A Re-Investigation of "Dognacskaite"

Abstract

Five specimens of "dognácskaite" from Dognecea (Caraş-Severin County, Banat, Romania), a poorly described substance, once considered a Cu-Bi sulfosalt, were studied by ore microscopy, SEM, EPMA, and XRPD methods. One of the specimens is probably that used for the original description by József Krenner. Every specimen proved to be a mixture with a similar mineral composition and texture. The main component of "dognácskaite" is bismuthinite rimmed by wittichenite (containing strings of native bismuth), the latter is in turn rimmed by copper sulfides (mainly djurleite with some covellite). Emplectite can also be found occasionally in the larger voids of bismuthinite. Magnetite (in some cases oxidized), chalcopyrite, bornite (replacing chalcopyrite) and rare sphalerite and tetradymite form inclusions in bismuthinite or in the rims surrounding it. Goethite, calcite, bismuth ochre and other unspecified fine-grained products of alteration are abundant in the voids. Data from earlier studies are easily explainable on the basis of this mineral assemblage, suggesting that every specimen of "dognácskaite" is a mixture of this kind. The samples may correspond to a (pyrite-) magnetite -chalcopyrite skarn ore replaced by a post-skarn hydrothermal bismuthinite ore, later affected by supergene copper enrichment then by oxidation processes. The exact locality of "dognácskaite" cannot be determined, but at least some of the specimens have been collected in the former Petri-Pauli (or Péter-Pál), now Petru şi Pavel mine on Mt. Danilii.