Abstract
Formation temperature and pressure conditions of intrusive rocks, including granitoids, are always urgent issues for geologists because they are closely related to the issues of origin and mineralogy of rocks. Biotite has been studied extensively and is often used to compare, classify magmas, determine the formation temperature, pressure, determine the phase and formation, determine the acid-base regime of the environment, the origin of the rock and the geochemical conditions of mineral formation. Biotite of Phu Tai massif belongs to the annite - siderophyllite series rich in Fe, high in Mg. According to the composition of biotite in them, the massif was formed at temperatures from 7450C to 802oC with an average of 773oC±12°C and at pressure from 1.38 to 2.29 kbar with an average of 1,72 ± 0.68 kbar, corresponding to a depth of ~ 5,21km. Granite of Phu Tai massif belongs to type I-granite. Biotite in the massif is rich in Cl and poor F, according to mineralization they belong to type-I: belonging to field number 2. Kyraminskyi mountain ridge granite, North Thien Son. Granitoid related to copper-molybdenum (Cu-Mo) mine.