Journal of Economic Geology (Jun 2019)
Comparison of geochemistry and porphyry copper mineralization efficiency in granitoids of the Sanandaj-Sirjan and Urumieh-Dokhtar zones; using rare earth elements geochemistry
Abstract
Introduction The formation of the Zagros orogenic belt is attributed to northeastward oblique subduction of the Neotethys beneath the western border of central Iran. This was followed by continental collision between the Afro-Arabian plate and the central Iran microcontinet (Zarasvandi et al., 2015). The Zagros orogen is characterized by three main parallel structural zones consisting of Zagros fold and thrust belt, the Sanandaj–Sirjan metamorphic zone, and the Urumieh–Dokhtar magmatic arc (Mohajjel et al., 2003). The Urumieh–Dokhtar magmatic arc is dominated by the widespread occurrence of Eocene to Quaternary intrusive and extrusive rocks. It is considered as being one of the main Cu bearing regions in the world, where world class giant porphyry deposits, as well as large and small sub-economic porphyry Cu ± Mo ± Au systems have been reported and investigated by many authors (Shafiei et al., 2009; Zarasvandi et al., 2005). In addition to UDMA, the Sanandaj-Sirjan zone (SSZ) hosts several Jurassic-Cretaceous intrusive complexes extending from the northwest to southeast SSZ. It should be noted that these granitoids are barren and porphyry mineralization has not been accompanied with these intrusions. This paper tried to compare the available geochemical data of productive granitoids in the Urumieh-Dokhtar (i.e., Dalli, Ali-Abad and Darreh-Zerreshk, Parkam, Sarcheshmeh, Meiduk and Sungun), and those of barren intrusions in the Sanandaj-Sirjan zone (i.e., Aligodarz, Bourujerd, Alvand, Astaneh, Hasan Robat, and Siah Koh). Materials and methods This investigation is based on the available geochemical data on the six barren intrusions in the SSZ (i.e., Aligodarz, Bourujerd, Alvand, Astaneh, Hasan Robat and Siah Kohe), and productive intrusive rocks (porphyry associated intrusions) in the UDMA (i.e., Dalli, Ali-Abad and Darreh-Zerreshk, Parkam, Sarcheshmeh, Meiduk and Sungun). Data for the UDMA porphyry intrusions (41 samples) were adopted from studies of Daneshjou (2014), Zarasvandi et al. (2005), Taghipour and Mohammadi Laghab (2014), Barzegar (2007), Taghipour (2007), and Hezarkhani (2006). Furthermore, the data of the SSZ barren intrusions (42 samples) comes from Esna Ashari et al. (2012), Khalaji et al. (2007), Aliani et al. (2012), Tahmasbi et al. (2010), Alirezaei and Hassanzadeh (2001), and Arvin et al. (2007). Two criteria were used for selection of 83 representative samples: (1) samples with a relatively similar mineralogical and compositional range (quartz diorite, quartz monzonite, granodiorite and granite), and (2) samples with the least amount of alteration (minimal amounts of Loss On Ignition; LOI wt.% = H2O + CO2). Results Productive intrusions in UDMA have positive Eu anomalies, LREE enrichment relative to HREE, and high Lan/Ybn ،Sr/Y، Dyn/Ybn، Lan/Smn ratios. In comparison, barren granitoids in the SSZ are characterized by steep downward LREE to HREE, negative Eu anomalies and low Lan/Ybn ، Sr/Y، Dyn/Ybn، Lan/Smn ratios. Discussion Based on the presented results, it is proved that due to the lack of considerable crustal thickness in SSZ (during the subduction of the Neotethyan oceanic lithosphere under the SSZ zone), and the presence of dry magma (low H2O contents), the SSZ granitoids exhibit barren characteristics. In contrast, during the ongoing processes of closure of Neo-Tethys and during compression and crustal shortening, magma mixing and evolution toward high magmatic water content lead to the increasing of metal endowment in the porphyry associated granitoids of (UDMA) It seems that magma generation from the melting of thickened lower crust (garnet amphibolite source) could be considered as one important key factors for the generation of metal-rich magmas with high oxidation state and high H2O contents has led to the development of porphyry Cu systems in the UDMA compared to those of SSZ granitoids. Acknowledgements The authors are grateful to the Shahid Chamran University of Ahvaz for the research funding by the Grant Commission in 2017. References Aliani, F., Maanijou, M., Sabouri, Z. and Sepahi, A.A., 2012. Petrology, geochemistry and geotectonic environment of the Alvand Intrusive Complex, Hamedan, Iran. Chemie der Erde-Geochemistry, 72(4): 363–383. 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