Part Of Urumieh-Dokhtar Magmatic Arc Research Articles

Magnetite chemistry of the Sarkuh Porphyry Cu deposit, Urumieh–Dokhtar Magmatic Arc (UDMA), Iran: A record of deviation from the path sulfide mineralization in the porphyry copper systems

The Miocene Sarkuh porphyry Cu deposit is located in the southwestern part of Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran. Compared with the neighboring giant Sarcheshmeh porphyry Cu deposit, this is a low-grade sub-economic porphyry Cu system (110 million tons @ 0.26 % Cu) characterized by an unusual abundance of magnetite. The present work tried to answer the question of whether or not there are differences in the hydrothermal system of Sarkuh, resulting in the lack of considerable mineralization. In this way, the mineral associations and EMPA data of magnetite were considered to distinguish the different stages of magnetite crystallization reflecting the magmatic-hydrothermal evolution of the Sarkuh deposit. They include (1) magmatic stage magnetite, including magnetite inclusions within primary silicate minerals (i.e., plagioclase and biotite), (2) pre-ore stage magnetite associated with potassic alteration assemblages, (3) main ore stage magnetite tightly associated with sulfide mineralization, and (4) late stage magnetite forming overgrowths on the sulfides. The results of EPMA analysis confirm that magnetite of these four stages differ in Mn, Fe, Ti, Mg, Al, Cr, and V concentrations. Higher V concentrations are found in the magmatic and pre-ore stages, whereas Al and Si reach the highest in the ore and late stages. Our data show that increasing fluid-rock interaction and changes in the oxygen fugacity, especially during the main ore stage extending to the late stage, are key factors controlling the trace element partitioning of magnetite. Most of ore stage magnetite formed at temperatures >500 °C and high temperatures prevailed during it. Magnetite crystallization after the main stage of sulfide mineralization accompanied by (partial) martitization indicate the increase of oxygen fugacity towards the late hydrothermal stage. This could explain why the ore and late stage magnetites show chemical similarities to those from sulfur-poor iron oxide copper‑gold (IOCG) deposits rather than porphyry deposits.

Evidence of gas plume model in porphyry copper deposits based on anatomy, fluid inclusions and H-O isotopes: Insight from Kahang deposit, Iran

The Kahang deposit (100 Mt at 0.6% Cu) is one of the important porphyry copper deposits in the central part of Urumieh-Dokhtar Magmatic Arc (UDMA), Iran. The mineralization occurs as chalcopyrite and molybdenite in quartz and anhydrite -bearing veinlets or breccias and is closely associated with sericitic and phyllic alterations. Through comprehensive studies of the deposit's anatomy, some previously overlooked evidence raised new questions about the ore-forming process in the Kahang deposit. The coexistence of sulfate and sulfide minerals as veinlets and breccias, pore space breccias, could not be justified solely based on a previously introduced concept (i.e., mixing high temperature-high salinity magmatic water with low temperature-low salinity meteoric water). Fluid inclusions were examined in quartz veinlets of the A1, A2, and B types, anhydrite veinlets, and sphalerite of the L type veinlets. There are three types of fluid inclusions: liquid-rich (L-type), vapor-rich (V-type), and hypersaline (H-type). According to microthermometry of fluid inclusions, the fluids associated with anhydrite veinlets have relatively high temperatures (390–495 °C, mean = 455 °C) and low salinities (12.8–20.9 wt% NaCl equiv.) On the contrary, temperatures below 400 °C justified the coexistence of sulfate and sulfide minerals. The low solubility of anhydrite in high-temperature waters, on the other hand, demonstrates the gas–solid reaction of SO2 (g) and plagioclase at such temperatures, as evidenced by fluid inclusions. Additionally, the fluid inclusions in quartz veinlets generated temperatures (290 to >600 °C) higher than those in the majority of other porphyry copper deposits. H-O isotopes indicated that magmatic fluids dominated, and meteoric waters played an insignificant role. These findings and observations supported the formation of the Kahang porphyry copper deposit as a result of a gas plume and the reactions of gas species with plagioclase to form anhydrite and sulfide minerals, as well as the formation of sericitic alteration in the host rock as a novel scenario.

