The Nangang-Gaogongdao ductile shear zone is a slice boundary tectonic zone with strong mylonitization, which formed by thrusting from the southeast to the northwest. The main minerals in rock, such as feldspar and biotite et al., had decomposited or altered with different degree, that resulted in compositional variation during ductile deformation. Thereinto, the variation of mobile components in the rock resulted from fluid infiltration, and the variation of immobile components was caused by the volume loss during mylonition. The isocon line slopes are determined by comparing the geochemical compositions of rocks before and after deformation of feldspar or albite quartz schist within the ductile shear zone. The mass balance calculation shows that the volume losses of protomylonite and mylonite during mylonition are 17% and 27% respectively. The mass balance analysis and isocon diagram indication that the loss of SiO_2 is largest, the next is Al_2O_3, and while FeO, CaO and Na_2O lose to different extent, showing that they are mobile components in the rock. MgO located over the isocon line, is the import components. The quartz vein or felsic band in mylonites formed by separation and transfer of SiO_2, Al_2O_3, Na_2O and FeO et al., which resulted from the saussuritization and sericitization of feldspar and the chloritization of biotite during mylonition. The volume loss and component variation during ductile shearing are the important richment mechanism of immobile components, and have the important guidance for researching the mechanism of felsic band and metalogenesis of precious metals deposits.