PETROLOGY
Year:2012 | Volume:2 | Issue:8|Papers Count:7

The study area which lies along the Uromieh-Dokhtar volcanic belt, comprises andesi-basalt, andesite, dacite, diorite and quartz-diorite with porphyry texture exposing as volcanic and sub volcanic bodies. The essential minerals of these rocks are plagioclase, amphibole, biotite and quartz accompanied by pyroxene and traces of k -feldspar. The propyllitic, potassic and phyllic alteration zones point to the occurrence of hydrothermal fluids. The studied amphiboles are Mg-enriched which ranges in composition from Mg-hornblende to actinolite. The biotites are also enriched in Mg, pointing to their formation in high oxygen fugacity conditions. The chemical features of these minerals are characteristics of porphyry Cu bearing intrusive rocks. The investigation of biotite chemistry shows that the fluid composition in the phyllic and potassic zones is different. The geothermometry of chlorites and biotites shows the temperatures of 275-323, 402-450oC and 249-256, 280-344oC for the potassic and phyllic zones respectively. These data are consistent with those of many worldwide porphyry Cu deposits.

The Khut deposit is located 40 Km west of Taft in the Yazd province and in the central Iranian volcano-plutonic belt. The intrusion of apophyses of granodiorite intrusion into the carbonate rocks of the Nayband Formation has led to the formation of marble, skarn and copper mineralization. The Khut skarn which is formed in the marble is calcic type and is divided into the garnet skarn and garnet-pyroxene skarn zones. Skarnification processes can be divided into the two distinct stages prograde and retrograde. The prograde stage is characterized by anhydrous calc-silicate minerals such as clinopyroxene and garnet. During retrograde stage, part of marble and anhydrous calc-silicates have been replaced by hydrous calc-silicates, sulfides, oxides and carbonates. The calc-silicate minerals in the Khut deposit were analayzed by electron microprobe. The comparison of chemical composition of garnet with the composition position of other calcic skarns show that the composition range of garnets in the Khut deposit is consistent with the composition range of garnet in the world's gold, iron and copper skarns. Also, the mineralogy and geochemistry of the Khut granitoid is similar to that of granitoids associated with skarn deposits. In this paper, by using petrographic and geochemical studies, the conditions of skarn formation in the Khut copper deposit is investigated.

The Lower Cretaceous pillow lavas and dibasic dykes are cropped out in several points in the North of Hajiabad belonging to Central Iran. The best exposure of these rocks is seen in Dum Kalagh Mountai. Field studies reveal that dykes intrude the pillow lavas and the space between the pillow lavas is filled by sediments, and the whole suite is covered by the Lower Cretaceous cherts and lime stones of the Biabanak formation. Minerals of these rocks are plagioclase (labradorite to albite), clinopyroxene (diopside), chloritized olivine, ilmenite, termolite -actinolite, epidote, prehnite, sericite, calcite, chlorite, pyrite and magnetite. Mineral chemistry of clinopyroxenes reveal a parental magma, with low H2O, high TiO2 content and high oxygen fugacity. Based on the geochemical studies, the primary magma of the pillow lavas is alkali basalt and that of the diabasic dykes is tholeiitic basalt. Geothermometry and barometry based on clinopyroxene chemistry display 750-850oC and 13-16 kbar. Geothermometry of chlorites shows 190-240oC and sub -sea floor metamorphism in the prehnite-pumpellyite facies. We conclude in this region, an aborted rift system developed during Lower Cretaceous. This study shows that rifting related to the opening of Neotethys is not exclusively limited to the Zagros geosuture and the surrounding area of the Central-East Iranian micro continental (CEIM).

The Eocene volcanic rocks in the south of Karkas region have been subjected to alteration by hydrothermal and the late magmatic fluids. These volcanics are acidic to intermediate in composition and they show calc-alkaline magmatic affinity. A regular distribution pattern is not observed in the alteration zones. The propyl tic zone forms the outermost part of the alteration facies. The propylitic and argillic have mostly a sharp boundary. The latter zone is characterized by kaolinite and veinlets of iron oxide (oxidized pyrite). The advance argillic zone, as dyke outcrop, occurs within argillic zone. It is also characterized by widespread alunite occurrences. On the base of EDS analysis and using K, Na, and Ca discrimination diagram, the acid-sulfate minerals are alunite to natroalunite in composition. The silicic zone is exposed the vicinity of advance argillic zone. The geochemical studies of rare earth elements in the studied altered zones indicate that silicic zone is depleted in REE, which may be deduced by high water/rock ratio and high activity of ion sulfate. The advance argillic zone displays LREE enriched and depletion in HREE which may be due to the presence of abundant alunite and the replacement of K by LREE in its structure. The REE-enrichment in argillic zone is notable. This can be related to the low acidity and immobility of these elements in this zone.

