142 GRAVEL AND PLACER MINING IN ALASKA. [bull. 263. 
15 to 17i cents per cubic } T ard. He recommends the method last 
mentioned as against bulldozing, or placing charge on top, as powder 
is saved and there is the additional advantage that much of the rock 
is thrown out of the cut. 
The practice of installing large and expensive derricks as an adjunct 
to hydraulic mining is not generally recommended for Alaskan work. 
SLUICES AND GOLD-SAVING APPLIANCES IN HYDRAULIC 
OPERATIONS. 
In the South Coast region the plant of the American Gold Mining 
Company in Silver Bow basin is characteristic. This sluice, while not 
in use during the season of 1904, has been operated since 1901, and is 
typical of the most favorable conditions under which hydraulic tail 
sluices can be constructed in southeast Alaska. 
A 9- by 10-foot tunnel, 3,300 feet in length, was driven through a 
spur of the mountain from the bank of Gold Greek to tap the gravel 
pit at the proper depth for reaching the lowest sag in the bed rock. 
The grade of the tunnel, like that of its contained sluice, is 4 inches 
to 12 feet. It was driven with air at the rate of 8 feet a day in slate, 
at a cost of $20 per foot. No timbering is used, with the exception 
of a few sets near the ends. 
The sluice running through the tunnel is 4 feet w T ide and 4 feet 10 
inches deep, inside measure, of 2-inch native lumber, lined with 1-inch 
"sand" or lining boards, all lumber planed and sized. The sills are! 
laid on bed rock, and are 6 inches square and 5 feet long, the posts 
being also of the same size. Posts and sills are braced by 1 by 8 inch 
pieces. The sluice is 3,700 feet long from the tunnel entrance and 
extends for 900 feet up the bed of the pit through the worked-out 
ground. Bowlders as large as 10 inches in diameter are handled in -j 
this sluice without difficulty. The amount of water used varies 
according to the season, but averages 2,500 inches. Riffles are 12- by 
12- by 12-inch spruce blocks set on end, separated by If- by 2-inch 
strips, set on edge and nailed with headless nails. The duty of a| 
miner's inch of water is 2 cubic yards per twenty-four hours. The 
amount of lumber necessary for constructing one box of a sluice, such 
as the above, approximately 1,100 feet, is probably excessive for the 
needs of the case. Local conditions in the North frequently result 
in increased expenditure for the sake of hastening work. About 25 , 
pounds of nails were consumed to each box, and $10 worth of labor. 
The cost will not fall greatly below $30 per box of 12 feet, exclusive 
of cost of tunneling and shooting out the bed rock to grade in carry- 
ing up the boxes through the pit. The annual cost of maintenance, 
including renewal of riffle blocks, which last two years, and renewal 
of lining boards, is approximately $1,000 a year. 
