Timing of magmatism, alteration-mineralization, and caldera evolution in the spahievo ore field, bulgaria' from laser-fusion ~(40)Ar/~(39)Ar dating

摘要

Ages of Oligocene magmatic rocks and alteration minerals along teh eastern edge of Borovitsa caldera were determined using ~(40)Ar/~(39)Ar laser-fusion methods. These new ages indicate that: (1) following emplacement of the Sarnitsa monzonite intrusion 32.90+-0.28 Ma, porphyry mineralization, and advanced-argillic alteration 32.82+-0.40 Ma, pre-caldera volcanism ended 32.31+-0.24 Ma, (2) ca. 1000 km~3 of rhyolitic ash flowsthat erupted 32.16+-0.32 Ma plus rhyolitic domes and dikes intruded 32.17+-0.26 Ma were followed by adularia-sericite alteration and base-metal+Au deposition 32.12+-0.28 Ma, and (3) the caldera collapsed with subsequent intrusion of a rhyolite dome 31.86+-0.22 Ma and quartztrachyte 32.75+-0.34 and melalatite dikes 31.76+-0.44 Ma. The inimate geographic and temporal associations imply connections between early monzonitic intrusion, Cu-Mo mineralization and advanced-argillic alteration on one hand, and younger rhyolitic magmatism, adularia-sericite alteration, and Au mineralization on the other. Deposition of Au ore prior to caldera collapse is an unusual contrast to well-studied systems in the western USA.