Geological and geochemical characteristics of theWeilasito Sn-Zn deposit, Inner Mongolia

The Weilasito Sn-Zn-Cu deposit is located in Keshiketen, Inner Mongolia, at latitude 44°5'5"N, longitude 117°29'53"E. The mineralization styles include granite-type Sn-Zn at the top of the granite, quartz vein type Sn-Zn ore near the granite, Cu-Zn sulfide vein and Pb-Zn-Ag sulfide vein distal from the granite. Based on petrology, geology and geochemistry of elements and chronology, the authors recognized the granite magma revolution, the origin of the deposit and the relations between the mineralization styles. LA-ICP-MS zircon U-Pb dating yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 139.5±1.2 Ma(MSWD=3.3)for the alkali feldspar granite pluton. There are multilevel phenocrysts in the pluton, and the crystallization sequence is albite-quartz-K-feldspar-albite-quartz, topaz, cassiterite, and sphalerite. The granite rich in SiO₂ and Rb, Cs, Nb, Ta, W, Mo, Bi, Cu, Zn, In etc., poor in Al₂O₃, TiO₂, TFe₂O₃, CaO and Sr, Ba etc., the An value of the albite is lower than 0.3, similar to data of the granite of Sn-W deposits in the Nanling belt. Late magma experienced magmatic-hydrothermal transitional stage as well as gradual continuous evolution to hydrothermal stage. The Si rich, F rich and S rich fluid phases were separated from the magma to form the droplets (pocket) of quartz, topaz, cassiterite-sphalerite respectively in the granite-type Sn-Zn ore. The fluid inclusions are melt, melt-fluid and liquid respectively. The granite-type Sn-Zn ore formed at the top of pluton at the magma-hydrothermal transitional stage, the quartz vein-type Sn-Zn ore occurs at the outer part and the sulfide-vein Cu-Zn, Pb-Zn-Ag ore of the hydrothermal stage occurs distal from the rock body. All of the ores and the plutons comprise the magmatic hydrothermal tin polymetallic metallogenic system. In Xilin Gol-Chifeng area, there are some Pb-Zn-Ag veins (deposits and/or mineralization) related to the acidic intrusive rocks. There probably exsit large-sized hydrothermal tin (tungsten) polymetallic deposits in the depth.