Making beaches to mine diamonds

Augetto GraigPushing the boundaries of development and progress does not come as a bigger challenge as when the obstacle is the very unpredictable and mighty Atlantic Ocean. Namibia’s historic and era-defining partnership with world diamond giant De Beers, Namdeb, is the epitome of heroic endeavour to overcome an insurmountable force of nature and claim treasure from the sea.At its Southern Coastal Mine (SCM), Namdeb literally moves the shoreline back to create dry beaches for conventional diamond mining. Every month, one million tons of material is dumped by truck at two strategic points along the desert coastline in the far south-west of the country, while diamond production from the 3 Plant facility deposits another 200 000 tons from tailings per month. To date, about 32 million tons have been deposited into the sea, of which nine million is dedicated to specific accretion.Massive diamond fieldProcess manager for strip mining at SCM, Tuhafeni Kamati, said: “The ancient Orange river and south-western coastline is a massive diamond field,” of gem quality river and ocean diamonds, and added that despite the official Life of Mine currently ending in 2022, everyone at Namdeb is committed to realising the vision of mining for the lustrous stones beyond 2050. Namdeb submitted an environmental management programme report in June, detailing its proposed accretion up to 2038, by when it wants to move the beaches westward by about 1.2km.“There are still lots of things that challenge that vision, but the work has never stopped,” he said. He explained that daily activities at SCM include accretion, which is how the new beaches are built, exploration, strip-mining, bed-rock cleaning and also treatment, recovery, sorting and canning of rough diamonds at 3 Plant. Concurrent exploration is important and the enormous Bauer BG 36 drill, with its two meter drilling diameter, continually plunges down to the footwall to produce sample material for the Southern Areas Sampling Plant, and plug this information back into the resource. Accretion Historically, accretion was achieved through various means including the use of a dredge to strip and discharge fluidized overburden material into the sea. Ingenious conveyor systems also transport plant treatment tailings and sand from strategic areas east of the haul road to the ocean. Accretion draws on two sources, namely the normal production stripping of overburden in production areas, and dedicated accretion from identified sand sources such as historic overburden dumps. The daily production target of 28 000 tons earth moved is predominantly for accretion.The highly qualified team also developed ‘beach nourishment’, which involves depositing sand along the beach and dumping overburden to create groynes jutting like jetties out into the waves to and providing earthmoving equipment access to the beaches to deposit the bulk of the material that northward oceanic current use to build new beaches along the coastline.Namdeb said the progression of accretion beaches results in a steepening of the offshore beach and over time an increase in longshore drift while the natural distribution of sand along the beach can create a more natural beach profile. Building beaches Elaborating on how they go about building beaches, Kamati said cross walls and ramps are erected, as well as strategic cross walls 1.5km apart, while a 30km seawall is maintained to design. “The seawall is the most western structure and faces the sea. It allows for our mechanised dry mining process and along with the groynes provide beach access as well as being our foremost protection mechanism. Beach nourishment is the gradual addition of material to build beaches to mine in the future. The process uses what is available,” he said. For example, bigger rocks are collected to be used as rip-rap to strengthen the seawall. Assisted by a fleet of rigid frame and articulated trucks and front-loaders, and guided by a continuously refined accretion model, beach nourishment relies on accuracy regarding where to accrete next. “We get really excited to see that what we predict is happening, and we are able to pinpoint where to direct our resources,” Kamati said. Current activities follow the lead set by a trial project at the U80 North mining cut in 2016, where material is deposited on the beach rather than on the groynes. The deposition area is west of the seawall and the trial hoped to advance a natural beach profile westward into the sea. Positive results at U80 North led to expansion to other priority areas and now beaches are being ‘nourished’ at U100, U0, G95, G85 and the G65 mining cuts. Beach nourishment is incorporated into the current mine plan which also calls for the continuous refinement of accretion prediction models, measurements and methodology.People-basedMeanwhile, teams of about 30 people do bulk excavation and use Transvac machines to suck up diamond-bearing gravel. “There is a limit to how much can be removed mechanically. The Transvac teams consist of bin and suction units. It is a people-based process and demands wholistic risk management,” he said, explaining that these teams often work 15 to 30 meters below the sea-level, protected only by the 20-metre-wide seawall that rises seven to 10 meters above the crushing waves. A fleet of rigid-frame trucks load and haul the ore from intermediate stockpile to the treatment plant where it goes through scalping, crushing, screening, scrubbing and dense media separation before the diamond concentrate is taken to the Red Area Complex and the waste is discharged into the sea. Stripping is achieved with excavators loading articulated dump trucks (ADT) because of their better manoeuvrability. Namdeb operates a stripping fleet consisting of both is own earth-moving vehicles and contracted vehilces to make up over 15 excavators and more that 50 articulated dump trucks.The risk-based approach used to ensure safety considers seawall and crosswall designs and geotechnical hazard assessments, and defines the controls required in the planning and management of geotechnical risks.Dynamic modelling of three tiers of risk include oceanographic risk assessment with coastal engineers, geotechnical risk assessment with geotechnicians and onsite risk assessment. Design and practicality are informed by hourly monitoring, especially during a storm period. Proactive weather monitoring is buoy-based and storm simulation predicts ocean and coastline weather behaviour for up to two weeks in advance. Storm warningBased on the severity of any storm, a predetermined trigger action plan kicks in to prevent worst-case scenarios and ensure that people can be moved out to safety, Kamati said. “Global warming makes things a lot less predictable, but we gain better understanding by collecting more information,” he said. Mine planner Neil Andrews added: “The system we use is not something out of a shop. Everyone is learning from it. Sharing information has enabled us to put the seawalls in safer areas”.augetto@republikein.com.na

Making beaches to mine diamonds

Comments

Namibian Sun 2025-01-06

Please login to leave a comment

Making beaches to mine diamonds

Comments

Namibian Sun 2025-01-06

Please login to leave a comment

Login