When Kleber Silva visited the Moanda mine for the first time in March 2018, he was surprised to see residual ore on some of the sites. "Too rocky to be processed with our current facilities," he was told. "No stone shall be unturned," he responded. Not wanting to waste the resource, the new head of the Mining & Metals Division suggested using dry screening to extract this part of the deposit. The project arose during a period when manganese ore output was growing: at three to four million metric tons a year at the time, it was on track for six tons in 2020 and seven soon after. It was also hoped that the project would relieve congestion in the washery, which was running at nearly 100% capacity. "Utilizing the hardened ore was a necessity," says geologist Raphaël Pacta.
“No stone shall be unturned“
At Comilog, production records never last long. This is thanks to the team led by Christophe Minguy, the manager of the mine, along with the constant improvements in industrial techniques. Dry processing was one of them. Until 2018, the hardest ore at Moanda was left untouched due to its physical characteristics: its facies had become too hardened by contact with water over the course of more than two billion years of geological evolution on the Haut-Ogooué plateaus. Operations focused mainly on the conventional, clay-like ore, which was highly abundant. While the ore was indeed high-grade (on the order of 30%), it needed to be concentrated by eliminating the clay and non-mineral matter, using a sophisticated mineralurgical transformation process performed at the Moanda washery (which scrubbed and sorted the ore by grain size). At the end of this process, the manganese content reached 46%, sometimes more...which boosted the market value of the manganese by 40%.
A young team and an old sorting screen
Alexandre Pires Guedes, the newly appointed Head of Operational Excellence at the Mining & Metals Division, was tasked with overseeing the project. Drawing on his experience in direct shipping ore from an iron mine in Liberia, he put together a formidable team: Michel Cormary at the DAI; several operational employees at Moanda, including Thibaut Martin, then Equipment Maintenance & Operations Manager, who had just started work on the edges of the plateau; Flore Mouele, who allocated one of the bedding plant areas for the mineral crushing process; Jeff Madouma, the future dry-processing manager; and Firmin Lassanana at Industrial Maintenance.
The CMM provided a screen that was no longer in use, which the team utilized for a test two months later to demonstrate the feasibility of dry processing. Once up and running, the old screen rattled and groaned, but it did the job. Production hit 50,000 metric tons in just a few months—then 500,000 in 2019.
Launching the industrial phase
Dry processing quickly lived up to the lofty expectations placed on it. The decision was made to move on to industrial-scale production. Roberto Rodriguez, Head of the Geology & Mining Department, went to work on it with Brice Mabicka, now at the Kouaoua mine in New Caledonia; Latyr Guéyé, Operational Excellence Manager; and the rest of the team. With the team in need of heavy equipment, crushing machines and mobile screens were immediately ordered from Ireland, while personnel underwent training.
Speed was required in order for Comilog to meet its goal of becoming the world's top manganese producer. On December 14, 2018, an Antonov 124-100, the world's second-largest cargo plane, with a carrying capacity of 100 metric tons, landed at Mvengué Airport, 30 kilometers from Moanda. On board were two Sandvik mobile screens, each one 32 tons and 18 meters long—which creates significant overhang. "We dealt with several challenges: we had to perform a series of maneuvers to get the equipment onto flat ramps and hydraulic trailers, and build an unloading bank at the end of the airport," remembers Chris Grigentin, our partner from Bolloré Logistics. Huge mats were laid out on the tarmac so that the crawler requisitioned to transport the screens didn't damage the runway. It traveled at 4 km/hr. Roger Endamne and Ulrich Nkazengani Ongonwou from Purchasing still smile when thinking about it, and are grateful to Gabonese officials for allowing the Antonov to land at the airport in Franceville. The governor of Haut-Ogooué was there in person, along with Léod-Paul Batolo, CEO of Comilog, who had supported the project from the outset. Shortly thereafter, the A124-100 made two other trips from England to drop off the crushing machines one by one. At 53 and 46 metric tons, the two machines were bulkier and much heavier than the screens. Two more arrived by sea in 2019, before boarding a train to Moanda operated by Setrag. The lengthy, 606-km journey would later be repeated by a third screen in late June.
