Abstract: By the study on ancient stress, fluid inclusions and composition of tectonites andstructural ores from gold deposits, the ore-forming mechanism of critical transition in ore-bearing ductile-brittle fractures is analyzed, involving the metallogenic dynamics, fluid evolution and the structural mechanism during the evolving process of fractures from ductile to brittle natures. It is concluded that the development of the fractures is also the process of ore-forming matter gathering and enriching, with corresponding change in the composition of ore-forming fluids.