Изображения страниц
PDF
EPUB

have deprived the hydrous coals of more or less of their water. The varieties may be roughly classed as follows :

Lignite, woody structure, 15 to 80 per cent. water.
Brown Coal, compact structure, 10 to 20 per cent. water.
Pitch Coal, conchoidal fracture, water usually under 10

per cent.

Bituminous or Coking Coal, laminated and cuboidal, water less than 5 per cent.

Anthracite, very dense and compact, practically anhy. drcus.

The principal coal fields are the following:

The North Auckland Coal Field extends from South of Wangarei to near the Bay of Islands, a distance of more than 80 miles. The field is bounded on the East by paleozoic slates and sandstones, and in the hollows of these rocks lie the beds of the Cretaceo-Tertiary formation, at the base of which are the coal seams. Near Wangarei Harbour these beds cover an area of about 16 square miles, with two seams of coal, the upper 41 feet and the lower or main seam 6 feet to 10 feet thick. The coal is pitch coal of good quality and is worked at the Whau-Whau and Kamo Collieries. Northerly from Kamo the surface is chiefly covered by basaltic and trachytic rocks for about 9 miles to Hikurangi, where numerous outcrops of seams have been noted, varying from 2 feet to 6 feet, but none have yet been worked. Further North the country is chiefly slates with tracts of overlying volcanic rocks to Kawa-Kawa, where a basin-like area of coal measures occurs, consisting of a series of green and brown sandstones and limestones, containing two seams of coal, the upper being 4 feet 3 inches thick, of inferior quality. The lower or main seam is from 6 to 15 feet thick Pitch Coal, hard, compact, and of good quality, and is now worked by the Bay of Islands Coal Company. A notable point about this coal is the large amount of sulphur it contains, stated at about 5 per cent., not, as is commonly the case, in the form of pyrites, but the greater part oxidised as free sulphuric acid, which is even said to communicate a sour taste to the coal, The total area of this basin is estimated at 10 square miles. North from Bay of Islands the country is chiefly volcanic, but at the head of Wangaroa Harbour a seam of Brown Coal is found outcropping among green sandstores.

Still more North at Mongonui coal outcrops are known to exist.

Dr. Hector, in 1865, received a specimen of Shale resembling Torbanite from this district, which contained 75 per cent volatile matters, but “no other specimen was found" and although Mr. McKay visited and searched the locality in 1875 he failed to find the deposit. It is needless to remark how valuable a workable bed of this mineral might prove if found in an accessible position.

Coromandel.- Small deposits of Brown coals have been found at several points of this peninsula, and quite recently a bed of excellent bituminous coal is reported from Tiaroa.

South Auckland or Waikato Coal Field.- So far back as1859, a coal seam about 6 feet thick was opened at Drury, 20 miles south of Auckland, but the coal was inferior, crumbling on exposure and the irregular floor of clay, bad roof and costly freight caused the works to be abandoned after 4 or 5 years. and they have since remained closed. The coal basin of the lower Waikato extends from Mercer southwards to Taupiri about 85 miles with a breadth of probably about 20 miles. The basement rocks of the country are palæozoic slates of undetermined age, very pyritous, and much disturbed, and which rise into a range of hills extending from near the Firth of Thames by Taupiri to near Waipa, and form the eastern and southern boundary of the coal basin. Upon their flanks and hollows repose a series of shales and sandstones with coal seams, supposed to be of Lower Greensand age, and these are in turn overlaid by the Leda Marls, the lowest beds of the Cretaceo Tertiary formation. The whole suggests the site of an ancient estuarine lagoon. On the East, within 7 or 8 miles of the Thames Gulf, a shaft was sunk at the Bridgewater Colliery, the measures passed through being : Leda Marls and Fire Clay

a

17 feet. Sandstone BROWN COAL Shale

2 55 2

The coal is good, but the venture has not been successful and the colliery is now closed, Near Taupiri Gorge, in the south, at the Taupiri Colliery, the coal is 31 feet thick, divided by a shale band; and at the Kupa-Kupa or Waikato Colliery the seam is from 18 to 23 feet. Both these collieries are working and help to supply Auckland city. It is estimated that not less than 150 million tons of coal are available in this district. At other points on the West and North-West outcrops of coal seams are known, but, partly owing to the objections of the natives, the district has not yet been fully examined. There appears at least strong presumptive evidence that coal will be found to underlie the greater part of the lower Waikato basin.

