DREDGING UPON THE KAWARAU.

Otago Witness, 5 December 1900, Page 21

DREDGING UPON THE KAWARAU.

(Frou Otjr Waxatipxt' Correspondent.) EIYER VEBSTJS DRY-LAND DBEDSIXG. Dredging naturally divides itself into river and dry-land dredging. Each division has its own advantages and its particular drawbacks. So far as experience goes, the best results have been obtained from the large rivers of Otago — namely, the Molyneux and the Kawarau, the richest places occurring where the stream is confined between rocky banks, the gold being deposited in leads of slightly-varying width. There is no surface soil or clay to interfere with the progress of the work and with the- saving of the gold, which is generally of a heavy and solid character. JBesides these advantages over dry-land dredging, there are other facilities which go to make dredging upon -large streams more profitable than on ground of equal richness, where no running stream exists large enough to allow the dredge free, easy, and unhampered movement in every 'direction desired.

On the other hand, in dry-land dredging there is immunity from floods, the more jj§Queral distribution of the gold, and, as a

rule, an absence of large and bothersome stones. One item that has worked-havoc to more than one dry-land dredging company, and which ought to have been foreseen, is the rise in the ground, requiring the dredge to be floated above the water-level of the surrounding country. I could mention at least two instances where, without instruments or measurement, it was plain to the unaided eye that it was physically impossible to work more than a very small portion of the ground before the fall jn the stream ran out.

Other items in dry-land dredging that deserve attention are the fact that ground more than ordinarily rich had already been worked when taken up for dredging purposes, and that in the heydey of the dredging boom too much was expected from the performance oi dredges fully up-to-date in poor ground. All this is not said for the purpose ol throwing cold water upon any division oi dredging operations. So far as dry-land dredging- is concerned, it is quite plain that it will flourish, and yield regular returns when the rivers are exhausted of their last spec of payable gold, after having been dredged and re-dredged. Shortly put, the case with river and dryland dredging stands thus: — If the investor goes for big and quick returns, he must go into - river claims and take the risk; if, on the other hand, he is satisfied with moderate and lasting .dividends the dry land investment is likely to meet his views. PRIVATE PABTY. What militates against the real value and importance of dry-land dredging is the fact that a great many private parties have taken to this mode of dredging, nearly all of whom " are doing remarkably well, many getting even princely yields from their jlaims, of which nothing is ever heard publicly — not a few of • them being afraid to let their gettings be known, for fear that the public knowledge of them may cauEe trouble or interference in the shape of being pegged off. It would, of course, be futile to make an estimate with any pretence to accuracy as to the amount of gold obtained by private companies, but at a rough guess the sum may be put down at about*soooa or 600oz per week. As is well known, there are also a numbet of private parties engaged in river-dredgingl THE KAWARATT AS A DREDGING FIELD. Comparatively speaking, the Kawarau River is still an unknown quantity — that portion worked near Cromwell by the Magnetic, Cromwell, Lady Ranfurly, and sister dredges being fed by gold country off the Carrick Range, which range also accounts for a good deal oi the Hartley and Riley gold, is a part by itself. But the portion extending from the Gorge, near Cromwell, to the junction of the Arrow River, about 18 oi 20 miles in length, is almost untouched, offering a field of considerable extent, the whole of which, with the exception of a few places, there is now sufficient reason to say, is dredgeable and payably |uiriferous, though perhaps not in an equal degree throughout the whole of .the 18 or 20 miles. THE CHARACTER OF THE KAWARATT. The character of the river for the distance here referred to is best described as a moun- ' tain gorge. On the south side of the stream ' .the rocky walls of the Remarkables rise to a - height of 7600 ft, abqye sea level, with here ' .and there a few basin-like expansions in, the valley of limited extent. ' The, north bank is ' .marked bjr'bo-M, abrupt dips descending from ' th' 2 Crown J&ange, 5700 ft high. -The gorge bears 'the ,mark« of sortie violent eruption or " convulsion of Nature, corresponding in direc- • tion with the middle section of Lake Wak'atipu, breaking that lake into two nearly equal parts, lengthwise. Some geologists, of the New Zealand Geological department ,are inclined to look upon this break through two mighty mountain ranges, which, however, might have formed one connected mass at one time, as a "fault" — that is, geologically speaking. It is to be hoped that dredging investors will find reason to consider .it in another light. THE FALL IN THE KIVEB. - At ils outflow from Lake Wakatipu the Kawa,rau is 1050 ft above sea level"; at Cromwell it has fallen to 525 ft (approximately) giving a fall of 13ft per mile. It is, therefore, the swiftest river in Otago, the Waiau haying a fall of only a little more than 10ft per mile, and the Molyneux, from Cromwell to the sea, slightly less than sft per mile: NEVIS BLTTFF FALLS. One of the greatest falls m the river is at what is called, with considerable geographical inaccuracy, the Nevis Bluff, because it is really Doolan's Creek Bluff. Thus bluff is a short mile upstream from Victoria Bridge. The height of the falls may be Eet down at about 25ft, and they are chiefly of artificial origin. Great ma°ses of roclc^blasted away to form the present road were sent bodily into the river, - the larger and harder rocks remaining to form. these falls, the smaller and softer debris being " washed away by the force of the current. This was done at a time when river-dredging for 1 gold was Uooked upon as an innocent and harmless fad. Now the obstruction raised has . become a real and grievous obstacle to dredging. It naturally follows that when a 'river . is blocked by a. dam across its course, the watei* •level is raised for a considerable distance up. stream from the dam. Such has' been the case in the present instance, and the Merrimac dredge is feeling the effects of it, of which more will be said when, that dredge comes to be spoken of. THE REMOVAL OF THE FALLS. The removal or reduction of these falls may be strongly recommended as a subject for immediate consideration by the directors of all the companies concerned. These companies are the Kawarau Consolidated, the Gibbston, the Merrimac, the Galvanic, arid also the Metallic. About 18 months ago a movement was set on foot, having for its ob--ject the removal of the falls in the Molyneux, at Doctor's Point, without any apparent practical object to be gained. A vote of publicmoney was obtained for the purpose. But for some reason or another the scheme was very properly droped. In the present instance the case is very different. A material reduction in the depth of dredging -means a good deal to the four or five companies concerned.

