Mano River returns to Sierra Leone

With Sierra Leone’s 10-year civil war formally declared over, and a United Nations force preserving the peace, Mano River Resources (MNO-V) is relaunching its prospecting program on three diamond exploration licences in the country’s interior.

The three licence areas, about 400 km east of the coastal capital city of Freetown, are adjacent to the Koidu kimberlite system, which has been mined periodically since the 1960s. The Koidu pipes have an average grade of 0.35 carat per tonne, and rough stones run an average US$200 per carat. Existing resources are believed to be on the order of 7.5 million tonnes.

The Koidu pipes are part of a kimberlite dyke swarm that Mano, based on its interpretation of Landsat satellite imagery, believes extends on to Mano’s Yengema and Njaiama-Nimikoro properties, and potentially southwest on to Nimini. The three properties cover the area to the southwest, where deeper levels of intense tropical weathering have previously hampered exploration for bedrock kimberlites.

Yengema, a 103-sq.-km property, is immediately west of the Koidu property. Yengema and the area around the Koidu pipes have long been centres of alluvial diamond mining, both by local craft miners and by larger-scale commercial operations. The areas produced about 9 million carats up to 1969. Small-scale alluvial diamond mining in the immediate Yengema area has produced diamonds that are distinct from the Koidu stones, suggesting that another bedrock source exists in the Yengema drainage area.

Njaiama-Nimikoro, a 103-sq.-km property immediately south of Yengema, is immediately up-drainage from alluvial diamond deposits at Kono on the Yengema property. The town of Njaiama is another centre of alluvial mining, and its diamonds (which can be highly coloured) are distinct from Yengema’s, suggesting a source somewhere along the strike extension of the Koidu dyke system, northeast of the property.

The 54-sq.-km Nimini concession lies west of Njaiama, covering a hilly area that drains eastward on to the other two concessions. It also includes an area where the southwest-striking fracture system, which hosts the Koidu dykes, meets a north-striking shear zone. Diamondiferous kimberlites are known to exist along the length of the shear zone, and Mano River geologists think potential structural weakness near the intersection of the two fault systems may allow kimberlites to intrude.

Kimberlite indicator minerals have been identified in three areas on the Nimini concession: Jopowahun, Njagbema and Konda. Konda also has some alluvial diamond workings.

Mano River plans stream sediment sampling in March and April, to identify heavy minerals characteristic of kimberlite in the stream sediments. The company expects to rely on geological mapping and heavy mineral sampling in stream sediments to locate targets, and will follow up with ground geophysics over possible kimberlite bedrock. Later, the company will trench the geophysical anomalies.

The strategy is identical to the one it used last year on its Kpo concession in Liberia, where it discovered six kimberlites, three of which proved to be diamondiferous.

The Kpo kimberlites were discovered after a 2-month sampling program in 2000. Heavy mineral concentration on stream-sediment samples returned large quantities of chromite, with garnet, chrome diopside and ilmenite. Electron microprobe analyses revealed the chromites were of the same high-magnesium, low-titanium type found as inclusions in diamond, and that the garnets were low-calcium, high-chromium G10 types typical of peridotitic kimberlite.

Follow-up soil sampling over target areas outlined in the stream-sediment survey revealed six kimberlites, with the four largest ones between 1.6 and 4 hectares in area.

The company also concluded a financing with London-listed Resources Investment Trust, which took down 2.1 million Mano River shares for 68,250, and also issued 68,750 shares in exchange for a further 2.5 million shares of Mano River.