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Mponeng

Above-ground operations at Mponeng mine.
Location
MponengLocation in South Africa
Province	Gauteng
Country	South Africa
Coordinates	26°26′10″S 27°25′50″E / 26.43611°S 27.43056°E / -26.43611; 27.43056
Owner
Company	Harmony Gold
Website	https://www.harmony.co.za

Mponeng is an ultra-deep tabular gold mine in South Africa in the Witwatersrand Basin of the Gauteng Province. Previously known as Western Deep Levels No1 Shaft, the mine began operations in 1986. It is one of the most substantial gold mines in the world in terms of production and magnitude, reaching over 4 kilometres (2.5 mi) below the surface. At this depth Mponeng takes the title of world's deepest mine from ground level, with aims to deepen the mine beyond 4km in order to reach more reserves. A trip from the surface to its deepest point takes over an hour. An Ecuadorian marathon runner completed a half marathon within the mine in 2017. The mine supports a very large number of people, companies and industries, including entire towns and cities.

Operations

History

As part of the Witwatersrand, the largest gold mineralization on earth, Mponeng is the result of the discovery of the basin by Europeans. Beginning in the 1850-70s a series of mineral discoveries were made in the area, including those of Pieter Jacobus Marais panning gold from a river and Henry Lewis finding quartz and gold vein on a farm, that led to the Witwatersrand Gold Rush in 1886. These discoveries led to many mining operations and after shaft sinking for about 5 years (1981) Mponeng officially began mining operations in 1986. Before Mponeng, the mine was known as the Western Deep Levels South Shaft or the No1 Shaft; the name Mponeng came into use in 1999.

The mine is estimated to be producing until 2029, when reserves may finally run out, the mine has been running since 1986 and has the possibility to run for 43 years. Current depths reach roughly 3.8km down, in the coming years of remaining production life of the mine it will likely reach beyond 4.2km depth. The mine has not been running continuously since the day of opening in 1986. A seismic event in March of 2020 resulted in a stoppage of operations due to fatalities. Like many other operations, Mponeng closed due to the COVID-19 pandemic in May 2020, but has since returned to production.

Striking in South Africa's mining district was apparent in the 1900s, for example the South African gold mine strike in August 1946. As Mponeng did not start operations until near the turn of the century there has not been many other notable strikes since then, other than 2012. In 2012, while AngloGold Ashanti was Mponeng's owner, strikes occurred. The strikes were a combined result of gold and platinum industry-worker issues in South Africa. AngloGold's position on the matter was to maintain safety, peace, and stability. The striking action of 2012 totaled nearly 16% of the total mining workforce of South Africa, not just Mponeng. AngloGold specifically experienced nearly 35,000 workers putting down their tools in the illegal strike. Although not at Mponeng, the strike of 2012 included a wildcat strike at a nearby platinum mine ended with 34 miners dying from police interactions.

Operations and ownership

Harmony Gold, Africa's largest gold producer, purchased Mponeng from AngloGold Ashanti (AGA) in 2020, for approximately $200 million. Harmony Gold also acquired Mine Waste Solutions as they gathered the remainder of AGA's assets in late 2020. As of 2022, all-in costs of production were US$1771/oz (US$1614/Troy oz). Even at near record high gold prices, Mponeng is barely breaking even. Gold is currently worth roughly US$2080/oz (US$1900/Troy oz). Over 5,400 metric tons of rock are excavated from Mponeng each day. Harmony Gold, aside from closures, has kept up operations:

The most recent publication from Harmony Gold outlines their 2023 year production:

• Produced: 7,449 kg (239,490 oz) of gold
• Grade: 8.43g/t
• Volume of ore milled: 884,000 tons

Physical conditions

The temperature of the rock reaches 66 °C (151 °F), and the mine pumps slurry ice underground to cool the tunnel air to below 30 °C (86 °F). A mixture of concrete, water, and rock is packed into excavated areas, which further acts as an insulator. Tunnel walls are secured by flexible shotcrete reinforced with steel fibers, which is further held in place by diamond-mesh netting.

