The Banmiaozi Gold Deposit is a large gold deposit in the Laoling gold polymetallic metallogenic belt in south Jilin.The geological conditions in the district are favorable and the metallogenic potentials are great.The granitic porphyry intrusions exposed in the district are related to gold mineralization and provide heat and material sources for gold mineralization.The electron microprobe (EPMA)of granitic porphyry biotite from Banmiaozi Gold District as well as related calculations was conducted.The results show that the granitic biotite is characterized by high Si,rich Mg and low Fe,with relatively high Mg mass rate,and belongs to magnesian biotite.According to the biotite composition estimation,the magmatic diagenetic temperature is 700 ℃-750 ℃,the O2 fugacity is -12--14,the depth is 5.0-6.5 km.The biotite composition reveals that the magma source has the feature of mixed crust and mantle sources and the granite is type I granite related to orogenic activities.The granitic porphyry is favorable for gold deposit genesis,and it is speculated that the Banmiaozi Gold Deposit is a medium shallow formation orogenic gold deposit related to the subduction of the ancient Pacific plate.