Two kinds of mylonite series rocks, felsic and mafic, have been recognized in the NW-striking shear zone of the Jiapigou gold belt. During ductile deformation, a large amount of fluid interacted intensively with the mylonite series rocks: plagioclases were sericitized and the An values declined rapidly, finally all of them were trans formed to albites; dark minerals were gradually replaced by chlorites (mostly ripidolite). Meanwhile, large-scale and extensive carbonation also took place, and the carbonatization minerals varied from calcite to dolomite and ankerite with the development of deformation. The δ~13C values of the carbonates are - 3. 0‰--5. 6‰ suggesting a deep source of carbon. The ductile deformation is nearly an iso-volume one (f_v=1). With the enhancement of shear deformation, SiO_2 in the two mylonite series rocks was depleted, while volatile components such as CO_2 and H_2O, and some ore-forming elements such as Au and S were obviously enriched. But it is noted that the enrichment of An in both the mylonite series rocks did not reach the paygrade of gold. The released SiO_2 from water-rock interactions occurred in the form of colloids and absorbed gold in the fluid. When brittle structures were formed locally in the ductile shear zone, the ore-forming fluids migrated to the structures along micro fractures, and precipitated auriferous quartz because of reduction of pressure and temperature. Fluid inclusion study shows that the temperature and pressure of the ore-forming fluids are 245-292℃ and 95.4-131. 7MPa respectively; the salinity is 12. 88-16. 33 wt% NaCl; the fluid-phase is rich in Ca~2+, K~+, Na~+, Mg~2+, F~- and Cl~-, while the gaseous phases are rich in CO_2 and CH_4. The δDand δ18 O values of the ore-forming fluid are - 84. 48‰- - 91. 73‰ and - 0. 247‰-+2.715‰ respectively, suggesting that the fluid is composed predominantly of meteoric water. Both kinds of mylonite series rocks, felsic and mafic, have been recognized in the NW-striking shear zone of the Jiapigou gold belt. A large amount of fluid interacted intensively with the mylonite series rocks: plagioclases were sericitized and the An values ​​declined rapidly, finally all of them were trans formed to albites; dark minerals were mostly replaced by chlorites (mostly ripidolite). large-scale and extensive carbonation also took place, and the carbonatization varieties varied from calcite to dolomite and ankerite with The development of deformation. The δ ~ 13C values ​​of the carbonates are - 3. 0 ‰ -5.6 ‰ suggesting a deep source of carbon. The ductile deformation is nearly an iso-volume one (f_v = 1). With the enhancement of shear deformation, SiO_2 in the two mylonite series rocks was depleted, while volatile components such as CO_2 and H_2O, and some ore-forming elements such as Au and S were marked enriched. But it is noted tha t the enrichment of An in both the mylonite series rocks did not reach the paygrade of gold. The released SiO_2 from water-rock interactions occurred in the form of colloids and absorbed gold in the fluid. When brittle structures were formed in the ductile shear zone, the ore-forming fluids migrated to the structures along micro fractures, and precipitated auriferous quartz because of reduction of pressure and temperature. Fluid inclusion study shows that the temperature and pressure of the ore-forming fluids are 245-292 ° C and 95.4- The liquid phase is rich in Ca ~ 2 +, K ~ +, Na ~ +, Mg ~ 2 +, F ~ - and Cl ~ -, while the gaseous phases are rich in CO_2 and CH_4. The δDand δ18O values ​​of the ore-forming fluid are - 84. 48 ‰ - - 91. 73 ‰ and -0.247 ‰ - + 2.715 ‰ respectively, suggesting that the fluid is composed predominantly of meteoric water.