Metallogenic implications of biotite chemical composition: Sample from Cu-Mo-Au mineralized granitoids of the Shah Jahan Batholith, NW Iran

Abstract

Igneous biotite has been analyzed from three I-type calc-alkaline intrusives of the Shah Jahan Batholith in NW Iran, which host several Cu-Mo-Au prospects. The X Mg (Mg/Mg+Fe) value of biotite is the most significant chemical factor and the relatively high value of X Mg corresponds to relatively high oxidation states of magma (estimated ƒ O2 is mostly 10 -12.5 to 10 -7.5 bars), which is in good agreement with their host intrusions' setting and related ore occurrences. Based on criteria of Al IV and Al VI values, all studied biotites are primary (Al VI = 0), and based on Al total values (2.23-2.82 apfu) are in distinctive ranges of mineralized granitoid (Al total =3.2 apfu).The maximum F content of biotite from the Shah Jahan intrusions is moderately higher than those from some other calc-alkaline intrusions related to Cu-Mo porphyries in the world, and in contrast, Cl content is relatively lower. It is likely a result of primary magmatic vs. secondary hydrothermal origin, as well as the Mg-rich characteristics of the biotite in Shah Jahan. X Mg values do not correlate with F and Cl contents of biotite, suggesting that biotite records changes in the F/OH and Cl/OH ratios in coexisting melt/fluids. It is consistent with F-compatible and Cl-incompatible behavior during fractional crystallization of wet calc-alkaline I-type granitoid magma generated at subduction related arc settings. The fugacity ratios of (H 2 O/HF), (H 2 O/HCl) and (HF/HCl) magmatic solutions coexisting with biotite illustrate similar trends in the three intrusions, which can be due to parental magma sources and/or indicate occurrence of similar magmatic processes prior to or contemporaneous with exsolution of fluids from melt. The observed trends caused F-depletions and Cl-enrichments within developed magmatic-hydrothermal systems which are one of the essential characteristics of potential Cu-Mo-Au mineralized I-type granitoids.

Rhenium abundance in molybdenites: a case study on vein-type Cu-Mo-Au mineralisation in the Qarachilar area, Sungun porphyry Cu and Siah Kamar porphyry Mo deposits, NW Iran

“…The gen e sis of min er ali sa tion hosted by the Qaradagh batholith is con tro ver sial, be ing pre sented as in tru sion-re lated gold (Mokhtari, 2008;Mokhtari et al, 2013) and vein-type Cu-Mo-Au (Rezai Aghdam and Sohrabi, 2010), as well as porphyry type Cu-Mo min er ali sa tion (e.g., Amini Fazl, 1994;Zakeri et al, 2011;Zakeri, 2013).…”