As the important mineral component of its cement, limestone will soon be mined from a new deposit by aggregates and construction materials company AfriSam’s Ulco cement plant, in the Northern Cape.

The relocated quarry will be capable of providing security of supply for about 40 years, and will need to deliver about two-million tonnes of limestone to Ulco each year.

“Mining is expected to begin in the second half of 2024, with an unusual topography in which the quarry will be mined into an escarpment,” says AfriSam cementitious executive Hannes Meyer.

As a result of the topography, he says transportation of mined material will be mainly downhill. “With the gradient of the haul road slopes limited to 5º, AfriSam’s truck-trailer combinations have been designed to be much more energy efficient than conventional offroad dump trucks.”

AfriSam Saldanha and strategic projects manager Gavin Venter adds that the enabling infrastructure for this quarry has been significant.

“After conducting a number of wide-spaced prospecting campaigns, as well as close-spaced drilling across 100 ha, we identified the best limestone reserves on our mining right on the opposite side of the R31 national road, which runs between the new site and the plant,” says Venter.

“This means it is necessary to construct tunnels under the road to facilitate safe access between the new quarry site and the existing plant. Adding to the complexity is that the large Gamagara water pipeline runs parallel to the road,” he adds.

The R31 road between Kimberley and Postmasburg carries high volumes of large ore trucks and abnormal-load mining equipment.

The road will be diverted in early 2024 to accommodate this traffic for about six months while extensive excavation and civil engineering work is undertaken to construct the tunnel underpass system.

“In compliance with the road authority’s requirements, the tunnels will traverse the full 32 m width of the road reserve to allow for future road widening, in addition to the pipeline servitude,” adds Venter.

The two tunnels will be over 50-m-long, and will be separated to enhance safety as there will be counterflow traffic to and from the plant.

The 5-m- by 5-m-wide tunnels will be excavated to 12 m below the R31 road level, and constructed as large culverts with steel reinforced in-situ cast concrete.

The design work ensured a tunnel alignment to suit the future possibility of an in-pit crusher and conveyer belt. If such an option was financially justified in future, AfriSam notes that it will provide an alternative method to feed crushed material to the existing preblending stockpiles.

The civils work also has to accommodate the 700-mm-diameter Gamagara pipeline, supplying the Northern Cape with water from the Vaal river. To avoid the risk of disrupting this water supply, a concrete bridge has been constructed parallel to the existing pipeline, inside which a new 100-m-stretch of pipeline was laid.

“This provided the necessary support for the pipeline so that excavation and controlled blasting can be conducted underneath,” explains Venter, adding that, as a further precaution, there is also a 100-mm-a-second vibration limit applied to any blasting activity around the pipeline bridge.

Work on the pipe bridge started in late 2022 and excavation work started in the third quarter of 2023, creating the initial slot on the south side of the R31.

The supply of readymix, which will include AfriSam cement, will come from Kimberley, about 80 km south. With ambient daytime temperatures that can rise to 40 ºC, this will require careful use of admixtures to achieve the required slump by the time readymix trucks arrive onsite.

Meanwhile, AfriSam commissioned various specialist studies as part of its environmental-impact assessment, to investigate the new quarry’s potential effects on wetlands, terrestrial life, hydrology, heritage and traffic.

The company reports that authorisation was granted to mine in the vicinity of water features on the proposed mining area, with a seasonal drainage line that had to be diverted to avoid the exit slot of the new haul road.