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The Elatsite porphyry copper deposit in the Panagyurishte ore district, Srednogorie zone, Bulgaria: U–Pb zircon geochronology and isotope-geochemical investigations of magmatism and ore genesis

By
Albrecht Von Quadt
Albrecht Von Quadt
Isotope Geochemistry and Mineral Resources, Department of Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich, Switzerland vonquadt@erdw.ethz.ch
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Irena Peytcheva
Irena Peytcheva
Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Science, 1113 Sofia, Bulgaria peytcheva@erdw.eth.ch
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Borislav Kamenov
Borislav Kamenov
Department of Mineralogy, Petrology and Economic Geology, Sofia University St. Kliment Ohridski, 15, Bd. Tzar Osvoboditel, 1505 Sofia, Bulgaria kamenov@gea.uni-sofia.bg
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Lorenz Fanger
Lorenz Fanger
Isotope Geochemistry and Mineral Resources, Department of Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich, Switzerland vonquadt@erdw.ethz.ch
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Christoph A. Heinrich
Christoph A. Heinrich
Isotope Geochemistry and Mineral Resources, Department of Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich, Switzerland vonquadt@erdw.ethz.ch
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M. Frank
M. Frank
Isotope Geochemistry and Mineral Resources, Department of Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich, Switzerland vonquadt@erdw.ethz.ch
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Published:
January 01, 2002

Abstract

Single zircons from several porphyry dykes bracketing the time of formation of the Elatsite porphyry Cu–Au deposit (Bulgaria) were dated by high-precision U–Pb isotope analysis, using thermal ionization mass spectrometry (TIMS). On the basis of cross-cutting relationships, and the mineralogy and geochemistry of igneous and altered rocks, five dyke units are distinguished. The earliest porphyry dyke is associated with, and overprinted by, the main stage of ore-related veining and potassic alteration. U–Pb analyses of zircons yield a mean 206Pb/238U age of 92.1 ± 0.3 Ma, interpreted to reflect the time of intrusion. Zircons of the latest ore forming dyke, crosscutting the main stage veins but still associated with minor potassic alteration and veining, give an intrusion age of 91.84 ± 0.3 Ma. Thus, ore mineralization is confined by individually dated igneous events, indicating that the entire time span for the ore-forming magmatism and high temperature hydrothermal activity extended over a maximum duration of 1.1 Ma, but probably much less. Zircon analyses of a late ore dyke cutting all ore veins and hosting pyrite as the only sulphide mineral give a concordant 206Pb/238U age of 91.42 ± 0.15 Ma. Based on a spatial relationships of the magnetite–bornite–chalcopyrite assemblage with coarse-grained hydrothermal biotite and K-feldspar, a Rb–Sr age of 90.55 ± 0.8 Ma is calculated using the two K-rich minerals. This age is interpreted as a closing date for the Rb–Sr system at T ≈ 300 °C consistent with published K–Ar data. Therefore the entire lifespan of the magmatic–hydrothermal system is estimated to have lasted about 1.2 Ma. Soon after, the Cretaceous complex was exposed by erosion, as shown by palaeontologically dated (Turonian; 91–88.5 Ma) sandstones containing fragments of porphyry dykes.

Geochemical discrimination ratios suggest a mixed mantle and crustal source of the Cretaceous magma. Isotope analyses of Sr, Nd and Hf confirm the conclusion that all porphyry rocks within and around the Elatsite deposit originate from an enriched mantle source at Cretaceous times, with crustal contamination indicated by moderately radiogenic Pb.

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Contents

Geological Society, London, Special Publications

The Timing and Location of Major Ore Deposits in an Evolving Orogen

D. J. Blundell
D. J. Blundell
Royal Holloway, University of London, UK
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F. Neubauer
F. Neubauer
University of Salzburg, Austria
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A. von Quadt
A. von Quadt
ETH-Z, Zurich, Switzerland
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Geological Society of London
Volume
204
ISBN electronic:
9781862394520
Publication date:
January 01, 2002

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