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III. —ECONOMIC GEOLOGY

(A) MINERAL OCCURRENCES

The minerals of industrial value which have so far been found in the Protectorate are the following:

    1. Coal.
    2. Lignite.
    3. Petroleum.
    4. Galena.
    5. Salt.
    6. Guano.
    7. Mica.
    8. Beryl.
    9. Garnet.
    10. Barite.
    11. Celestite.
    12. Molybdenite.
    13. Gypsum.
    14. Gold (doubtful).
    15. Clay.
    16. Talc or soapstone.
    17. Marble.
    18. Manganese ore.
    19. Kerogenous shales.
    20. Graphite.
    21. Diamonds (doubtful).
    22. Sands (doubtful).

1. COAL

Coal was found by the writer in the bed and on the side of Hedhed tug, a western tributary of Hodmo tug, which joins the latter some twelve miles south of Ankor. In 1915, samples of coal were sent for analysis to the Imperial Institute by Mr. H. M. O’Byrne, Chief of Customs at Berbera. These purported to come from a solid mass at the foot of Ambal Hill, 53 miles east of Berbera and 30 miles south of Karam, and from the banks of Ambal tug. As, however, subsequent examination by the present writer failed to disclose the presence of any coal in the vicinity of Ambal Hill or in the tug, but showed that the black, in part shaly, carbonaceous material exposed in considerable quantity under the Jurassic limestone in the hill and on the west side of the tug, is kerogenous shale associated with black carbonaceous limestone, it is fairly certain not only that the samples of coal were obtained for Mr. O’Byrne by Somalis, but that they actually came from Hedhed, and that the locality, Ambal Hill and tug, were loosely given for them owing to the unnamed and unexplored condition of this part of the country.

The deposit occurs about three and a quarter miles up Hedhed tug from its junction with Hodmo tug, south-south-west of the junction, in a fairly high tableland of Dubar Sandstone overlain by massive Eocene limestone and much dissected by precipitous ravines. The coal outcrops in a seam of an average thickness of two feet six inches, on both banks and in the bed of the tug. The main outcrop is on the east side of the tug, but an apparently smaller one—smaller, probably, owing to its length being obscured by debris – occurs on the west side. The seam, at first sight, appears to be horizontal, but it really dips west at the low angle of 5°, so that, after crossing the tug —being only a few inches above the level of the water—it is lost in the west side under the screes and limestone. Moreover, limestone boulders and debris obscure the seam to the south and north, up and down the tug. Both above and below the coal are very fine, somewhat soft, yellowish sandstones. At the chief outcrop the series of beds exposed from the visible base upwards are:

SomlegalAds

Yellowish sandstones of unknown thickness.

Coal, 2-3 feet thick.

Whitish sandstones, 2-3 feet thick.

Alternating thin beds of sandstone and calcareous shales, 12 feet thick.

Dark brownish-black carbonaceous shale, 6 feet thick.

Above the shales, massive Eocene limestone over 500 feet thick.

In the section, directly above the dark carbonaceous shales, is a recent conglomerate, which, as it is merely local and formed of ordinary river gravel, is not really a part of the series, but has been deposited on the exposed surface of the outcrop where it has jutted out beneath the limestone.

Under the circumstances, it was impossible to ascertain the true extent of the seam, but it outcrops on the west side for about 100 yards, and the carbonaceous shales above it extend up the tug for another 100 yards. The upper sandstones are present about 100 yards down the tug as a bed twelve feet thick, but no coal was visible under them.

Samples were taken from about eighteen inches from the exposed surface, and hence can scarcely be regarded as typical of the seam as a whole. They consisted of a dull black substance which might be classified either as sub-bituminous coal or as lignite. The structure was somewhat woody, with occasional thin bright bands. The material showed a tendency to split along the bedding planes, but at a distance of eighteen inches from the surface, blocks of considerable size could be hewn from the seam without any sign of splitting. Though in places, at the surface, there are small lumps and streaks of iron pyrites, this mineral occurs sporadically and in comparatively small amounts, and the bulk of the coal is apparently free from it.

The age of the coal is somewhat uncertain owing partly to the fact that the fossils from the overlying limestone have not yet been determined, and partly to the fact that no fossils have yet been found in the Dubar Sandstone, which elsewhere in the tableland underlies the limestone. As it is most probable, however, that the limestone is of Eocene age, and as, elsewhere in the Protectorate, the Dubar Sandstone clearly overlies conformably limestone of Jurassic age, the coal seam series would appear to be between Eocene and Jurassic in age, and to form either the lower part of the Eocene formation or the upper part of the Dubar Sandstone, which there is some reason for thinking to be of Cretaceous age.

The samples were analyzed at the Imperial Institute, and the following table gives the results of these analyses, together with corresponding figures obtained from the sample previously sent from Somaliland (in 1915), and for similar coal now being worked in the Udi district of Nigeria:

 Present Sample from Somaliland

 

Previous Sample from SomalilandSub-bituminous coal from Udi Colliery
 

Moisture at 105°C

Volatile matter

Fixed Carbon

Ash

Percent

13-24     14-27

36-87     35-05

38-11     37-88

11-78     12-80

Percent.