Mokau.-South of the Waikato field, on the River Mokau, outcrops of seams 2 feet to 6 feet thick, have been examined by Dr. Hector, who reports them to be pitch coal of good quality and probably of lower greensand age. The densely wooded nature of the country, which is in the hands of the natives, prevented the extent of the outcrops from being traced, but these were found at several miles apart.

Wellington.—Brown coal has been found in this province on the Wanganui and Rangitikei Rivers.

The Nelson or West Coast Coal Fields in the South Island are perhaps the most important in the colony. They occur as detached deposits in the hollows of the older rocks and extend from West Wanganui to Grey River about 150 miles. On the older rocks lie the sandstones, shales, and coal seams of lower greensand age, overlaid by the Cretaceo-Tertiaries. At Collingwood there are four seams of excellent bituminous coal, from 3 feet to 4 feet in gross thickness, but so mixed up with shale partings that the working of them has been repeatedly abandoned. At several points in the vicinity good outcrops are known. At West Wanganui inlet a four feet seam has been worked, but unsuccessfully.

The Buller Coal Field extends from the Mokihinui to the Buller, about 40 miles, with a maximum breadth of 7 miles. The country is broken and rough. Rising from the Buller River by a succession of terraces, at an elevation of from 1,500 to 2,500 feet, is a great bare plateau, sloping gently to the north-east, descending to sea level near the Mokihinui. Intersecting this plateau are well timbered, deep, precipitous gorges, on the sides of which are exposed sections of the coal seams. Of these there are two-an upper very irregular one of 1 foot to 5 feet thick, and a lower, the main seam, ranging from 8 feet to 53 feet thick. The quality varies in different parts from a tender, bituminous coking coal to a splint or cannel coal. Several attempts have been made to work this field, but not with very satisfactory results; recently however, the Westport Coal Company has opened a colliery which gives good promise. The quantity of coal available is estimated at one hundred and five million tons. The Buller River is the best port of the West Coast, and is capable of being greatly improved, and as the coal seams on the plateau are thick, compact, and of superior quality, and can be won in most cases by level drives, the difficulties of transport will eventually be overcome, and, with the judicious employment of capital and technical skill, there ought to be a good future before this district.

The Grey Coal Field, about 7 miles above the mouth of the River Grey, extends about 15 miles north and south. There are several seams, the principal one being 12 to 16 feet thick of bituminous coking coal, overlaid by sandstones and having a fireclay seat. This coal is probably the best gas coal in Australasia. There are working here the Brunner, the Coal Pit Heath, and the Wallsend Collieries. Defective transport and a shifting bar at the mouth of the Grey River, which limits vessels to a draft of 9 or 10 feet, are obstacles which have hitherto retarded the development of coal mining in this field, which is estimated to contain about four million tons of available coal.

Reefton is a gold mining town on the Inangahua River, east of Grey, where seams of Pitch coal from 6 feet to 21 feet thick are found and worked on a small scale for local use.

Nelson City.--Some Brown Coal beds found here have led to many unsuccessful attempts to work them; and at Picton also many trials have been made which have ended in disappointment. Recently a seam has been found at the head of Shakespeare Bay which promises better, and a com. pany has been formed to work it.

Westland.-At Kanieri some coal crops are found which have led to considerable sums being spent in prospecting trials, but no payable seams have been proved.

Further south, from near Paringa River to Moore River, a district extending north to south 25 miles by about 8 miles wide, is occupied by coal measures, and an outcrop of good bituminous coal 12 feet thick has been traced between 3 and 4 miles.

At Jackson's Bay, Cascade Point, and Martin Bay, extensive areas of coal measures are known to exist, but they have not yet been sufficiently examined to justify an opinion as to the value of the seams they contain.

The Malvern Hills Coal Field, about 30 miles west of Christchurch, comprises a district of about 180 square miles. "The beds of the great Brown coal formation lie along the east slopes of the hills, and descend towards the plains, beneath which they appear to dip. They consist of sands and shales, with several seams of coal, the thickest of which, however, is only 71 feet. The district has been extensively disturbed and broken by dykes of trachytic porphyry, and subsequently subjected to enormous denudation in the post pleiocene glacial period. In the western parts, only isolated patches of altered coal remain where basalt cappings have preserved the subjacent beds. The dykes and streams of lava have converted the coal within reach of their influence from Brown to Pitch, or glance coal, and, in some cases, as at Acheron Gorge, to anthracite. There are several collieries working in this field ; and the whole available coal is estimated by Dr. Haast at something under five million tons.

At Clent Hills and Mount Somers are coal seams, but they are of purely local importance.

Oamaru. Here two seams of Brown coal each 9 feet thick are worked on a small scale.'

« ПредыдущаяПродолжить »