IMWA2018 Coetzee 803.Pdf

Reconstructing Historical Mine Water Management Practices for a Portion of the East Rand Gold Field, South Africa Using Long-Term Map and Image Time Series Henk Coetzee Council for Geoscience, Private Bag X112, Pretoria, South Africa [email protected] Abstract Gold and uranium have been extracted from the conglomerates of the Witwatersrand since the late 19th Century. e development of the mining industry, its related indus- tries and the economic development which followed transformed the open farmland which had existed before mining into a highly urbanised and industrialised area, with a population of over 10 million people. While underground gold mining continues from rocks of the Witwatersrand Supergroup to the east, west and south of Johannesburg, formal mining ceased in the original three gold elds, the West Rand, Central Rand and East Rand, when the last mine stopped dewatering in 2010. Water in ows have been a challenge to mining since the early days, but in recent years, the rising water levels and consequent risk of pollution has received considerable attention. Historical and modern spatial data, covering more than a century of mining has been compiled and used to in- vestigate the hydrological evolution of a portion of the East Rand Gold eld, too unravel the engineering measures which were used to better manage water in the mining areas and to develop recommendations for improved water management in the future. Keywords: time series, spatial data, mine hydrology, Witwatersrand, East Rand Introduction the contribution of di erent gold producing History of gold mining in the Witwa- areas to world production in 1930, with the tersrand Transvaal contribution coming largely from the Witwatersrand. Multiple gold- and urani- Gold was discovered in South Africa’s Witwa- um-bearing conglomerate layers made up the tersrand – the area centred around what is now total resource in these areas. the cities of Johannesburg, Ehkurhuleni and Due to practical considerations such as Mogale City – in 1886. Mines developed rap- ventilation, access to remote areas of the work- idly along the strike of the outcropping Witwa- ings, pumping of water and safety consider- tersrand Supergroup conglomerates, with three ations, the mines within each gold eld are main gold elds, the West Rand, Central Rand all interconnected at depth. is facilitated and East Rand, developing, separated by geo- mining while all mines were operational, but logical features referred to as the Witpoortjie led to problems when mines started to close. Gap and Boksburg Gap, respectively. Ultimately, Mine closure was generally not managed with these three gold elds would extend along more consideration of all impacts, in particular the than 100km along strike, accessing the outcrop- potential of water entering one mine to ood ping Witwatersrand rocks in all three gold elds neighbouring mines. Because of this, as under- as well as the sub-outcrops below younger cover ground mines started to close, the water levels rocks in parts of the East Rand gold eld. within the closed mines would rise to the level ese three gold elds, along with other of interconnection with an adjacent mine and areas where the Witwatersrand strata are then start to ow to that mine, increasing the mined to the west, south west and east of the volume which the remaining mines needed original mining areas, have produced approx- to pump. Over time, the burden of pumping imately half of all the gold ever mined (Gold became too onerous for the remaining mines, Wage Negotiations 2015). Figure 1 shows hastening their eventual closures. Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G. (Editors) 803 10_Catchment Management BOOK.indb 803 9/3/18 12:36 PM 11th ICARD | IMWA | MWD Conference – “Risk to Opportunity” Figure 1 World gold production in 1930 (Potenza Figure 2 Steeply dipping stope in an early Witwa- et al. 1996) tersrand underground mining operation (Ball 2015) In 2010 the pumps at the Grootvlei Mine erates. is ridge acts as a continental water- in South Africa’s East Rand gold eld were shed, with the main drainage direction to the switched o , allowing the interconnected mine south, crossing the mining belt to the south. In workings of the gold eld to ood. is neces- parts of Johannesburg, an east-west drainage sitated the construction, by the South African direction is also present. State, of expensive pump-and-treat infrastructure to maintain a safe water level in the under- Mine water management in the Witwa- ground workings and reduce the impact of the tersrand discharge of mine water to the surface water Water in ows have been an ongoing prob- environment. In parallel to this process, e orts lem in the Witwatersrand’s gold mines, back are underway to reduce the seepage of surface to the earliest