In 2008, researchers looking for extremophile organisms discovered the bacterium Desulforudis audaxviator present within groundwater samples from kilometers deep in the mine. The name 'Audaxviator' comes from a Latin-language passage in the novel Journey to the Centre of the Earth by Jules Verne: "Descende, audax viator, et terrestre centrum attinges." ("Descend, bold traveller, and attain the centre of the Earth.")

Geology and gold bearing fractures

The mine sits in the Witwatersrand Basin and utilizes 2 horizons: Ventersdorp Contact Reef and Carbon Leader Reef. In the Mponeng mine the Ventersdorp Contact Reef is mainly interbedded quartzite and coarse conglomerates and constitutes only a meter or two of thickness. The Witwatersrand Basin has experienced many surges of thrusting in the past, resulting in abundant fractures. These small faults often correspond to depositional and sediment contacts. It is along these faults that mineralizing fluids flow, which lead to the precipitation or mineralisation of gold. This complicated geologic history associates with gold mineralization to a high degree, the Witwatersrand Basin holds nearly a third of gold reserves and is responsible for over 40% of all gold. Mponeng has a proven gold reserve of roughly 46 million ounces (over 1300 tons), more than 8x the second deepest gold mine 'Driefontein', also located in South Africa.

The gold mineralization is likely related to hydrothermal activity, and occurs in varying lithology of conglomerates, known as the reefs stated above. The stratigraphy that the gold is found in ranges in thickness, from around 10 cm to a 1-meter. Gold is found in these variable thickness layers of pebble lags, stacked fluvial deposits, and other stratigraphy. Mponeng specifically, gold is associated with previously mentioned thrust fracturing and with the following mineralisations:

• Steep quartz/sulphide-bearing fractures
• Sub-horizontal quartz fractures
• Sulphide-bearing fractures
• Ultracataclastics
• Mesophased hydrocarbons

As with most mines, Mponeng is limited to the structural control of the geology. The VCR mineralisation is governed by thrust-fracture systems discussed above, largely from the Lower Kliprivierberg age. The VCR and CLR themselves are around 2.7 billion years old, and have experienced lots of deformation and change.

Environmental impacts

South Africa has been dealing with the effects of mining-related pollution for years; the effects of mining-related environmental damage have been large given that mining is roughly 8% of the South African GDP. In 1998, mining industry contributed nearly 90% of the 533.6 million tons of waste that was produced annually. According to 1998 data, gold mining is the largest single source of pollution in South Africa. A large portion of this occurs in the Witwatersrand Basin, home to over 270 tailings storage facilities, covering 18,000 Ha.

Mining creates two main kinds of waste: waste rock piles and tailing storage facilities (TSFs). Waste rock piles are the rock that must be removed in order to reach the ore; for Mponeng, the waste rock piles are consideration due to the mine's depth. Tailings result from the crushing and grinding process of the ore, very fine silt sized material is produced and collected in mounds. Tailings especially come with severe environmental and health issues as they contain potentially hazardous chemicals. Long-term consequences are also of concern, whether the mine activities continue, halt, or a mine is abandoned, these TSFs can pose serious risk the surrounding environment. Pollution has been found to persist even after 72 years of mine abandonment.

Beyond the environment, the citizens of the Witwatersrand Basin have been complaining of windblown dust, most of which originates from partially rehabilitated TSFs. Anglo Ashanti began recording meteorological data in 2012 and Harmony Gold has since taken over monitoring after the acquisition in 2020. Citizens are concerned surrounding heavy metal content as well as silica content, as both pose serious health risks (silicosis, tuberculosis, bronchitis, chronic obstructive pulmonary disease (COPD), lung cancer). A study in 2020 found elevated value of silica and uranium in PM10 airborne pollution from TSFs of gold mines in the area.

In South Africa, heavy metal pollution from mining industry is the leading cause of soil and water pollution. The pollution stems from a few sources:

• Acid mine drainage (AMD)
• Salinization
• Elevated levels of potentially toxic elements (PTE)
  • Mainly heavy metals, also including arsenic (metalloid).
• Airborne dust

Environmental remediation

Two actions can begin to combat South Africa's pollution issues relating to gold mining, prevention of new pollution and remediation of old. The caveats of prevention and remediation are the fact that both of which are extremely difficult and expensive, neither the mining industry or South Africa could afford a completely turn around on pollution.

