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The Pamphlet Collection of Sir Robert Stout: Volume 70

(2)—Alluvial Mining

(2)—Alluvial Mining.

In the North Island alluvial mining is not carried on to any appreciable extent. During the year 1887 enormous excitement was caused in Auckland by the discovery, in a recent rhyolitic breccia, of a considerable percentage of gold. Thousands of acres of similar rock occur, and a company was formed to purchase 1,000 acres of land. Shares went up to double their nominal value, and scientific experts, who visited the ground, were most enthusiastic. On analysing the bullion it was found to contain far less silver than is usual in gold from this province, and to be identical, in fact, with the British gold coins in common use Subsequent microscopic investigation revealed the fact that so far from being water-worn the metallic fragments were spiral shavings such as might have been rubbed off a sovereign with a file. The perpetrator of the swindle was not discovered.

In the South Island the alluvial deposits are of enormous extent and value, indeed with the exception of Canterbury, where gold has not been found in paying quantities, almost the whole area is distinctly auriferous.

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It will be more convenient to take the gold-fields now under consideration geographically, commencing at the north-eastern corner, that is Marlborough Province, from which, at Mahikipawa and Wakamarina, gold" has been extracted. The first-named diggings are so far of small area, but have yielded freely, the output for 1890 being 3,000 ounces, but the present Workings arc becoming rapidly exhausted, and the known area is small. The Wakamarina field at one time supported a large population, which is now much reduced, and very little work is done.

Nelson Province contains the Collingwood gold-field, one of the first worked alluvial deposits of the colony, and at one time a rich place. The late Dr. Von Hochstetter, whose geological labours in New Zealand will always be regarded with respect and admiration, estimated the total value of the Aorere gold-field at £22,500,000, or £750,000 per square mile, but so far the yield is very far from these figures. Recently several dredges have been projected and possibly started, but the writer is unaware of the results obtained. Passing down the coast, the gold-fields of Karamea, Mohikinui, Upper Buller, Reefton, and Westport are arrived at, and still farther, Greymouth, Kumara, Hokitika, and Ross. In the early days the first-mentioned were of great importance, but the easily wrought ground is becoming scarce, and this class of raining has languished; no doubt this is also caused by the growing importance of the reefing industry. An interesting auriferous cement-deposit, in which the gold is accompanied by cassiterite, occurs near Reefton, at the base of the Cretacco-Tertiary rocks, but has not been profitably worked in situ, though its disintegration has given rise to some river workings.

Alluvial mining depends usually on a plentiful supply of water, and a dry season is very detrimental to its success. This factor does not influence the river-dredging claims, but that branch of the industry has not so far been largely developed on the west coast. About 22 miles from Westport, on the Buller River, the Whitecliffs Dredging Company has recently built a steam dredge, at a cost of about £4,000. The hull is 93feet long and 20-feet in beam. Water for washing is supplied by an 11-inches centrifugal pump. Wash-dirt is raised from the river-bed by a centre ladder, fitted with buckets, and after the large stones have been eliminated, is passed over gold-saving tables.*

The river-beds on this coast often contain large pieces of timber, which form awkward impediments, but as the ladders are usually driven by friction gearing, the probability of fracture is avoided.

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At the foot of the Mount Rochfort Range are several large sluicing claims, from which the wash-dirt, as there is no free fall, has to be elevated to considerable heights. The only system which has hitherto been able to accomplish this at a paying rate is the hydraulic elevator principle, whereby with a great pressure of water ejected through a nozzle into an inclined pipe, stones, sand, dirt, and gold are shot up together, The ground here is composed of gravel, sand, magnetite, garnets, and gold running in "leads." At the Fairmaid claim during 1890, the amount of material raised to a height of 36 feet was 62,201 cubic yards in 1,873 working hours, or an average of 265 cubic yards per shift of 8 hours. A large dredge was built to work the old beach-deposits a few miles north of the Buller River, but although the amount of stuff raised was highly satisfactory, the gold-saving appliances were entirely Inadequate, and the enterprise has, so far, ended in failure. Along almost the whole margin of the west coast are deposits of black ironsand, which contain not only in the raised beaches, away from the present wave-action, but on the borders of the ocean, and re-sorted by every storm, small proportions of gold; it is so fine, however (on account of the constant grinding action to which it is subject), that the greatest care is necessary to save it. Working these deposits, which are constantly forming and reforming, is called "beach-combing," and requires but little capital, while it yields sometimes a fair return, and is free from the hardship and danger of mining in the interior.

Great inducement exists to work the sea-beaches on a large scale, and of late years attempts have been made to construct various classes of dredges available for the purpose. Unfortunately, no system yet introduced appears capable of grappling with the inherent difficulties of the task, and to the writer's knowledge not one of the many companies floated has been successful.

