A deposit of this material has for a long time been known to occur on Mait Island, a few miles off the coast near the police-post Hais. It had been, until the last few years, more or less regularly shipped over a long period by Somalis to the Sultan of Makulla to be used as a fertilizer for tobacco crops, but, owing to tribal disagreements and jealousy between Somalis and Arabs, work on the island was brought to a standstill. Except to a few native sub-tribes and a few Arabs, little is known of the deposit. No expert examination has ever been made of its extent and thickness, and the only specimens of it obtainable on the mainland are those collected by natives. An attempt was made by the writer to visit it, but, owing to the absence of a suitable dhow, either at Hais or at Humbais, and owing to the rough weather which lasted all the time he was in the neighborhood of Hais and Mait, it was found impossible to get across in the time available. From Somalis, who had actually worked on the deposit, however, the following brief account of its nature was elicited.
The Island— which from the mainland appears quite white — is completely covered by the guano. The material occurs in two varieties: (a) the good stuff which forms the white layer that lies over the whole surface to a depth of two or three inches; (b) the inferior stuff which occurs in holes or cracks. The latter is the material collected when the Somalis work for anyone other than a white man or a Somali. Both varieties are of a brownish or buff color. The deposit is scraped up without any regard to grade or impurities, with the result that, when bagged, it is mixed with numerous feathers, fragments of rock, bones and beaks, and ranges from an impalpable powder to pieces the size of screened road-metal. The stuff from a depth below two inches is not collected, and little is known at present as to what is the formation on which the deposit lies.
A typical sample of the guano in the condition in which it is bagged was obtained from the Customs House in Berbera, and was separated by sieving into the following portions:
- Feathers, bones, etc.
- Portion retained on a sieve of 1/8-inch mesh.
- Portion passing an 1/8-inch but retained on a 1/20-inch mesh.
- Portion passing a 1/20-inch mesh.
Of a sample weighing about 20 lbs., the respective proportions under these divisions were:
- 0.8 percent.
- 25 percent.
- 17.5 percent.
- 56.7 percent.
Portions B, C and D were then analyzed and were found to contain the following amounts of phosphate, expressed as phosphoric anhydride (P2O5):
- 14.90 percent.
- 16.06 percent.
- 18.52 percent.
The analyses show that the phosphate occurs throughout the whole sample. An examination of the material retained on the 1/8-inch mesh indicates that the fragments in the fine powder included a small proportion of those of granite, of aplite, of flint, of black slate and of hornblendic gneiss. While, therefore, it would appear from the analyses that little advantage would be gained by rejecting any portion of the material of which the sample consisted, it is quite possible that the composition of the fragments varies considerably from place to place. In order to arrive at some conclusion as to the nature of the phosphate present, a few fragments were selected which were not obviously granitic or gneissic in character, and an analysis was made of them, with these results:
These figures show that only about 2.5 percent of calcium phosphate is present in the selected fragments, and that the greater part of the phosphoric acid occurs in combination with iron and aluminum, though it is obvious from the silica percentage that amongst the fragments was flint or the quartz probably of an igneous rock.
On the other hand, in connection with all the analyses, it must be borne in mind that until a proper examination is made of the deposit, and proper samples collected and analyzed, it does not follow that they prove the true mineral character of the deposit. It is clear that some calcium phosphate is present, and it is quite possible that material from different parts of the island may contain different proportions of the calcium and of the iron and aluminum compound.
In view of the agricultural possibilities in the Protectorate and the proximity of the deposit to Hais, it is important that some reliable information should be obtained in regard to it. It is important to know its extent and thickness, whether pits occur in which the material is concentrated by water, what steps should be taken to improve the quality of the material bagged, what is the nature of the bed-rock, and whether any rock-phosphate occurs beneath the overlying deposit, part of which is scraped off. From examination of the fragments in the bag brought from Berbera, it is clear that, in part, the island is composed of slate and gneiss with intrusive granite, but it is not known whether these rocks form the whole of the island or outcrop only in some places beneath the limestone cap. Even should it be found that most of the phosphate is an iron or aluminum compound, undoubtedly its quality can be considerably improved by sieving or screening before bagging. Moreover, though the presence of iron oxide and alumina is an objectionable feature in the manufacture of superphosphate when the amount reaches 10 percent, there is no reason why the guano cannot be used as a manure without conversion to superphosphate. It has in fact been used on Makulla. The phosphate in its natural state is in a form in which it is largely available for plant nutrition, and even if it could not be used for the manufacture of “soluble guano,” it could be used in its natural state as a fertilizer, after the simple process of fine grinding.