Immobilizing the PTEs in the TSFs is a main focus of pollution prevention and control.

• Liming the acidic tailings to a suitable pH (>5.5) can significantly reduce the mobility of cationic PTEs. This requires large amount of lime.
• Application of clays or organic matter with high cation capacity, with goal of PTE absorption.
• Application of sesquioxides (M₂O₃) which would immobilize oxy-anionic PTEs.
• Application of hydroxides or phosphates, similar effect of liming.

Other than prevention and remediation, it has been proposed that in order to protect environments remaining tailings materials should be removed from TSFs if containment is not secure.

Seismicity

Seismicity in mines is common as removing mass amounts of rock can change stress dynamics, especially if pre-existing faults exist. This seismicity is termed 'mining-induced seismicity', caused by the release of elastic strain but are often low moment magnitude. Reaching beyond 1,000 events a day, events of any size pose serious risk to mining operations and employees. It is not uncommon for equipment to be damaged, or have the collapse of drifts and stopes as a result of events.

On December 27, 2007 a dyke within Mponeng experienced a 1.9 magnitude event caused by stress change due to excavation within the mine. In March 2020 Mponeng experienced a magnitude 2 earthquake in which 3 people were killed. In deep mines, vertical stress can reach 80-100 MPa, equivalent to roughly 10 km under water. Seismicity in deep gold mines is common, and is often induced by mining activities. Two events can be considered:

• Type A - low moment magnitude (<1), clustered in time and space, within 100m of mining surface.
  • Induced by blasting, perturbation of excavating processes, closure of stopes.
• Type B - possible higher moment magnitude (>3), not clustered in time or space.
  • associated with friction dominated existing shear, tectonic earthquakes.

Most earthquakes at depth are mining related (Type A), typically associated with the beginning of a new stope.

Research

One way to move forward is a better understanding of rock burst and excavation methods. A better understanding can provide better safety protocols. A prominent use of deep mines and their associated, often low magnitude, earthquakes is to connect laboratory scale experiments to real world situations. There is also considerable research trying to understand nucleation of said earthquakes, and whether they work the same as larger earthquakes. In Mponeng, JAGUARS (Japanese-German Acoustic Emissions Research in South Africa) has emplaced a network of accelerometers and piezoelectric acoustic emissions sensors. These sensors can record very small moment magnitude earthquakes, capable of recording events with frequencies from 0.7 kHz to 200 kHz (M<0.5). In a one year period, 2007-2008, nearly 500,000 events were recorded, most of which with low (sub 25 kHz) frequencies. The JAGUARS network is placed below the Ventersdorp Contact Reef, there are eight Acoustic Emissions sensors, two strainmeters, and one triaxial accelerometer that make up the network.

See also

• Gold Mines
• Witwatersrand
• Seismicity
• Tailings
• Gauteng
• Acid mine drainage

