THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. ______________________________________ Vol. CXII. _________________________________________________________________________ New West African Coal Field.* In 1903, on the suggestion of the diiector of the Imperial Institute, a mineral survey was organised to obtain general information as to the probable mineral resources of Southern Nigeria and then to study the areas found to contain minerals likely to be of economic importance. The survey was continued until 1913, and nine summary reports of results have been published. One of the most important results obtained in the course of the survey was the discovery of large deposits of lignite and coal. Much lignite was found on both sides of the River Niger near Asaba, but this material was completely overshadowed in its importance as a fuel by the subsequent discovery of Udi-Okwoga coal field, so Called from the names of the native villages at its known southerly and northerly limits. The total area of the coal field as at present determined is about 1,800 square miles. The existence of coal in this area was first noted in 1909, and the work of determining the area of the field by the observation of outcrops, and later on by boring trials, was continued until the close of the survey in 1913. As the Government of Nigeria is the chief consumer of coal in the country for the use of the Government railways, the development of the coal field has been undertaken by-the Public Works Department, and, as shown later on, the working of the coal field has already reached an important stage. Now that a railway has been built from Port Harcourt to the best-known part of the coal field the resources of this area have assumed a still greater importance, and it is proposed in this ai tide to give a general account of the coal field and of its recent development. Geological Features. The youngest rocks of the Udi region are loose detrital sediments consisting of reddish sands. These occur at the surface, are very variable in thickness, and are regarded as belonging to the Benin sand series, which is of comparatively late tertiary age. These superficial sands lie unconformably on cretaceous strata, which are made up chiefly of sand- stones, shales and mudstones. It is in these cretaceous beds that the coal seams are found. The strata extepd over a raised plateau region for a distance of some 80 miles, stretching northward from the Udi district to the Okwoga district. The plateau surface rises some- what towards the north, and attains a height of over 2,000 ft. It slopes gradually to the west, and is not more than 200 ft. or so in height along the Oji river; it is bounded on the east by a scarp in which outcrops of coal are found. A line of outcrops stretches along this escarpment northwards from near the source of the Mamu river, south of Udi, to Otukpa north-west of Okwoga. The cretaceous beds are almost horizontal. On the whole there is a slight westerly dip, so that to the west of the above-mentioned scarp the coal occurs at some depth from the surface. A boring made at a locality to the west of Udi and 32 miles from Onitsha revealed two seams of coal at depths of 40^ ft. and 82| ft. respectively. In another boring still farther west, and 17 miles east of Onitsha, coal was found at a depth of 115 ft. Farther north coal outcrops have been observed as far west as lyokolla River, which is a few miles east of Ogrugru, and near the Anambra River. Nature of the Coal. The Udi coal is 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. The specific gravity varies, and for material not containing more than about 15 per cent, of ash the value ranges from about 116 to 1’32, with an average of about 1’23. As a rule, the coal is fairly free from mineral impurity, but occasionally it contains nests and films of amorphous clayey matter and pyrites. Films and patches of chalybite and kaolinite occur as infillings of the joint cracks and small crevices in the coal. The coal ignites readily, and burns with a bright, steady flame, giving off only a small amount of smoke. It does not cake or decrepitate on heating. The ash is usmlly white or light grey, and practically free from clinker. An analysis of a typical specimen of the coal taken from the 5 ft. seam now being developed gave the following results:—Fixed carbon, 48’41 per cent ; volatile matter, 38T8; ash, 7 79; moisture, 5 62; sulphur, 0’76 per cent.; calorific value, 6,969 calories. Distribution and Character of Seams. The localities in which coal seams of the Udi type are known to occur can be conveniently grouped as follow :— (1) Udi district, (2) Okwoga district, (3) Idah and western Okwoga districts, (4) Awka and western Udi districts. _____________________________________________________ * From the Bulletin of the Imperial Institute, FRIDAY, DECEMBER 29, 1916. (1) Udi District.