T39 Advances in the Understanding of Tectonic Settings and Structural Control of Ore Deposits

Sunday, 16 October 2005
1:30 PM - 5:30 PM


TETHYAN METALLOGENESIS: RE-OS GEOCHRONOLOGY OF THE PANAGYURISHTE DISTRICT, BULGARIA

Paper number: T39-14
Program: Technical Sessions
Time: 4:45 PM – 5:00 PM


Authors

  • A. Zimmerman Presenting Author
    Colorado State University, Fort Collins, CO
  • H. Stein
    Colorado State University, Fort Collins, CO
  • J. Hannah
    Colorado State University, Fort Collins, CO

Abstract

New rhenium-osmium (Re-Os) molybdenite ages help establish a definitive link between Tethyan tectonics and Balkan-Carpathian metallogenesis, previously hindered by the limited number of high precision ages for magmatic, volcanic, and metallogenic events. In the east-central heart of the Tethyan orogen is the Panagyurishte district of the Srednogorie Zone, Bulgaria, a north-south trending belt of Late Cretaceous paired porphyry and epithermal ore deposits associated with calc-alkaline volcanic centers and coeval intrusions. Multidisciplinary work, including high precision geochronology, is needed for a fundamental understanding of the tectonic-, district-, and deposit-scale spatial-temporal evolution of the Tethyan region. Four molybdenite-bearing Cu±Au±Mo±PGE porphyry systems were sampled for Re-Os age determinations. Direct dating of main-stage ore deposition furthers understanding of Tethyan tectonics by incorporating metallogenic ages into a growing collection of geochronologic, geophysical, and structural data. The Re-Os molybdenite results show a systematic age progression for porphyry mineralization from north to south in the Panagyurishte district over a 7 m.y. period. The northernmost deposit, Elatsite, a 319 Mt Cu+Au+PGE porphyry, is 92 Ma. The north-central Medet Cu+Au and Assarel Cu porphyry deposits (519 Mt combined) are 90 and 91 Ma, respectively. The southernmost Vlaikov Vruh Cu porphyry system, a 6.6 Mt past producer, is 87 Ma. The Re-Os geochronometer demonstrates that each deposit's main ore phase is short lived, <1 m.y., and each deposit, save the Medet-Assarel complex, appears to form during unique, resolvable, southward progressing pulses. The restricted metallogenic period with its distinct pulses suggests that short-lived tectonic events, rather than steady-state processes, are responsible for ore formation on the district scale. Perturbations from steady-state subduction, such as changes in slab angle, convergence rate, convergence direction (orthogonal vs. strike-slip), and/or subduction termination may play a role in ore formation. Additional Re-Os ages will temporally constrain regional tectonic interpretations for other deposits in the region, including those in Serbia and Romania.