References

1. Ziegler, Moritz; Reiter, Karsten; Heidbach, Oliver; Zang, Arno; Kwiatek, Grzegorz; Stromeyer, Dietrich; Dahm, Torsten; Dresen, Georg; Hofmann, Gerhard (1 October 2015). "Mining-Induced Stress Transfer and Its Relation to a M1.9 Seismic Event in an Ultra-deep South African Gold Mine". Pure and Applied Geophysics. 172 (10): 2557–2570. doi:10.1007/s00024-015-1033-x. ISSN 1420-9136.
2. ^ "Mponeng Overview". www.harmony.co.za. Retrieved 12 March 2024.
3. ^ Wadhams, Nick (11 March 2011). "Gold Standards: How miners dig for riches in a 2-mile-deep furnace" (Vol. 19 No. 3 ed.). Wired. p. 42.
4. "Mponeng Gold Mine, Gauteng". Mining Technology. Retrieved 17 February 2024.
5. Praveen (11 June 2019). "The top ten deepest mines in the world". Mining Technology. Retrieved 17 February 2024.
6. Manzi, M. (16 June 2014). "3D Seismic Imaging of the Ghost-Carbon Leader Reef of the World's Deepest Gold Mine - Mponeng Gold Mine, South Africa". EAGE. Proceedings 76th EAGE Conference and Exhibition Workshops. European Association of Geoscientists & Engineers: cp. doi:10.3997/2214-4609.20140511. ISBN 978-90-73834-90-3 – via EarthDoc.
7. Garcia, Sergio (23 September 2017). "Ecuadorian sets record in run 4,000m below surface". www.aa.com.tr. Retrieved 17 February 2024.
8. Vegter, Ivo (2019). "Why Mining Still Matters" (PDF). South Africa Institute of Race Relations.
9. Cairncross, Bruce (4 July 2021). "The Witwatersrand Goldfield, South Africa". Rocks & Minerals. 96 (4): 296–351. Bibcode:2021RoMin..96..296C. doi:10.1080/00357529.2021.1901207. ISSN 0035-7529.
10. ^ Barradas, Sheila. "Mponeng mine, South Africa". Mining Weekly. Retrieved 12 March 2024.
11. ^ "Mponeng Gold Mine, South Africa - The World's Deepest Mine". Retrieved 12 March 2024.
12. Bongaerts, Dion; Mazzola, Francesco; Wagner, Wolf (14 May 2021). "Closed for business: The mortality impact of business closures during the Covid-19 madness". PLOS ONE. 16 (5): e0251373. Bibcode:2021PLoSO..1651373B. doi:10.1371/journal.pone.0251373. ISSN 1932-6203. PMC 8121299. PMID 33989322.
13. James, Wilmot G. (1987). "Grounds for a Strike: South African Gold Mining in the 1940s". African Economic History (16): 1–22. doi:10.2307/3601267. ISSN 0145-2258. JSTOR 3601267.
14. ^ McKay, David. "Strikes shut down 40% of SA gold". Business. Retrieved 24 March 2024.
15. ^ Muhumuza, Rodney (4 October 2012). "Striking SAfrican miners find strength in numbers". CNBC. Retrieved 24 March 2024.
16. Smith, David (26 September 2012). "South African's goldmines beset by simmering resentment". The Guardian. ISSN 0261-3077. Retrieved 24 March 2024.
17. "Mponeng Gold Mine, South Africa - The World's Deepest Mine". Retrieved 12 March 2024.
18. Burron, Ian (13 April 2023). "How Low Can you go? The Challenges of Deep Mining | Geology for Investors". www.geologyforinvestors.com. Retrieved 17 February 2024.
19. "Gold Statistics and Information | U.S. Geological Survey". www.usgs.gov. Retrieved 16 February 2024.
20. Wadhams, Nick (11 March 2011). "Gold Standards: How miners dig for riches in a 2-mile-deep furnace" (Vol. 19 No. 3 ed.). Wired. p. 42.
21. ^ Wadhams, Nick (March 2011), "Gold Standards: How miners dig for riches in a 2-mile-deep furnace", Wired, vol. 19, no. 3, p. 42.
22. Timmer, John (9 October 2008). "In the deep, a community of one". Ars Technica. Retrieved 1 June 2015.
23. Brahic, Catherine. "Goldmine bug DNA may be key to alien life". New Scientist. Retrieved 16 May 2024.
