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Iron ore deposits currently being mined and those which may be mined in the future in Siberia using underground mining methods have various geomechanical conditions.A considerable part of the prospective reserves are situated in deep sections covered by rocks with a thickness of more than 250-300 m. The steeply dipping ore deposits have a length over the strike up to i000 m, a thickness of 20-300 m, and a width of about 600 m.The hardness of the ores and surrounding rocks limits extensive use of an ore caving system making use of large explosions leaving large open spaces [i]. For example, an orebody 300 m long, 200 m high, and with a maximum thickness of 85 m has been worked by separating it into three stages 60 m high.The volume of the worked-out space reaches 1.5 million m 3. During working of the third stage alternating opening of cracks in the wall of surrounding rock with a width up to 0.3 m and two large roof rock falls were observed.This sudden caving occurs with prolonged working of blind orebodies and they end with formation of a stable arch.

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