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

The paper describes the findings of minerals of the alunite supergroup (crandallite, hinsdalite, and alunite) in hematite-bearing fine-bedded massive sulfide ores with a higher total rare-earth-element (REE) content (up to 110 ppm). Crandallite forms elongated aggregates up to 120 µm in size with a rhythmically zoned structure and uneven REE distribution. Rare spherulitic aggregates up to 120 µm in size occur in assemblage with alunite, quartz, chlorite, and hematite. The high PbO content (7–19 wt %) is the main feature of crandallite. Some crandallite grains contain (wt %) up to 1.84 La₂O₃ and 1.03 Ce₂O₃, 0.85–1.73 Nd₂O₃, 0.39–0.54 Pr₂O₃, 0.52–2.70 BaO, 0.99–2.50 SrO, 0.34–0.55 UO₂, 0.30–0.69 ThO_2, and 0.32–0.57 CuO. Hinsdalite and alunite in the form of interstitial spherulites up to 30 µm in size and platy aggregates up to 20–30 µm long occur between chalcopyrite and barite. Alunite and hinsdalite contain V₂O₅ (up to 0.3 and 0.1 wt %, respectively). The formation of minerals is considered a result of mobilization of components from hyaloclasts and ore clasts in the presence of phosphorus, which was sourced from biogenic matter during the formation of late quartz–hematite assemblage.