Reconstructing physicochemical attributes using chemistry of biotite and chlorite in the Keder porphyry copper deposit, Kerman Cenozoic magmatic arc

The Keder porphyry copper deposit is located 14 km SW of Dehej in the north-eastern of Kerman Cenozoic magmatic arc. It is associated with diorite to quartz diorite intrusions. Considering the important role of oxygen fugacity, halogen content, and temperature in the mineralization efficiency of porphyry systems, the aims of present research is the investigation of these physicochemical attributes in the magmatic stage, as well as potassic alteration of Keder porphyry using biotite and chlorite chemistry. Compared with chlorite, biotite has high SiO2, K2O, TiO2 concentrations. On the other hand, Al2O3 has highest concentration in chlorite. The depletion of K2O and SiO2 are related to the formation of adularia and K-feldspar accompanying with the breakdown of biotite to chlorite. Biotite chemistry shows that the Keder intrusion is calc-alkaline in nature. Based on FeO/FeO+MgO vs MgO diagram, biotites from Keder intrusion plot within the mantle source (M) and to a lesser extent in the crustal materials field. Using the Si vs Fe2+/Fe2+ +Mg2+ diagram, secondary chlorites that replaced biotite plot collectively within clinochlore composition. Oxygen fugacities of Keder deposit occur in HM-NNO area. The investigation of geothermometry on biotites and chlorite in the Keder porphyry copper deposit shows a temperature range between 516-680° C and 180.19-369.87° C respectively. The log fH2O/fHF and log fH2O/fHCl values range between 4.57-5.77 and 4.34-4.62 that show water content is more than halogen content in Keder intrusion. According to XFe and XMg vs. XF/XOH and XCl/XOH, Cl fugacity was similar in Keder porphyry copper deposit. Finally, it seems that high temperature together with prevailing of high oxygen fugacities during potassic alteration (onset of sulfide mineralization) could be considered as important factors on low grade mineralization at Keder deposit.