Determining a suitable method for dewatering of ore reserves below 1040ml at Konkola mine, Zambia.

Abstract

Konkola Mine is one of the wettest mines in the world. It pumps about 350,000m3 of water per day. From the inception of mining operations in 1956, water has always posed a challenge to mining despite the use of dewatering strategy involving dewatering crosscuts and dewatering boreholes. The groundwater at the mine was mathematically modeled using MODFLOW software in 1989 and predictions of dewatering operations were made for periods of 1989 to 2020. However, in the last two decades, the implementation of the dewatering plan has lagged behind as a result of financial constraints faced by the Mine. The Footwall Aquifer at shaft No. 3 is behind by almost 3 years and the Hangingwall Aquifer at shaft No. 1 is behind by at least 13years. This has resulted in most of the reserves being underwater which poses a safety and mining challenge. The reserves below 1040mL cannot be mined until the Hangingwall Aquifer is dewatered below 1150mL Cave line. The dewatered reserves have almost 2 years to depletion hence this study was undertaken to determine a suitable dewatering method for reserves below 1040mL. The study also sought to establish whether the use of backfilling mining methods would reduce dewatering requirement for the mine. Drawdown simulations were done using the MODFLOW-VKD software. The water table was generated using MicroStation and Geovia Surpac software. The seepage points identified are the Kafue River, Kakosa Stream, discharge canals, Lubengele Dam, and Lubengele Stream. The study has established that more than 194,170m3/d of water could be excluded from seeping through the mine. An analysis of mines that use backfilling methods established that the use of backfill reduces hydraulic inflow paths into a Mine and also reduces the dewatering requirement. The results of the study indicate that the existing conventional dewatering approach (using crosscut and dewatering boreholes) coupled with surface water exclusion methods are the most viable for the reserves below 1040mL as opposed to deep surface wells. It was also found that dewatering requirement could be reduced in the mine by the application of backfill. The approximate cost of Conventional dewatering method (19 crosscuts and 190 boreholes) implementation was less than the cost for the Surface deep holes. Key Word: Mine operations, dewatering, Hangingwall Aquifer, backfilling