Abstract: The biotite monzolite that was discovered at 2170 meters below the surface in Linglong Gold Field in Jiaodong is not only used to find out the source of ore-forming material, but also is used to furnish new evidence for study the cause of mineralization of gold deposit. As the new rock types that was discovered in this area, Biotite monzonitichas the typical monzonitic texture under microscope. The non-metallic minerals composed the rock mainly are plagioclase, sodium feldspar, quartz, biotite and hornblende. It contains more metal minerals that mainly are pyrite and magnetitethan the other magmatic rocks in Northwest of Jiaodong. The biotite ⁴⁰Ar-³⁹Ar thermochronology indicate that the age of the formation of biotite monzonite is 123.7±1.5 Ma which was later than the time of formation of Linglong granite, Luanjiahe granite and Guojialing granites, and is very close with the age of the formation of Linglong Gold Deposit. Although it is not sure that the metal minerals in the gold ore bodies in Linglong gold field directly come from biotite monzonite, the result of analysis of the characteristics of their generation time demonstrate that the metal minerals and biotite monzonite form in the same period and come from the same originate. In the process of invasion of the Biotite monzonite magma, it supply ore-forming materials for the formation of gold mine, and provides energy and driving force for ore-forming elements and ore-forming fluid migration. It can be deduced that the gold mineralization is closely related with the intrusion of biotite monzonite