Geology and geochronology of the Xinqi WSn polymetallic deposit in the Tengchong block, western Yunnan, China

Abstract

Xinqi is one of the most significant tungsten‑tin polymetallic deposits in the Tengchong tin polymetallic metallogenic belt, Sanjiang area. However, the age of the mineralization and the potential parental granite for tungsten‑tin (WSn) deposits have not yet been constrained. In this study, the ore-forming process at Xinqi is categorized into five stages: potassic stage (Stage I), sodium stage (Stage II), greisen stage (Stage III), quartz-cassiterite-wolframite stage (Stage IV), and quartz-cassiterite-sulfide stage (Stage V). UPb dating of cassiterite and wolframite extracted from quartz vein ore in stages IV and V yields consistent ages of 65.4 ± 1 Ma and 64.65 ± 0.66 Ma, respectively, indicating that WSn mineralization occurred during the Late Cretaceous and is closely associated with the collision between the Indian and Eurasian plates. Integrating this data with previous findings on WSn mineralization ages in the Tengchong block suggests that tungsten‑tin mineralization in this area is closely linked to granite, predominantly occurring from the Early Cretaceous to the Paleogene. The ages of WSn mineralization at Xinqi align with the formation age of Guyong monzogranite (66.30 ± 0.23 Ma) but are approximately 15 Ma older than the Xinqi granite porphyry (51.66 ± 0.21 Ma). This correlation, along with the low oxygen fugacity of the monzogranite (the value of △FMQ from −2.54 to 1.50), indicates that the monzogranite plays a crucial role in tin enrichment and serves as the parental granite for WSn mineralization at Xinqi. The parental monzogranite exhibits low ε_Hf(t) values ranging from −10.94 to −19.54, suggesting that the ore-forming magma likely derived from ancient crust without mantle contamination. Furthermore, based on previous studies, we propose that a tin-rich continental crust exists in the Tengchong area, which has undergone a series of specific collisional orogenic events that led to the formation of granite and the associated tin mineralization in the Tengchong block.