Late Cretaceous age of the Crucea uranium ore deposit, East Carpathians, Romania

Abstract

U-Th-Pb chemical dating is a suitable technique for determining ages of minerals (e.g., uraninite, monazite) that have large amounts of U and/or Th such that the radiogenic Pb can be measured. We investigate the chemical age of bitumen-supported uraninite from the vein-type Crucea uranium deposit, which is located in the Tulghes Series basement of the East Carpathians. We find that uraninite has a crystallization age of 88.8 ± 4.9 Ma, much younger than the Paleozoic age of magmatic emplacement and metamorphism of the host rock. The age of uraninite mineralization corresponds well with the timing of Mid-to-Late Cretaceous thrust faulting in the East Carpathians fold and thrust belt, during which the Tulghes Series was thrust over organic carbon-rich black shales of the Ceahlau and Moldavides nappes. These thrust faults likely acted as conduits through which U-rich carbonaceous matter, extracted from the black shales, migrated upward to be emplaced as veins.