فهرست مطالب ملیحه گلستانی

The Gaz Boland area is located in the northwest of Shahr-e-Babak city within the southern extension of the Urumieh-Dokhtar magmatic arc. The extended convergence history of the Neo-Tethys Ocean between Arabia and Eurasia (from ∼150 to 0 Ma) comprised of a long-lasting period of subduction followed by continental collision during the Tertiary (Omrani et al., 2008). Following the collision, volcanism continued dramatically in some parts of the Urumieh-Dokhtar volcanic-plutonic belt, such as Pleistocene basic volcanism in the Shahr-e-Babak area in western Kerman. Thus, Neogene basalts in the Gaz Boland area in Kerman are known as the last magmatic activity of this part of Iran.

Ten samples of volcanic rocks were selected for geochemical analyses. All samples were analyzed for major elements by X-ray fluorescent (XRF) and trace elements using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), in the Kansaran Binaloud Co., Iran. The results of the analyses were evaluated using the GCDKIT software package.

Plio‐Pleistocene basaltic rocks are the youngest volcanic activity in the Gaz Boland area. The main texture of these rocks is porphyric with microlithic form and they contain major minerals of olivine, clinopyroxene, and plagioclase. Based on geochemical data, the volcanic rocks of the Gaz Boland region have been derived from a calc-alkaline magma. Moreover, examination of trace element diagrams of these lavas indicates that magma is related to the subduction zone and active continental margin. Based on various elemental ratios and diagrams, the volcanic rock-forming magma in the Gaz Boland area have been derived from the asthenospheric mantle deep in the subduction zone. The source rock composition of these basalts is garnet-bearing lherzolite, which has been slightly enriched during the subduction process by fluids originating from the subducting oceanic crust. The rock-forming magma was also contaminated by the continental crust during the ascent and has endured the AFC process.

The Gaz Boland calc-alkaline basalts show enrichment in LILE, LREE, Th, and U, but depletion in HFSE (Ta, Ti, and Hf) and HREE. These rocks show characteristics of subduction-related (active) continental margin tectonic environments. According to the Sm vs. Sm/Yb diagram (Aldanmaz et al., 2000), the Gaz Boland samples were plotted in the partial melting range of about 10 to 15% of a garnet-rich lherzolite source. Asthenospheric mantle-derived magmas have Nb/La ratios > 1 or La/Nb ≈ 0.7. A low Nb/La ratio (<0.5) indicates lithospheric mantle and high Nb/La ratio (>1) indicates asthenospheric mantle (Smith et al., 1999). On the other hand, lithospheric mantle-dependent magmas have a La/Nb ratio greater than 1, whereas, in asthenospheric mantle-derived magmas, it is about 0.7 (DePaolo and Daley, 2000). In volcanic rocks of the study area, La/Nb and Nb/La ratios are 0.2 to 0.7 and 1.5 to 4.8, respectively. In addition, volcanic arcs can be classified into highly enriched and poorly enriched categories based on Ce/Yb ratios. Enriched arcs are defined as having Ce/Yb >15 (Hawkesworth et al., 1991; Juteau and Maury 1997). The mean Ce/Yb of the Gaz Boland rocks is 9.7 which defines a poorly enriched arc signature. Certain chemical parameters can be used to assess the degree of contamination. For example, basaltic rocks affected by crustal contamination exhibit La/Ta ratios > 22 (Abdel-Rahman and Nassar, 2004) and Nb/Th ratios < 5 (Condie, 2003). The values of such elemental ratios in the Gaz Boland basalts are 18 to 64 and 3 to 5, respectively (Table 1), which suggest that the magma was subjected to crustal contamination.

