| چکیده انگلیسی مقاله |
Introduction
The Cenozoic Urumieh–Dokhtar magmatic arc (UDMA) in Iran is a part of the Alpine-Himalayan orogenic belt hosts well-known porphyry Cu ± Mo ± Au ± Ag and epithermal Cu (± Au) deposits (McInnes et al., 2003; Hou et al., 2011; Richards et al., 2012, and references therein). The southeastern portion of UDMA in Kerman province contains many of these porphyry copper deposits, known as the Kerman porphyry copper belt (KPCB), where the Seridune porphyry copper deposit (SPCD) is located in its central part. This study deals with petrography and geochemistry of selected samples from the drilling boreholes to discern the geochemical characteristics, hypabyssal emplacement, and the overall tectonic setting environment of these magmatic rocks responsible for the formation of Seridune porphyry bodies.
Geology
Seridune porphyry copper deposit, in the central part of KPCB in southeastern UDMA, is located in the northeast of the Sarcheshmeh porphyry copper mine. These intrusive bodies are intruded the Eocene volcanic rocks (i.e., andesite and dacite) and as a whole cut by N-S trending dacitic dykes.
Analytical methods
Based on fieldwork and petrographic studies, 14 samples of Seridune intrusive bodies with the lowest degree of alteration were selected for whole-rock geochemical analyses. Whole-rock major and trace-element compositions were analyzed using fusion Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma-Mass Spectrometry (ICP- MS) at the Zarazma company, Iran.
Petrography
Petrographic studies revealed that in the Seridune area, the composition of the intrusive body responsible for mineralization is predominantly granodiorite porphyry to quartz monzonite porphyry. The other intrusive bodies in the Seridune deposit show a range of compositions varying from granodiorite to monzonite. Mineralogically, they consist mainly of quartz, orthoclase, and plagioclase with variable amounts of biotite, and amphibole phenocrysts setting in a fine-grained groundmass of the same mineral assemblage creating porphyritic texture. Accessory minerals are opaque, zircon, apatite, and titanite. Sericite, chlorite, secondary biotite and secondary alkali feldspar, calcite, anhydrite, clay minerals, and epidote also occur as secondary phases.
Geochemistry
The results of whole rock analyses are presented in Table 1. In the A/CNK versus A/NK diagram (Shand, 1943), the hypabyssal intrusive Seridune porphyry intrusive body is meta-aluminous to slightly peraluminous, and other intrusive bodies in the Seridune deposit are also meta-aluminous nature. In the Seridune porphyry copper deposit, there is a negative correlation of P2O5 content with the increasing SiO2 content, similar to the I-type granite evolutionary trend (Chappell and White, 1992). On the chondrite-normalized REE patterns, there is a strong enrichment of LREE relative to HREE, whereas, on the primitive mantle-normalized multi-element diagrams, there are enrichments of large ion lithophile elements (LILE), Th and Sr, and depletions of high field strength elements (HFSE) including heavy rare earth elements (HREE).
Discussion and conclusions
The Seridune porphyry copper deposit exhibits LREE and LILE enrichment coupled with depletion in Nb and Ti elements, which is typical of subduction-related magmas. This characteristic results from lack of these elements in the source, and/or involvement of the crust in the magmatic processes. The Seridune porphyry intrusive body belongs to the calc-alkaline series and has metaluminous to slightly peraluminous features, whereas other intrusive bodies in the Seridune deposit belong to the calc-alkaline series with a meta-aluminous nature. These features are typical of I-type granites formed by partial melting of mantle wedge which triggered the melting of lower crustal rocks in subduction zones and active continental margins (Chappell and White, 1974; 2001). This type of granite in orogenic belts appears to be resulted from the interaction of main magma with the continental crust through the processes of assimilation-fractional crystallization (AFC) (Dilek et al., 2009). Furthermore, the high values of Th (3.5-5.2 ppm) in the Seridune intrusive bodies have been assigned to the effects of crust contamination (Kaygusuz et al., 2014). The high values of the Th/Nb ratio in the Seridune porphyry copper deposit may point to characteristics of arc-related magmas, enriched by the continental crustal melting. Considering the enrichment of the samples in incompatible elements (i.e. K, Th, Rb, La, Ce, and Nd) and the negative anomalies of Ti, P, Nb, and Eu, it can be argued that the Seridune intrusive bodies were formed by crystallization of melts derived from the melting of lower crustal metabasic rocks as a result of the injection of mantle-derived mafic magmas (Searle and Fryer, 1986; Harris et al., 1986; Chappell and White, 1992). Finally, it can be concluded that the Seridune deposit was originated in a volcanic arc setting. Based on geological background of the area, the formation of these rocks must be related to the subduction of the Neotethys oceanic crust beneath the Central Iranian Micro-continent. The parent magma likely resulted from the partial melting of the lower crust, while the upper crust played a significant role in contaminating the magma at shallower levels. |