GOLD AND PRECIOUS METAlS — High River starts feasibility study at Taparko

Tougouri, Burkina Faso — Having drilled-off a substantial gold resource at its Taparko project in this hot, dry region of West Africa, High River Gold (HRG-T) is ready to start designing a mine.

The company, which came to Taparko, 180 km northeast of Ouagadougou, in 1994, has held to a philosophy of bringing known prospects to the development stage. Taparko, with a 9.8-million-tonne resource grading 3.4 grams gold per tonne, is now ready for full feasibility.

The property is covered by a Mining Investment Agreement, a combined exploration and mining licence that has a 25-year term beginning in August 1996 (two 10-year extensions are provided for as well). High River has a 61.5% share in the project, privately held Canadian firm Incanore Resources holds 18.5% and the Burkina Fasan government retains 20%.

High River completed its US$5.9-million financial obligation to the project in November 1997, and each of the three partners now has a participating interest. The government is reducing its stake to a 10% carried interest plus a 3% royalty.

The showings at Taparko were discovered in 1980 by the government mining agency of what was then known as Upper Volta. A 1981 soil survey outlined three zones of gold enrichment in surface soils, and consultants financed by the World Bank did some initial drilling on a showing later named the GT zone.

The Taparko greenstone belt lies at the junction of three granitic blocks, so it is Y-shaped, with northwestern, northeastern and southern limbs. A major regional structure, the Markoye fault, strikes northeastward through the southern and northeastern limbs of the belt. Satellite imagery and VLF electromagnetic surveys have traced the main fault for at least 180 km.

A conjugate northwesterly striking shear system intersects the Markoye fault near the north end of High River’s property. This structure, christened the Taparko shear zone, is the principal control on the gold mineralization. It runs through a septum of tuffs and sedimentary rocks and dips about 40 to the east.

The metamorphic grade in the area is relatively high — lower amphibolite facies — and most of the rocks are amphibolites and tuff-derived schists.

The principal host rock is a banded quartz-feldspar schist, though some veins occur in granodiorite.

The gold is in quartz veins that strike slightly west of north and dip 45 to the east. The best grades occur in shoots in the veins plunging about 45 to the north. The system has been traced on surface for 6 km, and includes 10 surface showings; three of the showings — Zones 3 and 5 and the GT zone — have been drilled in enough detail for a resource estimate, on 20- to 40-metre spacings.

When unweathered, the quartz veins hold about 2-3% pyrite, plus trace amounts of chalcopyrite, galena and arsenopyrite. In the oxide zone, the quartz veins form ridges in the softer saprolite and laterite. The oxide zone typically forms a 20- to 30-metre cover over the unweathered rock.

Early metallurgical tests showed 97% recovery is possible using direct cyanidation. Most of the gold is fine-grained and about 80% is free.

High River estimated the resource in all categories at 9.8 million tonnes grading 3.4 grams gold per tonne. That figure can be divided into indicated and inferred resources for each of the three zones: the GT zone holds an indicated 1 million tonnes grading 4.9 grams plus an inferred 1.1 million tonnes grading 4.3 grams; Zone 3 holds an indicated 600,000 tonnes grading 3 grams and an inferred 2.2 million tonnes grading 2.9 grams; and Zone 5 holds an indicated 1.2 million tonnes grading 3.1 grams and an inferred 3.6 million tonnes grading 3.2 grams gold.

High River’s mining plan envisions open pits and heap-leach extraction facilities, for a total estimated capital cost of US$25-30 million. Annual production has been estimated at 90,000 oz. gold at cash costs of US$150 per oz. Preliminary pit limits estimate stripping ratios of between 4-to-1 and 5-to-1.

The mineralized zones are generally wider at depth in Zone 3, though this does not carry over to Zone 5. In Zone 5, however, the zones are wider than in Zone 3 or the GT Zone.

Rescan Engineering and Steffen Robertson and Kirsten are now carrying out a feasibility study to verify the company’s projections. The feasibility study, scheduled for completion in the last quarter of 1998, has a budget of US$1.9 million. The program includes 4,250 metres of infill drilling to confirm the resource, another 1,100 metres of drilling to provide samples for metallurgical testing, and pit design and analysis.

Visual grade control could not be trusted in the oxide material. “You’d have to assign assay limits,” said Driffield Cameron, High River’s vice-president of exploration. Limiting the project to the oxide resource, with the lower capital costs of open-pit mining and heap leaching, makes it possible for a smaller company like High River to get its arms around the project. Said Cameron, “That’s why we’re not looking at the underground potential on Zones 3 and 5, because that’s not in the picture for us.”

High River is also planning an exploration program on the other showings on the Taparko shear comprising 2,450 metres of drilling and 50 long surface trenches. The company also has plans to drill four other targets revealed by reconnaissance soil sampling. For that work, High River has earmarked US$2.8 million.

Orientation geophysical surveys over the known mineralization showed VLF electromagnetic surveys were useful in mapping large structures, while induced polarization and resistivity were better direct indicators of mineralization.

Soil geochemistry, which proved itself in the original reconnaissance of the area, will still form the backbone of the exploration program. High River plans detailed soil surveys over the new showings, on 20-by-50-metre grid intervals.