Structural and thermochronologic constraints on skarn rare-metal mineralization in the Cenozoic Cuonadong Dome, Southern Tibet

Abstract

Abstract The Cuonadong super-large Be-W-Sn rare metals deposits are hosted by skarns and marbles in the middle unit of the Cuonadong Dome. Rocks in the Cuonadong Dome record four major deformational events: D1, top-to-S thrust; D2, top-to-N extension; D3, approximately E–W extensional deformation; and D4, late collapse structural deformation. Skarns and/or marbles featured by the directional alignment of skarn minerals are exposed in garnet-staurolite-bearing mica schist, and are closely related to the deformed leucogranites and pegmatites. The boundary between leucogranites and skarns is locally gradual or sharp, which suggests that skarns and the deformed leucogranites resulted from the synkinematic magmatism and the strong activity of the STDS. Ar-Ar dating of muscovite from the deformed granites in the middle unit and biotite from granitic gneiss in the core yielded Ar-Ar plateau ages of 15.0 ± 0.2 Ma and 13.9 ± 0.4 Ma, respectively, which reflects the age of syntectonic magmatism, and the activity time of the STDS at the Cuonadong Dome, respectively. Ar-Ar dating of biotite from marble in the middle unit yielded Ar-Ar plateau age of 16.1 ± 0.2 Ma, which was interpreted as the formation age of the synkinematic skarns. Skarns in the Cuonadong Dome were related to the detachments and formed in association with the emplacement of leucogranites. Therefore, we suggest that the formation of the Cuonadong Be-W-Sn skarn deposit was contemporaneous with the intrusion of leucogranitic magma and the top-to-north extensional deformation along the STDS.