Unusual morphological forms of hodrušite from the Rozália vein, Hodruša-Hámre near Banská Štiavnica (Slovak Republic)

Abstract

Rare Cu–Bi sulphosalt, hodrusite, occurs in the Rozalia vein (levels X–XIV of the Rozalia mine, Hodrusa-Hamre ore deposit near Banska Stiavnica, central Slovakia) in two unusual morphological forms. The first type are brownish bronze thin acicular striated crystals, up to 3 mm long, in drusy cavities of quartz–hematite gangue, which are usually grouped into chaotic or irregular aggregates. The second hodrusite type comprises flattened columnar aggregates, up to 1.5 cm long, overgrown by hematite in quartz gangue. These aggregates are distinctly striated with brownish bronze colour and metallic lustre. Abundant W- and Al-rich hematite, chalcopyrite, kaolinite/dickite, siderite, baryte, rare bismuthinite and kupcikite were found in the association. The earliest columnar aggregates of hodrusite are locally substantially replaced by bismuthinite; these hodrusite–bismuthinite aggregates are further intensively pushed back by hematite displaying W- and Al-rich zones. Acicular crystals of hodrusite in gangue cavities were later than bismuthinite and hematite and their formation was related to remobilisation of Cu and Bi from earlier altered gangue. Powder X-ray diffraction data and chemical composition of both hodrusite types are similar; their unit-cell parameters were refined (monoclinic space group C2/m) as: a 17.552(5), b 3.905(1), c 27.167(9) A, β 92.44(3) o