Experimental Modeling of Noble and Chalcophile Elements Fractionation during Solidification of Cu-Fe-Ni-S Melt

Abstract

We carried out a directed crystallization of a melt of the following composition (in mol. %): Fe 31.79, Cu 15.94, Ni 1.70, S 50.20, Sn 0.05, As 0.04, Pt, Pd, Rh, Ru, Ag, Au, Se, Te, Bi, and Sb by 0.03. The obtained cylindrical sample consisted of monosulfide solid solution (mss), nonstoichometric isocubanite (icb*), and three modifications of intermediate solid solution (iss 1 , iss 2 , iss 3 ) crystallized from the melt. The simultaneous formation of two types of liquids separated during cooling of the parent sulfide melt was revealed. In the first, concentrations of noble metals associated with Bi, Sb, and Te were found. The second is related to Cu and was found to contain a large amount of S in addition to Bi and Sb. We established the main types of inclusions formed during fractional crystallization of Pt-bearing sulfide melt. It was shown that noble metals are concentrated in inclusions in the form of RuS 2 , PdTe 2 , (Pt,Pd)Te 2 , PtRhAsS, and Ag 2 Se, doped with Ag, Cu, and Pd, in mss and in the form of PtAs 2 ; Au-doped with Ag, Cu, and Pd; Ag 2 Te; and Pd(Bi,Sb) x Te 1−x in icb* and iss. As solid solutions in the base metal sulfides, Rh is present in mss, Sn in iss.Minerals 2019, 9, 531 2 of 18 independent phases both with the main elements and with other trace elements. Since the Noril'sk ores are an important industrial source of the platinum group elements (PGE), intense research on the regularities of Ag-Au-PGE mineralization has been carried out [1][2][3][4][20][21][22][23][24].Most geologists assume that magmatic sulfide liquids are the source of PGE [2,4,10,25]. In [24], a hypothesis is presented about the pneumatolytic genesis of compounds of noble metals. Both hypotheses are based on the results of geochemical observations and on experimental data [1,2,4,10,[17][18][19][26][27][28][29][30][31][32][33][34][35]. Fundamental knowledge about the behavior of noble metals is contained primarily in the phase diagram of the systems related to this problem (see the review in [36][37][38][39][40][41]). Useful information is contained in experimental data on the composition and structure of samples obtained by prolonged isothermal annealing of partially crystallized samples and further quenching to room temperature [30][31][32][36][37][38][39][40][41]. For example, in [36], diagrams of the following systems were described: Pd-Fe-S, Pd-Ni-S, Pd-Cu-S, Pd-Pt-S, Fe-Pt-S, Pt-Fe-As-S, Pt-Pd-As-S, Pd-Ni-As, Pd-Sb-Te, Pt-Pd-Sb, Pd-Bi-Te, Pd-Pt-Sb, and so on. In this case, the composition of the samples is chosen by the experimenter. By contrast, in our works, we studied samples obtained by directed crystallization of melts of a given composition [11][12][13][14][15][16][17][18][19]. Usually, this method is applied in the case of gradual solidification of a cylindrical sample from one end to another. In this process, the melt is separated from the crystallized mass by a single interface-the crystallization front. The difference in the compositions of the melt and coexisting solid phases leads to fractionation of th...

Metallogenic fingerprint of a metasomatized lithospheric mantle feeding gold endowment in the western Mediterranean basin

“…These observations suggest that the formation of nano-to-micrometer sized PGM likely preceded the precipitation of their host BMS. This hypothesis is consistent with the fact that refractory Pt(-Pd)-Te-Sn compounds have higher solidus temperatures (>1200 °C) than the liquidus tem-peratures of Cu-Fe-Ni-S melts (Sinyakova et al, 2016(Sinyakova et al, , 2019, suggesting they crystallize before being trapped into BMS. The enrichment in Sn in such Pt-rich PGM (Figs.…”

Петрология, Геохимия И Происхождение Сульфидоносных И Эпг-Минерализованных Троктолитов Из Зоны Конникова В Йоко-Довыренском Расслоенном Интрузиве

“…Rb (Naldrett, 2004). Сублинейный характер этих трендов находит простое объяснение, как результат монотонной эволюции состава сульфидов в процессах силикатно-сульфидной несмесимости по закону, вытекающему из рассмотрения бинарной системы силикатный расплав -сульфидная жидкость (Campbell, Naldrett, 1979): (Holwell, McDonald, 2007;Helmy et al, 2007;Дистлер и др., 2016;Синякова и др., 2017Sinyakova et al, 2019). Интересно, что близкие к мантийным отношения S/Se и аномально высокие S/Te в богатых продуктами Mss пегматоидных троктолитах (колонка 8 в табл.…”

“…11-12). Наконец, за рамками метасоматической парадигмы остается высокотемпературный интервал первого этапа (1100-800 о С), для которого существуют многочисленные экспериментальные данные о выделении висмотеллуридов и арсенидов Pt и Pd из сульфидных расплавов (Helmy et al, 2007(Helmy et al, , 2010Синякова и др., 2017Sinyakova et al, 2019).…”

3D computer model of the Co-Cu-CoS-Cu2S subsystem T-x-y diagram above 800°C

“…Furthermore, the theoretical analysis of the Fe-Ni-Cu-S system for the processes of the quasi-equilibrium directional solidification of the four-component melt was carried out [4,5] and the relationship between the phase diagram and the formation of primary zones in a directionally solidified material was examined [6].…”