A feasibility study on the expansion of Leagold Mining’s Los Filos mine, in Mexico, has shown potential for the development of the Bermejal underground mine, enlarging the Los Filos open pit, re-phasing the Bermejal open pit into two distinct open pits (Bermejal and Guadalupe), and construction of a carbon-in-leach (CIL) processing facility.
The study shows total gold production of 3.3 Moz over a 10-year mine life (2019 to 2028) at an average all-in sustaining cost of $795/oz at Los Filos. Post expansion (2021 onwards), average annual production would step up to 350,000 oz at an AISC of $759/oz, compared with 195,362 oz last year, which came from the existing heap leach facilities.
The capital cost came out at $180 million to develop the Bermejal underground and construct a new 4,000 t/d CIL plant with related infrastructure, with an NPV (5% discount) of $565 million generated using an average gold price of $1,250/oz.
Leagold CEO, Neil Woodyer, said: “When we acquired Los Filos in April 2017 from Goldcorp, we identified its potential to be developed into a long-life, low-cost operation with significant scale. During the 20 months since the acquisition, we have carried out extensive exploration programmes for both open pit and underground deposits, developed a 1,330-m ramp to access the orebody at Bermejal underground, completed the Bermejal underground mine design, completed comprehensive metallurgical testwork on all of the mineral deposits to support the CIL plant design, and learned a lot from current operations.
“The study identifies a new operating strategy, which includes three large open pits, two high-grade underground mines, the addition of a CIL plant to process the higher-grade ore, and the continued heap leaching of the lower-grade open-pit ore. The Los Filos expansion will also benefit from existing operations and excellent infrastructure. Approximately 51% of the gold production in the life of mine plan is from the CIL plant and 49% is from the existing heap leach facility.”
Woodyer added the company was now putting the study findings into its “overall corporate business model for planning and corporate financing purposes”, but he said it was “obviously a project we should undertake”.
Bermejal underground mine design and cost estimation was completed by SRK Consulting. A total of 11 km of horizontal and vertical development was planned during the initial development period and a further 45 km over the life of mine. The mine life extends for nine years producing 6.4 Mt at 6.57 g/t for contained gold of 1.348 Moz.
Mining costs of $99/t were based on contractor mining, with the mining method being underhand drift and fill with cemented rock fill (CRF) used as backfill. Bermejal underground will have a dedicated CRF production plant. The production rate averages 2,000 t/d and peaks at 2,150 t/d. Bermejal underground contributes 31% of the contained gold in the life of mine plan.
Los Filos Underground
The Los Filos underground mine is currently operating at over 1,800 t/d and, in the life of mine plan, averages 1,700 t/d with mining costs of $73/t based on owner and contract mining. Reduced operating costs, improved mining efficiencies and additional drilling have enabled the update of the Los Filos underground mine plan to extend to 2021. The reserves are 1.9 Mt at 5.50 g/t for a total of 338,000 oz.
Los Filos uses conventional open-pit mining methods with an owner-operated fleet supplemented with rental of additional equipment during peak production periods. The average open-pit mining costs are $1.41/t mined.
Los Filos Open Pit
The expanded Los Filos open pit has a proven and probable reserve of 42.7 Mt at 0.57 g/t containing 776,000 oz. The mine life was extended seven years to 2027. The Los Filos open pit has an overall strip ratio of 4:1
Bermejal and Guadalupe Open Pits
The Bermejal and Guadalupe open pits have been split into two open pits and rescheduled to mine the higher-grade Guadalupe ore earlier in the schedule, which significantly improves the economics, according to Leagold. Guadalupe has a proven and probable mineral reserve of 26.3 Mt at 1.55 g/t Au for 1.313 Moz. A pushback in 2020 will open this up as a separate open pit that has a 10-year life, Leagold says. The Guadalupe pit has an overall strip ratio of 8:1.
The Bermejal open pit extends for at least five years to 2025 based on the current reserves. Proven and probable mineral reserves are 34 Mt at 0.54 g/t Au for 588,000 oz. The overall strip ratio of the Bermejal open pit is 2.7:1.
CIL and heap leach processing
The CIL plant is expected to achieve higher recoveries (an average of 89.7%) and better financial returns than heap leach processing for the underground ore and the higher-grade portion of the open-pit ores.
“The plant also provides the ability to process some ore types that were previously not included in reserves as they were not amenable to heap leach processing; this includes material with an elevated sulphur content which exhibits lower gold recoveries at the crush sizes typically used in crushing for heap leach processing,” Leagold says.
The plant is predicted to process a total of 12.4 Mt at an average grade of ore feed of 4.63 g/t Au with an average recovery of 89.7% to produce 1.658 Moz gold.
The expansion feasibility study contemplates the existing heap leach facility continuing to operate throughout the full life of mine plan. A total of 95.6 Mt of ore with an average grade of 0.79 g/t Au will be placed on the leach pads and have an average recovery of 61.9% to produce approximately 1.5 Moz of gold.
Secondary recovery is expected to contribute an additional 111,000 oz from surface re-leaching and re-handling of previously leached ore, Leagold says.
Contributions to the gold production in the life of mine plan are 51% from the CIL plant, 46% from the heap leach and 3% from secondary recovery.