Padrt' Stock (Tepla-Barrandian Unit, Bohemian Massif): petrology, geochemistry, U-Pb zircon dating of granodiorite, and Re-Os age and origin of related molybdenite mineralization
Abstract
The Padrť Stock is a small (~5 km2) intrusion located near the SE margin of the Teplá-Barrandian Unit, Bohemian Massif, several kilometers away from the NW periphery of the Central Bohemian Plutonic Complex. On outcrops, which are all located close to the contact of the stock with Neoproterozoic sedimentary rocks, two types of granitoids were detected, fine- to medium-grained hornblende-biotite Padrť granodiorite, and, along its SW margin, fine- to medium-grained partly porphyritic biotite Teslíny leucogranite.
The U-Pb zircon dating of the more voluminous Padrť granodiorite by laser ablation ICP-MS yielded a magmatic age of 342.8 +- 1.1 Ma, which is slightly lower than are the published age data for the nearby Blatná suite granitoids of the Central Bohemian Plutonic Complex. The Re-Os dating of molybdenite occurring in quartz veins within a quartzite lens in close exocontact yielded ages of 337.2 +- 2.4 Ma and 339.8 +- 2.5 Ma (two samples).
The data indicate that the formation of molybdenite postdated that of the magmatic rock. This is in agreement with relatively low-temperature deposition of quartz related to formation of the molybdenite, as indicated by the fluid inclusions (280 to 300 C).