GOLD DREDGING IN BRITISH COLUMBIA, 1909
By ARTHUR. E. HEPBURN, Vancouver, BC.
Originally published in The Journal of the Canadian Mining Institute, 1909 (Vol. XII)
In presenting a paper dealing with the subject of gold-dredging in British Columbia, the writer hopes, by comparing conditions in this Province with those existing in other countries, to indicate the causes for the non-success heretofore of an industry, which elsewhere, and under less favourable natural conditions, has succeeded so well. At the present time, it may be observed, dredging areas are being acquired and large sums spent in dredging enterprises in the far north, on the verge of the Arctic Circle, where the working season is limited to a few months in the year, and where the ground is solidly frozen to bed-rock; and despite these drawbacks large fortunes are being won. But here at our very doors are richer and better fields for dredging enterprises; while, too, the facilities for working are eminently more favourable. If then the cause of past failure can be ascertained, it may be expected that attention will again be directed to this important and remunerative branch of industry in the Province.
The mining districts of British Columbia number in all about twenty, but in four only has dredging been carried on to any considerable extent, namely: Cassiar district, Cariboo district, Lillooet district and Yale district. A review of operations in these districts is annually published in the "Report of the Minister of Mines," and may be consulted by those desiring the information. The record, however, is one of almost unvaried mishaps or failure.
In the United States, where this branch of mining has been reduced to a science, dredging is carried on in numerous instances at a considerable profit. In order to investigate the conditions contributory to success in this direction, the writer recently visited the Sacramento Valley in California. The deposits on the eastern side of this valley lie at the base of the western slopes of the Sierra Nevada, and gold is found in the several streams debouching from the canyons. The deposits are all gravel, clay and silt. At the time these deposits were formed, the valley was a fresh water lake, which gradually filled up with detritus from the Sierra Nevada mountains. The gold bearing gravels of this deposit are of hard siliceous rock, well worn and rounded, and the gold found is fine flour gold, derived from ancient quartz reefs.
Operators in this district have displayed much common sense in the selection of ground, often rejecting otherwise rich areas, if the conditions were not suitable for dredging. Plant, moreover, has been specially designed to meet local requirements; while careful consideration has been given to every detail of working. The result is that these undertakings are invariably profitably conducted. ln California, experience has taught that to carry on dredging successfully, the following conditions must obtain:-
(1) The auriferous area must be sufficiently extensive to warrant capital outlay.
(2) The material should be uniform in character. Otherwise it is not possible to design a plant to work economically and satisfactorily.
(3) The depth of bed-rock should not be below the reach of the dredge.
(4) Bed-rock should be soft enough to enable the lip of the dredge to cut its surface; otherwise the gold, lying on the bed-rock and in its crevices, frequently constituting the principal source of wealth of the property, will not be recovered.
(5) The supply of water available must be sufficient both for
floating the dredger and for washing the dirt.
(6) The physical obstacles, such as excessive overburden, frozen gravel, etc., must not be so great that, to overcome them, cost would be excessive.
If these conditions are satisfactory, it is always possible to design a plant that will afford successful results; but on the other hand, if any of the above conditions are unfavourable, failure may be usually expected to follow. The Californian experience is that large and powerful plants are alone of service. The first cost of these is necessarily higher than that of lighter and weaker plants; but the former is effective, while the latter is not. Again, the force of men required to work a heavy plant is the same as would be employed on a lighter dredger; and while a consumption of fuel, on account of the increased horse-power is, of course, greater in the former case, this is offset by the increased and lessened cost of the daily output, the fewer stoppages for repairs and the fact that the larger plant is capable of working in ground which is beyond the capabilities of the light dredger to handle. The Californian dredger is designed to reach at least sixty feet below water surface level, and the gold-saving appliances are expected to save the fine flour gold. The cost of renewals are estimated at 36% at least of the original cost of the plant; in a weak machine this percentage would he very much higher.
It may be noted here in passing that when gravel is cemented, necessitating the use of dynamite to break it, the value of the ground per cubic yard should be higher than that of the loose gravel worked, as not only will the expense be greater for drilling and blasting, but usually it is necessary to work the ground over a second time, since the cementic fragments passing through the screens of the dredger, break with difficulty and carry much gold away with them.
With the knowledge gained in California, the writer visited the gold dredging areas of Canada, and in most instances found conditions here to be very similar to those obtaining in the South, with the exception, of course, that in our more northern latitudes the working season is shorter.
