AFRICA — Orezone cuts gold at Intiedougou — Magnetics, radiometrics useful in mapping host rocks

Drilling at the Intiedougou property in western Burkina Faso has uncovered promising gold mineralization in unweathered rock below known oxidized gold mineralization.

Tropical weathering in West Africa typically produces a profile of laterite — a hard, iron-rich soil — atop a soft, clay-rich saprolite. The saprolite can be tens of metres deep before it is succeeded by fresh silicate rock.

When rocks weather, the zones of gold mineralization they enclose weather, too. In the lateritic and saprolitic zones, oxide mineralization generally consists of free gold associated with iron oxides; at depth, in the fresh rock, it gives way to the gold and sulphides typical of Precambrian gold deposits elsewhere in the world.

Intiedougou is no exception, and now a program of diamond drilling has revealed gold and sulphides in the unweathered rock below a zone of oxide mineralization.

Orezone Resources (ORZ-M) and Geomaque Explorations (GEO-T) each are earning a 37.5% interest in the project by making a total of US$190,000 in cash payments and by performing US$2 million in exploration work over four years.

The two partners can acquire the remaining 25% for US$1.5 million. A 3% net smelter return also applies to the property, and three-quarters of that royalty can be bought for US$1.5 million.

The project’s first four diamond drill holes have indicated gold mineralization in unweathered intrusive and volcanic rocks, associated with disseminated sulphides. The most significant result was a 158-metre intersection with an average grade of 1.5 grams gold per tonne in hole 97-01; included in that was a 61.9-metre interval grading an average 3 grams per tonne. The hole was stopped in mineralization when the driller ran out of rods.

Three other holes also intersected the mineralized zone, with 97-04 cutting a 36.7-metre zone grading 1.1 grams gold per tonne; the lower two-thirds of the intersection was in unweathered rock. Three other narrower zones, all deeper in hole 97-04, returned grades of 1 to 1.7 grams.

A 13-metre intersection in 97-02 graded 1.5 grams near the top of the unweathered bedrock and an 11.9-metre intersection in 97-03 graded 1.8 grams in saprolitic material.

The last three holes in the program appear only to have intersected upper parts of the sulphide zone and Orezone plans to test the zone again with more drill holes.

Orezone had already outlined a zone of oxide mineralization in two earlier campaigns of reverse-circulation drilling, one comprising 72 holes and the other, 52. The mineralized oxide material has an average grade of 1.8 grams gold per tonne. It has a strike length of 250 metres and an average width of 45 metres.

The weathered zone ends at depths around 16 metres, giving way to fresh rock with very fine-grained disseminated sulphides — mainly pyrite, with some arsenopyrite — and some visible gold. The mineralization appears to occur on the intrusive contact between a syenite prophyry and an andesite unit.

Magnetic maps have allowed Orezone to outline the andesite unit, which may allow other targets along the contact to be tested.

The syenite porphyry also has a geophysical signature. Abundant potassium in the feldspar shows up on radiometric maps, which makes it possible to outline areas that may be underlain by the porphyry and compare their distribution with the andesite.

Part of Orezone’s recipe has been a check-assay program to confirm the results of the drill program. Fortunately, Burkina Faso has two laboratories owned and operated by groups well-known in Canadian mining circles. The routine fire-assay analyses have been done by Intertek, part of the Inchcape-Bondar Clegg group, and check analyses have been run at a lab operated by Calgary-based Loring Laboratories. Orezone is satisfied with the correlation between the results from the two labs.

The next set of drill targets will be selected with the aid of an induced-polarization survey, which should be able to detect the disseminated sulphides in the unweathered rock at depth. Regional-scale soil geochemistry is also scheduled, to assess other targets where coincident radiometric and magnetic anomalies suggest the syenite and andesite are in contact.