Mothae diamond mine is a high-value kimberlite diamond mine located in the highlands of Lesotho. It is owned by its operator Lucapa Diamond Company (70%) and the Government of the Kingdom of Lesotho (30%).
The Mothae kimberlite diamond project is being developed in two phases. The first phase started commercial production in December 2018, after the commissioning of a 1.1 million tonnes per annum (Mtpa) kimberlite treatment plant at the mine site in October 2018.
The second phase is expected to be operational by 2021, with the commissioning of another 1.1Mtpa treatment plant.
Mothae diamond project development history
The Mothae kimberlite mine was discovered by Basutoland Diamonds in 1961. Lucara Diamond, a company based in Canada, undertook the development of the mine in 2009 and carried out trial mining in November 2010.
The trial mining resulted in the production of more than 600,000 tonnes (t) of kimberlite and recovery of 23,000 carats (ct) of diamonds.
Lucapa Diamond Company, based in Australia, acquired the Mothae project from Lucara in January 2017. It was also issued the mining license for the project in the same month, which is valid until January 2027. The mining license can be further extended by ten years.
Mothae diamond project location and geology
Covering 20.52km², the mining lease area for the project is located on the southern edge of the Kaapvaal Craton, on the diamond-rich Maluti Mountains of Lesotho.
The Mothae diamond mine is located 135km east-northeast of the capital Maseru and approximately 7km north-west of the Letseng diamond mine.
The project geology is characterized by the intrusion of the volcaniclastic Mothae kimberlite into the amygdaloidal and non-amygdaloidal Mesozoic Drakensberg Group flood basalt.
The average elevation of Mothae kimberlite is 2,900m above sea level. The 1,000m-thick basalt layer is underlain by the Beaufort Group sediments of the Karoo Supergroup.
The Mothae kimberlite comprises South lobe, a pipe-like lobe with 5.05ha surface expression, connected to a similar North lobe via a central kimberlite body called Neck.
The total surface area of the mine is 8.8ha.
The Mothae kimberlite is estimated to hold more than one million carats of recoverable diamonds up to a depth of 300m.
Mining and processing at the Mothae diamond project
Conventional open-pit mining on 10m benches is carried out at the Mothae kimberlite mine. The mine employs drill-blast-load-haul operations for extracting the kimberlite resources.
The first phase of the mine targets the weathered kimberlite material present at the top, while the second phase will involve mining of the harder and unweathered kimberlite present below the pipe.
The extracted kimberlite resources are processed at the on-site 1.1Mtpa treatment plant that houses two X-ray transmission (XRT) diamond recovery modules, which are capable of recovering Type IIa diamonds out of the secondary crushing circuit.
Mothae diamond production
The Mothae diamond project produced 3,089ct of diamonds from 78,426t of kimberlite material, as of January 2019.
It also included the recovery of nine special diamonds with an individual weight of 10.8ct each.
The project site is accessible by a 5km-long gravel road connecting the Butha-Buthe tar road near Lesotho-South Africa border.
Power for the mining operations is sourced from Lesotho national grid. The power transmission lines are present within 5km of the Mothae project site.
Mineral Services Canada provided the geological exploration and evaluation details, while the on-site exploration work was undertaken by Remote Exploration Services (RES), under the ownership of Lucara Diamond.
MSA Group prepared the technical report and provided the mineral resource estimate for the project in 2013.
Minopex provided the processing plant during the trial mining phase of the Mothae diamond project in 2010.