In this paper, the authors report new zircon U-Pb ages, whole-rock major and trace elements composition and Sr-Nd isotopic data for the Baiyunshan alkalic rocks in the northern part of the western area of the Gejiu tin-polymetallic ore district. The Late Cretaceous age (80.0±0.6 Ma) using the zircon LA ICP-MS U-Pb dating for the alkalic syenites indicates that they occurred with the contemporaneous gabbrodiorites and granites. This suggests that these rocks were all formed during the same magmatic-tectonic event. The geochemical characteristics and Sr-Nd isotopic compositions indicate that the alkaline syenite and the nepheline syenite were derived from an enriched mantle, and subsequently underwent different evolution processes. Combined with the previous studies, the authors hold that the alkali rocks, intermediate-mafic rocks and ore-related granites were derived from the enriched lithospheric mantle, the normal lithospheric mantle and the crust source, respectively. In the Late Cretaceous, the parental melts of the alkali rocks and gabbrodiorite magmas were formed by partial melting of the heterogeneity of the lithosphere mantle triggered by an extensional tectonic setting. Uprising of the above mantle melts promoted the partial melting of middle-lower crust and formed the granitic melts. These Late Cretaceous magmatism caused the activity and enrichment of the ore-forming material within a mutual tectonic belt, and then formed the superlarge tin-polymetallic deposit in the Gejiu ore district. It can be said that the enriched mantle-derived alkaline magmatism not only offered energy during the formation and mineralization of the ore-bearing granitic magma but also played some other roles.