At Kumara, a gravel-deposit exists, which has been largely worked for many years. The auriferous leads are situated on the left-hand bank of the Teremakau River, and are covered by enormous thicknesses of gravel-drift. The ground is nearly 100 feet above the adjacent river, which has been declared a tailings channel, and the débris is got rid of by large tail-races, which debouch above water-level. Private enterprise having proved insufficient to carry out the requisite works, the Government stepped in and expended nearly £22,000 in the construction of a large sludge channel, into which the miners were permitted, under certain conditions, to discharge their tailings. Though of great assistance to the field, this proved a very costly undertaking for the colony, and in page 14 1890, after a loss in maintenance of nearly £24,000 had been incurred, it was handed over to trustees. As in other pails of the colony the gold-saving appliances here are very defective, and in the last report of the Mines Department some particulars are given relative to the amount of gold washed into the channel, and subsequently recovered by the Government. The race, it must he remembered, is not intended as a gold-saver, and is ill-adapted for the purpose, being deficient in width; but in spite of this fact, £3,638 was obtained in four years, and adding to this what must have been lost, gives at least £1,000 per annum wasted by the miners.

In former years wooden Burning was invariably used for the conveyance of water to the claims, but its many disadvantages have resulted in the almost universal use of iron or steel pipes, sometimes as large as 30 inches in diameter, Enormous quantities of this piping are in use, the returns for 1891 giving nearly 9¼-miles, varying from 11 inches in diameter up to 30 inches.

Farther to the south is the town of Hokitika, ones the centre of a prosperous gold-field district, and distinguished by all the feverish excitement of a new rush, now considerably sobered down, but containing still the elements of prosperity. The Humphries Gully United Company, at Arahura, has expended £90,000 on a large sluicing claim, but finds itself still short of water, and cannot at present do much more than meet expenses. To meet this difficulty the directors propose to raise an additional £25,000, in order to construct a water-race about 5 miles in length. Already they have constructed a race for a distance of about 10¾ miles, but the depth of auriferous drift is about 250 feet, and to remove this requires an enormous quantity of water.

At Ross, still farther to the south, extensive works have been carried out, and large yields of gold have been obtained. Even now, though the glory of the field has temporarily departed, the output is considerable. The largest company is the Ross United, which holds 260 acres on the Ross Flat, comprising nearly all the old claims. In sinking the shaft to a depth of 400 feet seven different gold-bearing strata were met with, it has not been possible to continue these workings, and the present operations are confined to surface-sluicing and elevating. Since the operations in the deep ground were suspended £23,787 worth of gold was obtained in the period commencing February, 1887, and ending March 30th, 1891. The surface-operations are carried on by the aid of the electric light, and when additional pumping power is provided the deep levels will doubtless resume their yield of gold. The Mont d'Or sluicing page 15 claim, in the vicinity of Ross, has a splendid record. For the twelve months ended November 30th, 1890, £4,516 worth of gold was produced, at a working cost of £1,501, The payable ground in sight is considered sufficient to last for many years, and an excellent tailings site—a matter of the greatest importance—is available. To the south of Rosa the country is extremely rough, and communication is difficult and sometimes dangerous. Notwithstanding these drawbacks, a mining population has settled there, and large areas of auriferous country are known to exist. Hitherto prospecting in these wilds has been carried on under great-difficulties, but the multitude of birds existing in the forest have enabled the explorer to dispense with heavy toads of provisions. Now, however, the weasel, imported by the Government at enormous expense to protect the sheep farmers of Otago and Canterbury from the ravages of the rabbit, has crossed the ranges and, acting on its well-known preference for feathers rather than fur, is fast reducing the interesting and valuable avi-fauna to a minimum.

Although the population in this district has of late years somewhat diminished, the yield of gold for 1890 shows an increase of 3,500 ounces over the preceding year.

Alluvial Workings in Otago.

Owing to the large extent of country and richness of yield Otago offers a large field for the alluvial miner. Notwithstanding the somewhat rigorous winters, the climate in the interior at moderate elevations is magnificent, and the soil, though barren when insufficiently supplied with water, is extremely fertile when properly irrigated. No one who has seen the grapes growing to perfection and ripening in the open air in the Clutha Valley can regard it otherwise than as one of the gardens of the world—a garden that requires only water. Now that roads have been opened and provisions are easily obtainable, the lot of the miner is comparatively easy; but the early prospectors, who faced the rigour of an almost Arctic winter amidst the snow and ice, the swollen rivers and unknown plains, where no timber exists for firewood and no living animal was to be found for food, endured great privations. Not that their reward fell short, for the early returns were enormous. Gabriel Read, in ten hours, with a butchers knife, obtained 10 ounces, and at Maori Point, on the Shotover River, a European and a Maori got 300 ounces in one day, A disputed piece of ground, 12-feet long and 5-feefc wide, was valued at £S,000, and subsequent events proved that this estimate was not exaggerated. At Carmichaels, above Skipper's, one dish of wash-dirt panned out 80 ounces.

