New titanite U–Pb and molybdenite Re–Os ages for a hydrothermal vein-type Cu deposit in the Lanping Basin, Yunnan, SW China: constraints on regional metallogeny and implications for exploration

The small Kedengjian volcanic rock-hosted hydrothermal vein-type Cu deposit (100,000 t Cu metal content at about 3% Cu) is located in the Lanping Basin, one of several Mesozoic–Cenozoic continental sedimentary basins in the northern part of the Indochina block and in the eastern part of the North Qiangtang block. Many sediment-hosted base metal ore deposits with ages of < 65 Ma, which coincide with the Indian–Asian continental collision or the Himalayan orogeny, are present in these basins and are collectively referred to as the Sanjiang sediment-hosted base metal metallogenic belt. The Kedengjian volcanic rock-hosted hydrothermal vein-type Cu deposit has been commonly regarded as part of the Cenozoic Sanjiang sediment-hosted base metal metallogenic belt. We determined the age of mineralization for the Kedengjian deposit using hydrothermal titanite and molybdenite. The U–Pb ages of the first and second generations of titanite are 107.4 ± 5.6 Ma and 100.1 ± 3.4 Ma (2 σ), respectively. The associated molybdenite yields a Re–Os isochron age of 98.2 ± 2.2 Ma (2 σ) and a mean age of 98.3 ± 2.2 Ma, which are identical (within analytical error) to the U–Pb age of the younger titanite. Our new results indicate that the Kedengjian deposit formed at ~ 100 Ma, much older than the Cenozoic sediment-hosted base metal deposits in the Lanping Basin. This significant age difference dismisses the Kedengjian deposit as a member of the Cenozoic Sanjiang sediment-hosted base metal metallogenic belt. The Kedengjian deposit formed during the Late Cretaceous subduction of the Neo-Tethys oceanic plate beneath the previously amalgamated Indochina and North Qiangtang blocks of the Asian continent. On the basis of this tectonic correlation, we suggest that there is potential for pre-Cenozoic hydrothermal Cu mineralization in the region.