نشریه پترولوژی
پیاپی 17 (بهار 1393)

The Kuh-e-Surmeh Pb-Zn deposit is located 50 km south of Firouzabad in the Zagrous mountain folding belt. The upper Permian carbonates of lower Dalan Formation are hosted by mineralization. Galena، sphalerite and pyrite are the main ore minerals and chalcopyrite and smithsonite have been found as the accessory minerals. Mineralogical paragenesis point to mineralization taken place in several stages. Based on the stable isotope analyses the δ34S values of the sulfide minerals are in the range of +10. 12 to +15. 2‰ and those of the sulfate minerals vary between +12. 8 to +14. 9 ‰. The δ18O and δ13C values of the white dolomites exhibit values in the range of -11. 29 to -18. 32‰ and -6. 08 to -8. 31‰ for δ18OPDB and δ13CPDB respectively. Geochemical evidences imply that thermochemical sulfate reduction processes have supplied required reduced sulfur for ore deposition، which seems to be provided through sulfates reduction in the Jahani salt dome. So the Kuh-e-Surmeh mineralization could be explained by mixing model. Dolomitization is affected by two different fluids. The main fluid originated from deeper hydrothermal or basinal sources related to the Precambrian rock units. These brine fluids have ascended through faults related salt diapirism. The second one is sourced from meteoric water. Comparing of sulfur isotope values of the Kuh-e-Surmeh deposit with other carbonate hosted base metal sulfides deposits، display that the mineralization is likely the Mississippi valley type.

The Sungun porphyry copper mine is located in the north of Varzeghan، Eastern- Azarbaijan province. The oldest rocks in the study area are limestone with the Cretaceous in age. Following the emplacement of intrusive porphyry body، four groups of dyke with various compositions have been intruded into the intrusive body. The intrusive is quartz-monzonitic in composition. There are four alteration zones including potassic، phyllic، propylitic and argillic in the Sungun porphyry body. The common texture in these rocks is porphyritic with cryptocrystalline matrix، and in dykes، microlitic and microlitic porphyry. The Sungun porphyry body evolved due to magmatic differentiation، fractional crystallization، assimilation and crustal contamination. The Sungun intrusive and associated dykes are meta-aluminous and belong to high-K calc-alkaline to shoshonitic magma series. In terms of tectonic setting، the Sungun body lies in syn- to post-collision volcanic arc. In the contact of the Sungun porphyry and the upper Cretceous limestones and marls، the Cu-Fe skarn developed in the north and the east. These skarns are divided into the endoskarn and exoskarn. Based on field geology and mineralogical studies، the exoskarn in Sungun is divided into pyroxene، garnet and epidote zones.

The Takht granitic batholith of Sirjan contains gabbro-diorite to alkali-feldspar granite in composition. The batholith was emplaced in the south of the Urmia-Dokhtar magmatic belt in the Oligo-Miocene. The depth and temperature of the emplacement of the batholith is between 5. 5 and 10. 5 km and 750 to 900°C، respectively. The crystallization conditions of the rocks were examined on the base of chemical composition of minerals using the thermometers and barometers description diagrams provided by previous researchers. Hydrous minerals such as biotite and amphibole crystallized along with plagioclase، quartz، clinopyroxene، titanite، apatite، and magnetite under subsolidus condition. The nature of the batholith is calc-alkaline and cordilleran I- type. Lithological changes in the batholith are due to fractional crystallization. The injection of the Takht batholith is related to the last stages of Neotethys subduction activity under neath the Central Iranian plate. Oblique subduction created appropriate spaces in the edge of the Central Iran. Hence، partial melting occurred due to decompression in the mantle wedge or base of the lower crust. The melts، which were gabbro-diorite to granite in composition، were injected into these spaces.

