2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 13
Presentation Time: 4:45 PM


ZIMMERMAN, A., STEIN, H. and HANNAH, J., AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80523, aaron.zimmerman@colostate.edu

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.