Modern Mining: Featured News

Roxgold Inc’s Yaramoko underground gold mine in Burkina Faso could soon be expanded with the addition of a satellite underground operation at the Bagassi South deposit. A Feasibility Study (FS) on the project, which would have an estimated average annual gold production of 40 000 ounces over a mine life of 4,2 years, has produced positive results and Roxgold envisages that – subject to the necessary permitting being obtained – construction could start early next year with the first ore being delivered late in 2018.

Located in the Houndé greenstone region of Burkina Faso, the high-grade (17,1 g/t) Yaramoko mine, which produced its first gold in May 2016, has proven to be a big success for TSX-listed Roxgold, with the original Feasibility Study assumptions being exceeded. By June this year, the mine – the only underground gold mine in Burkina Faso – had produced 141 000 oz of gold since start-up and Roxgold’s guidance for 2017 is 115 000 to 125 000 ounces at an AISC of US$740 to US$790 per ounce. The proposed Bagassi South project will be the first expansion project at Yaramoko.

Yaramoko Roxgold

The existing Yaramoko processing plant, seen here, will have to be expanded to a capacity of 400 000t/a (photo: Roxgold).

The Bagassi South Feasibility Study, led by SRK in partnership with Knight Piésold, DRA, African Underground Mining Services (AUMS) and Roxgold, focuses on the incorporation of the Bagassi South deposit into the Yaramoko permit, which is 90 %-owned by Roxgold. The existing 55 Zone mine and the processing plant are located approximately 1,8 km north of Bagassi South, which has proven and probable mineral reserves of 170 000 ounces of gold at 11,54 g/t Au.

Based on a gold price of US$1 300/oz, the FS indicates an after-tax NPV5% of US$50 million; an after-tax IRR of 53,2 %; average total cash costs of US$426/oz (including royalties); and an average AISC of US$630/oz. Pre-production capital is estimated at US$29,6 million with payback being achieved in 1,8 years.

The Bagassi South project will benefit from utilisation of existing infrastructure and personnel at 55 Zone. Mining contractor management, workshops, tailings and water dams, camps and grid power reticulation are all examples of existing infrastructure that reduce the overhead burden on Bagassi South as well as assist in the development timeline with shorter mobilisation periods.

As outlined in the FS, the initial access to the deposit will be via a single ramp from surface to the 5265 level (45 m below surface). The ramp will ultimately be developed to a depth of 260 m below surface (5055 level), providing access to 15 sub-levels on 15 m vertical intervals. The ramp will be centrally positioned along strike and three ore blocks will be accessed by on-vein development to the deposit limits. Similar to the operating 55 Zone, mining will be conducted using longhole retreat stoping with cemented rock backfill used to eliminate non-recoverable pillars to maximise mining recovery to 93 %.

The mine plan is based on a cut-off grade of 4,8 g/t gold and a minimum mining width of 1,2 m. It envisages a total production period of 4,2 years including three years at nominal rates of 350 tonnes per day (t/d) ore extraction and 48 000 ounces of gold per year.

The typical planned stope has a 25-m strike length, a vertical height of 15 m and the full vein width. Longhole stoping is planned for both narrow vein areas (17 % of ore production) and wider vein areas (83 %). Tonne-weighted average horizontal vein widths are 1,5 m in the narrow stoping areas and 6,3 m in the wider areas. External dilution applied averages 26,8 % for all stope tonnes with an estimated dilution grade of 1,22 g/t gold.

The initial mine plan is based on contractor mining with engineering and grade control provided by Roxgold. Owner mining is assumed after approximately 18 months of operation.

The project will require an expansion of the Yaramoko plant to increase capacity from 270 000 t/a to 400 000 t/a. The original design of the Yaramoko plant considered a future expansion and the necessary allowances were made in the layout and mechanical equipment selection to facilitate a modular type expansion. The expansion maintains the simple and robust design philosophy that was implemented originally.

The following upgrades are anticipated to facilitate the additional throughput and gold recovery:
 a secondary crushing circuit with a throughput of 100 t/h, operating at 70 % availability, and aiming to achieve a design crush of 80 % passing 20 mm;
 conversion of the SAG mill to a ball mill, achieving a throughput of 50,2 t/h, with an increased ball charge (20-27 % vol) operating at 91,3 % availability, and aiming to achieve a design grind of 80 % passing 90 µm;
 expansion of the CIL circuit, consisting of an additional two adsorption tanks and an 8 m diameter high rate thickener;
 expansion of the gravity circuit designed to recover 70 % of head grade consisting of an additional Acacia leach reactor and two electrowinning cells; and
 additional raw water storage and power reticulation infrastructure.

“The Bagassi South expansion adds substantial value to Roxgold by increasing Yaramoko gold project gold production by approximately 40 % to over 150 000 ounces in the near term. Like the neighbouring 55 Zone, the economics of this additional high-grade feed source are highly accretive and generate increased cashflow from a modest capital outlay,” comments John Dorward, President and CEO of Roxgold. “Consistent with our commitment to offer accretive growth while managing dilution, this expansion will be funded from our own balance sheet without the need for additional equity from our shareholders.”

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