1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. Institute of Geophysical Exploration of Jilin Province, Changchun 130012, China

Caoshan granite is the ore-forming rock mass of Baligou gold deposit. The authors studied the chemical composition of Caoshan biotites in the rock mass by electron microprobe, to understand the magma genesis and metallogenic potential. Results show that biotites from the Caoshan granite mass are magmatic magnesian biotites with high contents of Al, K, Mg and Ti,but low contents of Na and Ca. Based on 22 oxygen atoms, the number of cation and relevant parameters of the biotites are calculated, demonstrating high total aluminum (^TAl) and magnesian rate (Mg^#). The temperature, pressure, emplacement depth and oxygen fugacity of rock mass consolidation are estimated according to the chemical composition of biotites. Solidification temperature of rock is 750��~780��, solidification pressure is 131.77~143.89 MPa, depth of emplacement is 5.0~5.4 km, and oxygen fugacity f(O₂) is 10^-13~10^-14, indicating that the rock mass formed under medium depth, high temperature, and high oxygen fugacity. The chemical characteristics of biotites indicate that the rock is a type I granite. The magma is formed by the fusion of the crust and mantle material under the background that the Pacific Plate subducted toward the North China Plate and the crust was thickened. The high solidification temperature and oxygen fugacity of Caoshan granite are favorable for the Au element to get into post-magmatic ore-forming fluid, indicating good mineralization potential in the Baligou gold deposit.