Makovickyite and cupromakovickyite from the Obari mine, Yamagata Prefecture, Japan

Abstract

Makovickyite [(Ag,Cu)_1.5Bi_5.5S₉], and cupromakovickyite (Cu₈Ag₂Pb₄Bi₁₈S₃₆), members of the pavonite group, have been found from the Obari mine, Yamagata Prefecture, Japan. Both minerals are the first occurrence in Japan. Makovickyite occurs as irregular particles of 30-200 μm in the chalcopyrite-rich ore, and is intergrown with the exsolution lamellae of cupromakovickyite. Both minerals are associated with bismuthinite derivatives (bismuthinite, krupkaite, aikinite), possibly cuprobismutite homologous minerals, emplectite, tetradymite and chalcopyrite. The empirical formula of makovickyite is Ag_1.27Cu_2.60Pb_0.28Bi_10.23S₁₈ (based on ΣS = S + Te + Se = 18), which is classified as ⁱCu-bearing makovickyite. The unit-cell parameters from the X-ray single crystal of the mineral are a = 13.2524(5), b = 4.0523(2), c = 14.6775(6) Å, β = 99.487(3)°, V = 777.44(6) ų. The empirical formula of cupromakovickyite is Cu_8.66Ag_2.43Pb_2.32Bi_18.07S₃₆ (based on ΣS = S + Te + Se = 36). It is inferred that these minerals have been formed by high temperature (more than 300 °C) hydrothermal solutions in which Bi activity is relatively higher than Cu.