User:MacGuire Roughley/Mponeng Gold Mine

Lead
Mponeng is a gold mine in South Africa's Gauteng province, it is an ultra-deep tabular mine of the Witwatersrand Basin. [1]Previously known as Western Deep Levels #1 Shaft, the underground and surface works were commissioned in 1987. It extends over 4 kilometres (2.5 mi) below the surface,[2] and is considered to be one of the most substantial gold mines in the world.[3] It is also currently the world's deepest mine from ground level,[4] reaching a depth of 4 km (2.5 mi) below ground level, with aims to deepen the mine to reach additional reserves.[5] The trip from the surface to the bottom of the mine takes over an hour.[2]

Mining in South Africa has had a huge effect on the technologies of deep gold mining around the world, South Africa is even considered a pioneer of the trade.[6]

The mine utilizes 2 horizons; Ventersdorp Contact Reef (VCR) and Carbon Leader Reef (CLR). In the Mponeng mine the VCR is mainly interbedded quartzite and coarse conglomerates and constitutes only a meter or two of thickness.[7]

Over 5400 metric tonnes of rock are excavated from Mponeng each day.[2] At a price of $19.4 per gram of gold, the mine only needs to extract 10 grams of gold per ton excavated to remain profitable.[2] The mine contains at least two gold reefs, with the deepest one metre thick.[2]

As of 2022, all-in costs of production were US$1771/oz. Even at near record high gold prices, Mponeng is barely breaking even. [8]

Harmony Gold purchased Mponeng from AngloGold Ashanti in September 2020. Along with AGA's Mine Waste Solutions, Harmony paid approximately $300m.

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).[2] A mixture of concrete, water, and rock is packed into excavated areas, which further acts as an insulator.[2] Tunnel walls are secured by flexible shotcrete reinforced with steel fibers, which is further held in place by diamond-mesh netting.[2]

In 2008, researchers looking for extremophile organisms discovered the bacterium Desulforudis audaxviator present within groundwater samples from kilometers deep in the mine.[9]

In Pop Culture
Danny Forster visited the mine for the fifth episode of Build It Bigger's eighth season.

Millan Ludeña, an Ecuadorian marathon runner, became the first person to run a half-marathon fully underground in the deepest part of Mponeng Gold Mine. A Guinness World Records adjudicator was on hand to document the race and issued the certificate for the deepest half-marathon.[10]

Lead
Mponeng is a gold mine in South Africa's Gauteng province, it is an ultra-deep tabular mine of the Witwatersrand Basin. Previously known as Western Deep Levels #1 Shaft, the underground and surface works were commissioned in 1986. It extends over 4 kilometers (2.5 mi) below the surface, and is considered to be one of the most substantial gold mines in the world. It is also currently the world's deepest mine from ground level, reaching a depth of 4 km (2.5 mi) below ground level, with aims to deepen the mine to reach additional reserves. The trip from the surface to the bottom of the mine takes over an hour. Mining in South Africa has had a huge effect on the technologies of deep gold mining around the world, South Africa is even considered a pioneer of the trade.

Mponeng is a gold mine in South Africa's Gauteng Province, specifically it is an ultra-deep tabular mine of the Witwatersrand Basin. Previously know as Western Deep Levels No1 Shaft, the mine began operations in 1986. Considered to be one of the most substantial gold mine mines in world in production and magnitude, reaching over 4km (2.5 mi) below the surface. At this depth Mponeng takes the title of worlds 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 it's depth takes over an hour, but the harsh conditions of the mine did not stop an Ecuadorian marathon runner from completing a half marathon within the mine. Mponeng comes with economic, environmental, societal, and seismic relations but mining in South Africa has had a huge effect on the technologies of deep gold mining around the world, South Africa is even considered a pioneer of the trade.

