Bi-bearing and REE-free zálesíite from the Fuka mine, Okayama Prefecture, Japan

Abstract

Zálesíite is found to exist as hexagonal prismatic crystals (length: up to 1 mm; width: 10 μm) and fibrous aggregates in the alteration zone in crystalline limestone near gehlenite-spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. The mineral is pale green to emerald green in color with a silky to vitreous luster. Andradite, aragonite, bornite, cahnite, chalcocite, chalcopyrite, conichalcite, johnbaumite, and an unidentified Ca-Cu arsenate mineral coexist in the abovementioned limestone. From SEM-EDS analysis, the empirical formula of zálesíite is found to be (Ca0.74Bi0.26)Σ1.00(Cu5.80Ca0.18Ni0.01Zn0.01)Σ6.00[(As2.86Si0.12P0.02)Σ3.00(O11.14OH0.86)Σ12.00](OH)6·3H2O on the basis of the following calculation: 10 (M1 + M2 + X) + 6 (OH) + 3 (H2O). Zálesíite collected from the Fuka mine contains Bi and is free of REE. The unit cell parameters of the zálesíite crystals are a = 13.656(9), c = 5.850(4) Å, V = 945(1) Å3, and Z = 2. It is inferred that zálesíite is formed by the reaction between crystalline limestone, cahnite, johnbaumite, Cusulfide, and a Birich hydrothermal solution.