The island is still year by year the haunt of countless birds and the deposit is thus being annually increased.
It is of interest to note that some similar deposits have already been reported and described from the Aldabra group of islands in the Seychelles. On Assumption Island, the phosphate is chiefly phosphate of lime—though some iron and aluminum phosphate is also present—but on other islands of the group the amount of iron oxide and alumina amounts to 8 or 10 percent., and it is held by Mr. Dupont that even when this amount is present, the material could be used either for the manufacture of “soluble guano” or as a soil fertilizer after fine grinding. In the Seychelles, the pits contain material of richer quality than the surface guano, and it would certainly appear that the statements of the Somalis to the effect that the guano in holes and cracks on Mait Island is of inferior quality, are erroneous.
Samples of muscovite mica were sent from the Protectorate to the Imperial Institute for report as long ago as 1901, and these samples were submitted to firms of mica brokers for an estimate of their value. Though they were apparently rather small both as regards quantity and size, the brokers considered that they gave promise of good mica being found in the deposits, and that, in view of the cheapness of labor and freight, the deposits might pay to work.
As the uses to which mica is put and the consequent demand for it have increased very considerably since 1901, special attention was paid by the writer to the occurrence of the mineral within reasonable distance of the coast.
Muscovite mica, and, in places, pale biotite, proved to be very common in a large area of country comprising the foothills and northern and north-western slopes of the Mirsa plateau, about 40 miles south of Berbera, and also in the hills at the base of the Golis Range as far west as Mandera. The rocks of all this country are chiefly granitic and hornblendic gneisses intruded by granite-pegmatite dykes, some flesh-red, others white, others again pink-and-white owing to the presence of both pink and white microcline. Mica is most common in the pink-and-white, less common in the white, and rare in the flesh-red dykes. Everywhere on the track over the plateau from Mandera to Darass, books of the mineral are to be found of a size about two inches by two inches, and, at several spots, comparatively large deposits containing books up to four inches by four inches were met with. At Durriehauseh, for instance, on the west side of the plateau, there is a large dyke traceable for a length of 300 yards, and 30 feet in thickness, in which numerous large books of a pale biotite occur all over the surface, and a hole sunk at one spot for a depth of about three feet showed a solid mass of books of the mineral of an average size of four inches by four inches. Other dykes of similar appearance were seen in the neighborhood and there is a good prospect that other large deposits could be found by sinking or by blasting. The mica from this locality was of a pale brown tint, but, having been got from near the surface, was more or less weathered, cracked and discolored. Owing to lack of time and the necessary implements and labor, it was not possible to open out the deposit, but sufficient evidence existed in the hole sunk to show that the quality improves as the depth below the surface increases.
The smaller books from the track are of a pale green or amethyst tint and quite free from flaws.
The best indications, however, of the occurrence of good mica—muscovite—were, obtained in the foothills of the plateau, in the area lying between Hul Kaboba and Lafarug. A sample of excellent muscovite sent to the Imperial Institute in 1901, measuring over four inches by four inches and free from flaws was got from this area, and an inspection made by the writer of the vicinity of Humbeleh, near Lafarug, showed large quantities of the mineral forming small mounds at the base of the hills. Enough work could be done with a pick and a spade to prove that many of the mounds consisted very largely of mica books, and though the surface specimens exhibited cracks and hydration strains, it was clear that the quality of the mineral improved to a great extent with depth below the surface. Many of the books virtually free from serious flaws measured up to six inches by six inches, and it is very probable that, by the use of proper tools and blasting powder, considerable workable deposits of good quality could be opened up. The area is one which should be thoroughly prospected, and each mica occurrence should be opened up to a sufficient extent to enable thoroughly representative samples to be obtained for expert valuation both of the mineral and of the deposit, particularly as the area is within easy distance of Berbera, and transport to and from it presents no difficulties.
As it has been repeatedly asserted, on the strength of Somali reports, that good mica, together with cornelians and precious stones, occurred in Yubaleh Range in the Gadabursi district, an examination was made of this range. The rocks of which it is composed are similar to those of the Mirsa plateau, there are the same varieties of granite-pegmatite dykes, and a considerable amount of muscovite mica is present in the dykes. Not only, however, did the size of the books nowhere exceed two inches by two inches, but no considerable deposit composed of books even of this size was encountered. The alleged cornelians proved to be flesh-red microcline felspar or rounded pebbles of flesh-red quartz, and, in spite of a careful search, no precious stones were discovered. Brown garnet, however, is plentiful in the pegmatites, and it is most probable that this mineral was mistaken for a gemstone.
