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
Albrecht Von Quadt, Irena Peytcheva, Borislav Kamenov, Lorenz Fanger, Christoph A. Heinrich, M. Frank, 2002. "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", The Timing and Location of Major Ore Deposits in an Evolving Orogen, D. J. Blundell, F. Neubauer, A. von Quadt
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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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As an outcome of the European Science Foundation scientific programme, GEODE, on geodynamics and ore deposit evolution, this book examines the underlying geodynamic processes that lead to the formation of ore deposits in order to discover what controls the timing and location of major ore deposits in an evolving orogen.
A collection of 19 research papers examines various aspects of ore genesis in the context of the geodynamic processes occurring within an evolving orogen. Although the majority of papers relate to Europe, their findings have a global significance for metallogenesis.
The book will be of interest to all those involved in research or mineral exploration concerned with metallogenesis. In addition, ore deposits provide new evidence about magmatism associated with transient, rapid changes in plate motions and subduction processes in unusual tectonic settings, and are therefore of interest to those involved in both the magmatic and tectonic processes of orogenesis.