GOLD DREDGING.

Otago Witness, Issue 2328, 13 October 1898, Page 20

GOLD DREDGING.

No. V. In addition to the dredges referred to in our article of last Saturday Mr Roberts has been interested in a number of other dredges. The Golden Beach dredge, recently built hy Mr Roberts for working a beach claim, affords an object lesson in elevating and stacking tailings. The dredge, which is about the same size as that of the Molyneux Hydraulic Company, is really excavating a channel out of solid gravel from two and ahalf to three chains wide, with a height of working face above ivater level of from 18ft to 24ft, and a depth of 22ft below, or a total working face averaging 42ft. Af^er washing the material the tailings are stacked 28ft to 30ft above water level. The returns from this dredge prove its success no less than the value of the Golden Beach claim. Within eight weeks of commencing work the company was able to distribute two dividends of Is each amongst 13,000 shares. Since that time the returns have been even better, and the success of the Golden Beach , dredge will no doubt encourage investors to make • further inroads into the large alluvial Cats bordering the river which are known to contain geld. Engineers are confident that the eV>\ <' n g dredge is only in its infancy, and in r. - immediate future dredges will be built t? cope with ground hitherto deemed unsuitable for dredging. The hull of the Golden Beach dredge is 90ft long, with a width of 27£ ft, and depth of 6£ft aft and sft forward. - The engine is 20-horse. power. nominal, compound, surface condensing. The buckets have a capacity of four and a-half cubic feet. There are two screens and gold-saving tables with return underneath. The dredge complete was supplied under contract ' with the New Zealand Engineering Company of this city. Another dredge constructed by Mr Roberts is the Kawarau Dredging Company's dredge at Victoria Bridge on the Kawarau River. The company is an English one. The locality is known as the Horseshoe Bend, the river sweeping around a peninsula or neck of land for some three miles, the distance across the narrowest part being only about a quarter of a mile. Some eight or nine years ago it was proposed to tunnel through the narrow part and divert the river, thus enabling its bed to be worked. The result of the dredging so far has proved that the proposed tunnel would have been useless as far as working the river bottom is concerned. The dredge has seldom found the true bottom, and when it has the depth has been so great that the tunnel would not have been low enough to drain it. In consequence of the great depth the operations of the company have not been very encouraging, the chief obstacle being the large quantity of small drift shingle with which the i river is filled at that particular spot. The drift ! shingle contains no gold, and the bottom is hard reef. The dredge is under the management of Mr G. M'Lay, who is well known on the river. It is the intention of the company to have the dredge fitted with an elevator to work into the beaches at the mouth of the Nevis River, where it is hoped they will meet with better success. The hull of Dins dredge is 90ft long, width 25ft, and depth s£ft. It is built of hard wood and kauri, and is provided with a ladder capable of dredging to a depth of 45ffc. The bucket capacity is three cubic feet. The engine is 12-horse power nominal, surface condensing, by Marshall. The boiler is 16-horse power, by the same maker, and of a type specially constructed for dredges. The pontoons were built by Messrs Sutherland and Nelson, the machinery by Mr J. Anderson of Christchurch, the buckets, ladder, anS winches by the New Zealand Engineering Company, and the screens, gearing, etc., by Mr J. M'Gregor of Dunedin, Two other dredges recently designed by Mr Roberts are the Cambrians and Nil Desperandum dredges. / These are sister ships, and both are owned by private companies. The Cambrians dredge was built to work an alluvial flat at the Dunstan | Creek, at the confluence of the creek Avith the Cambrians Gully. In the early ditt^'n^ days the Cambrians Gully was very rich. With the primitive methods of mining of those days all the fine gold was washed away with the tailings ; and an attempt is being made to win back a portion of that gold by means of the hydraulic elevating system by Mr John Ewing, with very satisfactory results. The bottom is what miners term a "Maori bottom," consisting of water-M r orn stones embedded in a tenacious clay matrix. The dredge was built on the eastern side of the creek, a considerable distance away from the mouth of the gully. It. is now taking out a trial cut right across the flat, towards Mr Ewing's workings. So far the prospects have not been very cheering, but the owners confidently hope the returns will improve as the dredge approaches the mouth of the Cambrians Gully. A question has arisen as to whether the bottom is a suitable bottom to work on with dredge buckets, as

