Paragenesis of Cu-Fe ores from Ocna de Fier-Dognecea (Romania), typifying fluid plume mineralization in a proximal skarn setting

Abstract

Trace mineral assemblages in the bornite- and chalcopyrite-rich Cu-Fe zone of the Ocna de Fier-Dognecea skarn deposits, Banat, SW Romania provide additional constraints on the genesis of this classic zoned skarn system. Observed assemblages substantiate a model, in which the Cu-Fe zone forms the proximal fluid-plume root of the system. Observed trace mineral assemblages in the magnesian forsterite-bearing skarns crystallized at ~650°C in a volatile-rich environment, evidenced by widespread phlogopite, ludwigite, valleriite and apatite. The entire assemblage thus belongs to the initial stage of skarn formation. Prolonged cooling led to sequential exsolution of trace mineral phases from bornite and chalcopyrite during the retrograde stage, although still at temperatures in excess of 500°C. Bornite is typified by the abundance of exsolved phases along cleavage planes and along crystal margins, notably chalcopyrite and pyrrhotite, but also cobalt pentlandite, carrollite, wittichenite, galena, mawsonite, silver and electrum. Chalcopyrite hosts cobalt pentlandite, carrollite, wittichenite, galena and a sequence of Se- and Te-bearing minerals (kawazulite, bohdanowiczite, hessite, volynskite), along, although not restricted to, grain margins. The assemblage bornite-chalcopyrite-magnetite, with the trace phases, cobalt pentlandite, carrollite, wittichenite and various Se- and Te-bearing minerals represents a characteristic assemblage common to a disparate range of deposits formed at temperatures in excess of 500°C in the presence of volatiles and typified by relatively low fS2 fluids.

Minor and trace elements in bornite and associated Cu–(Fe)-sulfides: A LA-ICP-MS studyBornite mineral chemistry

“…Hypogene bornite, associated with magnetite and chalcopyrite, forms the early (hightemperature), proximal Cu-Fe core of the orefield (Cook and Ciobanu, 2001;Ciobanu and Cook, 2004). Bornite hosts lamellar exsolution of galena-(clausthalite) cross-cutting former valeriite-witichenite-chalcocite exsolutions ( Fig.…”

Roquesite and Associated Indium-Bearing Sulfides From a Paleoproterozoic Carbonate-Hosted Mineralization: Lindbom’s Prospect, Bergslagen, Sweden

“…Still, the presence of bornite-dominated composite sulfide inclusions in both oxides as well as in skarn silicates prove the existence of an earlier high-temperature stage of sulfide formation, dominated by bornite s.l. High-temperature (>500-600 °C) bornite or intermediate solid solution (iss) can accommodate a wide range of major and trace elements, which may then exsolve in the form of a diverse array of native metal and sulfide phases upon cooling (e.g., Cook et al 2011a, Cook & Ciobanu 2001 and references therein), a process which is exemplified at Lindbom's Prospect by the abundant bornite-hosted inclusions of native bismuth, chalcopyrite, wittichenite, and cuproan galena. Still, bornite equilibrated during decreasing temperatures is mostly very close to stoichiometric (Grguric & Putnis 1998, 1999, as is seen also in the Lindbom case, with the exception of its zinc contents ( Table 2).…”

A Re-Investigation of "Dognacskaite"

“…The Petri-Pauli mine was in the vicinity of the Simon Iuda orebody [see "Petru & Pavel adit" on the map published as Fig. 2 of Cook & Ciobanu (2001) or Fig. 1 of Ciobanu & Cook (2004)].…”