Chemical composition of biotite from the Kuh-e Dom pluton, Central Iran: implication for granitoid magmatism and related Cu–Au mineralization

Abstract

The composition of the Kuh-e Dom intrusion (NE Ardestan, Iran), in the Urumieh-Dokhtar magmatic belt, ranges from gabbro to granite. Several diabase dikes and numerous enclaves are common in the studied rocks. The intrusive rocks contain biotite as major or minor minerals (1–19 %). The biotites are Mg-rich typical for I-type calc-alkaline rocks related to subduction setting. The biotite chemistry in the acidic rocks suggests crystallization temperatures in the range of 720–750 °C. Oxygen fugacity of biotite has been buffered by the Ni-NiO buffer and the intrusion crystallized under high oxygen fugacity of −15.16 bars in the acidic rocks and –13.6 bars in the intermediate–basic rocks. The average calculated H2O fugacity of these rocks is about 3 bars. The average values of the calculated log (ƒH2O/ƒHF) of fluid in equilibrium with the chemical composition of biotite are 4.65 for the acidic and 4.2 for the intermediate–basic rocks. The average values of the calculated log (ƒH2O/ƒHCl) of fluids in equilibrium with the chemical composition of biotite are 3.81 in the acidic and 3.36 in the intermediate–basic rocks. These F and Cl values for biotites in the Kuh-e Dom intrusion are similar to those of high-Cl igneous rocks and porphyry Cu ore deposits. As the Kuh-e Dom biotites are primary, their crystallization from Cl-high magma is suggested. It seems that in the subduction zone, the release of Cl-bearing fluid from a subducted slab into the mantle, causing mantle metasomatism, plays an important role in the mineralization of the Kuh-e Dom.