Experimental Study of Partitioning of Tantalum, Niobium, Manganese, and Fluorine between Aqueous Fluoride Fluid and Granitic and Alkaline Melts

摘要

This study presents a new set of quantitative experimental data on the partitioning of Ta, Nb, Mn, and F between aqueous F-bearing fluid and water-saturated, Li- and F-rich haplogranite melts with varying alumina/alkali content at T= 650-850℃ and P = 100 MPa. The starting homogeneous glasses were preliminary obtained by melting of three gel mixtures of K_2O-Na_2O-Al_2O_3-SiO_2 composition with a variable Al_2O_3/(Na_2O+K_2O) ratio, ranging from 0.64 (alkaline) and 1.1 (near-normal) to 1.7 (alumina-rich). Ta, Nb, and Mn were originally present in glass only, whereas F was load in both the glass and the solution. The solution-to-glass weight ratio was 1.5-3.0. The compositions of quenched glass were measured by an electronic micro-probe, and those of the aqueous solution, with the ICP-MS and ICP-AES methods. The F concentration in the quenched solution was calculated from the mass balance. Under experimental conditions the partition coefficients of Ta, Nb, and Mn between the fluid and the granitic melt (weight ratio ~(fluid)C_(Ta)/~(melt)C_(Ta) = _(fluid/melt)are shown to be extremely low (0.001-0.008 for Ta, 0.001-0.022 for Nb, and 0.002-0.010 for Mn); thus, these metals partition preferentially into the melt. The coefficients ~(fluid/melt)D_(Ta) and ~(fluid/melt)D_(Nb) generally increase either with increasing alumina ratio A/NKM in the glass composition, or with rising temperature. The experiments also demonstrated that F preferentially concentrates in the me and the partition coefficients of F are below 1, being within the range of 0.1-0.7.