Hydraulic Mining in Westland.

Thames Star, Volume XVI, Issue 5018, 11 February 1885, Page 2

Hydraulic Mining in Westland.

Dr Hector, in his report for last year, says :—This will be the great industry of the future in Westland. I have pointed out the distribution of the gold drifts and the manner in which the enormous discharge of water from the Alpine sources had re-arranged and concentrated the auriferous drifts that had given { the enormous yield of gold in proportion to the number of mines which has so characterised the Westland goldfield. But this Very violent action has, by tutting deep river channels through the first-formed gold drifts, left undisturbed large areas of these drifts at a level inaccessible to the ordinary drainage system. By the construction of water races, and by the system of hydraulic mining, the resorting can be effected artificially and with profit. I had an opportunity of inspecting one of the most promising of these adventures about twelvo miles from Hokitika, where at Humphrey's Gully all the small claims are now amalgamated, so that about 200 acres is held by a company in one block. It forms a triangle in the junction of two tributary valleys to the Arahura River, so that it lies favourably-for getting rid of the tailings, which is the most important element in the success of a sluicing claim. The thickness of the gravel, is from 150 ft. to 500 ft., as the bottom on which it rests dips into the hill, which also rises rapidly on the surface., The gravel is of two kinds, b and c, which rests on a, a silt clay. The gravels (o) were the first found river beds on the. Coast, and are generally the richest, though the gold is hardly, if at all,; sorted out in these gravels in the form of defined leads. This gravel is very easily sluiced away, as the pebbles are of moderate aud about equal size, and are, moreover, rotten and decomposed, so that their surface washes away and all the gold is set free. In ordinary gravels, the pebbles are bard, and the gold is set in a dense feruginous cement that adheres with great strength to the surface of the stones. On the top of the terrace is (p) the newer gravel of j rery heterogeneous materials. This deposit contains huge blocks of stone mixed with sand, and fine gravel. The6o two deposits, b and c, are the chief repositories of gold on the West Coast, but c is not to uniformly auriferous as 5. Now as to tut richness of these gravels h aud c.

They have been tested in various ways— (1) by surface workings at various points I (2) by tunnels driven through the hill in various distances, aud (3) by sluicing the faces of the terraces. I made about twenty trials in the first way from various points and never failed to get a few specks of gold to each dish. .The' average from the middle of the deposit b gave ten specks to the dish of stuff about 15Ibs

weight. These specks areraged '095 of ft grain each which would (live the value pet load (equal to one cubio yard) of ldwt 4grs for each present, or for my trials lldwts 20grs—equal to '£2 6s per load. The layer near the junction of the deposits 6 and c in like manner gave £1 Is 6d per load on the average, and the deposit c gave an average of £2 14s per load. Theia results are remarkable, but I do not see how they can be erroneous. The tunnel works were purposely so put as to follow the richest layers, so that there is no wonder that they make the stuff appear even ' richer than the pan . prospecting. The third source of information is the best, and I understand that sluicing 500 loads of the gravel b gave 62|oz. of gold, or about 10s per load, which is probably about the real value of the stuff. Reducing the area to ICO acres and thickness^ to 100 yds. on the average, the claim will^ contain 60,000,000 loads of stuff, and it is only the question of the cost of getting that remaiut to be considered.. When the dam is finished it will have an area of 11 acres, and afford 55 head for 26 hours, with a possible inflow in dry* weather of ICO head. A short tunnel has only to be completed now, when 20 head will be at once available for: sluicing* Under the circumstances 20 heads should sluice about 16,000 loads per day; when taking one speck of' the smallest size (viz., '02 of a grain, valued at one-fifth of a farthing) to each load gives £12 10s a day, or £3750 per year of - 300 working days, which would be about half the interest at 10 per cent, on the capital already invested, so that two specks per load would pay the interest; and if it were an average sized speok to the dish— which is a very moderate estimate from the trials I have seen and described above— the yield would be £800 to £1500 per day, and taking the lowest of these figures, the claim will contain at present £3,000,000, and at the above rate be worked out in t wel ye years. Another large venture on the West Coast is the underground hydraulic sluicing at Boss. The mining operations seem to bo woll thought of, but the richuoss of the ground that is to be reached and worked is only known from hearsay reports of operations conducted, as an early date in the history of the goldftold. The expense of working will be greater than Humphrey's. As much of the. stuff has to be lifted and pumped, and it is evident that the auriferous gravel will require to be much richer than it need be at Humphrey's, and it is reported to be so, and that gold occurs, not dispersed through the gravels, but in well-defined layers or " false bottoms". But as long ago as 1868, when the first workings were in full operation, I used to doubt the extent of the layers. The one theory was this: that the layers were continuous like coal seams. The other theory was that they were a succession of marginal de« posits of a limited width ; and Lstill think this must be the correct theory. The difference in the probable value of the field on these two theories, 1 need not point out, is immense."