Characteristics and preliminary ~(40)Ar/~(39)Ar and ~(87)Sr/~(86)Sr data of the Upper Eocene sedimentary-hosted low-sulfidation gold deposits Ada Tepe and Rosino, SE Bulgaria: possible relation with core complex formation

摘要

Epithermal gold mineralization of low-sulfidation type in the Ada Tepe and Rosino deposits, SE Bulgaria is hosted in the older supradetachment sedimentary rocks of Maastrichtian-Paleocene age. This style of mineralization is lacking in the overlying Priabonian-Oligocene sedimentary rocks. ~(40)Ar/~(39)Ar ages of the metamorphic and magmatic rocks in the ore districts and the adularia from the alteration indicate that: (1) time of ore deposition at Ada Tepe and Rosino is 35 Ma and 36.0-36.5Ma, respectively, confirming field observation for an older age of the mineralization than the Priabonian sedimentation; (2) these ages are ～3 Ma older than the nearest rhyolitic magmatic activity and ～3 Ma younger than the closing temperatures of the micas from the nearby core complexes. The ~(87)Sr/~(86)Sr isotope ratios for the carbonate minerals exhibit prevailing metamorphic-derived composition for the Sr in the hydrothermal fluids. Thus, geographic distribution, stratigraphic location, ages and Sr isotope compositions of the Ada Tepe and Rosino deposits suggest for an intimate association of Au mineralization to the metamorphic core-complex formation rather than to nearest rhyolitic magmatism.