13-01

35-16

39-78

12-05

Percent.

5-62

38-18

48-41

7.79

Sulphur, percent.

Calorific value in small calories

Color of ash

0-65        0-48

5404       5070

pale huff    pale buff

0-64

5661

cream

0-76

6969

light grey

Using the factor 1.8 to transform small calories into British Thermal Units, the calorific value of the three samples of Somaliland coal are respectively:

B.T.U. 9,727, 9,126, 10,190.

It must be noted that the figures for the Udi coal were obtained from a sample of the material now being mined, and not from a prospecting sample. As the Somaliland material is really a prospecting sample obtained from the water level without any mining having been done, it is perhaps more reasonable to cite in comparison the results obtained from samples from the Udi district from comparatively undeveloped seams.

According to the Bulletin of the Imperial Institute, the following analyses can be cited:

Ofam River (Udi)

2’ seam.

Iyocha Stream (Udi)

5’ 5” seam.

Iyiku River 1’ 5” seamOkwaga DistrictUdi[12]

2’ 6” – 3’ 7 ½“ seam.

Inimini River

2’ seam.

Iyorba Stream 3’ 11” seam.
Fixed Carbon12.3044.8841.4243.3139.4943.63
Volatile matter33.8235.6037.4134.2634.9632.66
Ash18.4214.8911.6410.0714.0516.79
Moisture5.464.639.5312.3611.506.92
100.00100.00100.00100.00100.00100.00
Sulphur0.740.730.540.620.730.87
Calorific value in small calories5,9676,4375,9265,6305,4945,892

The Udi coal is stated to be of the sub-bituminous type, and usually of a dull-black appearance, though some of the seams show alternating bands of dull and more lustrous coal. As a rule, it is fairly free from mineral impurity, but occasionally contains nests and films of amorphous clayey matter and pyrites. The coal ignites readily, burns with a bright, steady flame, and gives off only a small amount of smoke. It does not cake or decrepitate on heating. The ash is usually white or light grey and practically free from clinker.

In the notes accompanying the results of analyses, the Imperial Institute remarks: “They (the coals from Somaliland) are all free-burning, show no tendency to coke, and are similar in type and appearance to the coal now being produced at the Udi Colliery in Nigeria, though somewhat inferior to it in heating power. … It seems probable that as seams of coal in Somaliland are opened up, material of higher calorific value and lower ash content will be obtained.”

In the light of these facts it appears important that, in the future interests of Somaliland, and in the interests of our knowledge of the coal resources of the Empire, this whole district should be thoroughly examined. The views held before 1914 as to what constituted coal of economic value have changed to a very large extent, and what with pressure-briquetting and low-temperature carbonization, it has now been found possible to use commercially coals and lignites which before 1914 were of practically no value. Moreover, it is a matter of experience that the calorific value of samples from coal-seams increases both as the seams are opened up and as other seams are met with at greater depths.

Therefore, search should be made for outcrops of other seams in the district. According to Somali reports—and experience shows that they usually have some basis of truth—there are at least four other localities in the district in which coal occurs, and it is alleged that in at least one of them there is more coal showing than in the seam discovered. The difficulty in regard to these occurrences is that the country south of Ankor as far as Las Dureh is quite unmapped, and even unexplored except by a few tribesmen, so that it is necessary either that native guides should be obtained who know this tract—and there are very few of them — or that traverses should be made of the tugs which dissect the tableland. The latter course is to be recommended, seeing that it would enable the outcrops to be properly located on a fairly reliable topographical plan.

Moreover, as it is unknown whether there are not other seams below the one outcropping, and, as, if there are, there is some prospect of coal of higher calorific value being obtained, the possibility of the occurrence of these should be investigated, if necessary, by boring. As the depth to which it would be necessary to bore would probably not exceed a few hundred feet, and as the rocks met with would be not harder than limestone and sandstone, a boring plant such as is used in Nigeria and elsewhere would be sufficient for the time being.

There is an abundance of excellent water in the ravine in which the seam outcrops, and doubtless equally good water occurs in some of the other ravines. Should it ultimately be found necessary to use timber for an adit, there is a considerable number of large trees in Hodmo tug with boles up to one foot in diameter, suitable for props.

2. LIGNITE

In notes on the official file in Berbera, supplied by the Chief of Customs, and according to Somali reports, an outcrop of coal was stated to occur on the southern slopes of Al Wein Range about 16 miles south-east of Berbera, near a well called Khal Der and in a stream known to the natives as Egmaleh tug.

After considerable difficulty, one outcrop of lignite was discovered by the writer on Egmaleh tug, about a mile north of Khal Der Well, and another about a mile from this one on a bearing 84° along the tug. The latter may be referred to as the East seam, and the former as the West seam. The seams occur in the Daban series of shales, clays and sandstones, which overlie the Gypsum Series, which itself, as already stated, lies conformably on top of the Eocene limestone. The age of the lignite cannot be known definitely until the determination by the paleontologists of the Natural History Museum of the suite of fossils from the Daban beds has been completed, but it is certainly post-Eocene, and hence considerably younger than that of the coal at Hedhed.

