Abstract: The Jinchuan No. 3 mine in Gansu province of China, is an ultrabasic lean ore and locates at east of fault F17 of Jinchuan mine area. With the improvement of mineral processing and smelting, exploiting of No. 3 mine is on the way. Understanding of in-situ stress state in deep mine can provide the scientific basis to extract and support roadway. In-situ stress measurement was conducted at 1 200 m level to achieve this goal. A improved hollow inclusion stress relief method was employed to obtain three-dimensional stress data of seven measurement sites, which were used to draw section stress-ellipses at different normal directions of each site. The measurement results indicate that at 520 m below the surface, the values of maximum principal stress are about 17-21 MPa, a medium stress level. The directions of the maximum principal stress are within NNW-NNE and NE-WE, and agree with regional stress field basically, and also show a new trend direction. It is probably two faults in No.3 mine area that pose an influence on the direction of the principal stress. However, some dips of maximum principal stress exceed 20° and the largest one is -49°, which reveals a change of horizontal-stress-orient stress field in Jinchuan mine. The result is of great significance in mine design and construction.

Key words: Jinchuan No.3 mine, hollow inclusion stress relief method, in-situ stress measurement, stress state characteristics