The Gaz Boland area is located in Kerman Province, northwest of Shahr-e-Babak. This area is a part of the volcanic-plutonic belt of Urumieh-Dokhtar. Most of the exposed rocks in this region belong to Eocene age, however, the basalts with Pleio-Pleistocene age have also a relatively limited distribution in the region. The main texture of the basalts is microlithicporphyric and olivine, clinopyroxene and plagioclase form the main minerals. Due to the weathering and alteration processes, secondary minerals such as calcite, chlorite, and iron oxides have formed in these rocks. Based on the analysis of X-ray microprobe, the composition of pyroxenes is diopside-augite. The chemical composition of clinopyroxenes confirms the calc-alkaline nature for their parent magma of, which originates from the subduction-related tectonic setting. Based on clinopyroxene thermobarometric studies, the parent magma of the rocks, when crystallization of the clinopyroxene mineral with approximately 10% water under a pressure of 2 to 8 kbar occured, formed during uplift and before the eruption. The magma temperature variations during the crystallization of clinopyroxenes ranges between 1130 and 1249 °C.

Fathabad area is located in northwest of the city of Zarand (Kerman province) in the Posht-e-Badam block of the central Iran structural zone. The Ordovician–Silurian gabbroic stocks have intruded into volcanic-sedimentary rocks of the Rizu series. The gabbros are mainly composed of clinopyroxene, kaersutite, plagioclase and biotite. Electron microprobe analyses demonstrate that the clinopyroxenes are aluminous diopside with alkaline-to-peralkaline affinity. Thermobarometry studies reveal a temperature ranging between 1121°C to 1184°C for the formation of clinopyroxene, in which the pressure varies from 6 to 11 kb. The chemical composition of clinopyroxene grains exhibit their association with oceanic island basalts that are related to intraplate rift environments. It seems that the Fathabad alkalic gabbroic stocks are related to the Ordovician–Silurian Paleo-Tethys rifting events that were emplaced during the back-arc extension in the northern margin of the Gondwana supercontinent.

IntroductionThe Iju porphyry copper deposit is located in the southern part of the Urumieh-Dokhtar magmatic arc (Dehaj-Sarduieh belt) within the Kerman copper belt (Dimitrijevic, 1973). The Porphyry Copper mineralization in the Iranian plate occurs dominantly along the Urumieh-Dokhtar arc, which has resulted from the subduction of the Arabian plate beneath the central Iran and the closure of the Neo-Tethys Ocean during the Alpine orogeny (Hassanzadeh, 1993). The Iju porphyry copper deposit with 25 million tons of ore reserves is one of the main copper deposits within the Kerman copper belt. The mining area is composed of upper Miocene volcanic and subvolcanic rocks (mineralized and barren subvolcanic rocks) and quaternary deposits. Two hydrothermal alteration zones of quartz-sericite-pyrite and propylitic zones can be identified in the Iju area. The copper mineralization in the Iju deposit occurs as disseminated, stockwork and hydrothermal breccia. In the hypogene zone, the mineral paragenesis include chalcopyrite, pyrite, with minor occurrences of bornite and magnetite. This paper reports geological, mineralogical, fluid inclusion and S isotope data from the Iju deposit in order to investigate ore-bearing fluids’ characteristics and the mechanisms of ore deposition.
Materials and methodsFifteen samples of syngenetic quartzꜪ bearing veinlets within the quartz-sericite-pyrite zone were selected from different depths across the seven boreholes. Quartz was used for double-polished thin sections and pyrite was used for sulfur isotope analysis. Fluid inclusion studies were performed using the Linkam cooling and heating stage, the THMSG 600 model. The syngenetic pyrite with thermometry quartz sample was used for the sulfur isotope experiments. Stable isotope analysis was performed at the Hatch Stable Isotope Laboratory in the University of Ottawa, Canada.
ResultsThe fluid inclusions of the Iju deposit represent a wide range in the homogenization temperatures between 140 to 480°C and salinity between 0.18 to >52.99 wt.% NaCl equiv., which are most similar to the results of the other Iranian porphyry copper deposits. Being located in the quartz-sericite-pyrite alteration zone, the results of thermometry indicates that ore deposition in the Iju deposit has occurred via mixing of magmatic and surface fluids. Variations in salinity and paragenesis of the saline multiphase fluid inclusions and two-phase gas-rich fluid inclusions indicate the occurrence of boiling phenomenon in some samples of the Iju deposit. The amount of δ34S for pyrite has a limited range close to zero (average, 0.229‰) that shows a magmatic origin for sulfur. Considering the presence of subvolcanic rocks, the type and extension of alteration zones, the structure and texture of ore bodies, thermometry results of fluid inclusions and sulfur isotope values, the Iju deposit is similar to porphyry copper deposits.
DiscussionIn the quartz-sericite-pyrite zone, three main groups of veinlets have been identified. The quartzꜪ veinlets are more abundant than the other types and they were selected for fluid inclusions and stable isotope studies. Petrographic studies of fluid inclusions identifies two groups of fluids including: 1- fluid inclusions without the halite phase, including the types L, L埤 and (L埤뗹, that is secondary), 2- fluid inclusions with halite phase, including the types L埡, L埡﹋, L埡﹋徒 and L埡﹋往. Homogenization temperature and salinity for the fluid inclusions without halite phase are as follows: 140 to 380°C and 0.18 to 24 wt.% NaCl (Fig. 8A and C) and for the fluid inclusions with halite phase they range from 230 to 480°C and 30 to 52 wt.% NaCl (Fig. 9A, B and D), In addition, the pressure and depth for the fluid inclusions containing halite phase are 750 bar and 3500 m on the average. Fluid inclusions available at the quartz veinlets of porphyry copper deposits can be formed in a wide range of chemical composition and under different temperature and pressure conditions (Rusk and Reed, 2008). The wide range in fluid inclusions data of the Iju deposit can be justified by physicochemical changes in the fluid as it is boiling and mixing with the surface fluids. Cooling, fluids mixing, boiling and fluid-rock reaction play important roles in the settling of chalcopyrite from the hydrothermal fluid and the dilution of saline ore-bearing fluids can cause the formation of copper ores from the ore-bearing fluid (Ulrich et al., 2002). Pyrite δ34S value ranges from -0.86 to .27‰ (average, .22‰) and the δ34SH2S value of the syngenetic fluid with pyrite ranges from -0.23 to -2.36‰ (average, -1.17‰). The limited and near zero range that is observed about δ34S value of the sulfur minerals indicates the controlling role of magmatic processes in the mineralization events (Chen et al., 2009).