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In the two years 1861 and 1862 over 1,000,000 ounces of gold were exported, by a mining population of 12,000 souls. This was from the river gravels and from the terraces immediately adjoining, but since, that date enormous areas have been discovered, not, it is true, so rich as Maori Point, but still carrying sufficient of the precious metal to repay handsomely any attempt at honest and systematic working.

At the Blue Spur, near Lawrence, is an interesting auriferous deposit of great value. It consista of coarse gravels and silts with decomposed schists, cemented together, and containing free gold. These rocks occupy a depression in the schists, and are, according to Mr. S, H. Cox, a true glacier deposit of Cretaceo-Tertiary age. According to recent information from the colony, the Director of the Geological Survey (Sir Jas. Hector) considers that the gravels have been involved in, and preserved by, a largo fault. While the cements themselves are comparatively poor, the re-wash derived from their disintegration has proved fabulously rich.

Formerly many claims were at work? and conflicting interests caused great loss and waste, but recently an English company has taken up nearly all the leases, with the object not only of working the tin tried ground, but of passing the abandoned tailings over gold-saving tables, Though much troubled by litigation and other delays, the proprietors seem now to be in a fair way to succeed. The amount of capital paid up is £90,000, of which £60,000 was given to the original shareholders. During 1890, 410,000 cubic yards of tailings, left by former workers, have been elevated by hydraulic nozzles to a height of about 60 feet. The yield was 1,478 ounces of gold, or an average value per cubic yard of 3½d., while the cost in wages was £2,580, or about 1½. per cubic yard, The system of raising wash-dirt is exceedingly interesting. Into the bottom of a 15-inch pipe, inclined at a slight angle to the vertical, and made of No. 12 B.W.G. steel, a nozzle is inserted, through which water at a pressure of 400 feet vertical head issues. Another jet breaks down the face, and sluices débris into the bottom of this elevator, to be shot up by the violent rush of water to a height of 60 feet with almost inconceivable violence. An iron hood over the top of the pipe serves to stop the ascent of the wash-dirt, and at the same time pulverizes the cement and frees the gold, which is saved by ripples or other means. (See Figs. 2 and 3, Plate XLVII., and Figs, 4, 5, 6, 7, and 8, Plate XLVIIL.) Before the introduction of this method, any ground from which there was no fall would not pay for working, and its use may be said to have revolutionized gold-mining in the colony. One grain to the cubic yard is shown by the above instance to pay, and it is a poor gold drift page 17 that will not yield this. All that is required is a large volume of water with a high pressure, and owing to its unequalled wealth in this direction, New Zealand will for many years offer ample inducements to alluvial miners. For at least a hundred miles the Glut ha River is a veritable Pactolus; enormous as has already been the drain on its resources, it is probably but a fraction of what will eventually be obtained. Water only is required to extract the hidden riches from the soil, but owing to the rough nature of the country and the innumerable vested interests involved, the task of bringing in a sufficient supply is one which presents almost insuperable difficulties. Still, with a large river flowing through the centre of the field, there is no reason to despair. Some day a scheme will be found for utilizing this great natural race, which will be used not only for sorting and arranging the auriferous deposits of its own bed, as it has done during untold centuries, but for washing away and destroying the enormous masses of gravel which it has so patiently and efficiently stored up.

For many years dredges, driven by the river-current acting on floating waterwheels, and belonging to private individuals, have done well, but it was found out that many of the richer parts, where eddies occurred, could not be worked, the flow of water being insufficient, so steam-power was introduced on a large scale, and although success has not rewarded every effort, this system has already been proved to be well adapted for the purpose, and the future will, in the writer's opinion, show enormous yields. The capital required is not large; £5,000 will provide a first-class ordinary centre-ladder dredge, and there is ample room. Where promotion money is lavished and preliminary expenses are allowed to grow to an unlimited extent claims have no chance; over-loading and watering of capital have been the curse of New Zealand, as of other mining, and have retarded its progress for many years. When legitimately and economically managed it offers an enormous field for capital and enterprise.

