Bluhm Burton Engineering (BBE) Projects has commissioned another turnkey surface refrigeration plant at Société des Mines de Loulo (SOMILO) SA gold mine in Mali, West Africa. The Loulo gold field, which includes the Gara, Yalea and Gounkoto deposits is less than 2km east of the border with Senegal (marked by the Falé river) on the West Mali gold belt. The refrigeration plant as well as other infrastructure will enable the mine to expand its operations and maintain its gold production output.

Client background

Société des Mines de Loulo (SOMILO) SA is an exploration and mining company and the owner of the Loulo gold mine, which in turn is owned 80% by Barrick Gold and 20% by the state of Mali.

Gold potential was first recognised by Syndicat Or joint venture between the Malian Direction Nationale de la Géologie et des Mines and the French Bureau de Recherches Géologiques et Minières (BRGM). The Gara gold deposit was discovered in 1981 by the Syndicat Or joint venture. In 1992, BHP Minerals Mali entered into an agreement with Société des Mines de Loulo for a joint venture that developed the Gara deposit into a Mineral Resource that was deemed sub-economic at the time.

During 1996, Randgold Resources acquired BHP Minerals Mali and undertook additional regional exploration, which resulted in the discovery of Yalea in 1997, the second of two deposits that make up Loulo Mine. In 2003, a feasibility study was undertaken at Loulo on a 12 Mt at 3.60 g/t Au for 1.4 Moz Ore Reserve, which led to the construction of an open pit mine in 2004. Production from Loulo mine started in 2005 as an open pit operation. The Loulo underground mine passed through the feasibility study stage in 2005, with development beginning in 2006. The first gold produced from Yalea underground was in 2008 and Gara underground in 2011.

Randgold Resources merged with Barrick Gold in 2018/2019. This mega-merger created the world’s biggest gold miner by market capitalisation. The merger was required to pool the companies’ resources to stay competitive in the industry.

The challenge

After commencing with open pit mining in 2005, the mine took the opportunity to start looking at mining underground. Underground mining at Loulo mine is relatively shallow, but being at low altitude in an equatorial region, the mine experiences a challenging climate of both humid and hot, through the various seasons, particularly when hot and humid occur at the same time, which is for most of the year.

These challenging climate conditions necessitated the turnkey construction and commissioning of a refrigeration plant at both Gara and Yalea dedicated downcast ventilation holes, in 2016, to cool the underground workings. Since 2016, both the Gara and Yalea underground mines have expanded production towards the south requiring further underground cooling.

The solution

An independent mine ventilation consultant prepared and issued an enquiry on behalf of SOMILO for a turnkey contract to build a 14MWR refrigeration plant at both Gara and Yalea dedicated downcast ventilation holes, in 2015. The BBE tender covered all technical, commercial and statutory requirements laid out in the enquiry documents and BBE Projects was awarded the turnkey contract by means of competitive tender, after a few rounds of technical and commercial queries. During the execution of the project, BBE Projects carried out detailed design, procurement, manufacturing, quality control, shipping, delivery, construction, erection, installation, supervision, project management, commissioning, testing, certification and hand-over of the refrigeration plants.

In a similar manner, SOMILO awarded BBE Projects a second turnkey contract to build a refrigeration plant at the Yalea South dedicated downcast ventilation hole in 2021. This time SOMILO requested that all equipment supplied by BBE Projects must be compatible and interchangeable with the existing refrigeration plants to minimise spares holding and to allow the mine to implement the same corrective and preventative maintenance schedules used at the existing plants.

The new refrigeration plant capacity is 8MWR and is smaller than the existing refrigeration plants, but with space reserved and design provisions made to expand the refrigeration system in future if required. The new refrigeration plant also has many improvements compared to the existing plant. These innovations were brought about during meetings and consultation with mine employees that maintain and operate the refrigeration plants.

The most notable innovation is the five-metre diameter steel inlet duct that connects the bulk air cooler to the dedicated downcast ventilation hole complete with a self-closing door positioned directly above the shaft to relieve shockwaves that occur during certain times of day due to blasting underground. The damper blades are of a relatively light construction allowing the blades to open with little pressure and close using adjustable counterweights.

The refrigeration machine is an 8MWR dual-compressor York YD with R134a refrigerant, housed in a plant room erected from steelwork that was designed, shop detailed and fabricated in South Africa. Dual compressors were selected to halve the maximum instantaneous start-up current of the refrigeration machines thereby mitigating the possibility of de-stabilising the mine’s power grid. The mine generates its own power by means of diesel generators and solar plants on site for mining operations.

The Bulk Air Cooler (BAC) is adjacent to the plant room, minimising interconnecting piping and thermal losses. The BAC basin is constructed from reinforced concrete with insulated panel side walls and roof to speed-up construction time, reduce time spent working at heights and increase thermal efficiency of the spray chamber. Similarly, the Condenser Cooling Tower (CCT) used for heat rejection is constructed from lightweight Fibreglass-Reinforced Plastic (FRP) components with similar benefits in cost, time and safety. Furthermore, FRP is a good alternative to concrete because of its high strength, lightweight and stability.

All civil, structural, mechanical and piping works were carried out by local contractors in line with the mine’s commitment to drive socio-economic development and training. Site construction, erection and assembly was supervised by BBE Projects with regular inspections by discipline specific engineers from BBE and OEMs.

Equipment for the refrigeration plant was sourced and shipped from all over the world. CCT fans and electrical motors from Brazil, FRP CCT structure and header piping from India, FRP CCT fan stacks from Poland, CCT gearboxes from Belgium, FRP CCT Cladding from Turkey, refrigerant from Dubai and the refrigeration machines from USA. The balance of the mechanical equipment (pumps, plant room crane, valves, piping, fasteners, etc.), EC&I equipment (transformers, MV Switchgear, MCC, cables, instrumentation, etc.) and civil material and structural steelwork (rebar, plant room steelwork, shaft inlet ducting, pipe supports, etc.) were consolidated and shipped from South Africa.

The construction of the refrigeration plant also came with a unique set of challenges such as changing the shipping route from Dakar port to Guinea port midway through the project because ECOWAS (Economic Community of West African States) imposed sanctions on Mali. Other challenges included delays due to storms at Durban port, and a major supplier going into liquidation (fortunately only near the end of the manufacturing process).

The result

BBE Projects is currently working on the Gara South Refrigeration plant that will be commissioned later this year, and the project is on track for completion in the third quarter of 2023. Once complete, the refrigeration system will enable mining in the largely untapped southern area of the orebody, extending the life of mine significantly.

By Admin

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