INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 4, ISSUE 08, AUGUST 2015 ISSN 2277-8616 101 IJSTR©2015 www.ijstr.org Open Pit Water Control Safety: A Case Of Nchanga Open Pit Mine, Zambia Silwamba C, Chileshe P R K Abstract: Mining in Chingola, Zambia, started underground in 1931, and was catastrophically flooded and closed. The present Nchanga Underground Mine (NUG) started in 1937. The Nchanga Open Pit (NOP) mine started in 1955, situated to the west of NUG, and partially overlying it. Open pit water control safety operations in the Nchanga-Chingola area, have successfully enabled the safe extraction of millions of tonnes of copper ore annually over the past 60 years, from NUG mining as well as the NOP. At the start, Nchanga mining license surface already had NUG, and many watershed divides, with the Nchanga and Chingola streams being the main streams feeding into Zambia’s second largest river, Kafue river, and 42% of the year was characterised by heavy rains ranging between 800mm to 1300mm per annum. In this paper, the presence of very significant amounts of seasonal rain and subsurface water in the mining area was identified as both a curse and a blessing. An excess in seasonal rain and subsurface water would disrupt both open pit and underground mining operations. In order for NOP to be operated successfully, stable and free from flooding, coping water management tactics were adopted from 1955 to 2015, including: 1. Underground mine pump chamber pumping system; 2. Piezometer instrumented boreholes; 3. Underground mine 1500-ft sub-haulage east borehole dewatering, beneath the open pit; 4. Nchanga and Chingola stream diversionary tunnel and open drains; 5. Nchanga stream causeway and embankment dam in the Matero School – Golf Club area; 6. Pit perimeter borehole pumping; 7. Outer and inner pit perimeter drains and bund walls; 8. In-pit ramp side drains; 9. In-pit sub-horizontal borehole geo-drains and water; and 10. Pit bottom sump pumps. Application of grout curtains along the Vistula River, Poland, was noted as a possibility in the right circumstances, although it had never been used at Nchanga Open Pit. An additional conclusion was that forward health, safety and environmental end-of-life planning was required for the extensive district-wide infrastructure of the open pit water control system, for public safety after life of mine. Index Terms: Bund wall, Chingola, drain, mine, Nchanga, open pit, pumping, safety, sump, strata, stream diversion, water, Zambia ———————————————————— 1 INTRODUCTION The presence of water in and around mining areas is both a blessing and a curse. A blessing in that water is needed to:  Suppress dust, in accordance with mining regulations;  Facilitate mineral processing operations, as plant water; and  Operate mining machinery such as drills and water monitors. On the other hand, water in the mining environment can be a curse in that open pit and underground mining operations are susceptible to flooding with injuries to personnel and loss of life, as well as property damage. On balance, uncontrolled water constrains mining production in open pits and underground mines. So everywhere where mining is contemplated or in progress, there must be a well structured plan to control water in the mining area in order to suppress the negative effects associated with it, while maximising the benefits. Historically in Zambia, the presence of water in the mining area has been at the root of many fatal accidents, including the Mufulira underground mine disaster of 1970 when 89 lives were lost (Chileshe, 1992) as well as the Nchanga Open Pit Disaster of 2001 (Silwamba and Chileshe, 2015), which resulted in the loss of ten lives. 1.1 NATURE OF THE WATER PROBLEM AT NCHANGA OPEN PIT The Nchanga Open Pit (NOP) mine was preceded by the Nchanga Underground Mine (NUG) when open pit operations commenced in 1955. At that time, the mining area was traversed by a number of streams, the largest of which were the Nchanga and Chingola streams (Fig. 1). Sub-surface strata near the copper bearing orebodies included aquifers such as the Upper Roan Dolomites (URD), Chingola Dolomite and Banded Sandstones (BSS), as well as the Nchanga Main Fault Zone and the Lamprophyre Dyke (Fig. 2). NUG mine experienced start-up problems with flooding in 1931 which lead to its closure and later re-opened in 1937, and has been in operation ever since, after mastering underground water management strategies. On commencement, NOP faced similar start up challenges to those of NUG in its early stages. In addition to water bearing strata, there were the added dimensions of streams, high seasonal rainfall and surface topography. NOP could not operate or grow successfully, due to the dangers of flooding, unless the seasonal rain water and sub surface strata water problems were resolved immediately or in phases across time. In achieving its water control objectives, NOP also had a duty to ensure it did not compromise the safety of the underlying NUG mine. Fig. 1: Surface Plan showing the current NOP Outline, other open pit workings, underground workings, the Nchanga Stream Diversionary tunnel and Chingola Stream Diversionary Open Drain. ___________________  Dr Peter R K Chileshe is Postgraduate Coordinator and Senior Lecturer Mining, Copperbelt University School of Mines and Mineral Sciences, P O Box 21692, Kitwe, Zambia email: peter.chileshe@cbu.ac.zm www.cbu.edu.zm  Cross Silwamba is Manager Open Pits, Konkola Copper Mines plc, Chingola, Zambia email: cross.silwamba@kcm.co.zm