Mothae Diamond Mine

Nestled in a valley close to the top of Lesotho’s diamond-rich Maluti mountains lies ASX-listed Lucapa Diamond Company’s new Mothae mine – the fourth diamond producing mine in the country.

Like its ‘famous’ neighbour Letšeng, the highest US$ per carat kimberlite mine in the world, Mothae comprises a high-value resource that holds the promise of recovering significant high value stones over its lifespan, which after six months of commercial operations (to June 2019) has already proven true.

LAURA CORNISH visited the mine to learn about the operation and its exciting potential.

Production start-up at Mothae, in which the government of Lesotho owns a free-carried 30% stake, represents a significant milestone – for both the country because of its economic contribution and for Lucapa, the company with the foresight to cost-effectively scale the mine and processing plant to ensure its long term profitability.

This article first appeared in Mining Review Africa Issue 7, 2019
Read the full digimag here or subscribe to receive a print copy here

First discovered in 1961 by Basotholand Diamonds, Mothae was most recently under the ownership of Canada’s Lucara Diamond Corp and the Lesotho government, from whom Lucapa acquired the asset in January 2017 for consideration of US$9 million.

With no grid power on site and its own vision for an expensive large-scale operation, Lucara was never able to deliver a feasible development plan for the mine.

Understanding the resource potential, Lucapa’s approach to building Mothae took an entirely different approach, which saw the company deliver a mine much smaller in size with significant scope for future expansion.

Consequently, Lucapa required a substantially smaller amount of capital to build the operation, enabling it to move from financing to construction and production in a short timeframe. 

As a result of this approach, the mine has low debt, which is unusual for the start-up period of new mine developments.

A closer look at the operation

A low grade but high-value resource like Letseng, the Mothae kimberlite pipe consists of a south lobe (south west, south centre and south east), connected to a smaller north lobe by an elongated central neck kimberlite body. It offers an indicated and inferred resource of >1 million carats contained within 39 Mt of material – excluding the neck area at present.

“Our known resource has only been drilled and quantified to a depth of 300 m and we are confident that in time we’ll expand this resource further as we explore the kimberlite’s deeper potential,” says Gideon Scheepers, Mothae general manager.

The South lobe is the largest portion of the mine in size with a surface area of 5.05 ha. This increases to 8.81 ha when combining the neck and north lobe.

As an open cast mine with a plan to double production in the mid-term future, Mothae has a healthy 14-year lifespan although as mentioned, this could increase as the mine is explored at depth.

For now, Lucapa is operating under a 10-year licence issued by the Government in 2017 – which is renewable for further 10-year periods.

Mothae’s new 1.1 Mtpa processing plant, designed, built and commissioned by diamond engineering expert Consulmet, was delivered in record time and incorporates innovative XRT sorting technology, which has already proven its worth.

Civil construction of the plant commenced in January 2018 creating a seamless path for the first ore to be treated just 11 months later in November.

“We recovered our first diamonds in November 2018 and exceeded the 150 tph design capacity a month later in December – all of which positioned the mine to achieve commercial production in January 2019,” Scheepers outlines.

To achieve a new plant build in such a short time is in itself an impressive achievement, but in Mothae’s case is more remarkable considering it was built during periods of heavy snowfall.

The logistics to travel several steep mountain passes to transport all the equipment to site added another dimension to the project’s requirements but even this posed no major difficulties or deadline challenges.

It took more than 170 truckloads to transport everything to site and the project was developed within its deadline expectations.

Stones a-plenty

Mothae has already generated significant revenue (US$7.3 million at an average $729/carat) from the first two sales of its rough diamonds at tender in Antwerp. And in May, the mine produced its first +100 carat diamond, just five months after commercial production commenced.

The stone is a gem-quality 126 carat diamond and represents the seventh +50 carat diamond recovered since Lucapa commenced its pre-production bulk sampling programme at Mothae in 2018.

The on-site team place their diamond recovery faith in Tomra XRT sorters, now being operated by Consulmet to ensure the machines work seamlessly at all times.

“We are delighted to have recovered our first +100 carat stone so early in our commercial mining campaign at Mothae, along with other rare Type IIa and fancy coloured gems, and look forward to unlocking the true value of this mine over the next decade and beyond,” Lucapa MD Stephen Wetherall stated upon announcement of the 126 carat diamond.

Scheepers adds: “Considering Mothae has recovered its first big diamond while still mining through the surface, weathered material, this mine’s potential is far-reaching.”

Commercial mining to date has also been restricted predominantly to the lower-margin diamond zones.

This was due to the decision to delay the scheduled dewatering of the main southern pit to preserve water required to enable the plant to operate at higher throughput rates in the second half of 2019.

The water in the southern pit will be transferred to the main 500 000 m³ water dam in H2 when the dam wall is completed. This will in turn enable Mothae to access the higher-margin diamond zones in the southern pit.

Exciting potential on the horizon

While the mine continues to build momentum on an operational level, and establish the necessary supporting infrastructure to accommodate its longer term requirements, another promising aspect remains the updated Mothae mine plan and the potential to double the plant’s throughput to 2.2 Mtpa.

The new mine plan will be released once mining commences in higher-margin zones in the southern pit. Throughput, grades and carats recovered are all ahead of plan to date.

Doubling production to 2.2 Mtpa could entail a second parallel plant. In the interim, the mine team is looking at plant optimisation work to further enhance its production capacity.

Infrastructure projects underway currently include the establishment of a new water dam. Construction commenced in May 2019 and with 165 000 m³ of weathered basalt fill to be placed and compacted, will be substantial in size.

The existing on-site accommodation is temporary and a new camp and site offices needs to be established. To date site selection has been completed and spatial planning is in progress.

“Our goal is to move into our new accommodation in 2020 – a necessity considering the current infrastructure sits within the existing pit shell,” Scheepers points out.

A new mine perimeter fence and new access road will conclude the mine’s immediate infrastructure requirements – both of which are already in execution as well.

Mutual care

While there are no communities within Mothae’s 46 km tenement, the mine maintains a healthy respect for the environment in which it operates and the people it employs.

The majority of the approximately 400 strong workforce comprises Lesotho nationals (97%) and 32% are female.

Employment creation is always well received in Lesotho and Mothae is providing a work environment that ensures its personnel are productive and committed to work delivery.

The atmosphere on site is positive and every team member eager to assist and contribute to ensuring the mine’s success. To be hosted on site by such an enthusiastic and positive team was a pleasure.

“We also have a preference for in-sourcing which results in good accountability, ownership, and pride from every employee on site,” Scheepers adds.

Having visited the Mothae operation, there is little doubt that the mine has great potential and will thrive well beyond its current fortunes. It was an investment well made by a smart Lucapa team that has delivered the company as a multiple-mine diamond producer, of which not many miners in the field have achieved.