BEHAVIOR OF NOBLE METALS DURING FRACTIONAL CRYSTALLIZATION
OF Cu–Fe–Ni–(Pt, Pd, Rh, Ir, Ru, Ag, Au, Te) SULFIDE MELTS
E.F. Sinyakova1, V.I. Kosyakov2, A.S. Borisenko1,3, and N.S. Karmanov1
1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2 A.V. Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Lavrent’eva 3, Novosibirsk, 630090, Russia
3 Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: System Cu–Fe–Ni–S, PGE, Te, fractional crystallization, zoning, pentlandite
Abstract
The method of quasi-equilibrium directional crystallization was used for experimental modeling of the be-havior of noble metals in the presence of Te during the fractional crystallization of Cu- and Ni-rich sulfide mag-ma. The experimental melt contained (mol. %): Fe = 18.5, Ni = 19.1, Cu = 16.7, S = 44.1, and Pt = Pd = Rh = = Ir = Ru = Ag = Au = Te = 0.2, i.e., is similar in composition to the massive pentlandite–bornite ores of plati-num–copper–nickel deposits of the Noril’sk group. The crystallized sample consists of six primary zones differ-ing in chemical and phase compositions. The main minerals crystallizing from the melt include the following sul-fide phases: bornite solid solution (bnss), quaternary solid solution (tss), described earlier in the literature, and three phases (cfpn, cnpn, and npn), which we attributed to pentlandite according to their chemical composition.
The primary phases crystallized from the melt decay on cooling with the formation of secondary phases. The cfpn, cnpn, and tss phases decay completely, and the npn and bnss phases, partly. As a result, secondary zoning forms in the sample. Formation of drop-like inclusions of telluride melt was observed in the end zone of the ingot.
The obtained data show that pentlandites and tss are the main high-temperature concentrators of PGE, with each of the macrophases showing specific PGE accumulation.
Eight types of impurity phases have been detected. They form by different mechanisms: crystallization from sulfide melt of refractory compounds, isolation from telluride melt, and formation through complete or par-tial decay of primary macro- and microphases.
A scheme of the zonal structure of the crystallized sample and the evolution of the phase composition during fractional crystallization has been constructed. It clearly demonstrates the intricate formation of primary and secondary major-component and impurity zonings and can be used to explain the nature of the zoned struc-ture of massive PGE-bearing pentlandite–bornite orebodies.
DOI: 10.15372/RGG2019050
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