Nickeltsumcorite, Pb(Ni,Fe3+)(2)(AsO4)(2)(H2O,OH)(2), a new tsumcorite-group mineral from Lavrion, Greece

摘要

A new tsumcorite-group mineral, nickeltsumcorite, Pb(Ni,Fe3+)(2)(AsO4)(2)(H2O,OH)(2), the Ni-dominant analogue of tsumcorite and cobalttsumcorite, was found in the oxidation zone of a hydrothermal orebody containing gersdorffite and galena at the Km-3 mine, Lavrion, Attiki Prefecture, Greece. It is associated with annabergite, nickellotharmeyerite, nickelaustinite, gaspeite, calcite, dolomite, aragonite, quartz, goethite, cerussite, arseniosiderite, mimetite, oxyplumboromeite and Mn oxides/hydroxides. Nickeltsumcorite occurs as open-work aggregates and interrupted crusts up to 3 mm x 5 mm in area and up to 0.2 mm thick. They typically consist of coarse radial spherulites or dense concentric nodules up to 0.15 mm in diameter. Bunches or hemispherical clusters of crude individuals and separate imperfect, elongated crystals (up to 0.02 mm long) are also observed. Nickeltsumcorite is yellow, brownish-yellow, light brown or brown, with a yellow streak and a vitreous lustre. The Mohs hardness is similar to 4. The mineral is brittle; one direction of distinct cleavage is observed under the microscope. D(calc.) = 5.02 g cm(-3). Nickeltsumcorite is optically biaxial (-), alpha = 1.82(2), beta = 1.87(1), gamma = 1.90(1), 2V(obs.) is large. The chemical composition (wt.%, electron-microprobe data, H2O by difference) is CaO 2.79, PbO 28.12, MgO 0.30, CoO 0.15, NiO 17.39, ZnO 0.76, Mn2O3 0.57, Fe2O3 6.83, As2O5 38.17, H2O 4.92, total 100.00. The empirical formula, calculated based on 10 O apfu, is (Pb0.76Ca0.30)(Sigma 1.06)(Ni1.39Fe0.513+Zn0.06Mn0.043+ Mg0.04Co0.01)(Sigma 2.05)As1.99O7.97[(H2O)(1.25)(OH)(0.78)]. The strongest reflections in the powder X-ray diffraction pattern [d,angstrom(I)(hkl)] are 4: 64(100)((1) over bar 11), 4.47(41)((2) over bar 01), 3.238(82)((1) over bar 12), 3.008(60)(201), 2.859(41)(021), 2.545(79)((3) over bar 12, 112), 2.545(79)((3) over bar 12, 112) and 2.505(61)(220, (2) over bar 03). The cation composition, powder X-ray diffraction data and IR spectrum show that nickeltsumcorite belongs to the tsumcorite structure type. The new mineral is monoclinic, space group C2/m, a = 9.124(8), b = 6.339(3), c = 7.567(7) angstrom, beta = 115.19(6)degrees, V = 396.0(7) angstrom(3) and Z = 2. Nickeltsumcorite forms a solid-solution series with nickellotharmeyerite.