COAL IN TARANAKI.

Taranaki Daily News, 12 September 1922, Page 2

COAL IN TARANAKI.

■ THE OHURA SUBDIVISION. ' / REPORT ON SURVEY. The annual report of the geological survey branch of the Mines Department includes the report of Mr. L. T. Grange #n the Ohura subdivision, which comprises the following survey districts: Aria, Tangitu, Rangi; Piopiotea West, and parts of Waro and Ohura, containing in all about 400 square fiiiles. The following extracts will no doubt be read with interest: The oldest rocks of the Ohura subdivision ar.e tertiary mudstones and alternating sandstones and mudstones continuous withthe Mahoenui beds of the adjacent Mokau district. They are followed by massive sandstone layers, which are in turn sub*' deeded by argillaceous sandstones. The whole series, which corresponds with the Mokau series of the Mokau subdivision, is over 1000 feet thick. In the western part I of the district the massive sandstones contain coal seams which, in at least parts .of the area, thin to the east. Where the coal measures are absent there is evidence of an unconformity at the base of the series. Overlying the Mokau series, in most places conformably, are beds placed in the Mohakatino series. In Tangitu, Rangi, and Piopiotea West survey districts an erosion interval is indicated at the contact by a band of conglomerate averaging 9 ft. in thickness, made up of standstone and mudstone boulders and a few greywacke pebbles, as well as by the slightly uneven surface of the underlying beds. Fully 700 ft. of strata, consisting principally of mudstone, in which occur bands, lenses, and pests of andesitic tuff, compose the Moha katino series. The tertiary sequence is closed by argillaceous sandstone, 70 ft. thick, which outcrops in two small areas in the north-west of Aria Survey District. This represents the Tongaporutu series. The rhyolitic breccia of the Ongarue Valley, near Wairniha, and of the high ridges farther west, the weathered brown pumice sprinkled over many of the upland slopes, and the white unconsolidated pumice of the terraces pf the Ongarue and Wanganui rivers, form the pleistocene and recent deposits.

ECONOMIC GEOLOGY.

Coal.—The outcrop portion of a large coalfield, an extension of the coal measures af the Mokau and Tangarakau districts,has been mapped in the Waitewhena, Panirau, Paraheka, and Mangaohutu valleys. The field extends almost continuously from the north to the south of the subdivision. Except for small areas capping high ridges, it is bounded on the west by the Aria fault; but to the east, at no greater distance than four miles from this fault, the *coal thins out and is not present farther eastward, although what is believed to be the coal horizon was observed at many points. The coal measures are about 70 ft. thick, and in places contain several seams, of which the lowest is always the main seam, the upper seams rarely exceeding 5 feet, in thickness. In the Waitewhena Valley, north of Ohura, the thickest coal occurs on the western side. Marco Creek and Mangarohe Stream show a practically continuous outcrop of a seam nowhere less than 10 feet thick. From the Mangarohe Stream north to the bridge over the Waitewhena the thickness varies from 12 feet to 9 feet. Directly east of Wa Trig, the coal thins to less than 6 ft, but thickens to 12 feet at Knight’s Mine, 38 chains north-east of the trig, and extends 60 chains farther northward with an average thickness of 9 ft. Near the source of the Waitewhena Stream the coal, here from 5 ft. to 10 ft. thick, as it approaches the Aria fault has a strong dip to the east. In the Pura Stream, immediately south of Marco Creek, most of the outcrops show more than 6 feet of coal, but south from this locality the seam is usually less than 6 ft. in thickness. On the eastern side of the Waitewhena Valley a thick seam can be traced from the mouth of Awawaro Stream for 55 chains to the south, but elsewhere few exposures of coal are more than 6 ft. thick.

The headwater streams of the Panirau, a large branch of the Mokau River, rise on the main ridge west of Waitewhena Valley. In this locality are many outcrops of coal, almost all over 6 ft. and most of them at least 10 ft. thick. From north to south, as the crow flies, these outcrops occur over a length of four miles. There is a large amount of workable coal in the ridge between the Waitewhena and Panirau basins.

In the Paraheka Valley the best outcrops extend from 14 chains north-north-east of Pukerewa Trig, south along the edge of the Aria fault to east of Munro. Trig, a distance of about one mile. Here five outcrops of 8 ft. or more were obThe seam dips strongly to the east, and in a short distance passes below drainage level. Two miles eastward, where the coal-horizon is again brought to the surface by faulting, no coal is present. In this locality the amount of workable coal t'o the dip can be determined only by boring.

At a point in the Mangaohutu Valley, about 2} miles south-east of Aria, a coalseam fully 17 ft. thick has been worked by Mr. A. Morgan from adits. A few chains from the entrances to the mine the seam lis cut off by a north-north-east-striking fault, east p.f which it has not yet been found. An outcrop showing 6 ft. (no roof observed) of coal, 50 chains west-south-west from the mine and 230 ft. above it. probably belongs to the same seam. Fifteen chains north from this outcrop a seam at the same high level is indicated by fragments of coal; but farther to the north no trace of coal was observed at or near this height. The evidence indicates either that the higher seam has thinned just north of the coal-fragments and that the seam worked in Morgan’s Mine is in a downthrown block, or that another fault lets down the strip of country between the fragmentary coal and Morgan’s Mine to below the level of the worked seam. Owing to the covering of bush and heavy fern and manuka, prospecting is difficult.