Journal of Economic Geology (Jun 2019)
Geology, Mineralization, Geochemical exploration, Petrogenesis, zircon U-Pb geochronology and Lu-Hf isotopes sub-volcanic rocks in the Simorgh prospect area, Lut Block, Eastern Iran
Abstract
Introduction The Simorgh prospect area is located in 113 km southwest of the Nehbandan in South Khorasan province. This area is part of the Tertiary volcanic-plutonic rocks in the center of the Lut block. The Lut Block, which is located at the eastern part of the Central Iranian Microcontinent (CIM), is famous by its complex tectonic evolution and extensive magmatic activities with a range of interesting geochemistry. Extensive magmatic activities in Lut Block have produced several types of mineralization events (Karimpour et al., 2012). Around the Simorgh prospect area, various mineral deposits, including Cu-Mo porphyry Dehsalm in 90 km southwest of Nehbandan have been reported (Arjmandzadeh and Santos 2013) and Mahoor copper (Miri Beydokhti et al., 2015). Until now there has not been a detailed studies on the Simorgh prospect area especially on granitoids. In this study, we present field investigations, geology, alteration, mineralization, geochemical exploration, Petrogenesis, zircon U-Pb geochronology and Hf isotopes of sub-volcanic rocks in the Simorgh prospect area. Materials and methods 1- Preparation of 336 thin sections for the study of petrography, alteration and mapping of geological and alteration maps. 2- Preparation and study of twenty-five polished thin sections and thirty-two polished blocks for mineralization studies. 3- Analysis of forty-five chip composite samples in the Zar Azma laboratory by using the fire assay method for Au element and ICP-OES for thirty-four elements. The solubilization method of 4- Acid (1EX) was used. 4- Analysis of one hundred and sixty core samples in the Zar Azma laboratory by using the fire assay method for Au element and ICP-OES for 34 elements (method 1EX). 5- Chemical analysis of seventeen samples of syn-mineralization sub-volvanic intrusive rocks with at least alteration, by ICP-MS for thirty-one trace and rare earth elements with LF100 method (alkali fusion) at the AcmeLabs Laboratory. 6- Separation of three samples from syn-mineralization sub-volcanic intrusive rocks for U-Pb zircon geochronolg by Quadruple Laser-Ablation ICP-MS at the CODES, the Tasmania University of Australia. 7- Analysis of three samples of syn-mineralization sub-volvanic intrusive rocks for Lu-Hf isotopes with multi-collector ICP-MS at the CCFS of Macquarie University of Sydney, Australia. Discussion and results Petrographic studies indicated that the composition of sub-volcanic rocks in the Simorgh area are diorite porphyry and pyroxene diorite porphyry stocks with granite porphyry and granodiorite porphyry dikes. Several alteration zones such as: propylitic, argillic, silicified quartz-sericite-pyrite (QSP) and carbonate-quartz-sericite-pyrite (CQSP) based on field and laboratory studies are identified Major oxides analysis shows that intrusive units are metaluminous to peraluminus, calc-alkaline to high-K calc-alkaline. More of these rocks belong to the I-type granitoid (Chappell and White, 2001), and they have been formed in a volcanic arc granitoids (VAG) tectonic setting (Pearce et al., 1984). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements, such as Rb, Sr, K, and Cs, and depletion in high field strength elements, e.g., Nb, Ti, P. Enrichment of LREE versus HREE and enrichment of LILE and depletion in HFSE indicate magma formation in the subduction zone. In the subduction zones, high oxygen fugacity leads to the depletion of Ti. All of the intrusive rocks have a negative Eu anomaly. The amount of Eu/Eu* in sub-volcanic units of the Simorgh area varies from 0.49 to 0.91. Therefore, negative Eu anomaly can be evidence of the partial presence of plagioclase in the origin (Tepper et al., 1993). Three types of mineralization occur in this area such as: veinlet, disseminated and hydrothermal breccia among which hydrothermal breccia is the most important. Pyrite is the most sulfide mineralization in the sub-volcanic and hydrothermal breccias. Compositional variations of elements within the Simorgh prospect are as follows: Cu = 2-240 ppm, Mo = 0.5-49 ppm, Zn = 9-935 ppm, Pb = 7-582 ppm, ppm, As = 2-207 ppm and Au = 1-93 ppb. In the Simorgh area, zircon U-Pb geochronology was carried out on syn-mineralization sub-volcanic intrusive rocks. The age of two granite porphyry dikes are 25.37±0.56 Ma and 25.94±0.76 Ma and the age of pyroxene porphyry diorite is 24.85±0.51 Ma (Chattian). Diorite porphyry is pre-mineralization because it is cut by granite porphyry dikes and pyroxene diorite porphyry, so diorite porphyry is the oldest sub-volcanic intrusive rock in this area. The low positive values of εHf(i) indicate that the origin of these sub-volcanic intrusive rocks is mantle, which has low contamination with the crust. According to the above evidence, the sub-volcanic units of this area are related to porphyry systems, and the hydrothermal breccias are the main host rock mineralization in this system. This system does not have any valuable mineralization expect pyrite, from the surface to 180 m depth. References Arjmandzadeh, R. and Santos, J.F., 2013. Sr-Nd isotope geochemistry and tectonomagmatic setting of the Dehsalm Cu-Mo porphyry mineralizing intrusives from Lut Block, eastern Iran. International Journal of Earth Sciences, 103(1): 123–140. Chappell, B. and White, A., 2001. Two contrasting granite types: 25 years later. Australian Journal Earth Sciences, 48(4): 489–499. Karimpour, M.H., Malekzadeh shafaroudi, A., Farmer, G.L. and Stern, C.R., 2012. Petrogenesis of Granitoids, U-Pb zircon geochronology, Sr-Nd Petrogenesis of granitoids, U-Pb zircon geochronology, Sr-Nd isotopic characteristics, and important occurrence of Tertiary mineralization within the Lut block, eastern Iran. Journal of Economic Geology, 4(1): 1–28. (in Persian with English abstract) Miri Beydokhti, R., Karimpour, M.H., Mazaheri, S.A., Santos, J.F. and Klötzlid, U., 2015. U-Pb zircon geochronology, Sr-Nd geochemistry, petrogenesis and tectonic setting of Mahoor granitoid rocks (Lut Block, Eastern Iran). Journal of Asian Earth Sciences, 111(1): 192–205. 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