—In this district the coal seams are well exposed in the ravines that cut through the escarpment forming the eastern limit of the plateau area. During the course of the mineral survey six distinct seams were found in this district, ranging from 2 in. to 5 ft. 8 in. in thickness. In the Udi neighbourhood there are four seams that reach a thickness of over 2 ft. The composition of the coals of the more important seams in this neighbourhood may be indicated by the following proximate analyses of two Udi specimens:— Stream Ofam River, behind Hausa Fixed carbon Volatile matter Ash Moisture 2 ft. seam. Barracks. 2 ft. 4 in. seam. Per cent. Per cent. 42’30 ... 48’20 33 82 ... 38’34 18’42 ... 8’45 5’46 ... 5’01 100’00 100’00 Sulphur 0’74 1’16 Calorific value 5,976 cal... 6,913 cal. Farther north numerous outcrops are seen in the sections exposed along the various rivers and their tributaries, notably the Atava, Nyaba, Olawba, Nyo, Azata, Obweti, Alia, Ekulu Abor, and lyoku rivers. This is the most important of the coal areas known at present in Nigeria, since it contains the thickest seam, which has a thickness of 5 ft. in the Azata River exposure, and increases in thickness to 5 ft. 8 in. in the Obweti River exposure, where it is now being developed. The following are analyses of samples obtained from this seam in various tributaries of the Obweti River :— Fixed carbon Volatile matter Ash Moisture lyocha Stream. 5 ft. 5 in. seam. Per cent. 44’88 35’60 14’89 4’63 lyuguwene Stream. 5 ft. 4 in. seam. Per cent. .. 49’70 .. 36’83 7’61 5’86 lyube Stream. 5 ft. 8 in. seam. Per cent. 48’18 37’36 7’42 7’04 100’00 100’00 100*00 Sulphur 0’73 0’67 1’15 Calorific value (cal.) 6,437 6,940 6,580 A sample of coal obtained more recently from th seam now being opened up, and stated to have been taken 100 ft. from the surface, presumably where the adit is being driven, had the following analysis com- position : Fixed carbon, 54 21 per cent.; volatile matter, 34’30; ash, 4’35; moisture, 7T4; sulphur, 0’50 per cent.; calorific value, 7,368 cal. This sample consisted of black compact coal of good quality, approximating more closely to the ordinary bituminous type of coal than did samples from the Udi field previously examined. The coal did not cake on burning, and it gave a pale buff ash. Examination of a large number of samples of coal collected in the Udi district has shown that the coal is fairly uniform in quality, and this is particularly true of the thick seam in the Obweti River exposures. A large number of samples from the Udi district as a whole showed extreme calorific values of 5,437 and 7,456, with an average of about 6,500. A number of samples from the main seam in the Obweti area showed extreme calorific values of 6,134 and 7,107, with an average of about 6,670. Okwoga District.—In the south of the Okwoga district lumps of transported coal have been found. Proceeding north-eastward from this locality, outcrops of coal have been found to the south-west of Okwoga in the Apalla, lyocha, and Afafa rivers. Analysis of samples from these localities gave the following results :— Apalla River. 3 ft. 3 in. lyocha River. 3ft. 2 in. Afafa River. 1ft. 4 in. Afafa River. 4 ft. 9 in. seam. seam seam. seam. Per cent. Per cent. Per cent. Per cent. Fixed carbon... 34’62 .. . 29*29 .. . 43’56 .. 43’47 Volatile matter 43’77 .. 39 55 .. . 35’82 .. . 37’59 Ash 4’60 .. 21’26 .. 8’59 .. 8’13 Moisture 12’01 .. 9’90 .. 12’03 .. 10’81 100’00 100’00 100’00 100’00 Sulphur 0’89 .. 0'67 0’49 .. 1’13 Cal. value (cal.) 6,552 .. 5,215 .. 5,912 .. 6,131 Specific gravity 1’3 .. 14 .. 1’3 . 1’3 All four samples consisted of black, sub-bituminous ’ coal, and, excepting the lyocha River sample, in which the percentage of ash was rather high, they represented coals of fairly good quality. Farther north still, and lying to the west of Okwoga? coal outcrops have been found near Orukuram and Otukpa. The two seams occurring between Orukuram and Okwoga are in the lyikor and Inimini Rivers, and No. 2922. are 1 ft. 5 in. and 2 ft. thick respectively. The seam occurring at Otukpa, to the north-west of Okwoga, is in the lyorba Stream, and is 3 ft. 11 in. thick. Samples from these three seams gave the following analysis :— lyikor River, nr. Inimini lyorba Orukuram. River. Stream. 