Behavior of macrocomponents during the formation of zonal sulfide ore on the basis of the experiment on the directional crystallization of Cu-Fe-Ni-S melt
E.F. Sinyakova1, D.A. Ulybin1,2,3, K.A. Kokh1, I.A. Kuzmin1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences,
Novosibirsk, Russia
2Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia
3Novosibirsk State University, Novosibirsk, Russia
Keywords: Cu-Fe-Ni-S system, phase equilibrium, zonality, fractional crystallization
Abstract
The quasi-equilibrium directional crystallization method was used to model a new type of zoning in the Cu-Fe-Ni-S system. A melt with the following composition (in at.%) was crystallized: 14.00 Cu, 30.00 Fe, 4.00 Ni, 51.00 S, and 0.1 each of Pt, Pd, Ag, Au, As, Te, Bi, Pb, Se, and Sn. Optical and electron microscopy, micro-X-ray spectral analysis, differential thermal analysis, and powder diffraction methods were used to analyze the composition and structure of the ingot. Based on the results of measuring the average solid phase composition, the distribution curves of macrocomponents in the ingot in the interval g from 0 to 0.81 (g is the fraction of crystallized melt) were plotted. The change of melt composition and distribution coefficients between solid phases and melt in the process of directed crystallization was also calculated. The obtained sample consists of three primary zones: the monosulfide solid solution with a composition ranging from (Fe₀.₇₅Ni₀.₁₀Cu₀.₀₆)0.91S to (Fe₀.₆₉Ni₀.₁₅Cu₀.₀₉)0.93S (Mss) the Zone I, and two intermediate solid solutions: ~ (Fe₀.₅₇Ni₀.₀₃Cu₀.₄₅)1.05S (Iss1) the Zone II and (Fe₀.₄₆Ni₀.₀₆Cu₀.₅₂)1.05S (Iss2) the Zone III. The peritectic character of the crystallization of Iss1 and Iss2
from the melt was established. The trajectories of melt and solid phases composition and series of conodes are plotted for Mss and Iss1 on the phase diagram of Cu-Fe-Ni-S system. Secondary zonality is described by the following sequence of phases: Pyh 1C + Pyh 3C + Icb + Ccp / Ccp + Iss + Fe-Pn, Sug / Ccp + Ni-Pn +NiS+Bn (Pyh - hexagonal pyrrhotite, Icb - isocubanite, Ccp - chalcopyrite, Pn - pentlandite, Sgk - sugakiite, Bn - bornite) and belongs to the high-sulfur pyrrhotite+cubanite-chalcopyrite type of ore body zonation.
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