Nigeria and its tin fields

by Albert Frederick Calvert

This portion is actually on the apex of the watershed. The streams which fall rapidly to the valley below on the west are crossed by numerous bars of granite and quartz reefs, which act as natural riffles, and have served to concentrate the ore in high values, but relatively small quantities of alluvial in the beds and banks of the streams. Good alluvial also occurs in patches amongst the granite hills away from the waterways.

The streams get a fairly regular supply of water from springs and the drainage of the many veins, but they are also subject to scouring floods caused by heavy but entirely local rains. The floods are breaking down the alluvial with great rapidity, and large quantities of ore must be washed down to the valley below every year.

During three months of somewhat irregular work last year we recovered 30 tons of black tin from Nos. 1 and 2 streams. Part of this was won by sluicing the alluvial banks, of which 2,736 cubic yards, worth 10 to 11 lbs. of black tin per yard, were worked. Operations were commenced from the boundary, the ground was worked fairly, and although superficially it only represents some 300 square yards, it gives a fair idea of the value of the bank deposits. The values, of course, would not apply to the alluvial apart from the streams, nor to that on No. 3 stream, where there is far less grade and more alluvial, but, taken as a whole, the proposition is decidedly the richest yet found in Nigeria. Until further prospecting has been done and a detailed survey carried out, it is impossible to give any accurate estimate of the payable alluvial available on this portion; as a hand-work proposition it is not of great extent (as will be gathered from my report to the Niger Company last December, a copy of which I attach), but as an area systematically worked with the aid of machinery, it is undoubtedly a property which should produce a large tonnage of tin over a period of many years.

The above-mentioned report also clearly sets forth the difficulties in the way of systematic mining, if it is to be regarded as a separate concern. I have carefully considered the methods suggested by Mr. Lush in his report. The first we have already tried. The second is impracticable, because we have no higher level at which we could conserve water for hydraulicing the whole of the alluvial deposits, and the third and fourth can only be considered in conjunction with one or both of the other portions of the N’Gell River.

A modification of the second suggestion might prove satisfactory as a temporary measure. It would be possible to conserve in a reservoir constructed near the head of one of the streams sufficient water to sluice by gravity—I do not think there would be pressure for hydraulicing—the alluvial in and near the main river and part of that about the three streams. The ground higher up the streams could not be worked by this means.

B

This portion of the river flows through the Niger Company’s area, as shown on the plan attached. The river, after leaving the town of N’Gell, falls into a fine open valley within which is an apparently deep basin filled in with loose gravels heavily charged with water.

Four important streams numbered 3, 4, 5, and 6, enter the river from the south, three of them having falls in the position marked on the plan.

In addition to the alluvial being washed down the main stream, this basin must also be enriched by the tin-bearing wash in the tributaries, which also show good prospects.