The Danchi metallogenic belt in northwestern Guangxi is an important non- ferrous metal mining base in south China. He and Ar isotopes of fluid inclusions trapped in pyrite from the Ma’anshan Pb- Zn deposit and the Dashan Sn- Zn deposit of the Mangchang ore field， the Tongkeng Sn- polymetallic deposit of the Dachang ore field, and the Qianzhupo Pb- Zn polymetallic deposit of the Wuxu ore field have been studied in this paper. The results indicate that the 3He/4He values (0. 79～5. 32 Ra) of the ore- forming fluid are between those of crustal fluid (0. 01～0. 05 Ra) and mantle fluid (6～9 Ra); the 40Ar/36Ar values (273～349) are close to or slightly higher than the atmospheric eigenvalue(295. 5). He and Ar isotopes show that mantle fluid was involved in the mineralization in the area， and the ore- forming fluid was a mixture of mantle fluid， crust- sourced magmatic fluid and saturated atmospheric water. Based on the comprehensive study of Devonian exhalative deposition, granitic intrusion and tectonic characteristics, it is concluded that mantle fluid involved in mineralization is a regional event in the area. Mantle fluid is mainly derived from mantle components rising along NW deep faults during the crust- mantle interaction. The diagenesis and mineralization of Danchi metallogenic belt are the products of the same tectonic- thermal event in the Late Yanshanian period, and belong to the epigenetic hydrothermal filling- metasomatic mineralization.