Acta Musei Moraviae

Replacement of hydrothermal chalcopyrite by bornite and Cu sulfides from the quarry of the cement factory Hranice: a hypogene minerogenetic process?

A new occurrence of a Cu-mineralization hosted by a post-Variscan calcite vein was found in the limestone quarry of the cement factory at the Hranice town (Moravo-Silesian Palaeozoic, Bohemian Massif, Czech Republic). In addition to previously known chalcopyrite and malachite, there were also identified bornite, native copper, cuprite, djurleite, covellite/yarrowite, spionkopite, anilite, geerite, and digenite/roxbyite. The accompanying minerals are dolomite-ankerite (Dol_31-72Ank_26-58Ktn_3-12), quartz, pyrite, minerals of the synchysite group (hydroxylsynchysite-(Y), hydroxylsynchysite-(Ce), synchysite-(Ce)), and limonite. The ore minerals constitute three respective associations which formed around grains of hypogene chalcopyrite I: A) limonite + malachite; B) bornite + Cu-sulfides + limonite; C) bornite + Cu-sulfides I, followed by chalcopyrite II, and then Cu-sulfides II and limonite. Genetically important is the recognition of second generation of chalcopyrite, to date unknown from other ore veins in the Moravo-Silesian Palaeozoic, indicating the participation of a new hydrothermal activity after crystallization of bornite and Cu-S phases I. The origin of bornite and Cu-S phases can either be associated with an episode of activity of weatheringrelated solutions incorporated into the hydrothermal activity, or these phases are also hydrothermal (hypogene). The available evidence does not allow to safely decide which scenario is valid in this case. The chemical composition of bornite and both generations of chalcopyrite is practically without any admixtures, with local minor manifestations of non-stoichiometry only. The Cu-sulfides and native copper show variably increased admixtures of Fe. Nevertheless, the coarse-grained development of spionkopite could be compatible with its hypogene origin.