GOLD POTENTIAL OF THE LIPTAKO BELT SOUTHWEST NIGER, WEST AFRICA

TOM BELL

BHP WORLD METALS

JUNE 1988

SUBMITTED TO MINISTRY OF MINES AND ENERGY, REPUBLIC OF NIGER

DECEMBER 1988

SUMMARY AND RECOMMENDATIONS

The Liptako is the northeastern limit of known Birimian age rocks which host the well known gold deposits of Ghana. Birimian age volcanic rocks are exposed in three main schist belts which are elongate in a northeast-southwest direction. The dominant lithologies are flows and pyroclastics of basaltic, basaltic-andesitic, and andesitic composition.

Exploration to date has consisted of prospecting by local miners, a regional minerals inventory by the BRGM just prior to and immediately after independence, and a small aid project sponsored by the Canadian Governmbr /ent to prove the potential of two of the anomalies discovered by the local miners. The local miners have been the most successful at exploration so far, locating at least 22 anomalies, 13 of which are still being mined by primitive methods. Most of the known anomalies are in the eastern most belt of Birimian volcanics called the Sirba River Schist Belt.

Styles of mineralization are diverse, including quartz-sulfide veins and stockworks in highly altered felsic alkaline intrusions, mineralogically simple quartz veins in altered pyroclastics, quartz-sulfide stockworks in altered pyroclastics, quartz-sulfide veins in contact metamorphic zones, and mineralized shear zones in flows and pyroclastics.

Mineralization consists of quartz-iron carbonate-sulfide-sericite assemblages with significant arsenic contents. Alteration halos are narrow in the shear zone types, wide in the simple quartz vein types, and pervasive in the stockwork types. The richest and potentially largest anomalies are the stockwork types in pervasively altered pyroclastic rocks.

Supergene enrichment and depletion have redistributed much of the gold in the ferrilitic weathering environment. Most of the anomalies are kaolinized by acid leaching of the highly pyritic host rocks. Coarse gold in the shallow sub-surface is common in most of the known anomalies. Reports by local miners consistently point to surface enrichment of coarse-grained gold, in a barren interval immediately below the surface enrichment zone, and a gradual increase in grade as the water table is approached. Pilot studies of this phenomenon are essential before sound conclusions can be drawn about the magnitude and significance of each anomaly.

The Sirba River Schist Belt has the greatest potential for gold mineralization of the three schist belts and should be requested for a Type A reconnaissance license in its entirety. Map 3 shows the proposed boundaries of the license.