Mining Mirror February 2019 | Page 19

Mine excursion Both open pits are mined in phases. In picture is a truck hauling material from the bottom of the Otjikoto Pit during Phase 2, which was in full swing when Mining Mirror visited. license in December 2012 and started construction a mere four months later. The first gold was poured two years later in December 2014 and the mine started commercial production on 1 March 2015. Hopes for exploration Otjikoto and Navachab are not the only gold deposits in Namibia. Several exploration companies have set up base here. In fact, results from several gold exploration projects around the country have been good and it is only a matter of time before Namibia’s third gold mine sees the light. B2Gold is currently doing exploration work at the Otjikoto area and also at Ondundu, in the Omaruru region, which is almost halfway between Navachab and Otjikoto. According to Mark Dawe, country manager and managing director of B2Gold Namibia, the company’s total exploration budget in 2018 is USD5.1- million. “Exploration in 2018 will include 17 000m of diamond drilling and 4 000m of rotary air blast (RAB) drilling, split between the Otjikoto Mine, the Ondundu, and other projects,” says Dawe. Dawe, a metallurgist by training, and his team at the Otjikoto Mine have managed to squeeze the proverbial blood from a rock. The B2Gold team and the Australian www.miningmirror.co.za engineering company Lycopodium have designed an efficient processing plant that boasts an average of 98.6% recovery for the YTD 2018 recovery rate (project to date is 98.4%) — an exemplary performance under challenging conditions. Efficient management Eric Barnard, acting general manager at Otjikoto and also a metallurgist, tells Mining Mirror that Otjikoto does not have the luxury of high-grade ore and therefore, the strategy is to manage the ore body and the plant feed as efficiently as possible. “We have to ensure that we mine the right grades at all times so that we can meet our production targets,” says Barnard. A low-grade operation like Otjikoto is never able to stockpile high-grade material for a rainy day. For management, this means constant planning. “To make such a low-grade operation work, one has to mine selectively,” says Peter Mawoyo, production manager at Otjikoto. “That includes the mining process in the two pits, and processing the material in the plant,” he adds. “We control the blend into the plant to ensure correct grade as well as to maximise recoveries during periods that we are fed with ore containing a high percentage of pyrrhotite. One of the criteria behind the need to carry selective grade control is to stabilise the percentage of sulphur contained in minerals such as pyrrhotite, thereby maximising gold recovery,” Barnard explains. Barnard says that when he first saw the mineralogy of the ore, he did not believe that recoveries in the high 90s could be achieved through a conventional mill/ leach gold processing plant. Because the ore at Otjikoto contains a high component of gravity recoverable gold (GRG), a plant was designed with a gravity circuit yielding exceptionally high recoveries. The grade at Otjikoto, nonetheless, remains low at about 1.6 grams per tonne. To recover the gold, Otjikoto mines a lot of waste, and moves on average about 106 000 tonnes of material per day, of which only approximately 10 000 tonnes are milled — thus at a high average stripping ratio of approximately 11:1, excluding the low-grade ore and approximately 7:1 if the low grade ore is taken into account. According to the original bankable feasibility study, the plant should operate at a recovery of about 96.7%. In addition to the higher recovery rates, the plant is processing more material than originally designed. The mining team is pushing 3.3 million tonnes run of mine (ROM) through the plant, while the plant was FEBRUARY 2019 MINING MIRROR [17]