The Miduk porphyry Cu deposit, Kerman, Iran: A geochemical analysis of the potassic zone including halogen element systematics related to Cu mineralization processes

Miduk hypogene and supergene porphyry Cu–Mo mineralization occurs within the Miocene porphyritic quartz–diorite and host Eocene plagioclase–hornblende phyric andesitic pyroclastic and flow sequence. Both the host rocks were extensively altered by hydrothermal fluids to dominantly potassic, phyllic, and argillic with interstitial to distal propylitic types.Biotite-bearing assemblages from the proximal potassic zone are dark to light brown and have Xphl from 0.56 to 0.68; F contents range from 0.15 to 1.8 wt.% and Cl contents range from 0.19 to 0.28 wt.%. Fluorine contents in the biotite negatively correlate with Xphl and XTi and Cl contents, and positively correlate with Xphl and SiO2. Calculated log (fH2O/fHF), log (fH2O/fHCl), and log (fHF/fHCl) values of fluid in equilibrium with these biotites ranging from 5.5 to 6.40, 4.64 to 4.79, and − 2.54 to − 1.68, respectively. Established halogen fugacity ratio contour lines are transected by the steeper slope of measured values of biotite composition; this suggests the fluid composition, fO2 and fS2 of the fluids, and reaction between wall rock and hydrothermal fluids play a key role in the resultant halogen fugacities recorded in biotite that is critical to interpreting metal complexing behaviour during magmatic-hydrothermal evolution. The intercept values of F [IV(F)] and Cl [IV(Cl)] for biotite from the potassic zone are similar to those of related plutonic rocks and other porphyry Cu deposits; the IV(Cl) tend to be more Cl-rich than comparable values of common igneous rocks. F-rich to F-poor biotite crystals from the Miduk deposit show a narrow range of F/Cl intercept values [IV(F/Cl)] consistent with porphyry Cu ore-forming fluids.