Pekov I. V., Khanin D. A., Yapaskurt V. O., Pakunova A. V., Ekimenkova I. A.

Minerals of the beudantite—segnititc series from the oxidation zone of Berezovskoe gold ore deposit, the Middle Urals: variations of chemical composition, behavior of admixtures, antimony-bearing varieties

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 3. P. 89-105

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Language: Russian

Abstract

In the oxidation zone of the Berezovskoe gold deposit (Middle Urals, Russia), minerals of the beudantite—segnitite series [idealized formulae — Pb(AsO₄)(SO₄)(OH)₆ and Pb(AsO₄)(AsO₃OH)(OH)₆, respectively] form a multicomponent solid-solution system with wide variations of As, S, Fe, Cu, and Sb contents and lesser variable contents of P, Cr, Zn, Pb, and K. Found minerals of this series correspond to range from beudantite with 1.25 S apfu down to S-free segnitite, with lacking segnitite between 1.57 and 1.79 As apfu. Segnitite in Berezovskoe deposit contains antimony, presumably pentavalent (up to 15.2 wt % Sb₂O₅ = 0.76 Sb apfu, that is the highest known Sb content in the alunite-supergroup minerals), that substitutes Fe3+. The Sb content increases together with increase of the As/S ratio. On the contrary, beudantite is Sb-free or very poor in Sb (0.00—0.03 Sb apfu). Many samples of segnitite are enriched in copper (up to 8.2 wt% CuO = 0.83 Cu apfu, that is unusually high Cu content for this mineral) and/or in zinc (up to 2.0 wt% ZnO = 0.19 Zn apfu). Both Cu and Zn substitute Fe. The generalized formula of a hypothetic end-member of the segnitite series with 1 Sb apfu is: Pb(Fe³⁺M²⁺Sb⁵⁺)(AsO₄)₂(OH)₆, in which M = Cu, Zn, Fe²⁺. The chemical evolution of the beudantite—segnitite series minerals in the Berezovskoe deposit is characterized by increase of the S/As ratio with decrease of the Sb content from early to late generations.

Key words: beudantite, segnitite, alunite supergroup, natural arsenates, antimony in arsenates, oxidation zone, Berezovskoe deposit, Urals.