The impact of mining

Development Policy21 Feb 2013Anthony Turton

The impact of mining on the quality of water resources should be given a place on the global agenda.

For some strange reason the water resource management discourse tends to ignore the impact of mining. Yet in my professional experience, the impact of mining on water resources, specifically in water-constrained economies, is significant enough to be raised as an issue in need of prioritization. Let me give an example to emphasize this point.

It is generally accepted international best practice to manage a river basin as a unit. It is also accepted that what happens upstream eventually impacts everything downstream. So let us apply these two principles to gold mining in South Africa. Once the richest gold deposits on earth, the Witwatersrand complex, triggered the Anglo-Boer War, in an attempt by a colonial power to control this enormous source of wealth.1 The actual location of the gold-bearing reef is along the continental watershed divide that separates the Atlantic from the Indian Oceans, via the headwaters of the Orange and the Limpopo river systems. After more than a century of mining, the headwaters of those two river basins are now littered with literally hundreds of mine dumps, where the crushed rock is stored in perpetuity.

Now to the water resource management agenda, in which three things are critical.

Firstly, the gold reef was overlain by a massive dolomitic aquifer system,2 the original source of the many streams that gave the name to the Witwatersrand – Ridge of White Waters. That complex aquifer system was drained to make deep-level mining safe,3 but is now flooding and returning to its original pre-mining hydrology.

Secondly, the gold-bearing reef was geologically associated with a sulphide-based mineral known as pyrite, the chemical combination of iron (Fe) and sulphur (S), known technically as 2FeS2. Pyrite oxidizes to form an acid in a process that becomes self-perpetuating once started. This is known as acid mine drainage (AMD) and it is currently the scourge of the gold and coal mining areas of South Africa.

Thirdly, pyrite-based ore bodies such as those found in the Witwatersrand goldfields are also rich in other heavy metals, including uranium.4 It is in this regard that the issue becomes interesting, because for most of the history of gold-mining in South Africa, uranium had no commercial value and was merely discarded as waste. The combined mine waste dumps that characterize the Johannesburg landscape contain a staggering 410,000 tonnes of uranium.

These three drivers now collectively manifest as a major threat to the water resources in the headwaters of two major river basins – the Orange and Limpopo – with potential downstream impacts felt across three countries (South Africa, Namibia, Mozambique). There is also a pollution plume moving through the karst system as the old voids flood. Let me therefore expand on the issue to explain why it deserves to be prioritized.

The process of acidification starts in the dumps located along the continental watershed divide, often sited on top of dolomite. The dumps consist of processed slurry known as tailings, with a high pH (10.5) resulting from the metallurgical recovery process used. Rainfall has a lower pH and this triggers the start of a chain reaction that once begun, becomes chemically self-perpetuating until all the elements are again in dynamic equilibrium.5 As the pH passes a threshold of about 5, uranium starts to become soluble. At a pH of 4.5 the uranium becomes highly mobile and concentrates in the upper crust of the dump. Simultaneously the pyrite triggers acid formation that results in a gradual seepage out of the base of the dump of a highly acidic flow of water also containing a range of heavy metals. This enters nearby wetlands where it starts to migrate downstream over time.6 The surface water found on these dumps after rain contains concentrated uranium, and when this dries out it becomes fine dust with a wide fallout zone. This uranium contamination spreads across the land in the headwaters of these major river basins, slowly migrating in response to the physics and chemistry of wind, water, gravity and atmospheric forces.

In my professional view, this is a significant challenge. More importantly, it is not on any priority list at any international forum, so the problem is rendered insidious with no significant funding, research or development of management best practice.

In conclusion, it is my professional opinion that the impact of mining on water resource management now deserves to be given a place on the global agenda. This is important because many of the mining operations are in developing countries where institutional oversight is limited. More importantly, the science needed to inform the remediation of impacted landscapes is grossly underfunded, lacking focus in the absence of an organizing framework.


  1. Turton, A.R., Schultz, C., Buckle, H, Kgomongoe, M., Malungani, T. & Drackner, M. 2006. Gold, Scorched Earth and Water: The Hydropolitics of Johannesburg. In Water Resources Development, Vol. 22., No. 2; 313-335.
  2. Buchanan, M. (Ed.) 2010. The Karst System of the Cradle of Humankind World Heritage Site: A Collection of 13 Issue Papers by the South African Karst Working Group. Pretoria: Water Research Commission. ISBN 978-1-77005-969-6
  3. Jordaan, J.M., Enslin, J.F., Kriel, J.P., Havemann, A.R., Kent, L.E. & Cable, W.H. 1960. Finale Verslag van die Tussendepartmentele Komitee insake Dolomitiese Mynwater: Verre Wes-Rand, Gerig aan sy Edele die Minister van Waterwese deur die Direkteur van Waterwese. (In Afrikaans translated as, Final Report of the Interdepartmental Committee on Dolomitic Mine-water: Far West-Rand, Directed at His Excellency the Minister of Water Affairs by the Director of Water Affairs). Pretoria: Department of Water Affairs.
  4. Coetzee, H. 1995. Radioactivity and the Leakage of Radioactive Waste Associated with Witwatersrand Gold and Uranium Mining. In Merkel, B. J., Hurst S., Löhnert E.P. & Struckmeier W. (Eds.) Proceedings Uranium Mining and Hydrogeology 1995, Freiberg, Germany: GeoCongress 1. – 583 S.; Köln (von Loga; ISBN 3-87361-256-9).
  5. Naicker, K., Cukrowska, E. & McCarthy, T.S. 2003. Acid mine drainage from gold mining activities in Johannesburg, South Africa, and environs. Environmental Pollution. (122) Pp. 29−40.
  6. Winde, F. 2009. Uranium Pollution of Water Resources in Mined-out and Active Goldfields of South Africa: A Case Study in the Wonderfonteinspruit Catchment on Extent and Sources of U-Contamination and Associated Health Risks. Paper presented at the International Mine Water Conference, 19 – 23 October 2009, Pretoria, South Africa. Available in the Proceedings: ISBN 978-0-9802623-5-3.