H.—34.

The fundamental attitudes to observe are bedding planes and fracture-cleavage planes ; bedding planes observations give a comprehensive view of the geological structure, and fracture-cleavage obseivations indicate the position and attitude of the axial planes of major and minor folds ; the angle the fracture cleavage makes with the bedding will indicate whether the particular limb where the observation was taken is overturned or in its normal position. Attitudes were measured along many sections, and these and other data, when plotted on the topographic maps, showed that the Aorere Series is closely folded along north-east to south-west lines. In the district between the Waitahu and Inangahua Rivers two main anticlines with their corresponding synclines were mapped, also several shorter folds that could not be traced far along their trends. The most easterly and major syncline in the belt examined was traced from the Waitahu River southward to Trig. A.H. and Murray Creek, and thence to the Inangahua River. An excellent section of this syncline can be studied a short distance north-west from Crushington to Lankey Creek. The synclinal axis continues southward up the valley of Union Creek. Toward Cornishtown and Globe Hill the eastward-dipping flank is complicated by minor folds and shears ; farther southward the axis persists and was traced in the heads of Union, Devil, and Fossicker Creeks to Inkermann Mine, and thence through the Scotia at Merrijigs to the Golden Lead. At several places the structure and position of the synclinal axis is complicated and obscure, but this is believed to be due to lack of clear sections and good rook exposures. The axis is sinuous, but the sinuosity tends to straighten where opportunity for good and close observation is possible. The beds along the flanks of this major syncline dip at high angles, 50° to 80°, but the dips tend to lessen toward the axis. In many places the flanking beds are overturned, this overturning is particularly characteristic of the east flank along its length extending from the Inangahua River northward to the Waitahu ; here the beds on the east-dipping flank have been overturned through 90° and dip at 70° to 80° to .the west. The overturning is accompanied by eastward-dipping thrusts faults of small displacement. Along the axis and for 300 ft. or 400 ft. east and west from it the rocks are extremely sheared and fractured. This syncline is the major structural feature of the area examined. The position of its axis is important economically, for the main gold-bearing lodes lie in shears and tension fractures on or close to its axis. There is little doubt that the synclinal trough, in the main, defines the position of the lodes. West from the major syncline is a sharply asymetric anticline with the steep limb dipping westward. A section is well exposed along the Crushington Road, south-east from Black's Point. The fold was traced northward into the heads of Anderson, Ajax, and Inglewood Creeks, and may be present in the Waitahu Valley. Southward it is doubtfully present in the head of Auld Creek, but it was not mapped in the bush country separating Auld from Devil Creek, and could not be identified with certainty in lower Devil Valley. - A second sharp syncline, extremely sheared and deformed, is present west of this anticline. A section of it is well exposed south-west from Black's Point where Auld Creek joins the Inangahua Valley. It can be traced southward up Auld Creek and north-east into Anderson, Ajax, and Inglewood Creeks, and is possibly present in the Waitahu Valley, the axis coincides in part with the Black's Point fault. Anderson's and the Bonanza lodes occur on or close to the sheared axis of this second syncline, and prospecting along it may reveal new ore-bodies. A major anticline can be traced in the Inangahua Valley, half a mile east from Reef ton ; its axis trends north-east, and, though obscured below terrace gravels, can be observed in the lower reaches of Anderson and Inglewood Creeks, on the Painkiller-Murray Creek Track, and in the Waitahu Valley. Southward from the Inangahua Valley this axis was not traced, and it seems to plunge in this direction. This anticline is crushed along its axial area, and in places has barren quartz lodes, but no important ore-body has yet been found along it. Auriferous Lodes. The gold-bearing lodes, and especially the valuable ones, lie along the main synclinal trough on the eastern limit of the area examined. From north to south these lodes are the Inglewood and possibly some minor ore-bodies to the north —Golden Fleece and Ajax, Golden Treasure, Perseverance, Royal, Venus, Energetic, Keep-it-Dark, and No. 2 South Keep-it-Dark. From the Inangahua Valley southward along the axis gold-bearing lodes have not been found for two miles, but in the vicinity of Cornishtown and Globe Hill the important Globe-Progress lode was mined. The relation of this orebody to the major syncline is not wholly clear, apparently the eastern portion of the lode, where it strikes north-south is along a shear on the complicated western limb of the syncline and the east-west striking portion cuts across the regional structure. Apparently a north-south branch from the main lode continues northward at least 400 ft., lying along the overturned and sheared axis of the major syncline. Southward from Cornishtown, the Gordon, Inkermann, Scotia, Cumberland, and Golden Lead lodes occur in shears close to, or on, this major synclinal axis. Minor anomalies to this generalization are noted, but it is reasonably well demonstrated that the richer and larger ore-bodies are emplaced along the synclinal trough, irregularities tend to disappear where clear exposures can be studied and the structure better understood. In shear zones and minor folds far from the axis only low-grade and barren quartz lodes occur, and these are small and few compared with the large bodies of barren and auriferous quartz along the synclinal trough. Anticlinal axes were not favourable sites for quartz deposition, although this statement may not apply to the whole of Reefton-lode belt; for example, a brief examination of the rocks close to the Blackwater Mine suggests that this valuable ore-body occurs along the sheared crest of a north-south anticline and one small low-grade lode, the Last Chance, is on the axis of the major anticline a short distance east from Reefton.

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