The fractures-controlled tin mineralization at the end of Late Cretaceous in the Songshan deposit, southwestern China: Constraints from U–Pb dating of zircon, garnet, and cassiterite

Abstract

The Songshan tin deposit is located in the northern Lincang granitic batholith along the Lancangjiang tin belt, Western Yunnan, southwestern China. The ore bodies mainly occur as tourmaline-quartz veins with NNE- and/or NW-trending in the Triassic Pinghejie granitic pluton, and the schist of the Proterozoic Songshan Formation. The previous study suggested the tin mineralization in the Songshan deposit should occur in the Triassic, but no directed age data support it. This hinders the understanding of the genesis of the Songshan tin deposit, especially the tin mineralization in the Lancangjiang tin belt. Here, we report the zircons U-Pb ages of 222.7 ± 1.6 and 222.0 ± 2.4 Ma for the granodiorite, 215.1 ± 1.5 and 223.0 ± 2.0 Ma for the biotite monzogranite, and 222.3 ± 2.3 Ma for the alter granite from the Pinghejie granitic pluton. The monazite from the monzogranite yields a U-Pb age of 212.8 ± 1.9 Ma. We also obtain two garnet U-Pb ages of 215.1 ± 8.7 Ma and 213.5 ± 7.2 Ma from skarn, and two cassiterite U-Pb ages of 76.6 ± 1.5 Ma and 79.6 ± 3.6 Ma from tin ores. These data suggest that tin mineralization in the Songshan deposit occurred at the end of Late Cretaceous, which is quite different from the ages of the Pinghejie granitic pluton emplaced and the formation of skarn. The zircon Hf isotopes (εHf(t) = –22 ∼ -12) and monazite Nd isotopes (εNd(t) = -13.04 ∼ -11.80) indicate that the Pinghejie granitic pluton was derived from the remelting of Paleoproterozoic crust. The paper concluded that the tin mineralization in the Songshan deposit occurred at the end of Late Cretaceous. It is another important metallogenic period in the Lancangjiang tin belt, which may be related to the subduction of the NeoTethys oceanic crust. The tin mineralization can not only occur in the magmatic arc, but also in the hinterland behind the magmatic arc.