Sahelian Goldfields pours first gold — Rehabilitation of Poura mine well under way

The 160-oz. gold bar poured May 7 at the Poura mine, in west-central Burkina Faso, won’t rock the gold market, but it represents an appropriate milestone on a long road back.

For Sahelian Goldfields (SHGI-C), the Toronto-based junior that has taken on the job of bringing Poura back into production, the pour is a welcome sign that the dormant mill is on its way to rehabilitation.

The gold came from 700 tonnes of stockpiled ore fed to the operating part of Poura’s mill, the gravity circuit. A flotation concentrate was also produced but will not be further processed until the mill’s cyanide circuit is back in operation.

For Burkina Faso, the pour marks the return of an important employer and foreign-exchange earner, whose absence hit this West African country’s economy hard.

The mine was operated between 1981 and 1995 by Soremi a company owned partly by the government of Burkina Faso and partly by the French government agency Bureau de Recherches Gologiques et Minires. The mine produced 600,000 oz.

gold before high costs forced it to close. “They were trying to make tonnage, and they were getting the tons and losing the grade,” said Peter Bojtos, a Sahelian director. The government, anxious to get gold production of 60,000 oz. per year back into Burkina Faso’s GDP, directed its mining agency to find a partner to get Poura back on its feet.

In March 1995, Soremib dealt an option to earn 90% of Poura to International Gold Resources, which committed to spend US$7.5 million on development work.

IGR brought in Echo Bay Mines (ECO-T), which was to earn a 45% interest in Poura, but Echo Bay, which had its own problems, subsequently dropped out.

Following an approach from IGR, the European Union’s mineral development agency, SYSMIN, came on board, issuing a grant of US$13.3 million for upgrades to the mine and equipment and for additional mine-site exploration.

Then Ashanti Goldfields (AHD.U-T) took over IGR, inheriting the development agreement.

Ashanti, with plenty on its plate already, dealt the option to Sahelian in exchange for 3 million Sahelian shares and 2 million warrants. The major also placed a representative on Sahelian’s board.

The task facing the company is to rehabilitate Poura’s mill, upgrade the hoist and bring in some new mine machinery. Under Soremib, the operation was under-capitalized and equipment was allowed to deteriorate. At the time of The Northern Miner’s visit, Sahelian had a jumbo drill on order, and was expecting to take delivery a few weeks later. In the meantime, drift development was being done entirely with jackleg drills. The shaft was also out of service, with a decline providing access to the workings.

Bojtos estimated the cost of returning the shaft to service at about US$1 million; the electric motor, apart from requiring a new drive shaft, was in good condition and the conveyances and headframe were sound. The hoist rope needed replacement, and work had to be done on the base of the shaft.

Under the terms of the SYSMIN grant, any capital equipment has to be new, not used, and must be bought from European Community countries or from member countries of the Lom Agreement, a development accord among French-speaking countries of West Africa. Consumables, which the grant will cover whatever the source, are generally bought in nearby Ghana.

The gold at Poura is in a nearly vertical quartz vein, the Filon Plaine, running northwest through a package of Birimian (early Proterozoic) volcanic and sedimentary rocks. A few subsidiary veins, at very shallow angles to the Filon Plaine, carry minor amounts of gold. Most of the ore zones form shoots in the vein that plunge moderately to the south.

Soremib mined about 2 million tonnes of ore grading 12.8 grams gold per tonne before operations shut down. Some came from a pair of shallow open pits, but the greater part was mined underground. About 500,000 tonnes of mineralized material remains in pillars, and Sahelian regards about 423,000 tonnes grading 10.8 grams as recoverable.

The vein, which expands to 8 metres in places and pinches to 1 metre in others, is actually a complex of several generations of veins. The principal mineralization is in ribbony veins that have 2-3% sulphides, but there are at least three other vein types, some of which are mineralized. Previously, shrinkage and longhole mining methods were used, but for remnant mining Sahelian will turn to cut-and-fill methods that will permit pillar recovery around old open stopes.

In new zones, longhole stoping should be practical at widths of 2.5 metres or more, with shrinkage being used elsewhere. The gold grade tends to drop below the mine’s cutoff when the vein pinches to less than a metre in width.

Ground conditions are generally good below the zone of weathering, and additional development at lower levels will provide some backfill. Bolting has not been used extensively in the mine.

Remnant mining is one thing, but Poura’s future depends on building up reserves. Since the structure is steeply dipping, and mining has extended only to a 300-metre depth, Poura has plenty of areas that show potential to add to reserves.

A number of down-dip extensions of known zones have not been tested.

Sahelian has concentrated its efforts on a drift at about the 300-metre level in the southern part of the mine. There, it is thought that mineralization may exist down-plunge from ore shoots on higher levels.

Completion of the drift from the south workings, near the shaft, across to workings at the same depth in the central part of the mine, will give Sahelian some idea of the available resource between 200 and 300 metres below surface.

A second target lies immediately below the northernmost open pit, where the Filon Plaine has not been drilled off. There, a number of shoots at upper levels of the underground mine are open and potentially connect to the old ore zones of the pit. “I’m really hoping for something out of this north end,” said Bojtos. “The whole north area is virgin territory as far as I’m concerned.”

Sahelian’s planned modifications to the mill start with material handling — in the present configuration, front-end loaders carry ore from the shaft collar to the gyratory crusher. Adding a conveyor and grizzly will mean steady feed for the crusher.

In the mill itself, the grinding circuit feeds two jigs and a table concentrator, with tailings returned to a ball mill and fed to a bank of flotation cells. The gravity circuit recovers about 40% of the gold.

The flotation concentrate goes to cyanide leach and thickener tanks, then the gold is adsorbed by carbon-in-leach, desorbed, and electrowon. One quirk in the mill design is an amalgamation unit that strips gold from the cathode; the amalgam is then smelted, though the cathode could be smelted directly.

Under the current redesign plan, the flotation circuit will be streamlined, and concentrates will go directly to a thickener and then to a carbon-in-pulp circuit in three Pachuca tanks for a 24- to 48-hour leach.

Surrounding the 11.5-sq-km mining concession, the Poura exploration permit area, 500 sq. km in size, sports a collection of prospects with similar geology to the Filon Plaine. The main structures in the area are shears that strike roughly north-south. Some are as wide as 20 metres.

Immediately north of the mine, three prospects were tested by the previous operator. To the east, a set of four soil anomalies are known and to the southeast, there are large areas with artisanal gold mining activity.