Lamellar minerals of the cuprobismutite series and related paděraite: a new occurrence and implications. The Canadian Mineralogist

An assemblage consisting of bismuthinite derivatives, mainly in the range gladite – oversubstituted bismuthinite (Cu0.833Pb0.833Bi19.167S30), makovickyite, and intergrowths of cuprobismutite and paděraite, with minor hodrushite, occurs in the Paulus mine, Ocna de Fier skarn deposit, southwestern Romania. Even though intimately intergrown with one another as sets of lamellae of varying thickness, with back-scattered electron images strongly suggesting that lamellar intergrowths of the two minerals extend below the size of the microprobe beam, homogeneous parts of lamellae or well-developed acicular crystals allow compositional characterization of the components. These are cuprobismutite, Cu8.07(Ag0.99Pb0.21Bi12.72)13.92S24.01, paděraite, Cu7.11(Ag0.36Pb1.20)1.56Bi11.28S22.05, and hodrushite, (Cu7.80Fe0.23)8.03(Ag0.35Pb0.12Cd0.02Bi11.49)11.98S21.99. Hodrushite is the least abundant component, containing minor but persistent Fe, up to 0.41 wt.%. An inverse correlation between Ag and Pb is seen between cuprobismutite (Agmin 2.34 wt.%, Agmax 2.75 wt.%) and paděraite (Pbmin 5.37 wt.%, Pbmax 7.34 wt.%). Compositions for each phase diverge somewhat from previously published data, suggesting that varying degrees of incorporation of Ag and, to a lesser extent, Pb, are features of the cuprobismutite homologous series and of the related paděraite. Ag appears to be an essential component of cuprobismutite, our data showing that 1 apfu Ag occupies the Bi position (14 apfu). Hodrushite differs from the type-locality material (Cu8.12Fe0.29Bi11.54S22), showing that the composition can depart from the ideal compositions within certain limits, with incorporation of Ag, Pb and Fe in the structure. Significantly, the number of Cu atoms is less than 8 apfu in the Ocn