The Late Cretaceous magmatism and Sn-Ag-Pb-Zn-W polymetallic mineralization in Bozhushan ore concentration area, southeast Yunnan

The tin-silver-lead-zinc-tungsten polymetallic ore concentration area of Bozhushan is located at the western edge of the South China Fold System and is an important part of the magmatic-mining belt in southeast Yunnan. The mineral resources in the area are rich, mainly tin-silver-zinc-tungsten deposits, and some other metal minerals (e.g. lead-zinc-iron-copper minerals). All the deposits are distributed around the Bozhushan rock body, among which the Bainiuchang ultra-large silver-polymetallic mine and the Guanfang large tungsten mine are the most typical. Studies have shown that the formation of the tin-silver-lead-zinc-tungsten deposits in the Bozhushan ore district is closely related to the Late Cretaceous magmatism, with the complex rock formations dating back to 91.2 to 84.1 Ma ago, and are the product of Late Cretaceous magmatism. The Late Cretaceous acidic magma was massively intruded along the intersection of the core of the Bozhushan anticline and the north-west trending fracture zone, and eventually led to the formation of the Bozhushan complex granite body and the Bainiuchang concealed granite body under the top-supporting and bottom-splitting action of the magma. The granite bodies of the Bozhushan unit show consistent geochemical characteristics with the Bainiuchang monzonitic granite and granite porphyry, as well as the Tuanshan and Guanfang granites, which are silica-rich (SiO₂ content of 65.48%~74.92%) and potassium-rich (K₂O content of 4.17%~6.06%). The rocks are enriched in light rare earth elements (LREEs), clearly enriched in large ion lithophile elements (LILEs), and relatively deficient in high field strength elements (HFSEs), with moderate negative europium anomalies. They belong to calcium alkaline to high potassium calcium alkaline quasi-aluminous to peraluminous S-type granites which formed in a geotectonic context of synclinal orogeny and transition to a post-collisional orogenic environment, being the result of orogeny. The migration and enrichment of mineralised material in the area mainly revolves around the granite bodies, led to the formation of siliciclastic W, Sn, and Fe deposits in the granite contact zone, magmatic hydrothermal Ag, Pb-Zn, Sn, and Cu in the clastic-carbonate construction and low-temperature hydrothermal Sb ores in the peripheral strata, which constitute a relatively complete magmatic hydrothermal mineralization system related to granite intrusion in the region.