GOLD DREDGING.

Otago Witness, Issue 2325, 22 September 1898, Page 18

GOLD DREDGING.

No. 11. The success of Scott's dredge led to the adoption of current wheels for supplying metive power to dredges, and in a short time a dozen current-wheel dredges were in operation on the Glutha River at different »?aco3. Of these eight have since had steam nower supplied to them, and although

some of these dredges did not pay, others have enriched their fortunate owners, some of whom have been able to retire and live on their means, while others have been able to invest their savings in larger dredges. One of the older type of current-wheel J dredges is still working in the river near . Alexandra. But the increasing tailings difficulty made greater power than the current wheel was able to supply necessary, , and steam power has since been almost uni- ! vorsally employed for gold dredging. In 1889 Mr Sew Hoy, an enterprising and wealthy Chinese merchant, well known to the mining community, took up a claim on the Shotover River, from > which rich golden harvests had been 1 won in former days. A company with a nominal capital of £3000 ' was formed*, divided into 300 shares of £10 | Reach, and a small steam bucket dredge placed on the claim. The ground had been ' worked over twice by Europeans and once by Chinamen, so that only the very finest fold, which it would not pay to extract y other methods, was left. In spite of ' that the dredge yielded such handsome re- j turns that the £310 shares increased in value to nearly £250 each. The enormous yields of the dredge created a good deal of excitement at tho time, and very soon the concern was floated into a much larger company of some 54,000 £2 shares, of which the pro- i moters secured the greater part. After 30s j per share had been paid up and 13 dividends i of 3d per share paid, the overloading proved i too much for even that rich claim, and the , I company went into liquidation. From the ! wreck of that company a syndicate was formed, which now owns three dredges, all • of which are paying well. The success of the Sew Hoy Company in what to the ordi- ] nary miner was considered worked-out ' ground, demonstrated the value of steamdredging for saving the fine gold from ground that would not pay to work in the old way, and led to quite a mining boom on the Clutha River and tributaries. The | dredge had proved that it was only neces- ' sary to put through a large quantity of wash, and to have proper gold-saving tables, to make low-grade ground, formerly considered valueless, highly remunerative. As ' a result claims were taken up in all kinds ! of places, regardless of the gold-bearing J i nature of the ground. Companies were J floated with excessive loading, and 19 steam > dredges were built at an average cost of £3500. Some did well, while others did not pay from a variety of causes, besides scarcity of gold in the claims. One dredge ' which won gold to the value of £32,000 ' in eight years only returned £4200 in divi- j dends to the shareholders. The unsuitable j nature of the plant, together with gross mismanagement, thus led to a rich claim , proving practically valueless. The ill-sue- J cess of some of the dredging ventures led j to a slump in dredge mining in 1892, and I 1 several of the companies' went into liquida- ! tion. The dredges, especially those placed | I upon the upper reaches of the Shotover, ; did not realise the golden dreams of the j promoters, and several were sold to private parties, who moved them down to the j Clutha River, between Alexandra and ! Clyde, where they won such a golden; har- I vest tnat public attention was again directed j to dredging as a means of remunerative . river mining. Claims were speedily pegged | off along the river bank and beaches, and the flotation of "dredging companies was briskly carried on. 1 Up to that time the dredges had only been working in the river beds and low beaches, but could not work the banks on account of the difficulty of stacking the tailings astern of the dredge. Irt June, 1894, while engaged at the Enterprise dredge, Mr W H. Cutten, of the firm of Cutten Broa. , of Duuedin, consulting engineers, was coiiironted with this difficulty, and took the matter in hand. He designed and constructed an appliance now called a " tailings elevator," which consists of a ladder fixed to the dredge and projecting over the stern, at an angle of about 35deg to the water level. On this ladder there is an endless chain of buckets or trays working over tumblers at the top and bottom of the ladder. The rougher portions of the tailings, after being washed and separated from the finer by the revolving screen, are delivered upon the elevator, carried up and stacked to any desired height, according to the length of the elevator. This was the first attempt to deal with the difficulty, and the success of Mr Cutten's contrivance has completely revolutionised the dredging industry. Claims have been taken up and dredges put to work ground that was previously considered too poor to pay. It also carried the dredging system beyond the river channel, and now several large dredges may be seen tearing down the high banks of the Clutha to a height in some cases of 40ft above the river . level, and passing the whole of the wash through the gold-saving appliances. By . means of this attachment the dredges are enabled to cut into the alluvial deposit laid down in backwashes of the river ages ago, and to win the golden treasure intermingled with the gravel, where it occurs in quantities not considered payable by the older order of miners. The Enterprise dredge is working in a beach about a quarter of a mile away from the river, between Alexandra and Clyde. The beach is about 3ft above the water level, and the tailings are being stacked about 12ft above that level. Probably the most advantageous positions for dredges are between Alexandra and Clyde. The auriferous wash lying on a clay bottom is fairly uniform in size, with a payable proportion of gold fairly well distributed throughout; The wash

