Primary, secondary, and admixture zonation of copper-nickel ores during fractional crystallization of sulfide melts

Abstract

Results of the study of massive ore bodies of mag� matic copper–nickel deposits demonstrate their het� erogeneous structure by mineral assemblages in vari� ous parts of the ore body, as well as by average chemical composition. Moreover, these characteristics may change spasmodically within the ore body. Conse� quently a definite sequence of zones with various ore types is formed in it [1–3]. Such sequences are not necessarily the same in different deposits, but accu� mulated results provide evidence for some similarity of the deposit structure and allow us to classify them by zonation types. The relation between such types and the average chemical composition of ores is evident. A number of reviews on description and primary classi� fication of varieties of ore body zonation for individual groups of deposits are available in the literature [1–5]. Explanation of this phenomenon involves concepts on the sequence of the phase formation during crystalli� zation of multicomponent melts of the Cu–Fe–Ni–S system. Data on mineralogical heterogeneity of ore bodies, as well as chemical heterogeneity of individual zones (chemical zonation), are available in the literature [6, 7]. It is controlled by both regularities of initial crystallization of sulfide melt and peculiarities of sub� solidus decomposition of initial phases. To understand the reasons for the zoned structure of ore bodies, we have to know the physicochemical history of their for� mation (namely, the time dependence of distribution of temperature and concentrations of components within the volume of the ore body during its cooling). Physicochemical reconstruction of the genetic history of the deposits is based on knowledge of phase rela