The first excursion was up the Fraser River, which, for a considerable stretch from the mouth, contains silt-covered flats with gravel below at great depth, and if gold exists, it could only be in very minute quantities carried down by the current from the natural riffles of the bars higher upstream. Above Agassiz, however, Chinamen were observed washing and saving the fine gold that the current had brought down through the Fraser Canyon. The bars between Agassiz and the canyon contained much fine gold, and here apparently is ideal dredging ground, although, of course, no definite opinion can be expressed until the area has been properly prospected by drilling. It is believed that this river stretch is now held by a number of companies, having leasehold rights thereof. After passing through the canyon of the Fraser River a broad valley opens up, just beyond which is situated the little town of Lytton, where, near the mouth of the Thompson River which enters the Fraser at this point, dredging has been undertaken, using, it is understood, a dredge of the New Zealand type. The current of the Fraser here is apparently very swift and hence would make dredging a somewhat risky undertaking. Leaving the Fraser at Lytton, the writer proceeded up the Thompson River to Kamloops, visiting Ashcroft en route. Between Ashcroft and Kamloops Lake the possibilities for dredging enterprises appear to be most promising, and several groups of Chinamen were observed sluicing on the bars and were said to be doing well. The banks on either side of this stream are terrace benches. Near Ashcroft the Bonapart Creek flows into the Thompson River. In the early days of mining in the Province much gold was recovered from this creek, and it is not unlikely that values are still contained in the deeper gravels. Another stream that formerly yielded good returns is Dead Man's River, a short distance east of Penney's.
The Basin of Kamloops Lake collects such gold as may come down stream from the upper reaches of the Thompson. About a mile from its head and some nine miles distant from the Kamloops, is Tranquille Creek, which, at one time, yielded a considerable amount of gold. It still contains gold at depth, while values may also be found nearer its source where the stream flows through the mountains. The bed of the river between Kamloops Lake and Kamloops consists chiefly of silt; bed-rock has, it is understood, never been reached and the gravel lies at a great depth. Approaching Kamloops the valley very appreciably widens out and, at the town, the North Thompson River joins the Thompson. East of Kamloops, the Thompson River is a mere sluggish stream and its bed contains no values. Up the North Thompson River the country changes very slightly for the first few miles, but gradually the valley converges and at a distance of about twelve or fourteen miles a series of riffles, bars and benches are encountered all more or less auriferous; while a number of small creeks, whose gravels carry Values to a considerable extent, flow into the main stream. The river continues thus for seventy-three miles to its junction with the Clearwater, which latter stream is so named on account of the clearness of its water, while that of the Thompson River is silty. The Clearwater is said to be auriferous.
On the Thompson River, between Jamison Creek and the first riffle, dredging operations have been carried on for some time past, the ground having been superficially operated, yielding at or near the surface about 6½c. to the cubic yard. This return proving disappointing, work here was suspended and the dredger moved to Tranquille Creek, where operations were again carried on for a time. This dredger was of the New Zealand type. Much of the fine gold was lost at first on the tables, but subsequently this defect was remedied and practically all the gold was saved. The machinery apparently, however, was not sufficiently strong for the work, as there were constant breakdowns and much time was lost in undertaking repairs. In dredging on the Thompson River a layer of clay was encountered at some depth below the bed. From this clay a few nuggets of small value were obtained; but had the clay been penetrated and the gravel below tested, there is reason to believe that better values would have been secured; for the gravel above the clay was evidently of recent deposition, and the gold therein was derived from the disintegration of the benches. The writer is of the opinion that systematic testing of the North Thompson and of the numerous creeks flowing into it above the first riffle, by drilling, would prove that these streams could be profitably worked by dredges.
The next point visited was Quesnel in the Cariboo district, which is reached from Ashcroft by the government road. The Fraser River gold is very fine and is chiefly found in the bed of the river and the terraces forming its banks. Very little gold is found in the Tertiary beds, but erosion thereof has resulted in the concentration of the gold in the lower terraces and in the river; and in places this concentration is sufficient to admit of profitable working. At the junction of the Fraser and Quesnel Rivers, sixty miles above Soda Creek, dredging was attempted with a machine of the dipper type, but proved unsuccessful; notwithstanding that, in the writer's opinion, conditions here are in every respect as favourable to dredging as in California.
Barkerville, situated some eighty miles distant from Quesnel, was reached on horseback. The intervening country is mainly a Quarternary drift. The Quesnel River, the course of which the road at first follows, has very little fall, and its bed is chiefly composed of fluviatile and glacial deposits; while, like the Fraser, its banks are terraced. The tributary streams for some distance from the Quesnel likewise have very little fall, but nearer their source they rise very rapidly. In the Barkerville district the greater part of the gold recovered is found in the upper reaches of the tributary streams and within a radius of about twelve miles of Barkerville. According to the Geological Survey of Canada, the auriferous deposits of Barkerville are due to the tertiary rivers. The majority of the present streams flow along the lines of the ancient rivers, but between is a heavy layer of modern detritus. On Williams Creek the workings, at the time of the writer's visit, had been carried down to a depth of 90 feet and on Lightning Creek to 110 feet. Most of the gold found in the Cariboo district occurs at depths below forty feet. The ground has been chiefly worked by shafts. From an open pit 90 feet deep, the first 15 feet proved to be old tailings and gave values as high as 15c. to the cubic yard; this was followed by 15 to 16 feet of gravel containing no value; next in order was a thin layer of clay succeeded by gravel, the pebbles increased in size towards the bottom, although no large boulders were present. In the lowest 6 feet of this gravel values were found up to $6.00 per cubic yard. In the case of another property a boring was made to a depth of 287 feet showing the following section: For the first 100 feet alternating gravel and clay containing no gold values; next, 150 feet of blue clay succeeded by 30 feet of gravel and clay to bed-rock; the gravel for a depth of from 7 to 8 feet above bed-rock was highly auriferous.