24. Manzi, M. (16 June 2014). "3D Seismic Imaging of the Ghost-Carbon Leader Reef of the World's Deepest Gold Mine - Mponeng Gold Mine, South Africa". EAGE. Proceedings 76th EAGE Conference and Exhibition Workshops. European Association of Geoscientists & Engineers: cp. doi:10.3997/2214-4609.20140511. ISBN 978-90-73834-90-3 – via EarthDoc.
25. ^ Jolley, S. J.; Freeman, S. R.; Barnicoat, A. C.; Phillips, G. M.; Knipe, R. J.; Pather, A.; Fox, N. P. C.; Strydom, D.; Birch, M. T. G.; Henderson, I. H. C.; Rowland, T. W. (1 June 2004). "Structural controls on Witwatersrand gold mineralisation". Journal of Structural Geology. 26 (6): 1067–1086. Bibcode:2004JSG....26.1067J. doi:10.1016/j.jsg.2003.11.011. ISSN 0191-8141.
26. ^ Cairncross, Bruce (4 July 2021). "The Witwatersrand Goldfield, South Africa". Rocks & Minerals. 96 (4): 296–351. Bibcode:2021RoMin..96..296C. doi:10.1080/00357529.2021.1901207. ISSN 0035-7529.
27. ^ Jolley, S. J.; Freeman, S. R.; Barnicoat, A. C.; Phillips, G. M.; Knipe, R. J.; Pather, A.; Fox, N. P. C.; Strydom, D.; Birch, M. T. G.; Henderson, I. H. C.; Rowland, T. W. (1 June 2004). "Structural controls on Witwatersrand gold mineralisation". Journal of Structural Geology. 26 (6): 1067–1086. Bibcode:2004JSG....26.1067J. doi:10.1016/j.jsg.2003.11.011. ISSN 0191-8141.
28. Jolley, S.J; Henderson, I.H.C; Barnicoat, A.C; Fox, N.P.C (1999). "Thrust-fracture network and hydrothermal gold mineralization: Witwatersrand Basin, South Africa". Geological Society, London, Special Publications. 155 (1): 153–165. Bibcode:1999GSLSP.155..153J. doi:10.1144/GSL.SP.1999.155.01.12.
29. Large, R.R; Meffre, S; Burnett, R; Guy, B; Bull, S; Gilbert, S; Goemann, K; Leonid, D (2013). "Evidence for an Intrabasinal Source and Multiple Concentration Processes in the Formation of the Carbon Leader Reef, Witwatersrand Supergroup, South Africa". Economic Geology. 108 (6): 1215–1241. Bibcode:2013EcGeo.108.1215L. doi:10.2113/econgeo.108.6.1215.
30. Möncks, Tycho (9 February 2023). "An Untapped Goldmine: Opportunities for South African Mining". BCG Global. Retrieved 9 April 2024.
31. ^ Laker, Michiel C. (June 2023). "Environmental Impacts of Gold Mining—With Special Reference to South Africa". Mining. 3 (2): 205–220. doi:10.3390/mining3020012. ISSN 2673-6489.
32. Praveen (11 June 2019). "The top ten deepest mines in the world". Mining Technology. Retrieved 17 February 2024.
33. ^ Mpanza, Mbalenhle; Adam, Elhadi; Moolla, Raeesa (January 2020). "Dust Deposition Impacts at a Liquidated Gold Mine Village: Gauteng Province in South Africa". International Journal of Environmental Research and Public Health. 17 (14): 4929. doi:10.3390/ijerph17144929. ISSN 1660-4601. PMC 7400412. PMID 32650563.
34. Maseki, J. (2017). "Health risk posed by enriched heavy metals (As, Cd, and Cr) in airborne particles from Witwatersrand gold tailings". Journal of the Southern African Institute of Mining and Metallurgy. 117 (7): 663–669. doi:10.17159/2411-9717/2017/v117n7a8.
35. Merget, R.; Bauer, T.; Küpper, H.; Philippou, S.; Bauer, H.; Breitstadt, R.; Bruening, T. (1 January 2002). "Health hazards due to the inhalation of amorphous silica". Archives of Toxicology. 75 (11): 625–634. doi:10.1007/s002040100266. ISSN 1432-0738. PMID 11876495.
36. Rösner, T.; van Schalkwyk, A. (1 October 2000). "The environmental impact of gold mine tailings footprints in the Johannesburg region, South Africa". Bulletin of Engineering Geology and the Environment. 59 (2): 137–148. Bibcode:2000BuEGE..59..137R. doi:10.1007/s100640000037. ISSN 1435-9537.