Several types of dredges have been employed: one, known as the Welman, depends for its action on the suction produced by a centrifugal pump. The following details describe one erected on the seacoast of Otago. The machinery comprises a 20-nominal horse-power engine and boiler of the locomotive type, with two fly-wheels, which are used to drive the pump with belt-gearing. The pump casing is of cast-iron, fitted with a manhole. The runner, also of castiron (recently, the writer understands, gun-metal has been employed), carried on the shaft is 2 feet 3 inches in diameter, in the form of three fans, which page 18 make 200 to 300 revolutions per minute. The delivery-pipe, which is 12 inches in diameter, conveys the wash-dirt to a height of 15 feet above water-level. The suction-pipe enters at one side of the pump and runs thence to the front of the dredge, where a universal joint is placed. This pipe, which is 17 feet in lengthy is actuated by a chain attached to the end and worked from a crane on board, and can thus move in either a horizontal or vertical plane. The end is bent at an angle of 90 degs. to form the nozzle, which is quite plain, except for a patented sleeve, about 8 feet in length, bolted to the main pipe so as to leave a small annular space. All the pipes are 12 inches in diameter, except just at the mouth of the nozzle, where the diameter is reduced to 11 inches, in order to prevent stones equal to the full capacity of the pipe from entering. The revolution of the fans causes an upward rush of water. This is replaced by a current downwards, between the sleeve and the enclosed pipe; this impinges on the ground, which is broken up, and sand, gravel, and stones, even up to 56 lbs. in weight, are washed up the pipe and delivered in a suitable position for being treated.

This machine, when of sufficient size, seems admirably adapted for raising moderately fine material, but in the beds of the large rivets, where huge stones occur, it is not so easy to work.

In at least one instance a Priestman grab-dredge has been tried, the Von Schmidt and Ball machines as well, and some other adaptations, but not with conspicuously favourable results.

Even after every provision has been made for raising material in necessary quantity, great difficulty is experienced in saving the gold, which, owing to the attrition of the river-gravels, is often exceedingly fine. The pontoons of a dredge are hardly a suitable place for the accommodation of wide and lengthy tables, and it is considered probable that of the gold dredged up from the river-beds a large proportion returns over the shoot.

While steam is most generally used as a motive power, the Sandhills Dredging Company, which has a claim on the Shotover River, has utilized electricity, and the following particulars which 'have been taken from the last departmental report for the colony may be of interest:—The dredge is on the centre-ladder principle, 80-feet long, 18 feet 3 inches in beam, and 4-feet 6-inches deep; the height of the tumbler above the deck is 16 feet, and the depth to which the buckets will dredge, 20 feet below water-level. The stones are separated from the sand in, a revolving screen, 10-feet long and 3-feet wide, and the fine material passes over tables covered with cocoanut matting, and set transversely with the hull of the dredge. The ultimate power of the machinery is 60 tons page 19 per hour, and the electromotive force is generated by two Brush-Victorian dynamos, hiving armatures 2 feet in diameter, and making about 500 revolutions per minute. This generates a current of 40 amperes, having an electromotive force of 650 volts. The source of power is a Pelton waterwheel, 4 feet 6 inches in diameter, and running at 213 revolutions per minute, with 500 feet head. The electrical plant is situated about a mile and a half farther up the Shotover River than the dredge, and the electric current is transmitted by a copper wire, about a quarter of an inch in thickness. The machinery is driven by belting. The total cost was about £7,500.

Results obtained from Mining Ventures.—As already stated, complies in New Zealand are obliged to publish annual returns, and from these the following figures are compiled:—

The total capital subscribed by companies in operation at the end of 1890 was £2,024,149, and of this amount the value of scrip given to shareholders, without any money being paid, amounted to the large sum of £810,533, or 44 per cent. The actual amount of cash paid was £496,754, while dividends had been paid to the extent of £593,066, leaving a total profit of £96,811, and it must be remembered that in these figures is included the capital recently absorbed by dredgers (£72,779), many of which have not yet had time to yield returns.

Gold-fields' Revenue and Earnings of Miners.—The amount received for gold-fields1 revenue in 1£90 was £19,074, and the gold duty yielded £16,961, making a total of £30,035, Dividing that among 13,409 miners gives an average sum per head per annum of £2 13s. 9d., without counting indirect taxation.

To estimate the average earnings of miners is an exceedingly difficult matter, but, taking the period ending March 31st, 1890, the figures come out as £51 2s. 7d. per man per annum, as against £59 16s. 6d. for the previous year. This reduction is attributed to the exceedingly dry season, and consequent scarcity of water.

The official returns for 1891 are not yet to hand, but the February papers give extracts from the late census, which tend to show how great is the introduction of machinery. Speaking of hydraulic gold-mining and gold-dredging, the Otago Witness, which devotes special attention to these interests, points oat that while the yield of gold has been only 533 ounces less than in two years previously, the number of works has been reduced from 124 to 74, and the number of hands employed from 617 to 495, thus confirming what the writer has attempted to point out, namely, that the small works must give way before the introduction of capital and improved mechanical contrivances.

* The February (1892) colonial papers report that the Whitecliffss Gold Dredging Company has gone into liquidation. The writer is unaware of more than one claim bearing this name.