Operations and Ownership
Harmony Gold, Africa's largest gold producer, purchased Mponeng from AngloGold Ashanti (AGA) in 2020, Harmony paid approximately $200m. 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 5400 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: 7449kg (239 490 oz) of gold
 * Grade: 8.43g/t
 * Volume of ore milled: 884 000 tons

History
Being a part of the Witwatersrand, the largest gold deposit on earth, Mponeng is the result of the discovery of the basin. Beginning in the 1850-70s a series of discoveries were made in the area, Pieter Jacob panning gold from a river and a Henry Lewis finding quartz and gold vein on a farm. 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 to be 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 possibly 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 be 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 most businesses, Mponeng closed its doors due to COVID-19 in May of 2020, but has since returned the producing. Striking in South Africa's mining district was apparent in the 1900s, for example the South African gold mine strike in August of 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. Back 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 there 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.  

Physical Conditions
The temperature of the rock reaches 66 °C (151 °F) and an overlying pressure of 100 MPa, 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 the popular novel "Journey to the Center of the Earth" (Jules Verne), which means 'descend, bold traveler, and attain the center of the Earth'.

Geology and Gold Bearing Fractures
The mine sits in the Witwatersrand Basin and utilizes 2 horizons; Ventersdorp Contact Reef (VCR) and Carbon Leader Reef (CLR). In the Mponeng mine the VCR 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 mineralization 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), that is more than 8x more than 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 10cm 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 mineralization's:

As with most mines, Mponeng is limited to the structural control of the geology. The VCR mineralization 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 deformation.
 * Steep quartz/sulphide-bearing fractures
 * Sub-horizontal quartz fractures
 * Sulphide-bearing fractures
 * Ultracataclastics
 * Mesophased hydrocarbons.

Environmental Impacts
South Africa has been dealing with the affects of mining related pollution for years, it comes with having such a large mining industry (roughly 8% GDP). In 1998, mining industry contributed nearly 90% of the 533.6 million tons of waste that was produced in the year. As displayed by the 1998 data, gold mining is the largest single source of pollution in South Africa. This is exaggerated in the Witwatersrand Basin, the basin is home to over 270 tailings storage facilities, covering 18,000 Ha.

Mining comes along 2 main kinds of waste, waste rock piles and tailing storage facilities (TSFs). Waste rock pile are the rock that must be removed in order to reach the ore, which in the case for Mponeng, is quite a lot as the mine is quite deep. 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 highly hazardous chemical properties. Long term consequences are also of concern, whether the mine activities continue, halt, or a mine is abounded, 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, Harmony gold has since taken over monitoring. Citizens are concerned surrounding heavy metal content as well as silica content, as both pose serious health risk (Silicosis, Tuberculosis, Bronchitis, Chromic 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 (PTEs)
 * Mainly heavy metals, also including arsenic (metalloid).
 * Airborne/Dust

Moving Forward
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. That doesn't mean efforts aren't or can't be made.

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' are still the release of elastic strain but are often low moment magnitude. Reaching beyond 1000 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 27th, 2007, a dyke within Mponeng experienced a 1.9 magnitude event. Caused by stress change due to excavation within the mine. In March of 2020 Mponeng experienced a magnitude 2 event, 3 were killed. In deep mines vertical stress can reach an astounding 80-100 MPa, equivalent to roughly 10km under water. Seismicity in deep gold mines is common, and is often induced by mining activities. 2 events can be considered :

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

Research and Safety
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 in placed below the Ventersdorp Contact Reef, there are 8 Acoustic Emissions sensor, 2 strainmeters, and one triaxial accelerometer that make up the network.

In Pop Culture
Released in 2010, the American television show 'Build it Bigger' (Powderhouse Productions) hosted by Danny Forster visited Mponeng Gold Mine. Millan Ludeña, an Ecuadorian marathon runner, became the first person to run a half-marathon fully underground in the deepest part of Mponeng Gold Mine. A Guinness World Records adjudicator was on hand to document the race and issued the certificate for the deepest half-marathon. It was Millan's goal to run as far, and as close to sun as he could. Later, after Mponeng, Millan run up Mt.Chimborazo in Ecuador.