Muscovite mica was also met with in Sigip Range, which is similar in composition to Yubaleh Range. So far as could be seen, the size of the books and the quantity of mica in the dykes were no greater than in Yubaleh. In any case, even if muscovite mica of marketable size and quality were to be found in either of these ranges, it would not pay to work at present on account of their distance from the nearest port (Zeyla), and the cost of transport.
It is asserted by Somalis that very good mica exists in the unexplored area north of Hargeisa, and, as the assertions are made by men who have seen material that is really of value, some reliance must be placed in them. Owing to the necessity of using the favorable season for an examination of the Warsangeli District, it was not possible to traverse this area.
It may be of benefit to give here some details obtained on request through the Imperial Institute from various mica brokers as to their requirements and the present price of the mineral.
There is no open mica market in the United Kingdom and current prices are not quoted, owing to the large number of grades and sizes marketed and the rapid fluctuations in supply and demand for some of them. Properly graded lots sent to a reliable broker will realize their current market value, less a small commission for selling.
It is of the utmost importance that mica sent to this country for sale should be properly trimmed, sorted, graded, and packed. If a broker can be sure that each parcel of a particular producer’s consignment will contain material of only one size and grade, properly trimmed and packed, that producer is assured of a much higher price for his mica, as, in other cases, the material has to he re-sorted on reaching the broker’s hands.
There is at present a good demand in London for sizes 2 inches by 1 inch and 2 inches by 2 inches if the quality is satisfactory, though they are not always so easy to dispose of. The smallest sizes are commonly used in the manufacture of “micanite,” for which thin splittings from 1/500inch to 1/10 inch are required.
As regards current values, it may be stated that consignments of mica have, in 1924, realized the following prices:
Clear good, No. 1 size … … … … 25s. per lb.
Clear good, No. 3 size … … … … 17s. per lb.
Slight stained, No. 1 size … … … … 16s. per lb.
Slight stained, No. 3 size … … … … 10s. 6d. per lb.
No. 6 size, good quality, loose … … … … 5d. per lb.
No. 5 size, good quality, pan packed … … … … 1s. 3d. per lb.
No. 5 size, best quality, pan packed … … … … 3s. 9d. per lb.
Associated with the mica in the large pegmatite at Durriehauseh, already referred to, large crystals of pale green beryl were found, some of them measuring a foot long and about six inches across, and all with more or less regular prismatic form. The mineral appeared to be distributed throughout the dyke, and even in a space of about five yards square six large crystals were counted. Moreover, that there are other beryl-bearing dykes in the vicinity is proved by the fact that, in tugs flowing northwards from the foothills somewhat to the east of Durriehauseh, crystals and small crystal fragments of the mineral were found. As beryl is at present of some commercial value—according to information in possession of the Imperial Institute, an offer of £10 per ton has been made for it by one firm—and, seeing that, if the experiments which are now being made to replace aluminum by the lighter beryllium in the manufacture of aeroplanes prove successful, it will be of greater commercial value, the area in which it has been found should be thoroughly prospected for further occurrences, a sufficient quantity should be sent to London as a trial sample, and should be taken to obtain a reasonably accurate estimate of the amount of the mineral that can be got from the area.
The crystals are both too large and of too pale a tint to be of much value in themselves as gemstones. As it is, however, not unusual to find that where beryl-bearihg pegmatites intrude greenstones, the beryl acquires a deeper shade of green at the contact and may then prove a marketable gemstone, the contacts of these dykes with either the hornblende gneiss or the talc-chlorite rocks of the plateau should be carefully examined.
Crystals of brownish and reddish-brown garnet are very common in the granite-pegmatites that intrude the granitic gneisses of the Protectorate, and small crystals of red garnet occur in considerable number in the hornblende gneiss of Darinwadu tug near Buk Gigo, south-east of Zeyla. In general, the mineral is not present in sufficient quantity and occurs too far from a port to be worth consideration.
In the mica pegmatites of the Mirsa Plateau, however, and particularly in those in the neighborhood of Humbeleh near Lafarug, the mineral was found in quantity sufficient to suggest that there may be amounts large enough to exploit. In one dyke, lumps of a dark reddish-brown garnet weighing several pounds were obtained. A sample of it, much weathered and iron-stained, was submitted to a firm of abrasive importers and manufacturers, who stated that, while it was too much weathered and decomposed to be in itself of any commercial value, there was a considerable probability that marketable material might be met with below the surface. The firm were of opinion that a further survey of the deposits was desirable, and were prepared, if better material were found, to make practical trials and arrange for its sale and distribution.
The fact that the mica, beryl and garnet all occur in the same neighborhood and are capable of being worked together will react favorably on the chances of exploiting these occurrences.
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