ifc is feared the buckets scraping over the stones may- disturb the gold and leave it in the paddocks. That could only be settled by pumping out the paddock to examine the bottom after the dredge has gone over it, and clearing up by hand labour. The ' dredge, under the management of Mr Swarm, is turning over a- large quantity of gravel and will be certain to pay well if the part ! of the claim towards which it is working comes up to expectations. The Nil Desperandum dredge was built to work a claim in the Manuherikia, next Ito the Ohatto Creek claim. The dredge is taking a prospecting cut across the claim, and has already turned over a considerable acreage. The results have not as yet I transpired. The dredgemaster is Mr D. j M'Master, and most of the hands working jon board are shareholders. Both dredges j are very powerful machines, equal in capacity ' to the largest dredges at work on the Moly- | neux River. The hulls are 60ft in length, / 30ft wide, and 6ft deep, with a well s£ft i wide. The pontoons are pointed at the bow, with the ladder projecting well over to allow the corners of the paddock to ba dredged. The buckets have a capacity of four and a-half cubic feet, and will dredge to a depth of 20ft when the ladder is at an angle of 45deg. Double screens with helices and gold-saving tables are fitted at either side of the dredge. The elevators are capable of stacking tailings to a height of SOft. The winches are powerful steam winches with Joy's valve geai\ The engine is 16-horse power nominal, and the boiler i 20-horse power, both by Marshall and Son. j The buckets and ladder, shafting, gearing, ; etc. , were supplied by the New Zealand Engineering Company, the screens and eleI vator by Mr Joseph Sparrow, and the > winches by A. Roberts and Sons, of Bendigo, ' Victoria. The pontoons were built by Messrs ■-Fleming and M'Kechnie. The centrifugal pumps with this dredge, and all those recently constructed, are by Tangye and Com- . pany. The contracts for these dredges were let in October, 1897, and the dredges commenced work in June, 1898, thus occupy. " ing about nine months in construction. I In addition to the dredges already afc ! work designed by him, Mr Roberts has in hand the Nevis Success dredge at Nevis i River. The pontoons of this dredge were ; completed last April, and the machinery has I been lying at the Garston railway station I for four months awaiting transit across the mountains. The dredge is expected to be ready in about a couple of months' time now, but that will depend upon the condition of the roads. The Golden Point Company's dredge is another large dredge being built to work a claim lying between the Ngapara Company's claim and that of the Molyneux Hydraulic Company on the Molyneux River. The pontoons are being built, and the machinery is at the Lawrence railway station awaiting carting to the claim. This dredge resembles J in many respects the Golden Beach dredpe \lt is, however, considerably larger. The ( elevator is 72ft in length, and is provided j with a shoot 20ft long, arranged so that it ; can be easily raised or lowered. By this t means the tailings may be easily delivered at 'least 80ft astern of the dredge, which will give ample working room to allow the higher portions of the claim to be worked. In order to support an elevafor of this kind a considerable departure had to be made j from the usual design of pontoons, the after | part being made wider and deeper than the j forward part. The dredge is very strongly } built. The sides are framed in combination j with the gantry and upper framing, so as to i form a complete truss. At the same time the ■ framing does not interfere with repairs being made tn the outer planking in the event I°J . tl l e IniU bein g damaged at any time. j lhis is an important point which is some- ; times overlooked in dredge construction. It Sis anticipated this dredge will be j ready to commence work about the | beginning of December. The bucket ' capacity is four and a-half cubic feet, and the machinery is driven by a 20-horse power compound condensing engine by Garrett and Sons, and a 25-horse power boiler designed by Mr Roberts. The whole of the . machinery, including buckets, ladder, gearing, etc. , was constructed by the New Zealand Engineering Company, the elevator by , the Dunedin Foundry Company, and the winches by A. Roberts, of Victoria. J Mr Roberts has a dredge for Macraes Flat ' also in hand. The pontoons are being built by Messrs Sutherland and Nelson, and the _ machinery by the Dunedin Foundry Com- ' pany. The first part of the machinery will leave Dunedin next Monday. The engine j and boiler are by Marshall and Son, and have been landed some time. Commencing with dredges to get at the gold in the channel of the Molyneux the engineers have now designed dredges for working beaches and alluvial flats wherever there is water available to float them after dredging out a basin for themselves, and wherever payable wash is known to exist. While river dredging was always deemed practicable, dredging on dry land was hardly thought of until the modern dredge with tailines elevator was designed*