BEHAVIOR OF microcomponents DURING volumetric AND DIRECTIONAL CRYSTALLIZATION OF Cu-Fe-Ni-S-(Pt, Pd, Ag, Au, As, Te, Bi, Pb, Se, Sn) MELT
E.F. Sinyakova1, D.A. Ulybin1,2,3, K.A. Kokh1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences,
Novosibirsk, Russia
3Novosibirsk State University, Novosibirsk, Russia
Keywords: Cu-Fe-Ni-S system, noble metals, chalcophile elements, sulfide zoning, fractional crystallization, volumetric crystallization, immiscibility
Abstract
The article presents the results obtained during the crystallization of a melt with the compositionin (in at. %): 14.0 Cu, 30.0 Fe, 4.0 Ni, 51.1 S, 0.1 each of Pt, Pd, Ag, Au, As, Bi, Pb, Se and Sn, in wt. %: 19.5 Cu, 36.7 Fe, 5.1 Ni, 35.8 S, 0.4 Pt, 0.2 Pd, 0.2 Ag, 0.4 Au, 0.2 As,0.5 Bi, 0.5 Pb, 0.2 Se and 0.3 Sn under isothermal conditions and with directional crystallization. Under gradient-free conditions, a homogeneous crystalline massif consisting of a mixture of monosulfide and intermediate solid solutions crystallizes from the melt. When cooled to room temperature, the monosulfide solid solution forms the pyrrhotite structure 1C, 3C, and the intermediate solid solution decomposes into a fine-grained mixture of isocubanite and chalcopyrite. Using the Bridgman-Stockbarger method, a three-zone ingot was obtained with the following sequence of phase crystallization from the melt: Mss / Iss1 / Iss2 and secondary zoning: chalcopyrite + pyrrhotite 1C, 3C + isocubanite (zone I) / chalcopyrite + low-temperature intermediate solid solution + Fe-pentlandite, sugakiite (zone II) / chalcopyrite + Ni-pentlandite + millerite + bornite (zone III). The specific influence of As, Bi, Pb, Se and Sn impurities on the behavior of Pt, Pd, Ag and Au under different crystallization conditions was revealed. In both experiments, solid solutions play a minor role in their concentration. The main amount of these impurities is released in the form of independent phases. The main role in their formation is played of immiscibility of the parent sulfide melt, resulting in the formation of a sulfide-metalloid melt, Ls-m, which concentrates impurities of Pt, Pd, Ag, Au, and chalcophile elements. The data on the directionally crystallized sample indicate a more complex process of immiscibility of the initial melt compared to its immiscibility during volumetric crystallization, namely 1) the simultaneous release of two types of liquids during cooling of the initial sulfide melt in zone II: one of these liquids is formed in the (Pd, Au)-(As, Bi) subsystem, and the second in the (Pt, Pd)-Pb-(S, Bi, As) subsystem; 2) in zone III, secondary immiscibility and phase formation processes may occur within the Ls-m droplets during cooling; 3) сoncentration of microphases at the end of the ingot in zone III.
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