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

摘要

Miduk hypogene and supergene porphyry Cu-Mo mineralization occurs within the Miocene porphyritic quartz-diorite and host Eocene plagiodase-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 X_(phl) 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 X_(phl) and X_(Ti)and CL contents, and positively correlate with X_(phl) 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.