Mining Mirror February 2019 | Page 23

Mine excursion carbon in pulp (CIP) circuit for recovery of gold in solution. The tailings stream from the CIP circuit is treated in a cyanide destruction circuit using the sulphur dioxide/air process, before being pumped to a lined tailings storage facility. Gold is recovered in the CIP circuit by loading it onto carbon, and the loaded carbon is sent to a split Anglo-American Research Laboratories (AARL) elution circuit. Gold solutions from the gravity-intensive leach circuit and elution circuit are treated in an electro-winning process, followed by smelting to produce doré bars. “The bottom line is that each mine has to adapt its processing plant according to what it has in the ground,” says Barnard. “B2Gold’s plant at Fekola in Mali also runs at high recoveries, although they have a grade of about 2 grams per tonne. The major difference is that Fekola doesn’t have a gravity circuit. The plant has a different design because the ore body it treats is completely different,” Barnard adds. Mining in phases “We started mining ore from the Otjikoto Pit. That was Phase 1. While we were mining at Otjikoto, we started with the stripping at Wolfshag, the other pit. As soon as the pushback at Otjikoto got under way during what we call Phase 2, mining of the Wolfshag ore body was initiated. It is an alternate cycle to ensure we have a continuous supply of ore to feed the processing plant. In 2018, we have been mining at Otjikoto Phase 2, while stripping at Wolfshag Phase 2,” explains Mawoyo. Mawoyo says the two biggest challenges in the pit are managing the complexity of the operation and reaching the daily target of 106 000 tonnes per day from both pits, which includes ore and waste. “We have to keep the equipment running, and the utilisation of the equipment has to be high for us to achieve those tonnages. At the moment, we have an 86% availability on the trucks. It will become a challenge though as we mine deeper and the equipment starts getting older. Moreover, the cycle times will also start increasing as we go deeper and as the dumps increase in size,” says Mawoyo. “Otjikoto uses conventional open-pit mining methods and is a fully owner- mined operation,” says Dawe and explains that the first phase of the mining cycle at Otjikoto is grade control drilling and sampling. “This is to better identify known ore zones and to develop ore polygons www.miningmirror.co.za Equipment used in the mine Production drills 2 × DK25 Sandvik 3 × MD6240 Caterpillar 1 × MD6290 Caterpillar Wall control drills 2 × MD5125 1 × MD5150 Haul trucks 18 × Caterpillar 100t 777D 5 × Caterpillar 100t 777E Hydraulic face shovels (waste stripping only) 2 × Caterpillar 6018 Hydraulic excavators (mainly ore loading) 2 × Liebherr 9250 1 × Liebherr 984 Wheel loaders (waste stripping and crusher feed) 1 × Caterpillar 992 2 × Caterpillar 990 that will aid in the selective mining of the ore body once blasted,” he says. After grade control drilling is completed, conventional blasthole rigs drill systematic blast patterns that are then charged and blasted. The blasted ore and waste are mined separately by large hydraulic excavators into awaiting 100-ton haul trucks. The trucks haul the blasted ore to the appropriate ore stockpiles in preparation for milling; blasted waste goes to its respective waste dumps. With the blasted ore and waste removed, the mining cycle can start over again with the required grade control drilling. “This continuous mining cycle will be used at Otjikoto to efficiently mine both ore and waste,” says Dawe. Otjikoto’s performance in 2018 higher-than-budgeted production and lower general and administrative costs and were lower than the prior-year quarter due to lower capital expenditures for mobile equipment purchases. Year-to-date, gold production at the Otjikoto Mine was 122 580 ounces of gold (year-to-date 2017 – 139 088 ounces), above budget by 3% (4 027 ounces). For the first nine months of 2018, Otjikoto’s cash operating costs were USD514 per ounce (year-to-date 2017 – USD459 per ounce), USD19 per ounce (4%) below budget, and AISC were USD747 per ounce (year-to-date 2017 – USD756 per ounce), USD15 per ounce (2%) below budget. Capital expenditures in the third quarter of 2018 totaled USD12-million, mainly consisting of USD6-million for pre-stripping, USD3-million for new equipment, and USD1-million in mobile equipment rebuilds. Capital expenditures for the nine months ended 30 September 2018 totaled USD41-million, mainly consisting of USD21-million for pre- stripping, USD10-million in mobile equipment rebuilds, and USD4-million for the new solar power plant. For full-year 2018, the Otjikoto Mine is expected to produce between 160 000 and 170 000 ounces of gold, primarily from the Otjikoto Pit, at cash operating costs of between USD480 and USD525 per ounce and AISC of between USD700 and USD750 per ounce. Otjikoto delivered another quarter of solid production, producing 42 403 ounces of gold in the third quarter of 2018. This exceeded budget by 4% (1 568 ounces), mainly due to higher-than-expected mill throughput (870 125 tonnes compared to budget of 831 781 tonnes and 873 516 tonnes in the third quarter of 2017). Mill recoveries also remained high and averaged 98.7%, exceeding both budget of 98.0% and 98.5% in the third quarter of 2017. Compared to the prior-year quarter, gold production was lower by 23% (12 748 ounces), as planned, due to a negligible amount of Wolfshag ore being mined in 2018 while Phase 2 of the Wolfshag Pit is being developed. Higher-grade ore production is planned to resume from the Wolfshag Pit in late 2019. As a result, the average grade processed in the quarter was 1.54 grams per tonne (g/t), compared to budget of 1.52g/t and 1.99g/t in the third quarter of 2017. For third quarter 2018, Otjikoto's cash operating costs were USD470 per ounce (Q3 2017 – USD447 per ounce), USD14 per ounce (3%) below budget, mainly the result of higher-than-budgeted production. Otjikoto’s all-in sustaining costs (AISC) were USD662 per ounce, well below budget by USD53 per ounce (7%) and USD147 per ounce (18%) lower than the prior-year quarter. Otjikoto’s AISC were below budget mainly due to FEBRUARY 2019 MINING MIRROR [21]