Trace Element Partitioning Between Fluorite and Hydrothermal Fluid

English Abstract:

Trace elements composition in gangue fluorite - generally its patterns and ratios -has been widely used to determine the source of solutes in hydrothermal fluid when studying the genesis of hydrothermal ore deposits. This is under the assumption that the trace element composition of fluorite is representative of the hydrothermal fluid from which the fluorite precipitated. However, the trace element compositions of minerals are strongly affected by the partitioning behavior of these elements. Therefore, in order to obtain information on the trace element composition of the hydrothermal fluid that no longer exists from fluorite, it is crucial to know the partition coefficients of the elements of interest between fluorite and fluid. It is well known that partition coefficients vary with physicochemical conditions, which can be predicted with Lattice-Strain model (see Blundy & Wood 1994). We are performing fluorite-fluid partitioning experiments to obtain a basic set of partition coefficients as a starting point to build a model using Lattice-Strain Theory, to extrapolate coefficients for any set of physicochemical conditions. We have successfully synthesized fluorite, verified by X-ray diffraction analysis, in aqueous solutions doped with trace elements at typical hydrothermal temperatures from 60 °C to 250 °C. Analysis of the trace elements concentration in synthesized fluorite and residual fluid from the 60 °C experiment using ICP-MS technique gave us the first set of partition coefficients, which are in general agreement with the data obtained by van Hinsberg (2010) using a different experimental approach. Once this model is built, natural fluorite crystals sampled in ore deposit will be analyzed for trace element content, and relevant partition coefficients will be applied to reconstruct the trace elemental composition of the ore-forming fluid.