ABSTRACT
The Lovozero rare-metal deposit, represented by a series of tabular flat-dipping ore bodies, has been produced by the Karnasurt and Umbozero underground mines since 1951. Geodetic observations have revealed the increase in the velocities of vertical interblock movements in the rock mass in 2–3 times as a result of mining operations. After the start of simultaneous excavation of two adjacent ore bodies by the Umbozero mine in 1990, large seismic events with a magnitude M L ≥ 2.0 began to occur, and their number increased and reached several tens per year. On August 17, 1999, the mine experienced a large tectonic rockburst with the magnitude of M L = 5.1, as a result of which the mine area of 650,000 m2 was damaged. A new intrablock fissure of more than 0.5 km grew from the interbed of the mined ore bodies to surface, with the ten-centimeter movements of the banks. The fissure was formed due to overlapping the gravitational-tectonic stress concentration zones caused by mine excavations on two contiguous ore bodies. Due to large damages, the Umbozero mine was closed in 2004. After this tectonic rockburst, large seismic events (M L > 1) began to occur at the Karnasurt mine and their recorded amount in recent years has reached more than two dozen.