More than 30% of production from dry processing
Dry processing has been incorporated into Comilog's production strategy, with a production target of 1.3 million metric tons by 2020, in addition to the 3.8 million tons produced through wet processing. Jeff Madouma, a dry-processing engineer, explains: "We're turning a previously untapped portion of this resource into a commercial product, without needing to wash it!". With this experience under their belts, it was nevertheless decided to supplement the process with modular washeries, in order to go further by tapping into all of the manganese contained in the hardened ores.
On site, the hardened ore, renamed "MVS" or "Minerai Voie Sèche" (dry-processed ore), is sometimes so hard that it takes a hydraulic rock-breaker to break up the slabs and mineral masses. "No stone shall be unturned," reiterates Kleber Silva constantly. The small pieces of "rocky" ore are transported on 100-ton dumpers to one of the two crushing/screening lines, which they emerge from in three piles and three sizes. In terms of characteristics, the new product is close enough to MMD that it can be mixed with it. Excavators are used to load the product onto a fleet of trucks, which either take it to the conveyor belt in the washery, or travel along a seven-kilometer road to a storage area close to the Moanda station, which was built in September 2019 to deal with the large volume of ore that needed to transported. This process has created a number of new jobs, particularly for drivers, as the operating model chosen for dry screening relies greatly on outsourcing this service and developing a local industrial base. Comilog maintains control thanks to Jeff Madouma (Quality), Ephrem Dibangoye, and Judicael Atchoungou (Maintenance Methods). Security is a major logistical concern.
Wild animals and water management
As seen from a topographic drone, the two crushing/screening lines resemble gigantic insects, whose red color contrasts sharply with the almost-black manganese. They are installed near the rim of the Bangombé Plateau, just before it drops off over the "edges" toward the highway and the city of Moanda.
These edges have been mined since 2015, initially using wet processing. They contain copious amounts of hardened mineral masses, also created by water, which is abundant here. The dry-screening technique is well-suited for this type of deposit. In this region, environmental and societal concerns are the biggest challenge. Maryse Kanga Mouyendi, an environmental engineer who worked on the plateau edges before being appointed as the mine's HSE Manager, explains: "We imposed three requirements on ourselves: to preserve the talwegs, the gallery forests, and the waterways." These areas are biodiversity hotspots that are home to wild animals such as antelopes, pangolins, porcupines, dwarf buffalos, mandrills, guenons, and panthers. As with every mine, water management is essential. Structures have been installed to clarify runoff water, before letting it return to its normal course. Similarly, sampling points have been set up to prevent contamination in the water.
Working with the neighboring communities
The plateau edges are part of the Comilog concession. For a long time, there was no mining activity in the area, which led numerous families to settle in, build homes, and cultivate home gardens. The men used the local waterways to fish, while the women washed cassava plants, an ancestral crop. The proximity of these communities, and the arrival of mining activity on the site, are a major societal issue.
That is where the CSR team led by Steve Wilson came in. In March 2017, an initial information campaign targeting officials and local residents was launched to explain the mining operations around the plateau edges, whether they involved wet processing or dry processing. Later, with the support of country officials, a socio-economic survey and an inventory of homes and farming plots were taken with the help of a specialist company, in accordance with the highest standards of the International Finance Corporation. To give the neighborhood committees and the departmental committee time to get together and liaise between Comilog and the affected populations, operations began in an area far away from any homes.
A can-do attitude
At Comilog, dry processing was added to wet processing thanks to a pragmatic investment. The teams responded with agility and speed, demonstrating a can-do attitude which, in the end, creates value for all stakeholders of the company. The entire geological profile is now exploitable, which has allowed Comilog to set a dry-screening production target of 2.3 million metric tons by 2021—32% of its total production.
A similar approach is already being launched for the Okouma plateau...