Geochemical characteristics of collisional and pre-collisional porphyry copper systems in Kerman Cenozoic Magmatic Arc, Iran: Using plagioclase, biotite and amphibole chemistry

Abstract

Kerman Cenozoic Magmatic Arc (KCMA) located in the southeastern part of Urumieh-Dokhtar Magmatic Bet (UDMB) hosts a number of world class and moderate to small porphyry copper deposits. The present work compares the silicate chemistry (plagioclase, biotite and amphibole) of Miocene collisional porphyries (e.g., Chahfiruzeh and Keder) with Eocene-Oligocene pre-collisional porphyry systems (e.g., Reagan and Daralou) in the KCMA. P (<200Mpa) and H2Omelt, in the all studied porphyry systems is analogous to those reported previously for other porphyry copper systems. All analyzed biotites are high-Mg with subduction-related calc-alkaline and medium to high oxygen fugacity character. However, the Al2O3 and TiO2 contents of amphibole indicate that studied porphyries had a crust-mantle mixed source. Pre-collisional porphyry systems with lowest degree of Cu mineralization simultaneity show lowest An% and Al* compared with that of collisional porphyries. The amphiboles represent calcic – calc alkaline moderately oxidant magmatic character (NNO). The plagioclase chemistry indicates that magmatic system in the collisional deposit is relatively closed exhibiting the low rate of mixing compared with pre-collisional deposits. The biotite chemistry indicates temperature decreasing from Keder to Reagan, Daralou and Chahfiruzeh, respectively. The lack of regular temperature die line in the pre-collisional porphyry systems could be effective in low grade mineralization. High biotite halogen fugacity ratios (fH2O/fHF and fH2O/fHCl > 1) imply water-rich nature of studied porphyry systems. The relative enrichment F in the collisional porphyry deposits (e.g., Keder) could be linked with enrichment of Mg in these systems.