Experimental calibration of the phlogopite fluorimeter at 500–700 °C and 1–4 kbar, and estimated HF concentrations of fluids associated with marble: Some examples

Abstract

Fluorine distribution between (OH,F)-phlogopite and hydrothermal fluid has been experimentally investigated at 500–700°C and 1–4 kbar. Initial phlogopite compositions and HF concentrations in the HF-H 2O fluid were varied from OH-phlogopite to F-phlogopite and from 0.001 to 0.1 mol/kg of H 2O, respectively. Compositions of both phlogopite and solution were measured after the runs. The experimental data yield the following equation for the phlogopite fluorimeter: log M T,P HF = X Mg[log (X F/(1 − X F)) − 1722/T(K) − 0.2112] + log α H 2O , where M T,P HF is a concentration in the fluid in mol/dm 3 at temperature and pressure of interest; X Mg and X F are, respectively, the mole fractions of Mg and F in the octahedral and hydroxyl sites of phlogopite; α H 2O is a water activity in fluid expressed as γ H 2O X H 2O , where X H 2O is a mole fraction and γ is a activity coefficient of water at T-P of fluid. The HF concentrations in natural fluids estimated by the fluorimeter equation range from 0.9·10 −3 to 1.4·10 −2 mol/dm 3 for phlogopite formation in marbles of different localities: Adirondack Mountains (USA), Cairo del Diablo (Central Spain), Aldan Shield and Pribaikal'ye (Russia), and southwestern Pamir Mountains (Tajikistan).