First Report On The Geology And Mineral Resources Of British Somaliland With Map

16. TALC (SOAPSTONE)

Thin veins of this mineral were found on the surface on the track from Darass to Dumoyera, about two miles east of Darass, on the Mirsa Plateau. The veins are obscured by scrub and grass, and their thickness could not be accurately determined. In this particular locality, however, it did not appear to exceed two or three inches. Nevertheless, on a small hill on the left of the track from Darass to Sheikh, there are large blocks of a greenish talc-chlorite rock. Considerable masses of this rock occur in situ in and around the hill, and as the veins of talc in all probability occur in it on the track, there is, therefore, a prospect of other veins or masses of talc being found elsewhere in the locality. The rock itself is used by Tomals as a furnace bed or natural forge in the manufacture of spears and crude tools.

17. MARBLE

On the track from Burao north-eastwards towards Ok Pass and about fifteen miles south-east of the Pass on the west of the track, are several small hills to which the name Demirjogh has been given. These hills are isolated, of a pale yellow or buff color, and at first sight appear to be formed largely of felsitic quartz porphyry. Closer examination shows them to consist in part of hornblende gneiss, in part of granitic gneiss with small dykes of coarse granite, but in large part of the pale yellow rock. The latter, on being broken, proves to be not an igneous rock at all, but a white crystalline limestone or marble of medium texture. The marble occurs in parallel bands, and in one hill there are as many as fifteen parallel bands from one foot to four feet wide. The strike of the bands in this hill is N. 15° E. and the dip is vertical. In one hill about a mile further to the north-east, the strike veers round from N. 15° E. to N. 40° E. and the dip is 60° to the north-west. In the third hill about three-quarters of a mile to the northeast, the strike veers round in a curve from N. 15° E. to N. 65° E., the change being due to the influence of intrusive granite-pegmatite dykes.

In the first hill, the marble is associated closely with black hornblende gneiss, which occurs not only in juxtaposition to the limestone mass, but as lenticles, xenoliths and dyke-like veins in it, and occurs also between the bands with the same strike as the marble. The lenticles are in places coarse epidiorite, in places almost a hornblendite, and in places appear as pale grey knots in the limestone.

The marble exhibits peculiar parallel lamination brought out by weathering, and in places the lines or edges of the laminae are curved to form three parts of a circle, apparently owing to the intrusion of a hornblende gneiss or a granite dyke. In the hill three-quarters of a mile to the northeast of the first, a granite-pegmatite also forms knots in the marble, but no contact minerals were found.

The comparative ages and relation to one another and to the surrounding country of the marble and the hornblende gneiss are important and complicated and are referred to elsewhere. Apparently, the limestone represents a very old sedimentary series that has not hitherto been recognized in the Protectorate.

Some of the hillocks are 150 feet wide, 600 feet long in the direction of the strike, and rise to forty feet above the level of the plain.

The marble is white on the fresh surface, slightly dolomitic, fairly hard, crystalline, and very tough, but probably of rather too coarse a texture for use as statuary marble. It may, however, in the future be of some local value as a building and ornamental stone. At the present time there is not, except possibly at Burao, sufficient need, in the Protectorate, of good building stone to compensate for the difficulty of transporting this marble.

A similar marble was met with on the track just northwest of Dorjibis, between Somadu and Borama in Western Somaliland. There it occurred as a band in a series of foliated quartz-mica schists. As the band, however, nowhere exceeded one foot in thickness, it could be of no other than scientific interest.

18. MANGANESE ORE

In 1917, a sample of calcareous wad sent from Berbera was reported on by the Imperial Institute. The report stated that the material contained 8.55 percent of manganese and that it should be ascertained how the deposit originated, since it might be traceable to beds of manganese ore of economic value. The locality given in the letter accompanying the sample was “from Jirba Hill, about 30 miles eastwards from Ali Wein.”

As Jirba Hill is a ridge over six miles long and two miles wide, it was a matter of some difficulty to locate the deposit, but it was eventually found in Bihen Gaha Pass, at the north end of the ridge, close to the easternmost of the three hot springs which issue from the Eocene limestone in the Pass.

The deposit forms a patch about 20 yards square, and the manganese is in the form of a black powder, intermixed with calcareous limestone, some salt, and finely divided carbonaceous material. The actual amount of manganese ore in the deposit is small, some of the travertine containing none of it, and, to judge from the evidence in a hole sunk in it, the deposit is patchy and extends downwards for only a few feet. To open out the deposit properly, however, blasting powder and more labor and tools than the writer was provided with would be necessary.

Samples of the black travertine from the side of the hot spring were analyzed at the Imperial Institute, and the results obtained are as follows:

These figures closely approximate to those obtained from the sample analyzed in 1917, and indicate that the ore is of such low grade as to be of no commercial value.

Nevertheless, because of the possibility of the existence of a deposit of psilomelane or of pyrolusite in the vicinity of, but not in contact with the springs, from which this wad might have been produced, a search of the surrounding hills was made. No deposit of manganese ore of appreciable size was discovered anywhere in the neighborhood, but in a ridge of massive Eocene limestone just north of the spring, small veins of calcium carbonate with streaks of manganese oxide through them, and cracks and joint-planes with a crust of dead-black manganese oxide intermixed with calcium carbonate were found. It would appear, therefore, that either this limestone originally contained a certain amount of manganese oxide probably as a sea-bottom deposit, or that beds formerly overlying the limestone contained a small amount of the ore; that in the former case, the manganese has become leached away and re-deposited in the cracks and joint planes along with secondary carbonate of lime; that, in the latter, the manganese oxide percolated in solution down through the cracks and joint planes and was re-deposited in a similar manner; and that, finally, this re-deposited oxide has again been leached out, and, coming in contact either with organic matter round the hot spring or with the mineralized water of the spring, has again been thrown out of solution in the calcareous wad.

