Exploring continuous surface mining alternative technology

The Vermeer T1255III-TL at Letšeng Diamonds on the day of its arrival after assembly was completed

According to Jaco Houman, senior manager: Technical and Projects, Gem Diamonds Technical Services, using a surface miner showed potential against the conventional drill and blast process, which was followed by a primary crusher. “The surface miner gives us the opportunity to effectively mine from the pit and produce a product that is similar to those two steps of drill and blast and primary crushing. From that perspective, we’re able to have a process that is potentially more cost-effective, and a process that’s more complementary to the rest of our diamond processing flowsheet,” he says.

The trial took place from June 2022 to September 2022 and had the following outcomes: • environmentally friendly • replacement of primary drill and blast, as well as secondary pecking activities • more cost-effective from a cost-per-tonne basis • more stable processing due to greater consistency in

Letšeng Diamond Mine in Lesotho conducted a trial to find an alternative technology that could result in reduced damage to the diamonds, ultimately recovering higher-value gems. Vermeer Equipment Suppliers’ T1255IIITL surface miner was used as part of a series of trials. product size distribution to the plant • more productivity and efficiency. The trial period initially started on a single shift basis and then moved to a 24-hour basis. “The effective productivity that we had planned for in our overall works programme for the production period was around 66% effective cutting time,” Houman says. We exceeded that target with the deployment of the surface miner. He adds that the instantaneous cutting rate was within the expected target. “Overall productivity in the trial was certainly in line with our expectations.” Although the machine was a new one on-site, no mechanical issues were experienced, and production was not affected. “The machine performed very well mechanically,” says Houman. He adds that short-term challenges that did arise were easy to overcome such as the inclusion of a dust suppression or extraction system in the full production unit. The minor challenges encountered during the trial provided key considerations that could lead to increased efficiency when taken into account. They include mining/cutting through different geological domains with varying

The Vermeer T1255III-TL in operation at Letšeng Diamonds during the trial

A new Vermeer T1255III-TL with integrated vacuum dust suppression system and 3D GPS automation

hardness, working on existing benches and in close proximity to bench crests, and mine planning among others. “If you are putting this into a mine where you are starting from scratch, I think it’s a lot easier putting a surface miner in there and reaping success earlier,” says Houman.

The Vermeer T1255IIITL Single Side Direct Drive is powered by a CAT C18 Tier 3 diesel engine. The mining drum on the machine has a cutting width of 3.70 m. Frank Beerthuis, MD at Vermeer Equipment Suppliers, explains that the unique features of the machine include the full hydrostatic direct drive of the mining drum, which maximises the energy being transferred to the GETs and thus increases productivity. Another feature is the elimination of wear items in the driveline such as chains and sprockets allowing for a significant reduction of opex. “Another unique feature is the tilt function of the mining drum. This patented design feature allows for automated three-dimensional cutting of a smooth mining floor while cutting direction, cutting depth and slope angle are being controlled through GPS automation,” explains Beerthuis. The machine also has a down-cut design that reduces the re-grind of mined rock. “As a result, the clients will experience a more uniform particle size distribution, reduced wear of GETs and higher production rates.”

Following three days of classroom training and a week of equipment operation with an instructor, the operators were deemed fit to run the equipment on their own. “Vermeer Equipment Suppliers has been on-site during the full period of the trial.” Beerthuis explains that on two-week rotations, senior service technicians from Vermeer carried out the preventative maintenance of the machine and replacement of any worn items during the full trial period.

The trial showed that using the Vermeer T1255IIITL surface miner is a viable option for an open pit diamond mine. “The key thing for us is potentially generating more revenue per tonne and the fact that we further mitigate the risk of potential damage to our diamonds,” concludes Houman.