Mr.
P. Wright, assistant engineer for water-supply, Beechworth District,
Australia, in giving his experience on the subject of the distribution
of gold in sluices, says: " With a sluice 12 inches wide, on an incline
of one foot to 48 feet, using 600 gallons per minute, I have found 95
per cent, of the gold within three feet of where the gravel was filled
into the sluice—where the gold was lying on a smooth board, and yet a
powerful current failed to move it." *
Distribution in Tail Sluices.—The
North Bloom-field tunnel (8,000 feet in length) has 1,800 feet of
sluices, paved with blocks at its upper end; but in the succeeding
6,200 feet no sluices are used, the tailings being allowed to run on
the bare bed-rock (a tough slate).
From
the rock-cut at the mouth of the tunnel a sluice paved with rocks
receives the tailings. From here on they are carried through sluices
and cuts and distributed over undercurrents which are set on different
grades, paved, in some instances, with rocks and blocks, and
occasionally arranged with longitudinal riffles covered with strap
iron. The grizzlies used are made of wrought iron, 1 by 4 inches in
size, set on edge. The discharge from the several undercurrents is
taken up by the main sluice and subsequently redischarged over the
succeeding undercurrent until the lowest sluice and undercurrent
finally discharge the tailings into the canon. From December 1, 1876,
to June 1, 1877, 354,000 24-hour miner's inches of water (2,230 cubic
feet each), conveying the tailings, passed through the main sluice and
tunnel and were discharged through the tail or lower sluice and
undercurrents.
* " The Gold Fields and Mineral Districts of Victoria," R. Brough Smythe, p. 133.
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