Fractal analysis and structural mapping for copper exploration in Veshnavah area, central part of Urumieh-Dokhtar Magmatic Arc (UDMA), Iran

Fractal analysis and structural mapping for copper exploration in Veshnavah area, central part of Urumieh-Dokhtar Magmatic Arc (UDMA), Iran

Zircon U-Pb Ages and Magmatic History of the Kashan Plutons in the Central Urumieh-Dokhtar Magmatic Arc, Iran: Evidence for Neotethyan Subduction during Paleogene-Neogene

The Kashan plutons are situated in the central part of Urumieh-Dokhtar magmatic arc recording subduction-related magmatism within the Alpine-Himalayan orogeny in Iran. These rocks consist of different calc-alkaline plutonic rocks including gabbro, gabbroic diorite, microdiorite, monzodiorite, tonalite, granodiorite, and granite. The plutons were emplaced into the Jurassic sedimentary units (Shemshak Formation) and the Eocene calc-alkaline volcanic and pyroclastic rocks. New U-Pb zircon ages show that the Kashan plutons formed during two main periods at 35.20±0.71 Ma in the Late Eocene (Priabonian) and at 18.90±0.84, 19.26±0.83, 19.30±1.2, and 17.3±1.8 Ma in the Early Miocene (Burdigalian). The reported events in the Kashan plutons imply the final phases of subductionrelated magmatism before the collision which happened between the Arabian and Iranian plates in the Middle Miocene. The plutonic activity in the Kashan region occurred during the transition from Eocene subduction-related setting to Middle Miocene collisional setting.

Geochemistry and zircon U-Pb geochronology of Miocene plutons in the Urumieh-Dokhtar magmatic arc, east Tafresh, Central Iran

ABSTRACT The Tafresh plutons that include Ahmadabab diorite, Vasfonjerd monzonite, Mehrezamin diorite and Chahak diorite, located to the east of Tafresh city, north-central Iran, are part of Urumieh-Dokhtar magmatic arc. U-Pb dating of zircon grains provides emplacement ages of 22.3 ± 1 Ma for the Ahmadabad diorite, and tightly clustered ages of 22.2 ± 0.2 Ma, 21.3 ± 0.2 Ma, and 21.7 ± 0.4 Ma for Vasfonjerd monzodiorite, Mehrezamin diorite-monzonite, and Chahak diorite-monzonite plutons, respectively. These rocks are metaluminous to weakly peraluminous, calc-alkaline, and characterized by enrichment in light rare earth elements, Nb-Ta negative anomalies, and high LILE/HFSE ratios. Tafresh plutonic rocks originated from a parental magma source and experienced different degrees of partial melting. Geochemical signatures of Tafresh plutonic rocks, such as a wide range of Y/Nb (2.7–8.4) and low Zr/Nb (19.5–35.) ratios, Nb/Ta (11.46–18.15), argue for mantle–crust interaction during generation of Tafresh magmas. Relatively low Nb/La ratios further indicate that the lithospheric mantle played a significant role in melt generation. HREE signatures (i.e. decrease Dy/Yb with increasing SiO2) preclude substantial involvement of garnet either in the residue, both during partial melting and fractionation of the magma. The plutons are a product of final stages of subduction-related magmatism prior to the collision between the Arabian and Eurasian tectonic plates.