Baft ophiolitic melange, as a part of ophiolitic melange belt of the Central Iran, is adjacent to Urumieh-Dokhtar magmatic assemblage in the north and Sanandaj-Sirjan metamorphic zone in the south. The ophiolitic complex has been emplaced in the Late Cretaceous time as a result of closure of Nain-Baft oceanic basin. The gabbros are the main constituent of the complex and occur as large intrusive bodies showing isotropic and rarely layered structures with hypidiomorphic granular to pegmatitic textures. The color index varies from melanocratic to lesser extent mesocratic and leucocratic. Geochemical studies reveal that gabbros are tholeiitic to calc-alkaline, low-Ti in nature and show similarity to N-MORB. The chondrite-normalized rare earth elements patterns are almost flat with slight enrichment in LREEs relative to HREEs which indicates a similarity in their origin. It seems that gabbros were derived from a depleted refractory mantle source in a subduction zone setting.

The Baft ophiolitic mélange, covering an area approximately 150 Km2, is located in the Esfandaghe-Khamrood melange belt. The main part of intrusive rocks in the Baft ophiolitic mélange consists of gabbros, mostly isotropic and occasionally as pegmatitic rocks. Plagiogranites, as veins and small outcrops, are common along with gabbros and doleritic dikes through the area. Plagiogranites consist of trondhjemite, albite granite and granophyre. Based on geochemical studies, gabbros and plagiogranites are belonging to tholeiitic-calc-alkaline magmatic series. Plagiogranites are metaluminous to slightly peraluminous and typologically show characteristics between oceanic ridge (OR) and I-type granites which is consistent with their formation in a supra-subduction zone environment. Chonderite normalized REE patterns of plagiogranites show slight enrichment in LREEs along with flat HREE patterns. Chonderite normalized REE pattern of gabbros are relatively flat with slight enrichment in LREEs compare to HREEs. The derivation of an acidic melt from a gabbroic phase through either fractional crystallization and/or partial melting is less likely. It appears that the origin of Baft ophiolitic melange plagiogranites must be related to doleritic phase, although partial melting of hornblend gabbro and/or amphibolite can be also considered for at least one of the samples.