Promap attend the IMSSA Mpumalanga visit to Ingula Power Station & Letseng Diamond Mine

IMSSA (The Institute of Mine Surveyors of South Africa) Mpumalanga were the proud hosts of the 2017 Technical Tour. With the tour taking in Ingula Hydro Power Station and the Letseng Diamond Mine in Lesotho, Promap were pleased to be able to attend as it provided an excellent opportunity to learn more about both power stations and big diamonds!

Ingula Hydro Power Station

To build a pumped storage scheme you need a specific combination of factors to be just right - the right geology, enough available water and two sites to build dams – close enough together, but with at least 400 meters difference in altitude, plus it needs to be close to the National Grid and close to existing infrastructure. 

Eskom started looking for such sites in the 1980's.  More than 90 potential sites were investigated with the best one selected north-east of Van Reenen's Pass, spanning the escarpment of the Little Drakensberg, and straddling the provincial boundary of the Free State and KwaZulu-Natal. This is also the continental watershed between the Vaal River catchment, flowing into the Atlantic Ocean, and the Tugela River catchment, flowing into the Indian Ocean.

Initially known as ‘Braamhoek’, the name changed to ‘Ingula’ in March 2007.  ‘Ingula’ alludes to the creamy contents at the top of a milk calabash.  The quest to find an appropriate name for Ingula Power Station was inspired by the mountains and foamy river-waters, and the rich cultural symbols and traditions of the indigenous people on both sides of the border.

The pumped storage scheme consists of an upper and a lower dam, each capable of holding approximately 22 million cubic metres of water.  The dams, 4.6km apart, are connected by underground waterways passing through a subterranean powerhouse with four 333 MW generators. To generate electricity during times of peak demand, water is released from the upper dam, passing through the pump/turbines, into the lower dam. During times of low energy demand, the pump/turbines are used to pump the water from the lower dam, back to the upper dam.

The Letseng Diamond Mine

Found in the landlocked Southern African kingdom of Lesotho,  the mine is jointly owned by Gem Diamonds, Ltd. and the government of Lesotho. At an elevation of 3,100m, it is the world's highest diamond mine and unusually for Africa, due to the elevation, temperatures at the mine drop to -20 °C, and snowfalls are common in winter.

The mine is known for producing huge diamonds, having the highest percentage of large diamonds (greater than 10 carats (2.0 g)), giving it the highest dollar value per carat of any diamond mine:

• October 2006 - the 603 carat (121 g) white diamond, named the Lesotho Promise, was unearthed, which until January 2018 was the largest reported find this century, the stone is of an exceptional colour, rated D, the top colour for diamonds. Previously the largest diamond found at Letseng was the 601 carat (120 g) Lesotho Brown which was recovered in 1967.
   
• September 2007 - a 493.27 carats (98.654 g) diamond was found, the 18th largest diamond ever found.  Named The Letseng Legacy, it was sold to the Graff-SAFDICO partnership for $10.4 million.
   
• September 2008 - a 478 carats (95.6 g) diamond of high quality, titled The  Leseli La Letšeng was found, the 20th largest diamond ever found. It is a type II D colour, with the potential to yield a 150 carats (30 g) cut stone. 
   
• November 2010 -  the discovery of two large rough white diamonds, weighing 196ct and 184ct.
   
• January 2018 -  the largest diamond yet discovered at Letseng was unearthed, a Type IIa D colour stone it measured in at 910 carats.

Promap would like to thank the IMSSA Mpumalanga Branch, Eskom and all at Ingula Hydro Power Station, plus staff at Letsendg Diamond Mine for their hospitality in hosting this most informative event.