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| Titel |
Cu isotope variability in Bavaria´s largest Cu-Zn deposit in Kupferberg (NE Bavaria, Germany) |
| VerfasserIn |
Stefan Höhn, Hartwig E. Frimmel, Vinciane Debaille, Wendy Debouge |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129619
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| Publikation (Nr.) |
 EGU/EGU2016-9757.pdf |
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| Zusammenfassung |
| Kupferberg, a small town c. 15 km northeast of Kulmbach, owns its existence to Bavaria′s
largest Cu-Zn deposit, which was mined intermittently from the 13th to the 19th
century. The deposit is located in the Saxothuringian Zone of the Variscan basement
in northeastern Bavaria. It is positioned between the allochthonous Münchberg
metamorphic complex in the east and a major northwest-southeast tending regional
fault zone, the “Franconian Lineament”, in the west. The deposit is hosted by an
Early Palaeozoic volcano-sedimentary succession of the Randschiefer Formation
(RF) and consists of a northwest-southeast directed string of several stratiform,
sulfide-rich ore lenses. These lenses show a remarkably simple mineralogy dominated by
quartz, carbonate, pyrite and chalcopyrite with minor amounts of sphalerite and
chlorite.
The genesis of the Cu-Zn mineralization has remained speculative. A purely syngenetic
model, supported by the generally laminated appearance of the ore, has to be questioned
because of the ore lenses occurring in different tectonic units. Urban & Vaché (1972)
proposed supergene enrichment between the Cretaceous and the Tertiary as most
critical. To test such a supergene versus hypogene Cu-mineralization, we investigated
the Cu isotopic composition of primary and secondary Cu phases as well as the
trace element distribution in three pyrite generations. The pyrite generation that is
coeval with the principal Cu-mineralization in the form of chalcopyrite has Co/Ni
ratios (on average 35) typical of hydrothermal, possibly metamorphic, formation.
Chalcopyrite, present at highly variable modal proportions, yielded a narrow range in δ65Cu
from -0.26 to 0.36 ‰Ḃoth the absolute values and the narrow range are similar to
the δ65Cu range known for hydrothermal chalcopyrite in crustal rocks (Markl et
al. 2006). Metamorphism has been shown to further restrict the range in δ65Cu
(Ikehata et al. 2011) – an effect that might be applicable to Kupferberg. In contrast,
undoubtedly supergene native copper and malachite yielded δ65Cu of as much as 1.75
‰ which is in line with observations on supergene Cu mineralization elsewhere
(Mathur and Fantle 2015). Our new results suggest a principle phase of hypogene
Cu-mineralization, possibly related to Variscan metamorphic fluid circulation, with
subsequent supergene Cu-mineralization due to interaction with groundwater having been
subordinate.
Literature
Ikehata, K., Notsu, K., Hirata, T. (2011): Copper isotope characteristics of copper-rich
minerals from Besshi-Type volcanogenic massive sulfide deposits, Japan, determined using a
femtosecond LA-MC-ICP-MS.- Economic Geology 106, 307-316.
Markl, G., Lahaye, Y., Schwinn, G. (2006): Copper isotopes of redox processes in
hydrothermal mineralization.- Geochimica et Cosmochimica Acta 70, 4215-4228.
Mathur, R. & Fantle, M.S. (2015): Copper isotopic perspectives on supergene processes:
Implications for the global Cu cycle.- Elements 11, 323-329.
Urban, H. & Vaché, R. (1972): Die Kupfererzlagerstätte von Kupferberg-Wirsberg
(Oberfranken) im Lichte neuer Aufschlüsse.- Geologica Bavarica 65, 74-106. |
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