About 75% of the coal from diversified miner Glencore’s Mpumalanga-based Tweefontein Optimisation Project (TOP) will be exported through the private-sector-owned Richards Bay Coal Terminal (RBCT), in KwaZulu-Natal, while the rest will be supplied to State-owned power utility Eskom and other inland customers.

TOP GM Allen Butcher says the company intends to send most of the coal to RBCT using rail, though the TOP also has capacity to transport small amounts of coal using trucks.

Nonetheless, he says the TOP’s emphasis is to transport as much coal as possible on rail to reduce the number of trucks on the road.

Butcher further notes that the project sent its first shipments of coal to the RBCT and Eskom last month.

Mining Method
Two pits have been opened at the TOP using the truck and shovel method, which employs the standard bench mining out of a boxcut.

However, Butcher says several of the new pits will be mined using dragline mining, as it is a highly efficient and cost-effective system.

Moreover, he says the mine will continue to use the truck and shovel method to mine the smaller pits, with this mining method also to be used for coaling and associated materials handling.

Butcher further points out that the old underground mines at Tweefontein comprise a network of underground intersecting tunnels, which resulted in up to 60% of the coal being left in situ as pillars and roof coal.

“Therefore, the only way to extract the coal efficiently is to go back and mine it from the top down, to mine the coal that was left in the old mine’s roof and support pillars.”

He adds that there is still one underground mine in operation that will supply about 20% of the coal to the new plant for a number of years to come.

Rehabilitation Strategy
Butcher highlights that the mine site rehabilitation process at the TOP  starts as soon as a boxcut is opened, as the material from the cut is taken to a stockpile and retained to close the final void.

“As progress is made on a pit, we transport the material cross-pit and keep an open void to ensure that immediate site rehabilitation is undertaken,” he says.

The mine has started with steady-state rehabilitation in the two pits that are currently open.

Butcher notes that more than four 60-m-wide cuts have already been back-filled, levelled, topsoiled and seeded in each pit.

Therefore, the mining operations remain moving voids until the pit has been completely mined out and, once all the resources have been extracted from the pit, all the material that was put on stockpile is filled into the pit. 

Butcher says that, depending on the geology at Tweefontein and the depth of the pit, there could be a surplus or a shortage of backfill material.

“We do our rehabilitation designs taking these possibilities into account and, if there is a slight surplus of material, we will raise the elevation as we backfill.

“However, if there is a shortage of material, we will slightly depress the surface; therefore, we do not leave a void,” he explains.

Instead, an area of the pit is left slightly lower than the original ground level. However, the main focus of the rehabilitation process is to keep the area free-draining so that water can “run off in a well-structured environmental condition”.

He comments that there is a significant focus on volume balance at Tweefontein to ensure that the mine does not leave big voids in the area once mining operations are complete.

“Therefore, once operations on the site are eventually concluded, Glencore will probably need to undertake only one year of final backfilling and surface levelling to ensure mine rehabilitation has been completed,” Butcher concludes.