DISTRIBUTION AND COCRYSTALLIZATION COEFFICIENTS OF ELEMENT ADMIXTURES IN PYRITE: HYDROTHERMAL EXPERIMENT AND CORRELATION LINKS IN MULTISYSTEMS
V.L. Tauson, S.V. Lipko, D.N. Babkin, N.V. Smagunov, O.Yu. Belozerova, Yu.V. Sokolnikova, A.N. Sapozhnikov
A.P. Vinogradov Institute of Geochemistry SB RAS, Irkutsk, Russia
Keywords: Pyrite, hydrothermal synthesis, multisystem, sampling, trace elements, distribution, cocrystallization coefficient, correlation analysis
Abstract
Method of thermogradient hydrothermal synthesis with internal fluid sampling in multicomponent systems at 450 °C and a pressure of 1 kbar was used for the first time to establish the distribution and cocrystallization coefficients of a number of typomorphic elements and noble metals in pyrite. All obtained information was subjected to correlation analysis, which made it possible to establish a number of features of the behavior of impurity elements in pyrite within hydrothermal multisystems. A new explanation is given for the role of As in the distribution of elements, related to the fact that for many of them (including Au), significant negative correlations of cocrystallization coefficients with As are observed: in its presence, they decrease, which is likely associated with the influence of arsenic on the complexation of impurity elements and may lead to a decoupling in the behavior of As and Au, as well as other trace elements in pyrite. It was shown for the first time that Cu can enter the pyrite structure up to ~1.2 mol.% CuS₂, and its high correlation with Co indicates a mechanism for this process related to the distortion of the crystal lattice of Co-pyrite and the formation of exchange-coupled Co²-Cu²⁺ pairs. Palladium, an element with high technological demand, exhibits a high dispersion of content in pyrite, despite an almost constant concentration in the fluid. The behavior of Pd is presumably related to the mechanism of its incorporation into pyrite, which requires the formation of vacancies in the metal sublattice and therefore depends on the sulfur activity in the system. From the standpoint of cocrystallization coefficients, indicator element ratios in pyrite are considered. It is shown that the Ni/Pd, Cu/Pd, As/Au, and Ni/Cu element pairs most accurately reflect these ratios in the ore-forming fluid. A justification is presented for the preference of the proposed methodology, which includes the use of growth hydrothermal experiments, sampling, cocrystallization coefficients, and correlation analysis, allowing for a more objective consideration of the problems of element distribution in geochemical multisystems.
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