphyritic texture with fine-grained to glassy matrix. Poikilitic, vesicular and trachytic textures are among other textures found here. The main phenocrysts are: plagioclase, hornblende, clinopyroxene, orthopyroxene and opaque minerals. Apatite is an accessory mineral and secondary minerals are: sericite, iddingsite, calcite and opaques. According to geochemical classification, the studied rocks are intermediate and they are plotted in the trachy-andesite field. Also, these rocks are plotted in the field of high-K calc-alkaline series. In the REE diagrams the studied rocks indicate enrichment of LREEs rather than HREEs. This enrichment of LREEs and depletion of HREEs are characteristic of calc-alkaline rocks of arc volcanoes. Based on various geochemical diagrams, tectonic setting of formation of studied rocks is analogous with tectonic features of post-collisional arc settings.

The south Avarzaman granitoid pluton with Cretaceous age is located in the west of Malayer. From tectonic point of view it is a part of plutonism events of Sanandaj-Sirjan zone. In this region, injection of this pluton into the Upper Triassic-Lower Jurassic sediments with low metamorphic grade, caused the generation of metamorphic halo which includes the Hornfels and Skarn mineralization. According to the petrography and field evidences, the main rocks of this pluton is made up of medium to coarse-grained granodiorite, monzogranite and quartzodiorite rocks with a lesser amount of tonalite and syeno-granitic type. Several aplitic and quartzitic dykes cut the plutonic and host rocks. Dominant texture of these rocks is granular and porphyroid. The whole rock and minerals such as biotite analysis was used for geochemistry and the tectonic setting showing the same results. Chemically, magma of these rocks is a high-K calc-alkaline suite. Considering the saturation degree of aluminum, it ranges from peraluminous to a little metaluminous and shows mostly S-type nature but also some tendency to I-type. The granitoid pluton in this area, by using composition of biotite, displays calc-alkaline and peraluminous nature with volcanic arc tectonic setting. Since the samples are enriched in LREE more than HREE and show depletion of some elements such as Ti, P, Sr, Nb, besides of locating in the range of VAG, this granitoid pluton is supposed to be created in a volcanic arc setting in response to the subduction of Neothetys oceanic crust beneath the Iranian plate.

The Atash Kuh fluorite-barite deposit in south of Delijan (Markazi province) is an example of epigenetic-hydrothermal ore deposit hosted by limestone, dolomitic limestone, schist and slate of the Shemshak and Badamu formations with early to middle Jurassic age. Fluorite mineralization mainly occurs in east-west trending veins dipping up to 70 ° in two separate veins with length of 150m and various thicknesses from 0.5 to 3 m. Fluorite and barite ore minerals of veins occur as open space filling, breccia, void filling and disseminated textures. The subordinate components in the veins include hematite, galena, pyrite, and chalcopyrite. Based on petrographic studies, three types of dolomite are recognized in the mineralized veins including fine crystalline dolomite, medium-coarse crystalline dolomite and coarse-grained zoned dolomite. The zoned dolomites are mostly present in the mineralized veins, which are all close to fault and mostly filled vugs of the brecciated ore body. Chemical composition of the zoned dolomite shows that concentration of the various elements such as Na (170 ppm on average), Mn (620 ppm on average), Fe (7670 ppm on average), Ba (1120 ppm on average), and Sr (88 ppm on average). The Ca/Mg molar ratio is between 1.0 and 1.3. The La/Lu ratios and chondrite-normalized patterns revealed that the fluorites and associated host rocks are enriched in light rare earth element (LREE) relative to heavy rare earth element (HREE). This indicates that the REE leaching from source rocks and fluid migration occurred under high-temperature and low-pH conditions. Furthermore, the negative Ce anomalies of the Atash Kuh fluorites indicate that the mineralizing fluids deposited fluorite under reducing conditions, which is in agreement with the presence of galena, pyrite and chalcopyrite sulfide minerals in the area. The high contents of Mn, Fe and Ba elements in the coarse-grained zoned dolomite s, and the plots of Tb/Ca versus Tb/La ratios in the fluorites indicate a hydrothermal origin for the fluorite-barite±sulfide veins of the Atash Kuh deposit.

This paper elucidates the compositional studies on biotites and plagioclases in granitoid rocks of Torud area to understand the geotectonic setting and geothermobarometry conditions. The Torud granitoids with Oligocene age are composed of quartzmonzonite to granite. The main minerals of granitoids are quartz, plagioclase, and K-feldspar. Other constituents are biotite, amphibole, sphene and opaque minerals. Various textures including granular, myrmekitic, graphic, and prethite are observed in these rocks. According to the calculations of mineral plagioclase thermometery in granitoid rocks, pressure was about 1.5 to 2.5 kbar and the temperature of crystallization have measured about 700 to 1000oC. Also, the compositions of biotites in intrusive bodies indicate that they are of magmatic origin with calc-alkaline affinities having formed in a tensional tectonic setting.

Cheshmeh-Siah Titanium deposit is located in 25 km south of Shahreza town in Isfahan province. It lies in the Shahreza-Abadeh-Hambast belt, a part of Sanandaj-Sirjan Zone. Geological, mineralogical, petrographical and geochemical studies indicated that a strongly altered and fractured combined black clay and diabase sill unit hosted the main titanium mineralization, mostly composed of anatase and ilmenite. Titanium mineralization occurs in large area of 1x0.3 km. XRF analyses of 30 samples, collected from trenches in the mineralized zone, showed an average grade of 8.25% TiO2. It appears that in this deposit a clay unit, which contains Mn nodules, were deposited in Lower Triassic and then intruded by several diabase sills. The whole clay unit and diabase sill was subsequently folded and fractured by tectonic activities and finally altered by weathering processes. Geological, mineralogical, petroraphical and geochemical evidences show that the main source of Ti is originally attributed to the diabase sill intrusion into the claystone unit. The fractured and folded claystone and diabase sill unit was affected by a lateritization process and formed the major Ti mineralization in Cheshmeh Siah deposit. After lateritization it appears that small part of titanium mineralization has been formed by effect of hydrothermal solutions containing Fe-Ti complexes, possibly originated from post basic magma.

The Koffaz area (58 km2) is situated in SE of Southern Khorasan Province. Uni-variant and multi-variant geo-statistical analysis revealed that copper (as an enriched element) has bimodal distribution and it is well-correlated with Cr, Co, Ni, Ti and Mg. This correlation is reasonable because the weak Cu-mineralization (in form of malachite & azurite) is hosted by mafic and ultramafic rocks (ophiolites) and altered andesites. On the other hand Cu has good correlation with Mn and no correlation with other mineralizing elements. Sidvarak, Ab-Kamarak, Solabest and Zard-e Madan indices are situated in anomalies No.1 and 2. Based on field investigations, no noticeable indices were in the anomalies No.3, 4 and 5.