Some high silica adakitic domes with rhyolite، dacite، trachy-dacite، trachy-andesite and andesite compositions belonging to upper Eocene-Pliocene، trending W-NW، intruded in to the Cretaceous-Paleocene ophiolitic complex، the Eocene volcano-sedimentary series and in some cases the Oligocene-Miocene sedimentary rocks، and enclose some fragments of these rocks as xenoliths. The most abundant minerals in these rocks are plagioclase and amphibole with various textures such as felsitic porphyric، microlitic porphyric، sieve، flow and glomeroporphyric. The presence of large volumes of detritic fragments of these adakitic domes in the Pliocene conglomerates and their absence in the Miocene detritus indicate uplifting and exposing of the studied domes in the earth surface in the Miocene-Pliocene interval. The parent magma of these rocks has calc-alkaline and per-aluminous nature which is characteristics of the arc volcanics. These rocks fall into 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 volcanic، can be observed in these rocks. According to the petrogenetic diagrams، the parental magma of the rocks studied generated by partial melting of an eclogitic-garnet amphibolitic source derived from metamorphism of the Sabzevar Neotethyan subducted oceanic slab underneath the southern edge of the eastern Alborz zone. Also، the magma has been subjected to assimilation، fractional crystallization (AFC) and crustal contamination during ascend to higher levels and emplacement into the ophiolitic belt. The presence of the xenoliths، corrosion and chemical disequilibrium of the phenocrysts and their sieve textures and (Sr87/Sr86) i ≈0. 7045 in these rocks support the occurrence of these processes.

The Khezr-Abad granitoid intrusive body is located in the north-west of Yazd province within Urumia-Dokhtar magmatic arc. The intrusion of this body into the Cretaceous carbonate rocks (Taft Formation)، gave rise to Hasht-kuh skarn mineralization with the following mineral assemblage: Garnet+ Clinopyroxene+Epidote+Tremolite-Actinolite+Chlorite+Calcite+Quartz Mineral associations studies show that pyroxene- garnet occurrence have most relations and are widespread in skarn. A detailed study of paragenetic relationships of skarn minerals clearly demonstrate that there are two stages in skarn evolution system، so the Hasht-kuh skarn can be considered as a polygenic skarn. On the basis of mineral chemistry data the garnet tends to be grossular and pyroxene is augite in composition. The peak temperature of contact metamorphism episode is accompanied by pyroxene crystallization in the early stage followed by overprinting of garnet formation. Due to presence of Al/Fe+3 periodic changes in fluids during garnet precipitation، zoning structure in some garnets was developed. The prevailing oxidation conditions during crystallization of fluids caused the instability of pyroxene (reducing ƒO2) and the growth of andradite garnet could be occurred at T<550°C in skarn system.

The Sarkhar and Bermani granitic rocks is located 300 km southeast of Mashhad، east of Sangan Mine، and northeastern Iran. Granitoid rock intruded older rocks such as crystalline limestone and dolomite and metavolcano-sedimentary rocks in the pre-Carbonifer age، and slate، quartzite، and conglomerate in the Carbonifer age. Monzogranite and syenogranite are two main intrusive rocks exposed in the study area. Biotite monzogranite porphyry and biotite microgranite are found mainly as dike cutting the intrusive rocks. The results of U-Pb zircon age dating of the monzogranite and syenogranite is 41 Ma (Middle Eocene). These intrusive rocks are older than granitoid associated with the Sangan mineralization. The texture of these rocks is hypidiomorphic granular and quartz، plagioclase، K-feldspar، hornblend، and biotite are the main minerals. Chemically، intrusive rocks are meta-aluminous to moderately peraluminous and shoshonitic. These intrusive rocks based on: K2O/Na2O= 1. 3 to 2. 2، Zr>200ppm، Nb>20 ppm، Ce>100 ppm، Y>30 ppm، Ga>20 ppm، and strong enrichment in REE specially in LREE plot in the field of A-type granite. However، the ratio of FeOt/FeOt+MgO is low (0. 5 to 0. 9) and they are magnesian character. Spider diagram normalized with average continental crust show enrichment in HFSE، Zr، Nb، Ga، Ta، Y، Hf and depletion in Ba and Sr. They belong to post orogenic granitoid. Granitoid associated with the magnetite mineralization at Sangan mine are I-type and originated from subduction zone. Granitoid rocks within the study area (east of Sangan mine) belonging to A2 group and generated by the magma from the continental crust.

