Semafo leaches Mana gold

Results from bottle-roll tests suggest the Wona and Nyafe oxide gold deposits in Burkina Faso are amenable to heap leaching, reports Semafo (SMF-T).

Wona and Nyafe are two of three deposits that make up the Mana project. The other, Maoula, sits 3 km south of Nyafe and has been traced for 600 metres along a northeastern strike, though it remains open at both ends, as well as at depth.

Ninety-one samples were taken from the Wona structure, each representing about 5 metres of reverse-circulation cuttings, starting at a depth of 7 metres and ending at 70 metres. Recovery rates varied from 86% to 98%, for an average of 93%.

X-ray diffraction tests on the cuttings show the presence of iron oxides and hydroxides (goethite and hematite), as well as the aluminum silicates muscovite and kaolinite.

From 23 Nyafe samples was extracted an average of 80% of the contained gold; however, individual recoveries varied from 5% to 87.2%, reflecting the presence of arsenopyrite in places. Gold grades varied from 0.86 to 21 grams per tonne; silver, from 1 to 31 grams; arsenic, from 2.8 grams to 1.6%; and iron, from 5% to 9%.

Samples from each structure were collected from holes drilled in 2002.

Metallurgical and mineralogical testing continues.

In late 2001, Semafo pegged Wona’s indicated resource at 3.5 million tonnes grading 2.38 grams gold per tonne, using a cutoff grade of 0.5 gram gold. Of the total resource, 1.8 million tonnes of oxide material run 2.45 grams gold; the remaining 1.7 million tonnes of sulphide material average 2.31 grams gold. The oxide resource has an average depth of 60 metres.

Mineralization, which has been traced over a strike length exceeding 2.4 km, is hosted by highly deformed acidic tuffs that dip steeply eastwards. Silicification and quartz-veining are common.

At Nyafe, which lies 8 km to the south, Semafo has outlined an indicated resource of 850,000 tonnes grading 8.44 grams gold per tonne. The deposit is associated with a major fault zone and is hosted by altered mafic schists interbedded with massive andesitic lavas. Here, quartz-veining is common as well.

Semafo has a 95% interest in the Mana property, 200 km west of the capital city of Ouagadougou. The junior also explores elsewhere in the country and throughout West Africa.