is intersected by numerous rich leads, which, when met in with considerably enhance the dredging returns. As showing the value of this dredging area it is worthy of note that there are no less than ten dredges at work on a reach of the river only seven miles in length, between Alexandra and Clyde, while five more are under construction. Furthermore, within a radius of seven miles of Alexandra there are 17 dredges at work, and'nine more under construction. Fourteen of the 17 dredge 3 now at work are yielding payable returns. A j good many of the dredges belong to prii vate companies, and as the returns are I not divulged, the average earnings of the 1 dredges cannot be computed. Those owned by public companies have their returns i published regularly. The Clyde Dredging Company's dredge, Moa, paid dividends to its shareholders amounting to £70 on each £50 share, and carried forward a substantial reserve, within 12 months from the starting date. In another case a dredge some 25 miles farther up the river, belongI ing to a private company, obtained a re- ■ turn of 6580z of gold for one week's work, and something over 2800oz for 12 months. The same company have since put on a couple of dredges at a cost of £5000 each. Thus it will be seen that the speedy development of the dredging industry has tended to a more powerful and costly style of dredge, to cope with the altered conditions that have arisen. Not content with winning back the gold scattered long ago in the river channel by the operation of natural forces, the dredge miner has turned hia attention to river flats and alluvial deposits wherever a sufficent wash carrying a low percentage of gold is known to occur ; for ground considered worthless some years ago can be made to pay by dredging. There are numerous examples of this throughout Otago, and dredges are retiirning handsome dividends from ground that was abandoned years ago by the ordinary sluice miner. T,ke result of the enormous impetus given to this system of mining by the employment of steam power, together with Mr W. H. Cutten's valuable accessory, the tailings elevator, is that there are now in operation in the South Island 69 dredges, of which no less than 64 are in Otago rivers, the other five being on the West Coast. Of these dredges 29 are owned by public companies and 40 by private companies, parties, or individuals. In addition to the dredges already in operation, 29 new dredges are in course of building, chiefly for Otago. The cost of the smallest dredge being built is about £2000, and the largest nearly £8000. The earlier experience of miners at dredging led to the belief that a larger size of bucket than two cubic feet would lift too much dirt to be efficiently washed, but later experience has proved that view to be erroneous, and now most of the buckets are made to carry from four to four and a-half cubic feet of wash. But that does not mark the limit of bucket for gold dredging, as the firm of Cutten Bros, have a dredge on hand the buckets for which will have a capacity of six cubic feet. From very small beginnings it. will thus be seen the evolution of the dredge for gold mining has been very speedy. The strong current of the Clutha no less than the great accumulation of tailings in the channel afford scope for a more powerful type of dredge than those already in operation ; and although Cutten Bros, are constructing the largest dredge yet built for this important work, that does not mean that the limit has been reached. As in shipbuilding all preconceived ideas had to be cast to ' the winds, so in dredging we may expect to see still larger and more powerful constructions placed upon the Clutha to get at its hidden wealth of gold. In view of the importance of the industry a description of the large dredge and its machinery as designed by Messrs Cutten Bros, will be acceptable to the mining community. That description we shall give in another article, together with some further useful information relating to the important gold dredging industry, — an industry the development of which has done much to help to make Otago prosperous, and from which greater things are anticipated in the immediate future.