Kpo Range MDA (200 km²)

The main alluvial diamond workings are found all along the northwestern edge of the Kpo schist belt with primary deposits in the area east of Weasua. The major drainages, including the Lofa River, appear to be structurally controlled in this area. In 1999 all of the alluvial workings were visited and mapped. It became apparent that the main focus of the local artisans was not on the Lofa River, but along smaller tributaries to it. Gravels along the Butulu, Wuegbeni and Wuedakena Creeks have all been exploited and continue to be so. The gravels were mapped and in many cases were classified as angular, suggesting that they have not travelled any significant distance and hence the diamonds potentially have a local source. A further field visit in February 2000 was made to collect a selection of heavy mineral samples as a pre-cursor to the onset of a detailed diamond exploration programme orientated towards the location of primary kimberlitic occurrences. Four samples were collected downstream of gravel diggings and all returned positive results. The most interesting samples were taken along to Butulu Creek and a small tributary to the Butulu called the Wuejua Creek. Here abundant kimberlitic chromites and garnets were recovered from samples, and one chrome diopside was also picked. Mineral chemistry analysis of these indicator minerals determined that a very large proportion of these are classified as G10 garnets, being derived from harzburgitic mantle (after Gurney, 1984). Furthermore, a large proportion of the have >12wt% MgO and >60wt% Cr₂O₃ and are classified as diamond inclusion chromites (after Fipke et al. 1995). The angular nature of the gravels coupled with the recovery of abundant diamond inclusion indicator minerals and a chrome diopside indicates that potentially diamondiferous kimberlites are present in the area to the east of Weasua in a localised area.

During May and June 2000 detailed sediment sampling was conducted around Weasua, through the collection of 72 samples. Many of these samples yielded abundant kimberlitic chromite supported by garnet, chrome diopside and ilmenite. A large number of these indicators have been probed and the mineral chemistry of the chromites and garnets is considered excellent. Many chromites are classified as diamond inclusion type chromites, whereas there are a very large percentage of G10 garnets from those garnets probed. These data indicate that some of the sources of the indicator minerals are likely to be diamond bearing. One macrodiamond in the +0.71mm size fraction was picked from one sample that also contains diamond inclusion chromites.

Follow up of a number of these anomalies (including 660 loam samples) has led to the discovery of 6 kimberlites in the Weasua area, of which 4 are confirmed pipes, 1 is a suspected pipe and 1 is of insignificant size. Small samples have been collected from K001 (1.6ha pipe), K002 (2 to 4ha pipe) and K003 (4ha pipe), which yielded both micro and macrodiamonds. The diamondiferous nature of these thee pipes is also confirmed by the fact that local artisans are mining diamondiferous gravels associated with, and downstream of, these pipes.

Kpo MDA Stream Sediment Sampling

Initial work on K004 and K006 has yielded encouraging results (including a diamond recovery from K4) and again both these kimberlites show significant artisanal diamond mining. A sample of K006 was processed for microdiamonds at Lakefield Research in Canada, but with negative results. This somewhat contrasts the garnet chemistry where all of the garnets probed (25 grains) were determined to be G10 in composition. Clearly a larger and more representative sample of K006 is required for diamond analysis. K005 has been determined to be of no interest and will not be investigated further.

It is clear from the regional anomalies though that many more kimberlites remain to be discovered in this new diamondiferous cluster and a work programme has been designed to bring these anomalies to account. The mineral chemistry of these anomalies is excellent and it is more than likely that some of these kimberlites will be diamondiferous.