Minerals of the Supergroup of Alunite in Layered Ores of the Yaman-Kasy Sulfide Deposit, Southern Urals: Morphology, Assemblages, and Chemical Composition

The article describes the findings of minerals of the alunite supergroup: crandallite, ginsdalite, and alunite in hematite-containing thin-layered pyrite ores with increased total REE contents (up to 110 ppm). Crandallite forms elongated aggregates (up to 120 microns) with a rhythmically zonal structure and an uneven distribution of REE in them. Less common are spherulite aggregates (up to 120 microns) in association with alunite, quartz, chlorite, and hematite. The main feature of crandallite is high Pb contents (7–19 wt % PbO). Individual grains of crandallite contain (wt %) up to 1.84 La₂O₃, up to 1.03 Ce₂O₃, 0.85–1.73 Nd₂O₃, 0.39–0.54 Pr₂O₃, as well as 0.52–2.70 BaO, 0.99–2.50 SrO, 0.34–0.55 UO₂, 0.30–0.69 ThO₂, and 0.32–0.57 CuO. Ginsdalite and alunite in the form of spherulites up to 30 microns in size and lamellar aggregates up to 20–30 microns in length are found in interstitials of chalcopyrite, barite. The chemical composition of alunite and ginsdalite contains minor V₂O₅ (up to 0.3 and 0.1 wt %, respectively). The formation of minerals is considered as a result of the mobilization of components from hyaloclasts and ore-clasts in the presence of phosphorus coming from biogenic matter during the formation of a late quartz-hematite association.