In many of the old placer-mining districts are still to be found large tracts of gold-bearing gravel not suitable to be worked with a dredge, because the bed is too shallow or the gulch too narrow. Frequently there is not enough grade to handle the gravel successfully by ground-sluicing or a bed-rock flume, or it contains too many boulders to be worked successfully with the ordinary hydraulic pipe or tube elevator.
In southwestern Oregon, two practical placer-miners named Ruble, after working for years trying to make money out of placer-ground containing many large boulders, invented and patented a hydraulic elevator of an entirely new type, and one that has been found to work very successfully in flat ground and in gravel containing many large boulders. It is a very simple contrivance.
A few years ago I acquired the property near Pierce City, Idaho, known as the American placer-mine. Various attempts had been made to work this ground. A bed-rock flume had been installed by one company, an Evans elevator by another, and still other methods were tried on a smaller scale. All were unsuccessful. I installed a Ruble elevator, and it has proved very satisfactory. Working under 100-ft. (pipe) head, the ground has been handled at a cost of a little less than 8 cents per cubic yard. The conditions at the American mine are exceptionally hard, the boulders being large, heavy, and numerous. Basalt boulders, up to a size of 16 by 18 by 32 in., have been elevated to a height of 16 or 17 ft., with a 4-in. nozzle-stream, under 100-ft. head. Boulders larger than this size are blasted.
At the American mine, a foreman, two pipemen, and two laborers are required per day of 24 hr. to operate the elevator. Several sizes of this elevator are in use, the one at the American mine being the 25-ft. size, having 25 ft. of grizzly 8 ft. wide. This elevator handles from 280 to 300 cu. yd. per day. In ground containing fewer and smaller boulders the capacity would be much greater and the cost of operation much less per day and per yard. At first I used two pipemen on each shift, one driving the gravel to the elevator, the other elevating it, each using a No. 2 giant with 4-in. nozzle. Later, I changed to No. 3 giants, using 5.5-in. nozzles, which enabled me to use all the water in one stream, dispensed with one pipeman on each shift, and materially reduced the cost of operation. I also found that I could handle about 25 per cent, more yardage in this manner than by dividing the water into two streams.
The elevator is so constructed that it is impossible to choke it. The elevator giant, or the giant that elevates the gravel, is placed in line with, and about 50 ft. from, the elevator, which leaves room for the field giant to pile up gravel in front of the elevator. The water is then shut off from the field giant, turned into the elevator giant, and the gravel run through the elevator. While this is being done, the field giant may be moved and reset, if necessary. In deep, undrainable ground, a water-lift is attached to the side of the elevator, to carry off all the water after using. The foreman and laborers can reset the giant while the pipeman keeps the water continually at work. The sluice-boxes may be cleaned up in about 2 hr., while the water is being used in the field giant. The laborers break up the large boulders, cut and burn brush, move and set the giants, help move the elevator, and make themselves generally useful.
The Ruble elevator is a combination of grizzly, undercurrent, and elevator. It separates the fine gravel from the coarse rock and boulders while in transit up the elevator, and does it perfectly. The fine gravel, sand, and gold drop through the grizzly into an apartment underneath the grating-floor, out of reach of the force of the hydraulic stream which is lifting the heavy rocks to the dump. The fine gravel, with its contents, is now acted upon by the water of the elevator giant, after it has lost its force, and with this water is delivered by means of an inclined, smooth floor under the grizzly to the sluice, which is the gold-saving department of the elevator. The fine gravel and sand, after passing the sluice, is delivered to a dump separate from the boulder-dump. Operating with fine material only, the sluices are closely and finely riffled, and are much wider than the usual sluice used for coarse rock, thus furnishing a large gold-saving area in a short sluice.
This appliance solves in an inexpensive and economical manner the difficult problems of inadequate dump, deep and un-drainable ground, and the handling of heavy boulders and wash. It effects a close saving of gold and an economical use of water and time.
The elevator rests on rollers, placed on skid-poles on the bed-rock, and is easily moved. When the gravel is washed from in front of the elevator and the space in the rear is filled with boulders and tailings, the bed-rock is cleaned up, a horse is hitched to the elevator, and it is moved forward to a new position nearer the gravel-bank, leaving room for a new boulder-dump in the rear. When horses are not available, the elevator can be moved by hand with a capstan. At the American mine the elevator is moved three or four times each month. It requires from 1 to 1.5 days to move and reset it. The sluice-boxes are usually cleaned up every second day. No time is lost in cleaning up, as the field giant is kept at work during that time.
A few of the points of merit of this elevator are :
1. It handles larger rocks, with less water, than other types of elevators.
2. It dispenses with the boulder-crew, either at the mine, ground-sluice, sluice-box, or dump, except in rare cases.
3. It saves the gold, and the gold-saving department may be protected by lock and key.
4. The gravel is picked up in close proximity to the giants, the gold immediately extracted, and the boulders and other waste material dropped back on bed-rock previously worked off, instead of being transported a long distance to the dump. It makes its own dump.
Strange as it may seem at first thought, it is easier to elevate the gravel than it is to drive it along the level bed-rock, as is shown when the water is divided into two equal streams, the field giant being unable to keep the elevator giant supplied with gravel. In driving the gravel along on the bed-rock, the water has more or less downward pressure, causing more friction, while on the approach and the grizzly, owing to the inclined construction, it is lifting the gravel and boulders, causing less friction or dragging.
Fig. 1 shows the operation of the elevator with one giant, the sluice discharging in the foreground.
Fig. 2 shows the elevator with two giants in operation.
Fig. 3 shows the interior appearance of the grizzly; also the sluice swung from its bearings, with the apron or approach removed in order to move ahead.
Fig. 4 shows boulder-dumps left by this elevator at the American mine.