Re-Os ages for the Elatsite Cu-Au deposit, Srednogorie zone, Bulgaria

Re-Os ages for six different molybdenite samples from the Elatsite deposit provide an opportunity to directly determine the age of ore mineralization for a Cretaceous subvolcanic Cu-Au system. There are two main stages of mineralization, an early magnetite-bornite-chalcopyrite stage (with noteable enrichments in Au-Pd-Pt), and a later chalcopyrite-pyrite stockwork stage where molybdenite first appears as a noteable sulfide phase at hand-specimen scale. In contrast to porphyry Cu systems that contain molybdenite throughout the paragenetic sequence, noteable molybdenite at Elatsite is restricted to a much narrower time interval. Our samples represent the main stage stockwork mineralization and their Re-Os ages range from 92.43 +/- 0.04 to 92.03 +/- 0.05 Ma (without Re-187 decay constant uncertainty). This suggests a minimum absolute life span of 400,000 +/- 90,000 years for the stockwork mineralization in a magmatic-hydrothermal system <1.5 km across at the subvolcanic level. The high Re concentrations in the molybdenite (300-2750 ppm, 1875 ppm median) support direct involvement of mantle in an arc-subduction environment. These new Re-Os data and recently published U-Pb ages for zircon are in very good agreement, again demonstrating that robust and consistent age results may be expected from the Re-Os chronometer in molybdenite.