148 GRAVEL AND PLACER MINING IN ALASKA. [bull. 263. 
one season. Through this sluice 1,000 cubic yards are washed in 
twenty-four hours with 250 miner's inches of water. It is stated that 
90 per cent of the gold is saved in the upper 6 boxes, only 1 per cent 
of the total gold being lost. The gold is mostly coarse and rough, but 
very fine gold is found. 
In the case of another operation working the Bonanza Creek benches 
it was stated that gold was found the entire length of a 2,000-foot 
bed-rock sluice, followed by 500 feet of 2-foot wooden sluice, on grade 
of 11 inches to the box length. Block riffles were used in the wooden 
sluice. A small nugget was picked up 2,000 feet from the head of the 
sluice. Another operator, using 360 feet of 20-inch sluice boxes, on 
12-inch grade, with iron-shod pole riffles, said that 2 per cent of his 
gold was escaping, and he was of the opinion that the installation of an- 
undercurrent would pay. 
In a hydraulic operation using 500 feet of boxes, 2 feet wide, 12- 
inch grade, with block riffles, and working a portion of the ''White 
Channel" gravels where the gold is very fine, bright, and smooth, it \ 
was said that 80 per cent was caught in the top box, 85 per cent inside 
the first 15 boxes, and that none was found in the two end boxes. 
In a bench hydraulic operation on Last Chance Creek, Klondike, a 
.small undercurrent with cocoa-matting riffles had been put in after 400 
feet of 2-foot sluices, with 12-inch grade, using block riffles. The 
undercurrent had given very satisfactory results, and a larger one was 
being constructed in addition. a 
The above data indicate that where hydraulicking is possible in the 
Klondike, the gold-saving appliances are fairly adequate to the needs 
of the operations. As all hydraulic mining in that region is limited to i 
ancient channels lying at an elevation of 200 feet or more above the 
present streams, water is exceedingly scarce, and sluicing methods 
must be adapted to this condition. These methods also depend on the 
necessity of impounding tailings on steep hillsides (see PL XXV, B), . 
the high cost of labor ($7.50 a day), and of lumber ($80 per thousand 
feet), the necessity of making quick and frequent clean-ups, and the 
different economic ratio which obtains in recovering gold from small 
patches of rich gravel as distinguished from large bodies of low-grade 
gravel. When it is well established, therefore, that no great percent-' 
age of gold is escaping, it is likely that the extra cost of installing 
and maintaining complicated saving appliances would overbalance the 
increase in gold recovered. The use of drops in the sluices, and 
lessening of grade, might, it is likely, result in an increased saving, 
with no extra expense of maintenance, except in the wear of riffles at i| 
certain points in the sluices. 
aSee Bowie, A. J., jr.: A Practical Treatise on Hydraulic Mining in California, p. 231, for full 
description of undercurrents and the method of leading gravel to them from the main sluice. 
