PETROLOGY
Year:2018 | Volume:8 | Issue:32 |Papers Count:6

In the north of Kerman city, between Deh-Bazargan and Sarasiab 6 villages and along the Koohbanan fault, several lamprophyric dykes have been intruded the Shemshak, Bidu and Hodjedk Formations. The dykes show porphyry and glomeroporphyry textures and contain coarse-grained phenocrysts of olivine (30 vol.%), pyroxene (20 vol.%) and amphibole (5 vol.%) crystals in a matrix containing 10 vol.% plagioclase and sanidine microlites, fine-grained pyroxene (20 vol.%) and amphiboles (5 vol.%). Electron microprobe analyses show that the pyroxenes are diopside (Fs7.84-15.11) - (Wo42.20-46.75) - (En41.57-49.24), olivines are chrysolite (Fo85.79-91.20), plagioclases are labradorite (An50.94-66.30) and opaque inclusions in olivines are chrome-spinel (Cr1.3-1.25) - (Fe0.708-0.548) - (Al0.518-0.433). Petrographical evidences such as lack of coarse-grained felsic minerals, the presence of porphyritic texture and the co-existence of coarse-grained pyroxene, olivine and amphibole minerals as well as the similar oxides contents of SiO2 (44.25-46.435 wt.%), MgO (5.81-19.125 wt.%), Na2O (1.55-2.035 wt.%), K2O (1.18-1.715 wt.%) to the average of the well-known alkaline lamprophyres (SiO2=42.5 wt.%, MgO=7.25 wt.%, Na2O=35 wt.%, K2O=25 wt.%), suggest that the studied dykes are similar to the alkaline lamprophyres (monchiquites) rather than calcalkaline spessartites. Thermo-barometric studies of pyroxenes show that the rocks under discussion have been formed under pressure of 5-10 Kb and temperature of 700-900oC with less than 10 percent water contents. Whole rock chemical analyses of the studied lamprophyres indicate that the parent magmas were alkaline type and originated from a metasomatized spinel-garnet-lhezrolite mantle source containing hydrous minerals, then they were emplaced in a post-collisional arc setting.

The Agh-Daragh study area in the north of Ahar is located in Ahar-Arasbaran zone. The area is distinguished by W, Cu and Au metal endowment and has been explored during stream sediment and heavy mineral exploration. At least, three mineral occurrences are detected in Agh-Daragh area including Cu stockwork-disseminated mineralization in Chupanlar (occurred in Omz quartz-monzonite), Cu-Au±W vein-type mineralization in Ayran Goli (occurred in Og granodiorite), and Fe±Cu skarn in Gowdal (occurred between quartz-monzonite unit and crystallized carbonate). Chemically, Agh-Daragh mineralizationrelated metaluminous granitoids belong to oxidized, I-type and high-K calc-alkaline to shoshonitic series. They have SiO2=63.5–67.6 wt%, Al2O3=14–16.5 wt%, and K2O/Na2O =0.5–1.8. Moreover, LILE enrichment relative to HFSE depletion and HREE in the granitoids and the dikes occurred due to fluid-melt interaction, which are characteristics of subduction tectonic environment. In their magmatic evolution, the Agh-Daragh intrusive rocks underwent a transition from the early intrusive phases belonging to granodiorite (Og unit) with low K/Na and Fe2O3/FeO ratios and to the late intrusive phases belonging to quartz-monzonite (Omz unit) enriched in K (K/Na>1) and oxidized (Fe2O3/FeO>1). It seems that high content of volatiles in high-K and oxygenate magmas occurs due to saturation of magmatic melt in water under a lower degree of quartz-monzonite crystallization immediately preceding Cu-Au±W mineralization at Agh-Daragh intrusive suite. Combining our field geology and geochemical-metallogenic evidences, we conclude that the mineralization in Agh-Daragh area mostly occurred in accompany with late quartzmonzonite stocks; as a result, identification of high-K intrusive rocks and related dikes have important implications for proceeding exploration planning specially indicating of drilling points, and further refines the basis for mineral exploration in Sheyviar Dagh intrusive suite and subsequently in Ahar-Arasbaran metallogenic zone.