The journey to Willow River is made through Beaver Pass at the head of which is a lake. The Pass itself is filled with glacial gravel and boulder clay. The fall of the Willow River is, perhaps, some 10 to 15 feet to the mile. There are numerous small bars of fine gravel showing a few colours. Here and there are bluffs of an older formation, consisting of gravel, sand and clay, resembling the upper gravel found in some parts of California, and carrying no values. Generally bed-rock is at a great depth. In places Willow Creek splits into numerous channels, most of which are blocked with drift wood; the islands so formed are almost barren of gold. Some of these side streams have been worked to a small extent, but there are no indications of past working on the main stream. The superficial gravels are too poor to work, and the rich pay dirt lies at too great a depth. At the head of the streams, where the deposits are shallow, the rich pay-dirt has been reached, and mining in a small way has been undertaken, but 20 miles from the heads of the several streams no bed-rock has been struck, and thus work has been impossible. The bed-rock when found is of soft shale and slate easily worked by a dredger. The benches were worked in the "sixties," and proved very rich. In Cariboo, the length of the working season is about 180 days, and this relatively short season has, of course, to be taken into consideration when determining the dredging prospects. But the writer is fully convinced that a systematic examination of the head waters of the Cariboo streams with a drill, would well repay the cost.
While the writer had no opportunity of visiting Atlin and the other mining divisions in the Cassiar district, he has inspected the principal placer grounds so far discovered in the Yukon. This country apparently affords great potentialities for successful dredging enterprise, but conditions must be carefully studied. Thus, by reason of the extreme shortness of the season, the lack of fuel throughout a large section of the district, in many cases the absence of water, together with the high rate of wages and high cost generally, the value of the ground must necessarily be proportionately greater than in most sections of British Columbia to render operations profitable. Nevertheless, in spite of the many difficulties, reaches on the rivers and creeks have been acquired by companies who have installed on these properties modern and carefully designed plants which are earning handsome returns.
Much of the ground in the Yukon is, unfortunately, frozen to bed-rock, but it thaws readily when the over-burden is removed and the surface is exposed; thus, a sufficient area of thawed gravel may, in many localities, be readily kept ahead of a dredger so as to ensure no suspension of operations on this account. In certain localities, as for example, Bonanza Creek, timber is scarce, and consequently until coal is procurable fuel must necessarily constitute an expensive item. In other localities, however, such as Eureka Creek, timber is abundant. The problem of transportation is also one to be reckoned with, but conditions in this respect are improving every season, since the government is expending large sums annually on road making and is also encouraging the construction of railways.
New and promising possibilities for dredging are also developing in the Omineca district. The conditions here are eminently favourable. The region is undoubtedly rich in gold, and although the lack of cheap and adequate transportation facilities is a present difliculty, this drawback will ere long be removed by the operation through the district of one or more of the new transcontinental railways now in progress of construction.
In passing, it may be noted as strange that in a country so rich in platinum as British Columbia, no effort is made to save the platinum and other precious metals beside gold; this is not universally so, but is generally the case. Perhaps, the reason is that platinum and other precious metals do not readily amalgamate with mercury, and thus are lost when running over the amalgam plate, still they can always be caught after leaving this. Platinum is easily discernible, but some of the other precious metals are not so easily seen, and unless occurring in very large quantities are not noticed, but pass into the tailings.
In the matter of estimating dredging costs, the following notes regarding necessary staff, etc., may be of assistance:
One dredgemaster, one engineer for each shift, one winchman for each shift, one deckhand for each shift, two men to handle fuel during the day shifts, two men around the camp including the cook. When the head lines and side lines have to be shifted, all hands help. It will also be necessary to add a blacksmith to the staff to make repairs in the case of outlying districts. Wages of course vary in different localities. To the above must be added the cost of fuel, oil, and a few contingent expenses. The price of fuel varies with the locality. Dredgers now generally are made to give an output of 4,000 cubic yards per diem, that is in two runs of 10 hours each. The output varies with the nature of the gravel to be dug, and dredgers are being made with much higher capacities. The annual output depends greatly on the total number of hours run, and this of course depends on the stoppages for repairs. The working cost per cubic yard runs under the above circumstances to from 2½ cents to 7½ cents per cubic yard; though in certain localities, where the cost of labour and fuel is abnormally high, the cost is increased.
In conclusion, while, as already shown, the opportunities for profitable dredging in British Columbia are eminently favourable, the mistakes of the past must not be repeated. These mistakes may be attributed to two causes: first, that insufficient care and attention was given to prospecting, and ground not adapted to dredging was, in consequence, selected. Secondly, the dredges employed were far too light in construction and were not designed to suit special requirements. Moreover, the mistake has been made in the past of too blindly copying the designs of plants in use in other countries, on the assumption that a plant in successful operation elsewhere would necessarily answer all requirements. No matter how good the territory, returns cannot be expected unless work is scientifically organized and carried out; but the writer is convinced that the areas above described will well repay careful and systematic examination.
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