Extensional magmatism in a continental collision zone,Tafresh area, western central Iran: structural, geochemical and mineralogical considerations

The Tafresh area, located on the middle part of Urumieh-Dokhtar magmatic arc, is a suitable area for considering the effects of tectonic structures on development of the volcanic facies in the magmatic provinces. The main structure in the area is a dextral fault (so called Rahjerd Fault) that has produced the local extensional basins and also the parallel dyke swarms (or feeder dykes) on its both sides. So, the pyroclastic deposits, basaltic-andesitic lava flows, parallel dyke swarms were appeared by explosive subaqueous and then effusive subaerial eruptions and eventually a dioritic stock intruded in the volcanic pile. Petrologically, the magmatic rocks are belonged to the calcalkaline suite that had been changed and evolved in the magma chambers of local extensional basins in a collisional tectonic setting. The mineral chemistry and geochemical modeling as well as the coexistence of different mineral paragenesis of plagioclases (An47-72 and An17-37), pyroxenes (diopside and pigeonite) and amphiboles (magnesiohastingsite and magnesiohornblende) reveal that the AFC process is a dominant process in the magma chamber. Also, according to geothermobarometric calculations, the investigated volcanic rocks of the area could be grouped into two types: one type with higher P-T (>6Kbar and about 900 °C) including Eocene pigeonite-magnesiohastingsite bearing andesites (PHA) and Miocene andesites and other with lower P-T (1-4 Kbar and 600- 800 °C) including the Eocene diopside-magnesiohornblende bearing andesites (DHA) and the dioritic stock.

Petrology, Geochemistry and Tectonomagmatic Evolution of Hezar Igneous Complex (Rayen- South of Kerman- Iran): the First Description of an Arc Remnant of the Neotethyan Subduction Zone

The Hezar Igneous Complex (HIC) in the south-eastern part of Urumieh-Dokhtar magmatic arc, is the most prominent magmatic feature in the Kerman Porphyry Copper Belt, that understanding magmatic evolution of which may shed light on the tectonomagmatic development of this less-studied part of an important magmatic arc in the Neotethys realm. The HIC has been developed in the the intersection of the NS-striking Sabzevaran fault and the NW-SE striking Rafsanjan-Rayen fault. It is indicated that the possible place of the conduit and vent is in Jalas Mountain which has been splitted later by the Sabzevaran fault into Minor and Major Jalas. The current summit had been constructed by ascending magma chamber under the HIC that constitutes the Kamali Mountain at the south of the summit. Some plutonic rocks of the HIC are exposed at Kamali Mountain. The subalkaline rocks of this complex mainly are composed of different pyroclastic and lava flow rocks, acidic to basic in composition, showing the evidences of fractional crystallization and mineral segregation. Sequential explosive and effusive eruptions with Strombolian to Vulcanian types are evident in the successive volcanic layers. The compositional trend shows the melting of spinel lherzolite, not garnet lherzolite. The subduction-related mechanism of the magma genesis has been indicated by IAB nature of the magma formation in geochemical diagrams.

Petrogenesis of Plio-Quaternary post-collisional ultrapotassic volcanism in NW of Marand, NW Iran

Post-collisional potassic and ultrapotassic (UP) alkaline magmas were erupted northwest of Marand in northern part of Urumieh-Dokhtar magmatic arc (UDMA) during Plio-Quaternary. The studied rocks display microlithic porphyritic texture with phenocrysts of clinopyroxene, leucite, and plagioclase ± biotite ± olivine. The UP volcanic rocks are mostly silica undersaturated with normative nepheline, high Mg#, and high K 2O/Na 2O ratios. They are characterized by significant enrichment in LILE and LREE and depletion in selected high-field-strength elements, such as Nb, Ta and Ti. All of the studied samples display fractionated REE pattern (Ce/Yb) N = (15.39–18.08) and negative Eu anomalies (Eu/Eu∗ = 0.71–0.78). Furthermore, they exhibit high Ba/Nb (41–60) and Ba/Ta (682–1139) ratios, which are a typical feature of subduction related-magmas. Rare-earth element modeling, Rb/Sr and Ba/Rb ratios indicate that they can be generated from low degree partial melting of lithospheric mantle with phlogopite-garnet peridotite source. We suggest that post-collisional volcanic activity during late Miocene to Quaternary occurred by rollback and slab breakoff processes after Neo-Tethys subduction. The slab breakoff mechanism would have caused the direct contact of hot asthenospheric mantle with metasomatised sub-continental lithospheric mantle and also has increased the thermal gradient, which weakened the lithosphere and assisted to lithospheric extension and magma ascent.