Conceptual engineering designs on resumption of mining operations and flooding protection in Mir Mine

Abstract

Selection of a geotechnology for underground mining in Mir Mine, in challenging hydrogeological conditions has been the point under hot discussion for a few decades. An associate issue is protection of underground excavations from flooding. The latter problem is critical at interfaces of kimberlite and freely soluble host rock salt. After termination of surface mining operations, out of two variants of underground mining systems with cemented backfill or with bulk caving, the scenario with backfilling and with dry conservation of the open pit was selected. Dry conservation means fill of dolerite layer on the pit bottom, placement of water-proof film on this layer and outlet of all inflows via a drainage day drift and vertical boreholes. No other activities on protection of the mine from halite-undersaturated brine inflows from the pit were provided by the adopted design solutions. In the chosen scenario, above the impermeable film, a water body generated had varied volume subject to the ratio of water inflows in the pit and flow rate of discharge boreholes. Water inflows in the mine resulted in uncontrollable growth of salt karst at the kimberlite–rock salt interface, and in the subsequent degradation of the interface due dissolution of salt in the contact zone and owing to filling of fractures with dissolved salt inside the ore body. Based on the implemented research, the authors assess prospects for the resumption of operations in the mine by stoping with caving. Such technology seems to be most advisable in the given hydrogeological conditions. In this case, it is required to start with catchment of ground water inflows in the pit by means of arrangement of internal and external drainage loops.