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A Romance of Lake Wakatipu

Note 16.—River (Gold) Dredging

Note 16.—River (Gold) Dredging.

Mr. Henry A. Gordon, M. Inst. C.E., Inspecting Engineer for the colony, reports: A large number of dredges have been constructed to work the ocean beaches and river-beds, many of which have proved successful in their operations. Several descriptions of dredges have been so employed—namely, the centre-bucket, the Welman, Ball, and Von Schmidt dredges, as well as the Priestman grab; but the centre-bucket dredge is the favourite one for working gravel-flats and river-beds. All these dredges are, however, defective in washing-appliances. The hulls, or pontoons, on which the dredging machinery is placed, are too small to admit of good separating-appliances and gold-saving tables being constructed. Improvements are being however made in these, and before long we may reasonably hope that this system of gold-mining will be successfully carried on, and the ocean beaches and river-beds will be made to yield up their hidden treasures. There are now a large number of centre-buckets dredging on the Clutha, Kawarau, and Shotover Rivers, and most of these are seen to be profitable ventures. The latest constructed is worked by electro-motive force, generated about a mile and a half distant from the place where dredging operations are carried on, thus showing that our streams and rivers can be utilised as a power to generate this force, which can be transmitted long distances on a small copper-wire to the place where machinery requires to be erected. The subscribed capital of companies employed in this particular branch of mining represents £322,585, of which £72,879 has been paid up.

"Anno Domini 2000," written by Sir Julius Vogel, is a work dealing with a correlative to the pursuit. So difficult is it assumed to be that the writer page 117has relegated it amongst the achievements of future generations. Although weak in detail, the plot has a certain boldness and vigour in its conception, which merits attention at the hands of enterprise and energy. Whether it be a secret of the movement or not we cannot pretend to tell, but it is true that enterprise on the lines laid down by the writer are already contemplated. In pursuance of solicitations made by the localities more particularly interested the Mines Department of the colonial service has authorised its inspecting engineer to examine into and report upon the feasibility of constructing a system of look-gates, so as to dam up the Clutha at its sources, and thereby enable the channel to be worked. The proposal is certainly plucky; but no one familiar with the progress of events in southern New Zealand can doubt but that it is an enterprise characteristic of the place. In the prosecution of inquiries made on the spot, Mr. Gordon gauged the three principal insets from the lakes: Wanaka, 10,000 sluice-heads per minute; Wakatipu, 14,000; and Hawea, 3,200. These measurements were taken in the month of January, when the water is considerably higher than during the winter months. The winter discharge, which, in these ice-bound regions is always the lowest may be put down at from one-half to one-third less than in summer. Lock-gates or barriers to dam the water back into its lake-reservoirs can, it is ascertained, be erected. Distributing these discharges over the areas of their respective lakes the outflow might, under the most disadvantageous conditions within the memory of man, be confined for a period of twelve days on a stretch without doing material damage to the neighbourhood. That simply means, with a proper system of lockage, the river-bed would be exposed for that length of time, or for longer periods, according to the season of the year and other concomitants. The richly auriferous portion of the river is 167 miles in extent—viz., Clutha branch, 37 miles; Kawarau, 40 miles; and from the junction of the united streams to the mouth of the Tuapeka, 90 miles. The possibilities arising out of the completion of this scheme are simply incalculable. As stated in the body of the narrative, the fame of the river arose out of a find of 87lb weight of the highest-priced gold, scraped from crevices of a rock in the channel; the water happening at the time to be at a low level, to which it has not since fallen. It has been urged the enormous discharge of tailings, consequent upon river-bank and tributary stream sluicing operations, must have filled-in the channel to a great depth. Observations made on that score have elicited the information that the bed of the river has been raised about 8ft. from its original level before gold was discovered. At no place does the débris lie to a greater depth than 3ft., and at places more exposed to the scour it does not rest at all. Even the débris, if it could be secured, would now prove valuable, immensely so; and that of itself would, so to speak, anticipate the process for getting down to the solid. Gabriel's Gully tailings, which have been washed and rewashed half a dozen times by both European and Chinese labour, are again being treated on payable terms; and sludge-channels all over the province have been instrumental in recovering a vast amount of treasure. If, then, these can be operated on successfully, how much more so must the river débris be payable. It is not only a tailing deposit at first hand, but it is constantly getting enriched by the river current. Kawarau branch, on the other hand, is a great mountain torrent, intercepted by huge boulders and jutting rooks, forming an endless succession of whirlpools and eddies. The story told in the narrative of a human being caught in one of these eddies and held in suspense for weeks is no mere fancy-sketch, but a ghastly reality. Bullocks and horses have been similarly caught and kept dangling in the stream for lengthened periods. It follows, then, if such bodies can be arrested, substances like gold could not possibly escape; so that the probabilities are these whirlpools and eddies are sinks in which the gold of ages has accumulated. The project is, to this extent, a feasible one, and, as we have already hinted, its eventualities are incalculable. The upper or top banks have paid well; the gold being all, without exception, water-worn. If, then, the top layers are rich it stands to reason the under-ground, on which the water is incessantly acting, must be enormously so. Of this we may be assured, with such vital interests at stake Otago will not rest satisfied page 118until it has tested the question raised by "Anno Domini 2000," even although the time predicted by the author may not have arrived for its accomplishment.