In work on shallow placer deposits by individuals the results differ greatly, both according to the strength and skill of the worker and to the contents of the gravel. Under the best conditions of climate a strong, well-nourished, American digger may be able to raise by the shovel from 10 to 12 cubic yards of gravel per day, and throw it into a receptacle 3 feet above the ground. Native labour cannot be expected to affect so much, and in French Guiana it is reckoned that only about half a cubic yard of earth per man per day can be shovelled into the sluice. If the workman must wash the gravel, as well as raise it, much less can be accomplished. For an active man, it is a fair day’s work to dig and wash from fifteen to twenty pans of dirt, the amount treated thus not exceeding about 10 cubic feet. On the other hand, with the cradle, the output may be from 1½ to 2 cubic yards per man in a day, while with the long-tom it may rise to 3 or 4 cubic yards per man. In the Siberian trough, only from 1 to 1¼ cubic yards can be treated by one worker per day, but a larger percentage of the gold is believed to be saved in this apparatus. The minimum contents in gold, which will make the gravel worth treating, depends, of course, on the cost of labour in the country in which the deposit exists, since few men will continue to work for less reward than they could obtain in other employments. In early times, in California and Australia, when the virgin shallow deposits were being worked, large sums were often realised by individual diggers, cases being on record in which 5 ozs. of gold were obtained from one pan of bed-rock scrapings lying under heavy gravel, and earnings of several hundred dollars per day were not uncommon. The results obtained on the Klondike in Canada are still more remarkable.
Concerted work, with the aid of the sluice, is much more effective; in California gravel containing about 1 pennyweight of gold per cubic yard is worked at a profit, the dirt being lifted into the sluice by hand-labour, and the tailings removed by sluicing with water; at Ballarat, in Australia, where the gravel is raised to the surface from underground workings through a vertical shaft several hundred feet deep, and subsequently washed, 12 grains of gold per cubic yard of material pay for the treatment, while in Siberia, as stated below, the cost is even less. In French Guiana, the unhealthiness of the climate and the cost of supplies render it impossible to work gravel containing less than about 3 pennyweights of gold per cubic yard.
In Siberia, the distance of the workings from the nearest town, and the traditions of the industry, require workmen to be hired by the year, or, in cases where no work is attempted in winter, for the season. The total cost of treatment of the gravels varies greatly with its geographical position. On the banks of the Lena, where the season only lasts for five months, it is estimated that the gravel must contain 2 zollatniks of gold per 100 poods, or 4 1/3 dwts. per cubic yard ; but in the neighbourhood of Ekaterineberg, the deposits in the bed of the Pechma, a tributary of the Obi, are worked when they only contain from 8 to 9 grains per cubic yard.
The cost of working the perennially frozen placers is much more, but Levat gives an instance in which a bed of gravel, 9 feet thick, yielding about 1¼ dwts. per yard, and covered by 100 feet of barren material, was worked at Malamalski in the Trans-Baikal.
The cost of hydraulic mining depends largely on the magnitude of the operations. With large quantities of water available at a cheap rate, and big banks of soft gravel, the cost has been reduced in California, while the average cost was about low cents, and only in exceptional cases amounted to as much as 5x higher per cubic yard.
The relative costs of working the various classes of gold deposits in California by methods applicable to the respective classes.