In any case, so far as is shown by the evidence at present available, the deposit is of no commercial value and no other deposits of the mineral worthy of any attention occur in the vicinity.

19. KEROGENOUS SHALES

As already stated in the section dealing with Petroleum, kerogenous shales were found in several localities in the country examined. Samples of them were collected from each locality and three of them have been analyzed at the Imperial Institute, viz.:

(1) That from the bed of the Durdur Ad tug near Meragelleh, in the Gadabursi District.

(2) That from the same tug but from a different spot in the bed.

(3) That from a gorge west-north-west of Bihen Gaha springs, south of Karam.

The results obtained on distillation were:

The oil produced was dark-brown and limpid, and had the characteristic smell of shale oil. Considerable quantities of sulphuretted hydrogen were evolved during the distillation.

The yields of oil from these three specimens are low and the quantities of ammonium sulphate obtained are smaller than those obtained from low-grade Scottish oil-shales.

It would not be remunerative to exploit material of the quality represented by these specimens.

On the other hand, the analyses prove conclusively that the black and brown shales underlying the Jurassic limestone in various parts of the Protectorate are kerogenous.

Moreover, the samples obtained were merely surface samples that had been exposed to the atmosphere for long periods, and it is possible that fresher material from some distance below the surface would give a larger return of oil. In view, however, of the inaccessibility of the best of the shales—those at Meragelleh —it is unlikely that they would ever pay to exploit.

20. GRAPHITE

Graphite was found as a constituent of a fine-grained, friable, very quartzose gneiss on the right bank of Ulauleh tug, half-way up the tug on the track from Durrieodera and Elaudu, in the south-west of the Gadabursi District. The mineral occurs in the rock in considerable amount as fine flakes, but the extent to which the rock itself occurs could not be determined on account of undergrowth and debris. Though no workable deposit was seen, the discovery of the mineral is of interest, because it indicates a mode of occurrence similar to that in other African Protectorates.

21. DIAMONDS

Assertions have been made by a South African syndicate that diamonds occur and have been found in the south-east of the Protectorate, and an application was made by it for permission to prospect for them in the neighborhood of Kirrit. This part of the country, being at least 150 miles south of Berbers, was, of course, outside the limits for the time being prescribed for investigation by the writer, but at the request of the Governor, a visit was paid to Kirrit to determine whether there was any promise of diamonds being found there. The neighborhood of Kirrit consists of Eocene limestone ridges—such as Dur Dab, and gysum hills — such as Kirrit Hill itself— which in the coastal regions belong to a series overlying the Eocene limestone. Though the whole area within a radius of five miles from Kirrit Hill was examined, no diamondiferous rocks or sands were found in it, and, having regard to the lithological character of this area, there does not appear to be the slightest chance of diamonds being found naturally in it. It is, of course, not known on what gounds the assertions of the syndicate have been based, but whatever blue clay exists—and none comparable to the Kimberley blue clay was found by the writer—cannot, in this neighborhood, be of other than a sedimentary origin, and of the Eocene or post-Eocene stratigraphical series.

On the other hand, it by no means follows that, because Kirrit was given by the syndicate as a base or starting-point, the diamonds alleged to have been found or expected to be found necessarily came or would come from Kirrit itself or even from its immediate vicinity. Indeed, it is most unlikely that the actual locality at which they may occur would be divulged, and most probable that it would be at a considerable distance from this spot, though not so far as would prevent it from being used as a convenient base on the motor road from Burao.

The country to the south, west and east of Kirrit has not been geologically examined, and though the surroundings of Kirrit itself are formed of limestone and gypsum, the common occurrence in Somali nomenclature in the district of the words “madu,” “madoba” (meaning “black”), applied to hills rather suggests that the rocks of the district are not all limestone and gypsum, but that some of them may be of extrusive or intrusive origin. It would appear, therefore, that either an expert examination of the whole district should be made, or that the activities of the syndicate and the results achieved should be kept under expert observation and duly recorded in the interests of the Administration.

22. SANDS

In all, forty-four samples of sand were collected from various tugs, examined roughly on the spot by the aid of a magnifying glass, and then concentrated by panning where water was available, by passing them through a 20-mesh sieve where no water could be obtained. These sands have been further investigated at the Imperial Institute in part by electromagnetic separation, in part by further careful panning. No valuable minerals, however, have been discovered in them.[21] They consist almost wholly of hornblende, magnetite, ilmenite, felspar and quartz on the one hand, and of mica, garnet, zircon, ilmenite, magnetite, quartz, felspar on the other, i.e., they are sands derived in the one case from hornblende schists and gneisses, on the other from granite gneisses, granites and granite-pegmatite. From the two areas in which there is a prospect of the occurrence of gold, no sand samples were obtained for reasons already given.

Transport and Labor

The chief mineral deposits are all within forty miles of the sea-coast; the galena, coal, lignite and petroleum are within thirty miles. Transport in the Protectorate is by camels, of which there are very large numbers, according to one authority nearly a quarter of a million. A burden camel will carry loads up to 300 lbs. weight, will travel from 16 to 20 miles per day, and the cost of transport is one rupee (about 1s. 4d. per camel per day), the camel owner providing his own equipment and rations.

There is plenty of unskilled coolie labor, the direct control of which is best placed in the hands of a Somali overseer. The rate of pay ranges from 8 to 12 annas per man per day, exclusive of rations, and the cost of the latter at the Government rate is about 3 _1/2 annas per man per day.

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