The Pamphlet Collection of Sir Robert Stout: Volume 71
(7) Otago Coal-fields
(7) Otago Coal-fields.
There were in Otago, in 1891, no less than 80 coal-mines on the official list, of which 20 did not produce, or at any rate were not returned as producing, any coal. The total yield was 164,870 tons, or 11,558 tons less than in the preceding year, but of this total 110,042 tons came from 5 mines, leaving 54,828 tons, or an average of 731 tons each for the remaining 55 working pits. Many of these are mere opencast excavations, into which carts are driven, and where the fuel is got as cheaply as it is probably possible for it to be obtained under any circumstances.
A Pet Cent. | B Per Cent. | |
---|---|---|
Fixed carbon | 51.38 | 55.00 |
Hydrocarbons | 22.78 | 24.83 |
Water | 19.92 | 13.89 |
Aah | 5.69 | 6.28 |
99.77 | 100.00 |
The measures dip E.S.E., at 10 degs., below the sea, where they have been explored to a small extent, and where in all probability a very large area exists. Rising to the west they form an anticlinal arch, which is terminated westward by a syncline, from the base of which they again rise, at high angles, into the hill known as Puke Ivitai. In 1880, the output was 36,066 tons, but it has since considerably fallen off, and in 1891, only 7,814 tons was raised, making 4,298 tons less than the pre-ceding year, and a total of 228,242 tons since the opening of the workings-Two seams are mined, with a thickness varying in one case from 2 to 12 feet, and in the other from I foot to 4 feet. The output is raised partly by a shaft measuring 16 feet 6 inches by 6 feet and 200 feet deep—(lately, the writer believes, this has been deepened)—and the water in tanks which automatically fill aud empty themselves. The workings are free from gas, but the slack is remarkably subject to spontaneous combustion, and great trouble and expense have resulted from this fact. The roof also is very bad.
In the same district, but in the trough of the syncline to which reference has been made, is the Allandale coal-mine, commenced about the year 1887. This seems already to have outstripped the older mine in output, for in 1891, the production was 10,735 tons. The seam is 7 feet in maximum thickness, and is worked by a dip drive, up which a small fixed engine draws the wagons. By now the pit-mouth is, presumably, connected with the railway by a train road.
The extension of the coal-measures beneath the Palmerston flat is a matter of conjecture, but it is to be hoped that this may prove to be the case, for the coal at this locality is of good quality and the situation favourable.
No further important deposit is known until the city of Dunedin is passed, about 6 miles from which centre, on the main south line, is the page 86 Green Island coal-field. The coal here produced is of inferior quality, but the scam (only one is worked) is 19 feet thick, and the measures consist of sands, clays, ferruginous gravels, shales, and fireclays, resting uncou-formably upon the upturned edges of highly metamorphosed rocks of unknown age, and dipping to thu north-east at an angle of 1 in 10 beneath a thick sandstone of Tertiary age, which is again overlain by the volcanic rocks of the Dunedin basin.
The field has been opened for about thirty-three years, and very numerous pits have been commenced, many of which have been lost owing to spontaneous fires, which are very rife. The tenure of the land is freehold, and the royalty usually 1s. per ton. A very large proportion of the seam is lost, as only 7 feet to 8 feet is worked in the first place by the room-and-rance system, and 3 feet more is got in coming back. In 1891, eight mines were at work, employing 138 men, who turned out 50,318 tons, a considerable amount less than the output in some former years.
Of these eight mines only three were connected with the railway, and one (Abbotsroyd colliery) has private telephonic communication with Dunedin. The produce of this field has, when first got, a lustrous appearance and dark brown colour, but desiccates rapidly on exposure to the air. It burns freely with a slightly unpleasant smell, and leaves a bulky incandescent ash. Notwithstanding these defects, it is a fairly popular second-rate fuel in and about Dunedin.
The mines are entirely free from explosive gas, and accidents of any kind are rare.
Per Cent. | Per Cent. | Per Cent. | |
Fixed carbon | 40.84 | 36.00 | 35.70 |
Hydrocarbons | 36.57 | 42.50 | 39.80 |
Water | 18.67 | 19.00 | 23.10 |
Ash | 3.92 | 0.90 | 1.40 |
100.00 | 98.40 | 100.00 | |
Sulphur | 0.90 | 3.66 |
The Clutha coal-field, which next comes under consideration, is of large area, extending from the Clutha river on the south to 9 miles north of the Tokomariro river, a distance of 20 miles.
The formation consists of conglomerates, sandstones, clays, and shales, with coal-seams, forming ranges of hills 700 feet high in the neighbourhood of Kaitangata, and of less altitude to the north where they rise again on the flanks of Mount Misery, which is composed of schists.
The first mine was opened in 1858, aud although enjoying the advantage of financial assistance from the Provincial Government, was not a success.
page 87In 1891, thirteen mines were at work, but if the output from the Kaitangata Railway and Coal Company's mine (58,945 tons) he deducted, the remainder is under 10,000 tuns. The mine belonging to this company is a good example of a successfully-managed Colonial colliery, at which the coal is by no means first-class, but the working of which has been for many yours highly profitable. Originally two companies held rival interests, but in 1880 the Kaitangata Railway and Coal Company bought out the neighbouring proprietors, and have since worked the whole area.