days of mining. Scott (1995) water to the underground mines to limit the reports that acid mine drainage was well cost of pumping and treating mine water. known as early as 1903, with many later ref- Spatial development around the Witwa- erences to the problem (e.g. Hocking 1986). tersrand mines Scott (1995) also describes the construction From the outcrops, the conglomerate lay- of canals to carry surface water over the un- ers dip to the south, with very steep dips in dermined zone, thereby reducing the ingress some areas (Fig 2). is necessitated develop- of water to the underground workings, in at ment to great depths, with the mines becom- least two locations in the Central Rand. e ing the deepest in the world by the early 20th issue of acid mine drainage in the Witwa- century, and led to a pattern of development, tersrand rose to prominence around the time with urban development to the north of the that the last mines were closing and the pre- outrop, extending along the mining belt to the vention of ingress was highlighted in a report west and east from Johannesburg. A subsid- to a high-level government committee ap- ence-prone zone to the south of the outcrop pointed to address this issue (Coetzee et al. has been le largely undeveloped, with the 2011). is report recommended the instal- exception of some tailings storage facilities in lation of pump-and-treat systems to maintain this area. To the south of this zone, additional environmentally safe water levels in the un- urban development, including the southern derground workings while, inter-alia, devel- suburbs of Johannesburg and the township oping and implementing measures to reduce Soweto developed. ingress to the underground mine workings. e Witwatersrand (meaning “ridge of In addition to pumping water from the white waters” in Afrikaans) refers to the ridge workings, the early miners developed exten- de ned by quartzite layers which lie strati- sive surface infrastructure to carry water over graphically below the gold-bearing conglom- their shallow workings, reducing the volume 804 Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G. (Editors) 10_Catchment Management BOOK.indb 804 9/3/18 12:36 PM 11th ICARD | IMWA | MWD Conference – “Risk to Opportunity” to be pumped. Unfortunately, many of the de- Analysis of historical spatial tailed records related to this infrastructure are information no longer accessible, although the remains to A collection of spatial information has been these structures can be identi ed in the eld assembled, which has been used to attempt in some areas. to reconstruct a hydrological history of the Time series analysis area. is includes geological and topographic maps, aerial photographs, satellite images Time series analysis is commonly carried out and underground mine plans. A limited set on spatial data sets. is may be quantitative, of maps is presented (Figs 3, 4 and 5). Within using measured or calculated quantities such this area, a number of areas of surface water as re ectance, vegetation indices etc. For this accumulation have been identi ed, which study, a qualitative approach has been fol- were canalised during the period of active lowed due to the length of time over which mining (Fig 3 b and Fig 4a). changes need to be detected – more than 100 An important feature in this area is an years – and the variety of spatial data avail- old clay quarry, where brick clay was mined able. from the younger Karoo Supergroup cover Study area: the East Rand outcrop zone (showing in grey on Fig 3 a). On the 1939 topographic map (Fig 3 b), this is marked Background studies on mine water ingress as Steenmakery (Afrikaans for brickworks) (Esterhuyse et al. 2008) have identi ed a zone (in the eastern portion of the map, south of in the northern part of the East Rand Gold- the railway line. e Main Reef sub-outcrops eld where the gold-bearing Witwatersrand here below the Karoo cover and was mined strata outcrop (Fig 3 a) and were mined from via an incline sha . By 1953 (Fig 4 a), an un- the surface to considerable depth. vegetated area is seen at this point, while con- Figure 3 a. Geological map from 1916 (Mellor 1916), showing an area of wetland development, perpendicu- lar to the strike of the Witwatersrand strata (orange colour with the Main Reef showing by a dashed line immediately south of the railway. b. Extract from a topographic map of the same area in 1939, showing the development of canals, conveying water across the mining area (south of the Main Reef outcrop). Identi ed mine sha s shown as green blocks. Wolkersdorfer, Ch.; Sartz, L.; Weber, A.; Burgess, J.; Tremblay, G. (Editors) 805 10_Catchment Management BOOK.indb 805 9/3/18 12:36 PM 11th ICARD | IMWA | MWD Conference – “Risk to Opportunity” Figure 4 a. Aerial photograph of the study area from 1953.

Load more