Thallium-rich murunskite from the Lovozero pluton, Kola Peninsula, and partitioning of alkali metals and thallium between sulfide minerals

Abstract

A new thallium-rich variety of murunskite has been found in the Palitra peralkaline pegmatite at Mount Kedykverpakhk, the Lovozero alkaline pluton, Kola Peninsula, Russia. This mineral occurs as a flattened dark bronze segregation (0.3 × 0.8 × 0.8 mm) overgrowing ussingite in a cavity. The chemical composition is as follows, wt %: 8.35 K, 24.31 Tl, 29.01 Cu, 14.58 Fe, 23.26 S, total is 99.51. The empirical formula is (K1.18Tl0.66)1.84(Cu2.53Fe1.45)3.98S4.02. According to X-ray powder diffraction data, the dimensions of the tetragonal unit cell are: a = 3.869 (1), c = 13.206 (6) A, V = 197.7 (2) A3. This variety is the closest to the intermediate member of the murunskite-thalcusite series. The youngest mineral complex of the Palitra Pegmatite includes four sulfides belonging to three different structure types. These sulfides also may be regarded as three topological types distinguished by the arrangement of alkali metal atoms in their structures: (1) bartonite and chlorbartonite belonging to the zero-dimensional topological type with K atoms in isolated cells, (2) pautovite pertaining to the one-dimensional type with Cs (+Rb, K, Tl) atoms making up chains in ample tunnels, and (3) murunskite belonging to the two-dimensional type with K (+Tl) atoms forming sheets. There is pronounced partitioning of K (Cs + Rb) and Tl between these sulfides: bartonite and chlorbartonite contain 9.5–9.7 wt % K and 0.2 wt % Tl; pautovite, 36.1 wt % Cs, 1.3 wt % Rb, 0.5 wt % Tl, and 0.2 wt % K; and murunskite, 8.35 wt % K and 24.31 wt % Tl.