1 ft. 5 in. seam. 2 ft. seam. 3 ft. 11 in.seam Fixed carbon Volatile matter Ash *... Moisture Per cent. 41’42 37’41 11’64 9’53 Per cent. 43’31 ... 34’26 ... 10’07 ... 12’36 . Per cent. .. 39’49 .. 34’96 14’05 .. 11’50 100 00 100-00 100’00 Sulphur 0 54 0’62 0’73 Calorific value (cal.) 5,936 .. 5,630 5,494 Specific gravity 1’25 1’30 1’35 The samples were rather friable as compared with typical Udi coal, but from the standpoint of calorific/ value and chemical composition, they are of moderately good quality. Idah and Western Okwoga Districts.—To the west of Okwoga, and near the western boundary of the Okwoga district, coal crops out at the Aluma Spring, Enugu (10 in. seam); at lyobo Spring, Obimo (3 ft. 6 in. seam), and the lyokolla River, between Upabi and Adani, a few miles east of Ogrugru (1 ft. 8 in. seam) Another outcrop was found at a locality three miles south-east of Angba (6 in. seam) in the Idah district. Samples of these coals gave the following composition :— Aluma lyobo Spring, lyokolla South- naat r\Y’ Spring Obimo. River. Angba. * 10 in. 3 ft. 6 in. 1ft. Sin. 6 in. seam. seam. seam. seam. Per cent. Per cent. Per cent. Per cent. Fixed carbon... 36’88 ... 18’52 ... 44’61 ... 10’65 Volatile matter 34’36 ... 24’85 ... 34’59 ... 18’13 Ash 19’29 ... 50’09 ... 15 06 ... 68’75 Moisture 9’47 6’54 ... 5’74 ... 2’47 100’00 ... 100’00 ... 100’00 ... 100’00 Sulphur 5’62 0’90 ... 0’76 ... 1’32 Cal. value (cal.) 5,269 ... 2,428 ... 6,299 ... 2,0“ 8 Specific gravity 1’28-1’48 1’7 ... 1’3 1’71-2’28 The lyokolla River sample consisted of dull-black sub-bituminous coal of moderately good quality, though the percentage of ash was rather high. The still greater ash in the Aluma Spring sample, and its high sulphur content render it of poor quality, whilst the other two samples are of little or no value as fuel, owing to their shaly character and consequent high percentage of ash. The outcrop at lyokolla River, a few miles east of Ogrugru and near the Anambra River, is of special interest as being the most westerly in the northern area. It is situated 45 miles in a direct line west of the outcrop at Otukpa to the north-west of Okwoga. Awka and Western Udi Districts.—Borings for coal were made in the area to the west of Udi, eight holes being, drilled in the neighbourhood of Onit- sha, to an average depth of 200 ft. A 4-in. seam of black and apparently sub-bituminous coal was struck at Nofia, 17 miles east of Onitsha, at a depth of 115 ft., but the amount obtained was too small for analysis. Coal was next found 32 miles from Onitsha, two seams being struck at Oba Obenagu in the west of the Udi district, viz., a 3 ft. 10 in. seam at a depth of 40| ft. and a 2 ft. 3 in. seam at 82^ ft. The borehole was continued to 190 ft., but no further seam was encountered. The samples obtained at Oha Obenagu consisted of black sub-bituminous coal. 3 ft. 10 in. seam. 2 ft. 3in. seam. Per cent. Per cent. Fixed carbon ....... 50’46 ... 36’06 Volatile matter ..... 34*54 ... 29’13 Ash ................ 7’35 ... 29’10 Moisture............ 7’65 ... 5’71 ............ 100’00 1’24 5,114 100’00 Sulphur ................ 2’60 Calorific value (cal.) ... 6,801 Whilst the coal from the 3 ft. 10 in. seam is of good quality in most respects, its sulphur percentage is rather high; and the material from the 2 ft. 3 in. seam is of comparatively poor quality owing to the high percentage of ash. At a distance of 34 miles from Onitsha, near the Oji River, three seams were struck—viz., a 6 in. seam at 19 ft, a 1 ft. 1 in. seam at 39 ft., and a 1 ft. 6 in. seam at 51| ft. The specimens obtained, however, were too small for analysis, and the boring was stopped at 272 ft. Both here and at Oha Obenagu a strong flow of artesian water was reached at a depth of about 90 ft. Surface prospecting was also carried on as far as possible in this district. A 4 in. seam, previously located at Obinoffia, was found to widen out to 1 ft. 6 in, on being traced northward, and the following seams were also located:—A 2 ft. seam at Achallowa, a 1ft. 2 in. seam between Achallowa and Amandim, and a 3 ft. 2 in. seam in the Oba River near Oha Obenagu.