In its primitive form, the dipper dredge consists of a barge or pontoon, to the side of which is attached a long pole carrying a strong canvas or hide bag, or iron bucket, which is termed a ladle, spoon, scoop, or dipper, and which at times is provided with a blade or shovel. To the dipper end of the pole, is fastened a rope or chain, carried back to a hand-winch in the dredge, by which means the dipper is raised. In working, the dredge is moored in the stream, the dipper is lowered, drawn along the bottom, and then raised by the winch. The operation is slow and laborious, and even under the most favourable conditions cannot raise more than 2 or 3 tons of gravel per hour. Nevertheless, in the early days of gold-dredging on the Clutha, when the virgin ground in the river was not, as now, buried beneath vast deposits of tailings, good results were attained, and not a few small fortunes built up, as the result of operations with these machines. This primitive dredge, which may still be seen in operation for channel-clearing, has been largely improved in speed and capacity by the substitution of steam for handpower, and in the form of the modern steam-shovel machine has a more extended use for gold-dredging. The principal American makers of this type of dredge are the Marion Steam Shovel Company, of Marion, Ohio, and the Bucyrus Steam Shovel Company, of Wisconsin. Two instances of the successful use of these machines are cited in the report of the Minister of Mines, in British Columbia, for 1897. In the first, Mr. W. F. Gore, the General Superintendent of the New Fraser River Gold Mining Co., in reply to an inquiry from Mr. F. Sones, Gold Commissioner, Clinton, states: “ We have made dredging a known quantity, and an absolute success, not through the medium of any new invention, or combination of patents, but through the operation of a harbour dredge of the kind known as the dipper dredge, which was built to our order by the Marion Steam Shovel Company, of Marion Ohio. The dredge lifts 1 cubic yards of material at a time, thus enabling us to work from 1,000 to 1,200 yards of material per day. For sluicing purposes, we have two direct centrifugal pumps, which raise about 7,500 gallons of water each per minute. These discharge into hoppers above the grizzlies; and the sluices and usual riffles do the rest. To my mind, it is one of the neatest and prettiest mining operations ever conducted. The scow or vessel on which the machinery is placed is 82 ft. by 38 ft. The boilers are 80 to 100 h.-p., with engines powerful enough to lift 55 tons.” “ In a personal interview, since receiving his report,” adds Mr. Sones, “ Mr. Gore informed me that the vessel and machinery were finished about the end of October last, and they hauled out into the stream for a test and to smooth bearings. Everything worked to perfection; the dipper went under the water and came up full.

Both Mr. Gore and Mr. Davidson, the mechanical engineer, assure me that they are perfectly satisfied that they can handle the gravels in the Fraser River. The gravels last worked are from 3 ft. to 4 ft. thick, resting on a stratum of hard pan.” The second instance is thus described by Mr. G. C. Tunstall, Gold Commissioner, Kamloops: “It is pleasing to note the comparative success attending the operations of the Beatty Gold Mining & Dredging Company, which are still in progress below North Bend, on Boston Bar (Fraser River). The dredge referred to is provided with a shovel or dipper, under perfect control of the machinery, capable of being swung around, and submerged anywhere within a certain radius, and with a capacity, at each hoist, of 1½ tons of gravel, in less than one minute. The amount of material raised per diem is estimated at 800 cubic yards, and this is deposited on an inclined iron grating, or “ grizzly,” lying on a scow moored alongside, by which the large rocks are deposited in the river, while the smaller stones and gravel are carried into a dump-box placed underneath, and run thence into sluice-boxes furnished with different kinds of plates, riffles, and under-currents, supplied with quicksilver to save the fine gold. The shovel raises a certain amount of water, but not sufficient to run off the gravel, and a further supply for washing is provided by means of a pump. The gold is found beneath a layer of boulders, lying at or near the surface of the river bottom. Difficulty is frequently encountered in moving the scow by reason of the large rocks precipitated from the “ grizzly,” forming a bar in a comparatively short time, but measures will be taken to avoid this obstacle in future. The machinery is capable of working to a depth of 26 ft. As no coarse gold has been obtained, I would infer that operations did not extend as far as bed-rock, where it should be found in large quantities in the crevices and seams, under conditions which may probably render its recovery a difficult matter. The mining season is confined to the period of low water. The cost of this dredge was $18,000 (£ 3,600), and seven men are employed. The large boulders are hoisted on scows, and dumped at a distance down stream.”

It is argued against the dipper dredge that it is ill adapted to dredging for gold, since it disturbs the gravel in the act of digging; and some of the gold, especially the fine metal, is floated away and lost. Moreover, it is unable to make a direct side cut across a river or bar, so as to systematically work and clear up the ground. Other objections are, that the material, being supplied intermittently, necessitates special arrangements for feeding the wash, in a continuous stream, to the gold saving tables; the intermittent action, moreover, throws more strain on the entire plant than the continuous work of the bucket dredge; finally, for equal capacity, the dipper dredge requires two to three times the crew of the bucket dredge, and the cost of running is nearly twice as great, the figures, according to Mr. R. H. Postlethwaite, of San Francisco, Cal., being 7 cents and upwards per cubic yard for the shovel, against from 3 to 5 cents for the bucket dredge. It is, however, well to remember that this form of dredge is, in many positions, economical of operation. This remark more especially applies to ground where the presence of numerous large boulders hampers the operation of other machines.

Suction Pump Dredges

The Grabs or Clam Shell Dredge

The Bucket Dredge

Classification of Bucket Dredges