Project Title

Record Deep Drilling, Northern Cape

Date

February 2020

Location

Northern Cape, South Africa

Client

Torque Africa

Business Sectors

Mineral Resources

Services (Technical Disciplines)

Mincon MR range exploration tools

Project Objectives/Outcomes

Mincon South Africa supported Torque Africa Exploration at a mineral green-field exploration drill site in the Northern Cape province of South Africa.

Torque Africa is a long-time Mincon customer and has extensive experience in deep-hole RC drilling. For the project in the Northern Cape, a new Mincon reverse-circulation (RC) system was used, successfully drilling to 1,019m in just nine days.

With this new benchmark, the world of exploration drilling can now match diamond coring systems to a 1km depth, with all the advantages of air-powered RC systems.

Our Role

Between 10 and 15 February, 2020, work began on setting up a site for exploration drilling at a remote green-field site in the Northern Cape province of South Africa.

Torque Africa Exploration, a leading South African drilling company moved onto site with one of his company’s Thor 8000 RC truck-mount drill rigs – a proven powerhouse for its chosen method of deep-hole drilling.

With the nearest town more than 120 kilometres away, it is no small undertaking to set up camp in the middle of nowhere.  When drilling exploration holes to 1,000 metres or more with conventional diamond drilling techniques, it’s not uncommon to be on site for up to three months requiring a lot of time, money, and careful management of scarce resources.

However, for this project Torque Africa elected to use the latest products in the Mincon MR range of exploration tools. These reverse-circulation (RC) tools use a variation of the familiar air-powered down-the-hole (DTH) hammer, but designed to flush cuttings through an inner tube. Until recently, such air-powered RC systems were only used for exploration drilling up to 500 or 600 metres- but changes to Mincon’s newest RC hammers meant that Torque could expect reliable performance to drill much deeper.

Drilling commenced on 17 February 2020, using a Mincon MR120 RC hammer and a 143mm drill bit. After reaching a depth of 114 metres the team retrieved the drill string from the hole, after which the first four metres of the hole was reamed and widened to install a temporary casing. When drilling resumed the team used a new, 140mm RC drill bit, equipped with polycrystalline diamond-impregnated carbide buttons.

Progress was approximately 120 metres per day, which included retrieving the drill string at 637 metres in order to change sample tubes and swapping to a new, 137mm RC drill bit.

The process of retrieving a drill string is straightforward, but time-consuming. After lifting each pipe out of the hole it needs to be unscrewed, removed, and the the remaining pipes reattached. This is repeated, six metres at at a time, for the entire length of the drill string – more than 600 metres at this point. Deep-hole drilling projects can become incredibly expensive if multiple drill-string retrievals are required, but this can be offset by using durable, reliable equipment that consistently delivers high levels of performance.

On day eight of the project, Torque Africa Exploration resumed drilling with the fresh 137mm drill bit – only the third bit required for the project. In order to reduce time on site, a decision was also made to move to a 24-hour drilling schedule.

Rapid progress was made: in just two days the team powered through 382 metres of hard granite and rushing groundwater to reach a depth of 1,019 metres and making this one of the deepest exploration holes drilled using air RC tools, putting the technology on par with diamond coring as a solution for deep-hole drilling.

A post-drilling survey was conducted to verify the depth and straightness of the drill hole, with the survey report indicating a hole deviation of only 0.83 degrees. This exceeds the performance of competing technologies and proves yet another benefit of air RC systems.

A record-depth hole drilled in record time would be a pointless achievement if sample cuttings were unusable, though. Fortunately, this is where the air RC approach has yet another advantage: consistently returning uncontaminated sample cuttings to the surface. This is due to cuttings being flushed up through a sample tube rather than being exposed to the drilled hole.

Samples continued to be collected even after encountering extensive groundwater at 886 metres. For every metre drilled, a sample was collected, bagged, and tagged, allowing geologists to analyse the ground conditions and mineral content.

With this remarkable achievement, Mincon believes that air RC systems are now a strong alternative to coring-based exploration solutions. The hole drilled by Torque Africa Exploration proves that it’s possible for air RC systems to drill past 1,000 metres while collecting samples, using significantly less time, resources, and money.

Geoscience Ireland Contact

Gerry O’Connor (gerryoconnor@mincon.com)