East Seam. —The exposure in the face of the cliff which forms the south bank of Egmaleh tug at this spot is as follows—from top to bottom of the cliff:

12 feet of greyish-white detritus.

6-8 feet of coarse and fine gypseous, sandy beds, in places with coarse sandy conglomerate patches.

1 foot of gypseous chocolate-colored carbonaceous shales.

4 feet of chocolate-colored clays separated by thin gypsum veins.

Lignite seam 1-1 1/2 foot thick.

3 feet of chocolate-colored clays.

The seam extends along the cliff (which faces north) for about three chains. Its average thickness is about fifteen inches; it dips S. 10° E. at an angle of 10°, and strikes E. 10° N.; and it appears to thin out eastwards, though the outcrop becomes obscured by debris. The lignite is jointed in two directions, roughly east-west and north-south, and along the joint planes and bedding-planes are thin plates of selenite. The whole series of clays in fact is gypseous. Though the lignite disappears westwards along the south bank of the tug, the chocolate-colored carbonaceous shales occur along the bank, so that the lignite is probably beneath them, though not visible. The north bank of the tug has been mostly eroded away.

West Seam. — In dip, strike, thickness of seam, character and sequence of associated beds above and below it, this seam is the same as the East one, and, in all probability, though no proof was obtained, it is merely a part of the latter. The outcrop, however, is traceable for only about twenty yards.

The material from both localities is a lustrous black lignite, that from the west seam splitting readily along the bedding-planes, that from the east weathering at the surface into brownish friable lumps. The West seam appears rather blacker and somewhat harder than the East one. Samples from both outcrops were analyzed at the Imperial Institute, and from the results a comparison was made with lignite from Nigeria, with lignite briquettes from Breunsdorf in Germany, and with lignite from Austria. The figures obtained were as follows:

Lignite from SomalilandNigerian Lignite from OkpanamBreunsdorf Lignite BriquettesAustrian Lignite from Aussig
WestEast
PercentPercentPercentPercentPercent
Moisture at 105° C9.6811.4512.3615.6722.22
Volatile matter46.5146.0047.4348.2836.72
Fixed Carbon34.4934.8931.4128.5938.60
Ash9.327.668.807.462.46
100.00100.00100.00100.00100.00
Sulphur … percent6.865.421.393.290.69
Calorific value in small calories5,7335,2115,8205,5755,603
In B.T.U10,3199,380

The notes accompanying the results state that in all these analyses the amount of moisture recorded is the quantity found in the samples as received at the Institute. The amounts present in the lignites as mined would be considerably higher.

The two Somaliland lignites showed no coking properties, and are noteworthy for their high percentage of Sulphur, which, being largely present as gypsum, would seriously affect their value as fuel. It seems probable, however, that when the lignite seams are opened up much of the Sulphur in the unweathered material will be found to be present as pyrites, which could probably be removed to a great extent by a suitable method of washing. The fuel would then need briquetting. In other respects, the Somaliland lignite compares fairly well with German lignite briquettes as produced at Breunsdorf for industrial purposes and with Nigerian lignite from Okpanam.

With regard to the Sulphur content, it should be noted that the Gypsum Series occurs in Al Wein in great thickness and at a higher level than the top of the outcrop of the Daban Series (the rocks dip at a considerable angle to the south), the floor of the numerous ravines on the south slopes of the range is composed of gypsum, and the tugs of these ravines have all cut through the Daban Series in the vicinity of Al Wein. It is at least possible, therefore, that much of the gypsum in the joint and bedding planes of the lignite has not been produced from pyrites in the latter, but is the result of crystallization of calcium sulphate in solution in the percolating water of these tugs, and that, therefore, as the seams are opened up and particularly should further seams be discovered at greater depths and at greater distances southwards from Al Wein, the content of gypsum will be smaller. In the lignite samples obtained, no pyrites whatever have been found.

The occurrence of this lignite and the fact that it clearly compares favorably both with Nigerian lignite and with briquettes made from Breunsdorf lignite, render it advisable that a search be made for outcrops in the locality, and that if possible some trial boring be carried out with the object of locating other seams below those found. The higher calorific value of the west than of the east seam rather suggests that other seams below them may be superior in calorific value to both of them. Should further search for outcrops or by means of a boring plant prove the existence of a considerable quantity of lignite, the material may be made of commercial value by treatment by low-temperature carbonization or by a briquetting process. The latter process particularly would increase the density and calorific value of the fuel, render it practically impervious to moisture, and eliminate any tendency to disintegrate either when stored or during use. The best method of treatment to be employed could be determined at the Imperial Institute on trial samples of sufficient size. The outcrops are within easy distance of Berbera and transport would present no difficulties.

The statement has been made that the coal at Hedhed is a continuation, of the lignite seam at Khal Der. There is no connection whatever between them. The coal at Hedhed is older than the massive Eocene limestone, and is either Lower Eocene or Upper Dubar Sandstone (possibly Cretaceous), whereas the lignite at Khal Der and in Egmaleh tug is certainly post-Eocene.

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