Geochronology, mineralization and prospecting implication of the Paleoproterozoic Shaliuquan Nb-Ta pegmatite deposit in the northern Tibetan Plateau

Abstract

A large number of Archean and Paleoproterozoic pegmatite rare-metal deposits exist worldwide, but few Precambrian pegmatite deposits have been reported in China, especially in the Tibetan Plateau. The Precambrian pegmatite deposits are still poorly studied. The Shaliuquan pegmatite, located in Quanji Massif, is a rare pegmatite-type Nb-Ta deposit in the northern Tibetan Plateau. Columbite-tantalite group minerals (CGMs) from three pegmatite samples give the U-Pb ages of 1844.2 ± 8.1 Ma, 1831.2 ± 12.2 Ma and 1848.0 ± 18.7 Ma, respectively. The U-Pb ages of CGMs show that the Shaliuquan pegmatite is a rare Paleoproterozoic pegmatite rare-metal deposit in the Tibetan Plateau. This is supported by the Precambrian 40Ar/39Ar plateau age of muscovites from two pegmatite samples (1094–1518 Ma), representing the metamorphic events after formation. As for the formation of Shaliuquan pegmatites, we argue that the hydrothermal processes in the late stage of the pegmatite evolution play a vital role for the enrichment and mineralization of Ta, which is evidenced by texture and compositions of CGMs and zircons. The formation of the Shaliuquan pegmatites is a response to the assembly of the Columbia supercontinent. The discovery of the Precambrian Shaliuquan pegmatite deposit implies that the Quanji Massif in the northern margin of the Qaidam Basin, which has an ancient mature metasediments basement and thick continental crust, has great potential for prospecting the Paleoproterozoic pegmatite rare-metal deposits.