Geochronology of the Chakabeishan Li–(Be) rare-element pegmatite, Zongwulong orogenic belt, northwest China: Constraints from columbite–tantalite U–Pb and muscovite–lepidolite 40Ar/39Ar dating

Abstract

Lithium–(beryllium) are important strategic metals in modern industries. The Markam–Yajiang–Karakoram (MYK) giant Li ore belt (>14 Mt Li2O) is located in the central Qinghai–Tibetan Plateau, and is a world-class Li deposit belt. The reported pegmatite deposits in the belt are mainly found in the Tianshuihai–Songpan–Garzê Terrane (TSGT) and are generally considered to be related to Late Triassic S-type granites and flysch sedimentary rocks. Recently, abundant pegmatite veins have also been discovered in an adjacent terrane (i.e., the North Qaidam Terrane) to the north of the MYK belt, but it is unclear whether these newly discovered pegmatites are genetic related to the MYK belt. Here, we report high-precision columbite–tantalite (i.e., coltan) U–Pb ages and muscovite–lepidolite 40Ar/39Ar ages for the Li–(Be) rare-element pegmatites from the North Qaidam Terrane (NQT) in the Chakabeishan area of the Zongwulong orogenic belt. Coltan grains from three spodumene-bearing pegmatite samples yielded weighted-mean 207Pb-corrected U–Pb ages of 214.9 ± 1.7, 217.0 ± 2.3, and 215.0 ± 1.5 Ma. Muscovite 40Ar/39Ar dating of two spodumene-bearing pegmatite samples and one barren pegmatite sample yielded plateau ages of 213.00 ± 0.97, 211.67 ± 0.35, and 211.78 ± 0.29 Ma, respectively. A lepidolite 40Ar/39Ar age for a lepidolite-bearing pegmatite is 216.62 ± 0.88 Ma. The subtle age differences obtained by the different methods are within reasonable error estimates or may be due to different closure temperatures. The ore-forming ages of the Chakabeishan Li–(Be) rare-element pegmatites are similar to those of Li–(Be) pegmatite deposits in the MYK belt. This and data from previous studies suggest that the Chakabeishan Li–(Be) rare-element pegmatites were also formed in a post-collisional setting after the closure of the Paleo-Tethys (Anyemaqen) Ocean. This study has important implications for understanding the origins of the MYK Li ore belt, indicating that the formation of these Li deposits was not solely associated with the Late Triassic S-type granites and flysch sedimentary rocks. Our results may also have implications for exploration, which extends the potential area of Li deposits from the Tianshuihai–Songpan–Garzê Terrane to the North Qaidam Terrane.