The Nasrand pluton of Oligo-Miocene age، which is located approximately 40 km south-east of Ardestan، intruded into the Eocene volcanic rocks of the Urumieh-Dokhtar magmatic belt. This pluton consists mainly of granite and granodiorite. The Nasrand plutonic rocks are metaluminous، weakly peraluminous، with mineralogical and geochemical characteristics of I-type، calc-alkaline to K bearing calc-alkaline granite. The granitic rocks as well as their host volcanic rocks have been crosscut by a series of NE-SW trending diabasic dikes. The plutonic rocks are characterized by enrichment of LREE and LILE، depletion of HREE and HFSE، the negative anomalies of Ti، Nb interpreted to reflect the emplacement of the granitic rocks as well as the diabasic dikes in an active continental margin. The positive anomalies of Rb، K، Th، U and the negative anomalies of Nb،Ti، Eu، Ba، Sr associated with high Ba/Nb (46-139) and Ba/La (17-77) ratios suggest that fusion of continental crust has played an important role in the genesis of the Nasrand granitic rocks and diabasic dikes.

The Molataleb granitoid lies in the Sanandaj-Sirjan Zone and composed of granodiorites، tonalites and minor diorites which intruded into the Jurassic (Lias-Dogger) shales and slates. Quartz، plagioclase، orthoclase، biotite، amphibole، tourmaline، andalusite، garnet، apatite and zircon are the major and minor minerals of these rocks. The essential petrological characteristics of the body are، the P2O5 content decreases versus the SiO2 wt% increases، the content of aluminium saturation index (ASI= 1-1. 1)، the trend of increasing of Zr vs SiO2، the chemistry of biotites and the formation temperature of the body (500-700°C)، all are the remarkable features of low temperature medium peraluminous I-type granites. The descending trend of Al2O3، TiO2، Eu and Zr against Larsen Index and also the decrease of K/Rb ratio versus Rb suggest fractional crystallization of plagioclase in the studied granitoid samples. The chondrite-normalized REE''s diagrams display LREE''s enrichment relative to HREE''s. This can be owing to low degree partial melting or relatively enrichment of alkali elements in the source rocks associated with subduction zone. The alkali elements enrichment may be due to crustal contamination. Also، the high level of LILE''s and the HFSE''s depletion indicates that magmatism occurred in subduction of Neotethyan oceanic crust beneath Central Iranian microplate and the studied intrusive body is classified as volcanic arc granite (VAG).

The study area is located 39 km northwest of Naein and is a part of the Urumieh- Dokhtar volcano plutonic arc. The volcanic and pyroclastic rocks have been altered by hydrothermal fluids. According to field studies and petrographic observations the predominant rock types are basaltic andesite، andesite، dacite، rhyolite، tuff and ignimbrite which are related to the Eocene volcanic activity period. According to mineralogical and geochemical studies there are four different alteration zones including propylitic، phyllic، argillic and silicic. Furthermore، using the satellite data processing the existence of the hydrothermal alteration zones are established which the most widespread one is argillic. The REE''s behavior displays different patterns in various alteration zones. The negative Eu anomaly in the argillic zone points to the presence of clay mineral. The silica bearing samples are highly depleted in REE content due to whole destruction of host rock minerals، decreasing of PH and increasing of fluid/ rock ratio. Base on mass changes during hydrothermal alterations processes، there are depletion and enrichment of some elements in alteration zones. Incidentally enrichment is determined in propylitic zone and silicic zone show the most depletion.