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Minerals 2018, 8(7), 282; https://doi.org/10.3390/min8070282

Trace Element Partitioning Dualism under Mineral–Fluid Interaction: Origin and Geochemical Significance

A.P.Vinogradov Institute of Geochemistry, Siberian Branch of Russian Academy of Sciences, Irkutsk 664033, Russia
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Received: 3 May 2018 / Revised: 25 June 2018 / Accepted: 26 June 2018 / Published: 30 June 2018
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Abstract

Trace element (TE) partitioning in the system “mineral-hydrothermal solution” is studied by the method of thermo-gradient crystal growth coupled with internal sampling of a fluid phase. The analytical procedure used enables evaluating of structurally bound and superficially bound modes of TE in crystals and determining corresponding dual partition coefficients. The case of precious metals (PM—Au, Pt, Pd) at 450 and 500 °C and 100 MPa pressure is considered. The minerals are pyrite, As-pyrite, magnetite, Mn-magnetite and hematite and fluids are ammonium chloride-based hydrothermal solutions. The partition coefficients for structural and surficial modes, Dpstr and Dpsur, are found to be unexpectedly high (except for Au in pyrite). High concentrations of PM are attributed to superficial nonautonomous phases (NAPs), which can be considered as primary concentrators of PM. We also have studied the co-crystallization (exchange) coefficients (De) of REE (Ce, Eu, Er, Yb) and Fe in magnetite and hematite at 450 °C and 100 MPa. Desur is elevated to two orders of magnitude as compared to Destr. It is shown that not only physicochemical parameters affect REE distribution in hydrothermal systems, but also NAP presence and its composition. The crystal growth mechanism specified by the agency of NAP is suggested. The study of PM distribution in natural pyrite of gold-ore deposits supported the importance of differentiating between structurally and superficially bound TE modes for correct use of experimental D values to determining element concentrations in ore-forming fluids. View Full-Text
Keywords: trace elements; partitioning; precious metals; rare earth elements; hydrothermal experiment; partition and co-crystallization coefficients; structurally and superficially bound modes; pyrite; magnetite; hematite; single crystals; AAS-GF; ICP-MS; XPS trace elements; partitioning; precious metals; rare earth elements; hydrothermal experiment; partition and co-crystallization coefficients; structurally and superficially bound modes; pyrite; magnetite; hematite; single crystals; AAS-GF; ICP-MS; XPS
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Tauson, V.L.; Lipko, S.V.; Smagunov, N.V.; Kravtsova, R.G. Trace Element Partitioning Dualism under Mineral–Fluid Interaction: Origin and Geochemical Significance. Minerals 2018, 8, 282.

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