Nor does the removal of the falls present any great engineering or financial difficulty. No doubt a pound for pound vote could be obtained from the Mines department for this work, for which £200 or £300 would ba smple. Neither does the' removal of the fall^ endanger the stability of either bank of the river, by taking away the foot of a landslip, inviting more material to pome down tban was take i away. As already stated, the falls were made by rocks sent into the rivers from road blasting" operations. If these rocks were now removed to a depth of 10ft or 15ft, the river Dec! would be left as it was for thousands — perhaps for millions— of years before the falls were made.

OBJECriONS TO THE / BBMOVAL. As- may naturally be expected, there would: ' be objections to the removal of the falls from parties down stream, having an addict i tional body of tailings turned lose upon theic«

£n the Doctor's Point fall case this was a Veal and potent objection, for. the thing was a stupid fad_, serving no real purpose. In the present instance it is different. In the first place, the Kawarau, at Gibbston, compared with the Molyneux, is a narrow stream, containing per foot of its length only a small modicum of tailings as against the latter river. In the second place, the removal may be so regulated as to pay out the tailings gradually, at the rate? say, of lft in depth per week, giving an increase in the quantity of tailings that would be scarcely felt down stream. In the third place, it would be a dog-in-the-manger proceeding if the parties objected to the partial removal of the falls, such removal ■being of so great • importance and .benefit to A\e companies concerned, and of so little — and that .only temporary — annoyance to themselves." The directors of the companies concerned should lose no time in attending to the removal of the falls at the Nevis Bluff. >- . GEOLOGY OF THE KAWARAU VALLEY. The Kawarau "Valley and the gold in it has long- been a' staggerer to miners, and to geologists perhaps more so. In the ordinary conception of ideal, gold-bearing rivers and gullies, it is necessary that they head from some high peak in the range to which they •belong. In practice this is found to be the case,- leading to the once cherished and sworn ■Co, but now exploded, idea f/hat such gold as rivers or cresks contain had come from one common source, situated Somewhere near ftheir heads. r The' Kawarau helps to give this motion its quiebus. Taking its rise in a large Sake', 60 miles long and 1070 ft deep, the question is. "Where did the river get its gold from? And be it remembered the outflow is not ironl the foot of the lake, suggesting on ancient but now vanished river, but from an insignificant armlet, midloAgth of the lake. Leaving the portions of the Kawarau from the Gorge to Cromwell out of the consideration, there are, the Nevis and the Roaring Meg excepted, no streams of any magnitude or extraordinary richness in gold paying into the IKawarau. Where, then, did the gold come from? A TH3OP.Y. Without going too far down into the abyss tof times -past, we may suppose that there was a time when what is at present known as the Gardrona River was the continuation of the Nevis. -Such a supposition would require the total 'Jeversion of the "fall of the coun»try." Fortunately for this theory, there is abundant evidence that when the Middle Island of New Zealand was the backbone or a now drowned continent, the general fall of Otago, which is to-day to the soiith, was to the north. Lakes Wanaka, Wakatipu, and the rest of them paid out their water at the ends which are now their heads ; all large rivers ran in an opposite direction to what they do now — in short, we are living in' a complete geological topsy-turveydom, which can easily be made to account for the existence of the Kawarau Valley as we know 1 Nor is this all. Such a theory would be just the thing to account for the gold in the valley.' For, supposing that when, from some innate headstrongness, the Nevis declined to reverse its course, or being prevented doing bo by the hardness of the rocks of the BemarKables, the Kawarau, in the eternal fitness of things, burst up the Nevis, breaking" it in two, swallowing up the gold the destroyed portions contained, and you' have -an answer to your question of "where the Kawarau got its gold from. . .» - Looking at a map of 'Otago, it willjje seen that the Nevis and the Cardrona are the only streams of any magnitude that still persist in their northerly course, for the explanation of, which the writer has neither read •tfor' heard rf stronger theories or arguments than the above, mirth-provoking as they may appear. To clinch these arguments it may be pointed out that the course of 'the Nevis and that of the Caidrona are on the same line, cut across at right angles by the Kavarau.