Modern Mining: Featured News

ASX-listed Avenira has appointed Wood (formerly Amec Foster Wheeler) as the lead engineering contractor for the Bankable Feasibility Study (BFS) currently underway on its 80 %-owned Baobab phosphate project, located 145 km east of Dakar in Senegal. Avenira is planning an expansion and upgrade of the existing beneficiation plant at its Gadde Bissik mine.

The objective of the BFS is to provide a definitive design basis for detailed engineering and construction management for a plant with a nominal capacity of 1 Mt of high-quality phosphate rock concentrate per year. The scope of the study includes mining, processing and a tailings storage facility. Wood will develop operating and capital cost estimates to a ±10 % accuracy. This will also provide for detailed economic modelling to assist in raising funds to advance the project into commercial production.

Baobab 1

The product drying area at the Baobab phosphate project in Senegal.

The BFS will build on the conceptual study conducted by Hatch in 2017 and on the experience accumulated from mining activities on site since 2016. It will follow a two-stage approach. Phase 1 is a Feasibility Study to deliver an AACE Class 4 cost estimate and is expected to be completed by early July 2018. Phase 2 will deliver a BFS including an AACE Class 3 cost estimate and is projected to be completed by the end of 2018.

Avenira has been involved with Baobab since 2014 and successfully achieved its first production in September 2016, just 10 months after the decision to mine was taken. The mine operates under a Small Mine Permit (SMP) which currently covers 5 km2 and allows unlimited production from the Gadde Bissik prospect. Open-pit, free-dig mining operations are undertaken by a mining contractor.

The current plant, which has a nameplate capacity of 500 kt/a, was commissioned in August 2016. The mineralogy of the deposit is straightforward with well-defined silica and apatite grains enabling beneficiation to a high-grade commercial concentrate to be achieved using well-known and widely applied flotation technologies.

The project’s indicated mineral resource is now estimated at 42 Mt at 19,4 % P2O5 at a cut-off grade of 10 % P2O5, with the inferred mineral resource estimated at 320 Mt at 16 % P2O5, also at a cut-off grade of 10 % P2O5.

The expansion and upgrade project will include a flotation step and a magnetic separation step to improve P2O5 recovery from around 50 % currently to approximately 70 %, to reduce the silica assay and to control iron levels in the concentrate, as well as a drying process unit to control product moisture at the commercial target at all times, annual wet season included. The 2017 conceptual study estimated (to a ±30 % accuracy) that the project would involve an upfront capital expenditure of US$53,4 million.

The magnetic separation step will ensure that Fe2O3 content meets customer requirements. Magnetic separation test work has been carried out on both rare earth dry roll and on wet high-intensity technologies at Eriez Magnetics Central Test Laboratory in Erie, Pennsylvania in the US, with both types of processes achieving effective separation of ferruginous particles from the rock concentrates at the laboratory scale.

The flotation step will reduce the SiO2 in the concentrate to the levels required by customers. Extensive laboratory scale flotation tests have been performed in Florida and have demonstrated at that scale that the target separation performance can be met by reverse flotation of silica (SiO2) using amine-based reagents.

Current testwork includes on-site bench scale flotation testing using actual mine water on various samples extracted from the Gadde Bissik open pit, plus settling and dewatering tests of tailings and final concentrate product by process technology suppliers. Large samples of coarse and fine flotation feed material have also been prepared for upcoming pilot scale flotation runs for technology selection.

Comminution testwork has been performed at FLSmidth’s Minerals Testing and Research Centre in Salt Lake City in Utah in the US to evaluate the hardness and abrasiveness characteristics of the larger rock sizes in Baobab’s ore from the Gadde Bissik mine and provide data for crushing and milling equipment selection and design.

A number of appointments have been made to support the BFS. Ibrahima Gaye, a phosphate industry professional with over 35 years of experience in phosphate mining and beneficiation in Senegal, has joined the Baobab project team while Glenn Gruber, a phosphate beneficiation specialist with over 45 years’ experience in industrial minerals has joined the Wood team for the BFS as process expert. In addition, consultant Henry Lamb, a geologist with 40 years’ experience in the mining, geology and exploration of phosphate deposits and the operation and maintenance of phosphate mineral projects in the US and internationally, is actively supporting the BFS work.

Photos courtesy of Avenira

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