The workable seams are four in number, the uppermost 3 feet 6 inches in thickness, and about 250 feet below this is a 9 feet seam which has not been worked. At a further depth of 250 feet is the main seam, upwards of 35 feet in thickness. From the small seam about 7,000 tons was taken in 1876-77, but it has been for many years abandoned. About 150 feet below the main seam is another, 19 feet in thickness which was discovered by chance in 1889, but this enterprising company would appear not to be contented with even these quantities of coal, for the recent Dunedin papers state that they have purchased a diamond drill, capable of boring 2,000 feet, in order to prove the lower measures. The main seam is a good deal broken, and in places highly inclined; the roof is a hard quartzose conglomerate, 70 feet thick, and auriferous, though not sufficiently so to be workable. The floor is moderately hard. In the original mine the seam dipped at 1 in 7, and on approaching the dip Look a plunge at 45 degs. Inclines were driven on the full angle and levels on the strike close to the roof; from these levels bords were driven to the floor. These workings eventually were closed, owing to a very heavy weight which came on. In the flat portion of the lease, the system was ordinary bord-and-pillar. About 8 feet of coal was got at first, and afterwards as much of the top coal as possible. It will readily be understood that during this operation the working-places were of enornons height, and hence some change became necessary, when the following system was tried. At the first operation about 10 feet vertically was taken and sufficient laterally to bring on a weight which crushed the pillars into the floor; the whole area was allowed to settle, and the upper portion of the already partially-worked bords was then taken out. Of course, an enormous proportion of the seam was sacrificed by this system, but this appears unavoidable in cases of so thick a deposit. The coal is raised by an engine-plane 1,076 feet long and 9 feet wide by 6 feet 6 inches high, dipping 1 in 5 through the conglomerate and measures, This road, which is very hard in places, and in which some water was met with, was constructed by means of rock drills driven by compressed air, in six months.
page 88The seam gives off some explosive gas, and the slack ignites very readily. In a paper mad in 1890, Mr. Shore, the manager, gives some interesting details on this point, one of which may be reproduced:—
A few years ago an incident occurred having a remarkable bearing on the rapid generation of spontaneous combustion under favourable circumstances. Pending the erection of air-compressing machinery, steam was temporarily conveyed a along a dip tunnel for pumping purposes; 3 inches pipes enclosed in a 12 inches by 12 inches wooden box filled with sand were used. The loaded trucks by accident left the tram rails. Anxious to get operations started, the men turned one of the trucks, loaded with wet dross, over on top of the box containing the steam-pipe. The temperature of the tunnel, which was used as an upcast, was 74 degs. Fahr. Twenty-two hours from being turned over the truck was found to be on fire. When removing the truck the dross (about 7 cwt.) had the appearance of newly-prepared asphalte.
A. Per Cent. | B. Per Cent. | C. Per Cent. | |
---|---|---|---|
Fixed Carbon | 41.96 | 30.42 | 41.47 |
Hydrocarbons | 35.49 | 39.01 | 37.28 |
Water | 15-85 | 16.71 | 17.48 |
Ash | 6.69 | 4.76 | 3.76 |
99.99 | 99.99 | 99.99 | |
Sulphur | 0.838 | 1.141 | 1.071 |
In addition to the property described above, the company owns a freehold coal-bearing estate of 2,200 acres near Tokomnriro, 41 miles from Dunedin.
The working of the Kaitangata colliery has been for many years very free from accident, but in 1879, before the enforcement of mining regulations hy Government, a disastrous explosion occurred, which killed 3 persons, and left the 31 remaining in the mine to die of afterdamp. In a few weeks the sum of £15,378 was subscribed in the colony for the benefit of the widows and orphans, £10,000 of this sum being raised in Otago alone. In the beginning of 1890, £14,631 had been paid in direct alimony and £563 in expenses; and notwithstanding this large disbursement, thene was £11,645 left to the credit of the fund. The writer gathers from the Colonial newspapers that legislative action has been taken, and that the capital has been placed in the hands of trustees as a fund for general mining accidents.
Near the Kaitangata Railway and Coal Company's mine, a company known as the Castle Hill Coal-mining Company has of late years been engaged in sinking a shaft. Some time ago a borehole proved the coal at 400 feet, and a small shaft was put down, striking a good seam. Since then a 13 feet circular shaft has been commenced, which was to cut the coal at 600 feet. Brickworks were established and a railway built to connect with the existing private line. Unfortunately a great deal of water and running sand was met with, which overpowered the pumping appliances, and when the sinking was resumed, after standing for some time, the sides were found to be damaged, Information under date February, 1893, is to the effect that the shaft is abandoned, and the workings will lie approached by a cross-measure drift dipping 1 in 4½.
Scattered throughout the interior of Otago are numerous small mines, many of them openwork, and employing only u man or two for a short time.