پترولوژی (Jun 2024)
Geochemistry of trace and rare earth elements of the productive intrusions in the Kuh-Kapout porphyry copper deposit, Urumieh–Dokhtar magmatic arc
Abstract
IntroductionThe Cenozoic Urumieh-Dokhtar magmatic arc has characteristics similar to those of Andean-type magmatic arcs. Various types of magmatism occurred in this arc including calc-alkaline and K-rich calc-alkaline magmatism and less of them alkaline magmatism (Shahabpour, 1982). Kerman porphyry copper belt (KPCB) in the southern part of this arc includes two types of granitoids: (1) Jebal Barez-type (late Eocene–early Miocene) associated with minor Cu-mineralization, and (2) Kuh Panj-type (middle Miocene–Pliocene), which is associated with major porphyry copper deposits (Mirzababaei et al., 2016). Kuh-kapout porphyry deposit (Eocene) in the southern part of KPCB is affected by Jebal Barez type granitoids. This deposit has been studied to determine the genesis of magmatism, mineralization and tectonic setting, by the whole rock geochemistry of quartz diorite intrusions, this evaluation is based on trace and REEs geochemistry data.Regional GeologyThis area is located in the southern part of the Urumieh–Dokhtar magmatic belt and in the Kerman porphyry copper belt. Arc-related magmatism events in this region include Paleocene to Oligocene magmatism and including andesite- dacite volcanic-sedimentary rocks with porphyry texture and quartz diorite intrusions with porphyry texture. In these rocks on the surface, there are intermediate argillic alteration events, and with increasing depth, quartz-sericite-pyrite zone and then potassic and alkali (potassium)-feldspar-sericite-chlorite-anhydrite zone are observed. Quartz diorite rocks include plagioclase and hornblende crystals (about 30 to 40 percent), biotite (10 to 15 percent), and potassium feldspar and quartz. Potassic alteration zone in depth is recognized by hydrothermal biotite, K-feldspar, magnetite and anhydrite. Mineralization in quartz diorite intrusions is more in the form of pyrite, chalcopyrite, and magnetite in association with the potassic alteration zone. Andesite-dacite volcanic-sedimentary rocks and quartz diorite rocks intruded by post-mineralized and barren micro diorite intrusion.Analytical methodThe samples were selected based on field observations and changes in mineralization-alteration rates from the weak alteration section of the quartz-sericite zone. For analyzing trace and rare earth elements, Samples were analyzed by the multi-acid method and used the Microwave Digest. Many of handpick and drill core samples were prepared to form thin sections for microscopic studiesAlteration and mineralizationIn this area, different types of hydrothermal alteration events including potassic, phyllic, propylitic, argillic and K-feldspar- chlorite- sericite, occurred that was influenced by fractures and faults. Quartz diorite intrusive rocks shows intense potassic and phyllic alteration zone, the main type of hydrothermal alteration zone is potassic and contains quartz ± chalcopyrite ± pyrite ± magnetite as mineralized veins and scattered event of pyrite, chalcopyrite, and magnetite. The phyllic alteration zone includes pyrite, which increases with depth. In the quartz-sericite-pyrite alteration zone, abundant chlorite and plagioclase are observed in the groundmass along with the occurrence of pyrite and anhydrite, and Cu mineralization in the form of scattered chalcopyrite.Whole rock chemistryIn this study, it seems that due to the presence of phases such as garnet and hornblende in the magma in the origin, a fractionation between HFSEs and LILEs has occurred (Green, 2006). Remaining of HFSEs and HREEs in the origin lead to low amounts of these elements in the resulting magma. The occurrence of negative anomalies in these elements, on the other hand, can be due to crustal contamination with mantle magmatism during their ascent to the surface. Anomaly in trace elements and ratios of REEs and trace elements, emphasizes that magmatism originated from the volcanic arc and subsequent events, according to the Th/Nb-Ba/Th diagrams and the La/Sm-Sm/Yb diagram, including the presence of lower crustal contamination and the significant role of fluid in the production of metasomatized magmatism. According to the studies on data normalized to the primary mantle, a depletion in Ba and Nb values and an enrichment in Rb and Cs have occurred.DiscussionStudying trace and rare earth elements in porphyry copper deposits is useful for determining the mineralization and fertility of magmatism, tectonomagmatism-setting, crustal contamination, and mantle metasomatism. Th-Co diagram (Hastie et al., 2007) and Th/Yb-Ta/Yb diagram (Hastie et al., 2007) indicate that most of the samples in this study area were plotted in the calc-alkaline magma region of the diagrams. Using the Sm/Yb versus La/Sm diagram (Aldanmaz et al., 2000) in the quartz diorite rocks shows a magmatism with higher Sm/Yb ratios than what is usually found for the spinel lherzolite. The plotting of the samples on diagrams indicates that the samples are located near the spinel + garnet lherzolite trend, indicating that the early magmatism originated from the spinel + garnet lherzolite mantle. High values of Ba/Th compared to low values of Th/Nb emphasize the contamination of subducting material or lower crust with magma; the (Dy/Yb)CN-Sr/Nd (Kelemen et al., 2003) diagram indicated that the process of fractional crystallization of plagioclase was effective in the evolution of magma; and finally, the study of samples in this deposit shows the relatively high water content in the magmatism, associated with the presence of garnet in the source and magma contaminated with the lower crust (Temel et al., 1998). In order to investigate the tectonic environment of the deposit, the diagrams of Pearce et al. (1984) were used. The samples are located in the active continental margin and associated with collision magmatism.Conclusionsanalysis of the trace and REEs of the quartz diorite rocks in the region, a magmatism related to the arc with the calc-alkaline series can be recognized. In terms of the evolution of magmatism, according to the interpretation of trace element data, from the origin to the surface, it can be considered a magmatism that originated from the partial melting of magma with the metasomatized spinel + garnet lherzolite composition in the source with the presence of garnet and amphibole phases. In terms of geochemical properties magmatism is more similar to Kuh-Panj type granitoid than the Jabal Barez type; and it is placed in the category of semi-economic to economic magmatism. Based on studies of trace elements from whole rock data, the tectonomagmatism of the rocks in the region is in the range of the active continental margin to collision setting.
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