@article{HoehnFrimmelDebailleetal.2021,
  author    = {H{\"o}hn, Stefan and Frimmel, Hartwig E. and Debaille, Vinciane and Price, Westley},
  title     = {Pre-Klondikean oxidation prepared the ground for Broken Hill-type mineralization in South Africa},
  series = {Terra Nova},
  volume    = {33},
  journal   = {Terra Nova},
  number    = {2},
  doi       = {10.1111/ter.12502},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218545},
  pages     = {168 -- 173},
  year      = {2021},
  abstract  = {New Cu isotope data obtained on chalcopyrite from the Black Mountain and the Broken Hill deposits in the medium- to high-grade metamorphic Aggeneys-Gamsberg ore district (South Africa) require a revision of our understanding of the genesis of metamorphic Broken Hill-type massive sulphide deposits. Chalcopyrite from both deposits revealed unusually wide ranges in δ\(^{65}\)Cu (-2.41 to 2.84 per mille NIST 976 standard) in combination with distinctly positive mean values (0.27 and 0.94 per mille, respectively). This is interpreted to reflect derivation from various silicate and oxide precursor minerals in which Cu occurred in higher oxidation states. Together with the observation of a typical supergene base metal distribution within the deposits and their spatial association with an unconformity only meters above the ore horizon, our new data are best explained by supergene oxidation of originally possibly SEDEX deposits prior to metamorphic sulphide formation, between the Okiepian (1,210-1,180 Ma) and Klondikean (1,040-1,020 Ma) orogenic events.},
  language  = {en}
}
@article{HoehnFrimmelPrince2021,
  author    = {H{\"o}hn, Stefan and Frimmel, Hartwig E. and Prince, Westley},
  title     = {Syn-metamorphic sulfidation of the Gamsberg zinc deposit, South Africa},
  series = {Mineralogy and Petrology},
  volume    = {115},
  journal   = {Mineralogy and Petrology},
  number    = {6},
  issn      = {1438-1168},
  doi       = {10.1007/s00710-021-00764-w},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-268574},
  pages     = {709-728},
  year      = {2021},
  abstract  = {The Mesoproterozoic Aggeneys-Gamsberg ore district, South Africa, is one of the world´s largest sulfidic base metal concentrations and well-known as a prime example of Broken Hill-type base metal deposits, traditionally interpreted as metamorphosed SEDEX deposits. Within this district, the Gamsberg deposit stands out for its huge size and strongly Zn-dominated ore ( >14 Mt contained Zn). New electron microprobe analyses and element abundance maps of sulfides and silicates point to fluid-driven sulfidation during retrograde metamorphism. Differences in the chemistry of sulfide inclusions within zoned garnet grains reflect different degrees of interaction of sulfides with high metal/sulfur-ratio with a sulfur-rich metamorphic fluid. Independent evidence of sulfidation during retrograde metamorphism comes from graphic-textured sulfide aggregates that previously have been interpreted as quenched sulfidic melts, replacement of pyrrhotite by pyrite along micro-fractures, and sulfides in phyllic alteration zones. Limited availability of fluid under retrograde conditions caused locally different degrees of segregation of Fe-rich sphalerite into Zn-rich sphalerite and pyrite, and thus considerable heterogeneity in sphalerite chemistry. The invoked sulfur-rich metamorphic fluids would have been able to sulfidize base metal-rich zones in the whole deposit and thus camouflage a potential pre-metamorphic oxidation. These findings support the recently established hypothesis of a pre-Klondikean weathering-induced oxidation event and challenge the traditional explanation of Broken Hill-type deposits as merely metamorphosed SEDEX deposits. Instead, we suggest that the massive sulfide deposits experienced a complex history, starting with initial SEDEX-type mineralization, followed by near-surface oxidation with spatial metal separation, and then sulfidation of this oxidized ore during medium- to high-grade metamorphism.},
  language  = {en}
}