In the central part of the Sanandaj-Sirjan zone, there is an ultramafic rock exposure (hornblendite and pyroxenite) adjacent to Molataleb felsic complex completely located between Azna and Aligoodarz towns. The ultramafic rocks are actually cumulates derived from boninitic magma. During Upper Triassic-Lower Jurassic time the boninitic magma has been originated from mantle wedge as the result of initiation of Neo-Tethys subduction. Later, when subduction was proceeding, the felsic rocks crystallized in Middle Jurassic. Major elements composition of olivine, pyroxene, amphibole and minor plagioclase from the ultramafic rocks reveals crystallization from a sub-alkaline to calc-alkaline magma in a subduction zone setting. Primary minerals have chemical characteristics typical of those derived from a magma with low oxygen fugacity. Different methods for minerals thermobarometry indicate that amphiboles crystallized in relatively low temperature (880oC) but crystallization condition of other minerals corresponds to higher temperatures (1000-1200oc). They were crystallized at pressure condition equal to 5.85 kbar corresponding to the depth of ~17 km. It is not common that a mantle wedge at the depth of ~17 km to be affected by such high thermal gradient during the normal subduction process. Asthenospheric flow around the subducting slab edge during subduction initiation can explain high thermal gradient prevailed the infant mantle wedge. This mechanism corresponds to the boninitic nature of the ultramafic rocks.

The Iju porphyry copper deposit is located 72 km NE of Shahr-e- Babak in the western part of the Dehaj - Sardueih zone in the Kerman Cenozoic volcano - plutonic belt. In this deposit, the Miocene granitoids with dominant composition of granite, granodiorite, tonalite and quartz diorite were intruded in the Eocene volcanic and pyroclastic sequences. The potassic, propylitic, potassic-phyllic, phyllic and argillic facies are the main hydrothermal alterations in the Iju intrusive masses. Nevertheless, the hypogene mineralization is manly occurred in the potassic alteration. The aim of present work is the investigation of reequilibrated biotite and chlorite chemistry to characterize the potassic alteration in the onset of mineralization. Also, the chlorite data is used for assessing the geochemical changes owing to chloritization of biotite. Based on reequilibrated biotites, it is proved that oxygen fugacity during the potassic alteration was high so that mostly belongs to the hematite- magnetite buffering district. Moreover, the temperature in the onset of sulphide mineralization has an average of 399.85oC. According to variations in Log (¦H2O/¦HF) and Log (¦H2O/¦HCl) values, it seems that non-homogenous hydrothermal fluids were contributed in the formation of potassic alteration in the Iju deposit. Secondary chlorites that replaced biotite have clinochlore composition and chloritization occurred around 325.48 to 373.51oC. The chloritization process lead to Mg increasing as well as significant K2O and SiO2 decreasing contents due to the formation of K-feldspar minerals. Overall, it seems that high temperatures and the prevailing of high oxygen fugacity could be considered as one of main reasons for the low sulphide mineralization and the sub-economic nature of the Iju porphyry deposit.

The southwest Salmas metamorphosed mafic-intermediate intrusive rocks are located in Sanandaj-Sirjan zone in NW of Iran. The metamorphosed intrusives rocks comprisemetagabbro and metadiorite that intruded the Precambrian metamorphosed volcanicsedimentary rocks. U-Pb zircon dating of two samples of metagabbro rocks yielded age of Ca. 548.7±2.5 Ma to 553.1±7.0 Ma and one sample of metadiorite rock yielded age of 542±6.5 Ma (late Neoproterozoic-Cambrian). Based on the obtained geochemical results, these rocks were crystallized from subduction-related melts.The ef (t) values of these rocks are variable from+6.2 to+14.16. Hf model ages of mafic-intermediate rocks from the SW Salmas show values of 593-1000 Ma (Neoproterozoic). U-Pb zircon dating and Hf isotope results indicate that late Neoproterozoic-Cambrian metamorphosed mafic-intermediate intrusive rocks in the northwest of Iran were related to widespread magmatism (Cadomian magmatism) along the northern margin of Gondwana.

The Darvazeh pluton is located in the south of Qorveh. Olivine gabbro, diorite, quartz monzonite and granite rocks are rock forming of this body, but this paper is focused on the leucocratic to mesocratic rocks (quartz monzonitic and granitic rocks). These rocks were effected by dynamic tectonic activity during the intrusion and according to the distance of shear zone; deformation can be classified to cataclastic, protomylonite and mylonite. Microstructure evidences including the presence of porphyroclasts, bending of crystals and their twining, myrmekitic and pertite textures which caused by stress. Based on the microstructure features, deformations occurred at temperature of about 500-600oC. The geochemical data suggested that the felsic rocks belong to calcalkaline, ferroan, I-type and metaluminous to slightly peraluminous series. Enrichment in LREE/HREE; negative anomalies of Ba, Ti, P, Sr, Nb and U, Th, Pb positive anomalies and Th/Ta ratios indicate continental arc setting. The presence of mafic enclaves, high volume of granite and negative trend of Zr versus SiO2, all suggest that the felsic rocks were generated via partial melting process. According to geochemical characteristics, the studied granitoid was originated by partial melting of meta basaltic rocks in the lower crust.