ASX-listed Magnum Mining has begun a key trial mining and processing programme at its 74 %-owned Gravelotte emerald project, located in Limpopo Province.
The programme is designed to provide critical information to assist with the re-establishment of commercial mining operations at Gravelotte – which was a major producer of emeralds over several decades up until the early 1980s.
It is designed to confirm historical emerald grades, optimise mining and processing techniques and recoveries, and allow the company to establish the value of the emeralds produced in the open market.
Emeralds were discovered in Limpopo Province in 1927 and, since then, several companies have explored for and mined within the broader region for emeralds. From 1929 to 1982, the total recorded emerald production from the Gravelotte project – as well as the area surrounding the nearby Gravelotte township – was nearly 113 million carats.
It is reported that, during the 1960s, the Gravelotte project was the largest mine of its type in the world, employing over 400 sorters.
During the past 36 months, Magnum has worked to re-establish the historical database and develop a strong understanding of the geology, structure and controls of mineralisation within the project area.
Magnum has maintained extensive mine site infrastructure at Gravelotte including mine offices, a laboratory, administration offices, a health clinic, a club house, and a mine hostel that can accommodate 350 mine workers. In addition, the mine site is serviced by Eskom grid power, has a sealed road to the mine gate and has a working airstrip and explosives magazine.
An extensive database of information is available for the Gravelotte project. This database covers the historical open pits – Cobra North, Cobra South and Discovery.
The Cobra pits were developed on a hill and only mined to approximately 10 m below plain level. The Discovery pit was developed near the cessation of historic mine operations and at its deepest point is only around 25 m below plain level.
Historical records indicate that the average recovered grade from hard rock mining in the final two decades of mining was around 6,2 g/t (31 carats/tonne).
Included within the mining lease are an estimated 850 000 tonnes of coarse tailings and untreated ore, contained within multiple dumps (Dumps). The Dumps are mostly from the historic mining and processing of the Cobra and Discovery pits.
Mine records show that, in the period from 1977 to 1982, an estimated 50 000 tonnes from the Dumps were processed for a recovered grade of 2,7 g/t of emerald (13,5 carats/tonne).
The 10 000-tonne trial mining and processing exercise has been designed by Magnum as an important precursor to potential commercial mining operations at Gravelotte. The programme will be conducted in two phases, with around 2 000 tonnes sourced from the Dumps and around 8 000 tonnes sourced from the Cobra and Discovery pits.
Based on the average recovered grades from the hard rock and waste dump processing over the nearly 70-year production history of Gravelotte, the trial mining exercise is projected to recover more than 250 000 carats of emerald.
Mobilisation of contractors to site began in late February and the mining of around 2 100 tonnes from the Waste Dumps has now been completed. Processing of this material – which will involve crushing, screening and hand sorting – has commenced and will be carried out within the company’s mine site facilities.
Mining of the hard rock is expected to commence in April 2018, with a more precise timing to be advised once scheduling of the mining equipment has been confirmed.