In the southeast of Uromieh-Dokhtar volcanic belt, southeast of Bardsir (kerman province), there are numerous gabbroic, dioritic and tonalitic intrusive bodies crosscutting the basaltic, andesitic lava flows and the pyroclastic of the Eocene age. The widespread distribution of intrusive rocks in the studied area, mineralogical similarity between these plutons and the volcanics as well as very similar chemical compositions of these two groups of rocks in different geochemical and tectonomagmatic discrimination diagrams suggest that the plutonic and the volcanic rocks may have been originated from the same origin. Geochemical characteristics indicate that the intrusive are calcalkaline and LREE-enrichment as compared with HREE, high contents of LILE relative to HFSE and the significant anomalies of Nb, Ti and P reveal that they belong to a subduction-related magmatism. All these evidences show that in the studied area parental magmas of both plutonic and volcanic rocks have been originated from partial melting of a metasomatized mantle wedge. The mantle probably enriched in incompatible elements by the slab derived fluids.

The petro graphical studies of carbonate rocks of Jurassic Dalichai and Lar Formations in Ahvanu region (North of Damghan) resulted in recognition and separation of five different types of dolomite including 1-Fine to medium planar dolomite rhombs, scattered in matrix; Rd1; 2- Coarse crystalline, euhedral mosaic dolomite, Rd2; 3- Medium to coarse crystalline, anhedral mosaic dolomites, Rd3; 4- Coarse-crystalline, euhedral to subhedral dolomite cements, Cd1; and 5- Coarse to very coarse crystalline, saddle dolomite cements, Cd2. Rd1, Rd2 and Rd3 dolomite textures are replaced in origin, whereas Cd1 and Cd2 dolomites are commonly as cements. Thin and polished section studies along with field observation indicated that ore is hosted by Rd3 dolomite. d18O (PDB) and d13C (PDB) values vary from -4.95 to -5.95% (average -5.53%) and 2.32 to 1.68% (average 0.072%), respectively. Considering petrography, paragenesis and stable isotope data, the dolomites in the Dalichai Formation of Ahvanu area are interpreted to have been formed in the subsurface during mechanical compaction at shallow to intermediate burial depths. Also, based on minor elements study, calcite is the primary mineral in the studied carbonates.

The Vash granitoid is located in NW Natanz and is a part of Uromieh-Dokhtar magmatic belt in Central Iran. This pluton is probably of Oligo-Miocene age and is the result of extensive magmatism which occurred during and post of the Alpine Orogeny. The composition of the pluton ranges from granodiorite to tonalite. The main minerals are quartz, plagioclase, alkali-feldspar and ferromagnesian minerals are biotite and amphibole. It contains a number of dioritic enclaves with different sizes. Based on geochemical studies, the Vash granitiod is similar to those of the subalkaline, calc-alkaline series, metaluminous, and displays typical features of magnesian I-type granites. The pluton is characterized by enrichment in large ion lithophile elements (LILE) such as Rb, Ba, K, Ce and depletion in high field strength elements (HFSE) such as Y, Nb and Zr. The chondrite normalized REE patterns are characterized by moderate to high LREE enrichment [(La/Yb)N=7.93-13.17] and unfractionated HREE [(Gd/Yb)N=1.09 to 1.88]. Granodiorites show least fractionated in HREE and a weak negative Eu anomalies (Eu/Eu*=0.69-1.16). The studied magma was likely derived from primary magma in the lower crust originated by partial meling of crustal protoliths as well as basaltic magmas formed by partial melting of mantle wedges. The v ash granitoid displays mineralogical and geochemical characteristics typical of volcanic arc granites related to an active continental margin. Tectonic setting of Vash granitoid may be syn-subduction magmatism or post-collisional magmatism due to extensional phases after collision of Lut micro continent and Arabic plate.