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MINERALS OF THE SYSTEM ZnS–CdS FROM FUMAROLES OF THE KUDRIAVY VOLCANO, ITURUP ISLAND, KURILES, RUSSIA

Ilya V. Chaplygin^1,, Nadezhda N. Mozgova¹, Andrey V. Mokhov¹, Elizaveta V. Koporulina¹, Heinz-Jürgen Bernhardt² and Igor A. Bryzgalov³

¹ IGEM, Russian Academy of Sciences, Staromonetny 35, Moscow 119017, Russia
² Zentrale Elektronen-Mikrosonde, Ruhr Universität Bochum, D–44780 Bochum, Germany
³ Department of Geology, Moscow State University, Moscow 119899, Russia

E-mail address: ichap{at}igem.ru

Minerals of the system ZnS–CdS formed between 400 and 725°C in active fumaroles at the Kudriavy volcano, Iturup Island, Russia, were studied using scanning electron microscopy with energy dispersion, X-ray diffraction and with an electron microprobe. The composition of these minerals varies widely: Zn 2.46–57.7, Cd 2.38–69.5, Fe 0.72–13.6 wt.%, and thus covers almost the entire ZnS–CdS series. Two types of solid solutions occur: cubic, from 0 to 8 mol.% CdS, and hexagonal, from 17 to 100 mol.% CdS, separated by a two-phase transition zone. Three different mechanisms of substitution account for the range of composition: Zn-for-Fe in sphalerite, Zn-for-Cd in wurtzite–greenockite, and Cd-for-Fe in greenockite. The incorporation of Cu and In, up to 2.92 and 4.75 wt.%, respectively, is noted in sphalerite, and up to 1.27 wt.% Cu and 2.75 wt.% In, respectively, in minerals of the wurtzite–greenockite series. Both elements evidently occur as the roquesite component in solid solution. Zinc-rich species are metal-deficient, whereas Cd-rich species are sulfur-deficient. The range of nonstoichiometry in minerals of the system ZnS–CdS studied is in the order of 2.6 at.%, or 0.05 apfu S. We conclude that there is not a complete solid-solution between wurtzite and greenockite in the temperature range studied owing to a phase transition in ZnS and a change in the structure type. Phase relations for the temperature range studied proved to be identical with those established for synthetic compounds. In a fumarolic environment, crystals of Cd-rich sulfides of the system ZnS–CdS precipitate mainly at lower temperatures (400°C) than those of Zn (up to 725°C).

Keywords: Zn–Cd sulfides, sphalerite, wurtzite, greenockite, solid solution, indium, fumaroles, Kudriavy volcano, Iturup Island, Kuril Archipelago, Russia.