| Реферат: | eng: For the first time in ore deposits of Vietnam, a mineral phase containing Au, Bi, and S as major elements was found in the gold ore of the Dakripen deposit. Pb is also present as a minor isomorphic impurity. Rare irregular or ellipsoid grains of that mineral up to 35 μm in size were identified in polished sections together with pyrite; galena; sphalerite; bismuthinite; ikunolite; native bismuth; and, occasionally, gold. All these species are related to the third stage of the ore formation. In reflected light, the mineral is bluish white, the reflectance is comparable with ikunolite and slightly higher than that of bismuthinite, and weak pleochroism and visible anisotropy are established. The mineral is opaque and brittle without internal reflections. According to 18 microprobe analyses, its average chemical composition and quantitative variations for the major elements are as follows (wt %): 14.02 (13.11-14.58) Au, 76.37 (74.93-76.91) Bi, 0.49 (0.10-1.00) Pb, 9.80 (8.87-10.07) S, and 100.68 in total. The empirical formula calculated for the average element contents-Au 0.96(Bi 4.91Pb 0.03) 4.94S 4.10-is similar to the idealized formula of jonassonite from the Nagybörzsöny deposit (Hungary)-Au(Bi,Pb) 5S 4-approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The typical mineral assemblage, optical properties, and chemical composition of this mineral allow us to regard it as a low-Pb variety of jonassonite. It may be assumed that the real formula of jonassonite without sporadic impurities of Pb and other elements must be AuBi 5S 4, as was stated before in the first communication of the Commission on New Minerals and Mineral Names of the International Mineralogical Association and is typical of minerals from Kazakhstan, Russia, Japan, Germany, the Czech Republic, the United States, and Australia. © 2011 Pleiades Publishing, Ltd.
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