37. ^ Li, T.; Cai, M.F.; Cai, M. (December 2007). "A review of mining-induced seismicity in China". International Journal of Rock Mechanics and Mining Sciences. 44 (8): 1149–1171. Bibcode:2007IJRMM..44.1149L. doi:10.1016/j.ijrmms.2007.06.002. ISSN 1365-1609.
38. ^ Richardson, Eliza; Jordan, Thomas H. (2002). "Seismicity in Deep Gold Mines of South Africa: Implications for Tectonic Earthquakes". Bulletin of the Seismological Society of America. 92 (5): 1766–1782. Bibcode:2002BuSSA..92.1766R. doi:10.1785/0120000226.
39. Reporter, Creamer Media. "Three killed in fall of ground at AngloGold's Mponeng". Mining Weekly. Retrieved 12 March 2024.
40. US Department of Commerce, National Oceanic and Atmospheric Administration. "How does pressure change with ocean depth?". oceanservice.noaa.gov. Retrieved 8 March 2024.
41. Ziegler, Moritz; Reiter, Karsten; Heidbach, Oliver; Zang, Arno; Kwiatek, Grzegorz; Stromeyer, Dietrich; Dahm, Torsten; Dresen, Georg; Hofmann, Gerhard (1 October 2015). "Mining-Induced Stress Transfer and Its Relation to a M1.9 Seismic Event in an Ultra-deep South African Gold Mine". Pure and Applied Geophysics. 172 (10): 2557–2570. doi:10.1007/s00024-015-1033-x. ISSN 1420-9136. S2CID 199492287.
42. Kozłowska, Maria; Orlecka-Sikora, Beata; Kwiatek, Grzegorz; Boettcher, Margaret S.; Dresen, Georg (19 December 2014). "Nanoseismicity and picoseismicity rate changes from static stress triggering caused by a M w 2.2 earthquake in Mponeng gold mine, South Africa". Journal of Geophysical Research: Solid Earth. 120 (1): 290–307. doi:10.1002/2014JB011410. ISSN 2169-9313 – via AGU.
43. Kwiatek, G.; Plenkers, K.; Nakatani, Y.; Yabe, Y.; Dresen, G. (2010). "Frequency-Magnitude Characteristics Down to Magnitude -4.4 for Induced Seismicity Recorded at Mponeng Gold Mine, South Africa". Bulletin of the Seismological Society of America. 100 (3): 1165–1173. Bibcode:2010BuSSA.100.1165K. doi:10.1785/0120090277 – via GeoScienceWorld.
44. Riemer, K. L.; Durrheim, R. J. (25 September 2012). "Mining seismicity in the Witwatersrand Basin: monitoring, mechanisms and mitigation strategies in perspective". Journal of Rock Mechanics and Geotechnical Engineering. 4 (3): 228–249. Bibcode:2012JRMGE...4..228R. doi:10.3724/SP.J.1235.2012.00228. ISSN 1674-7755.
45. ^ Plenkers, K.; Kwiatek, G.; Nakatani, M.; Dresen, G. (1 May 2010). "Observation of Seismic Events with Frequencies f > 25 kHz at Mponeng Deep Gold Mine, South Africa". Seismological Research Letters. 81 (3): 467–479. Bibcode:2010SeiRL..81..467P. doi:10.1785/gssrl.81.3.467. ISSN 0895-0695.
46. Li, T.; Cai, M. F.; Cai, M. (1 December 2007). "A review of mining-induced seismicity in China". International Journal of Rock Mechanics and Mining Sciences. 44 (8): 1149–1171. Bibcode:2007IJRMM..44.1149L. doi:10.1016/j.ijrmms.2007.06.002. ISSN 1365-1609.
47. ^ Kwiatek, G; Plenkers, K; Nakatani, M; Yabe, Y; Dressen, G; JAGUARS-Group (2010). "Frequency-Magnitude Characteristics Down to Magnitude -4.4 for Induced Seismicity Recorded at Mponeng Gold Mine, South Africa". Bulletin of the Seismological Society of America. 100 (3): 1165–1173. Bibcode:2010BuSSA.100.1165K. doi:10.1785/0120090277 – via GeoScienceWorld.
48. ^ Kwiatek, G; Plenkers, K; Drensen, G; JAGUARS Research Group (2011). "Source Parameters of Picoseismicity Recorded at Mponeng Deep Gold Mine, South Africa: Implications for Scaling Relations". Bulletin of the Seismological Society of America. 101 (6): 2592–2608. Bibcode:2011BuSSA.101.2592K. doi:10.1785/0120110094 – via GeoScienceWorld.
49. "JAGUARS – induced.pl". www.induced.pl. Retrieved 8 March 2024.

• Gold mines in South Africa
• Economy of Gauteng