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88 PRELIMINARY INVESTIGATIONS. Gold Deposits in California
California as they arc generally found to be in the Ural Mountains.
A
black sand, composed chiefly of glancing grains of magnetic iron,
generally accompanies the precious metal, though it occurs also without
it.
Dr.
T. Sterry Hunt, speaking of the impressions which prevail in reference
to the presence of black sand in auriferous alluvions, very
appropriately remarks that "similar black sand residues, consisting
chiefly of various ores of iron (sometimes oxide of tin and other
minerals), may be obtained from the washing of almost all sands and
gravels derived from crystalline rocks, and the occurrence of a black
sand, therefore, in no way indicates the presence of gold. When,
however, this metal is present in gravel, it, from its great weight,
remains behind with the black sand and dense matters in the residue
after washing." *
Explorations at Malakoff.—The
explorations of the North Bloomfield Company furnish a remarkable
instance of the extent to which preliminary worjk lias been
successfully carried on. To determine the value of their claims and the
feasibility of working them, four prospect shafts were sunk to
ascertain the value of the gravel, the position of the channel, and the
depth to the bed-rock. No. 1 shaft struck the bed-rock of the main
channel at a depth of two hundred and seven feet, one hundred and
thirty-five feet of which was in blue gravel averaging 41 cents per
cubic yard. Drifts were driven from the bottom of this shaft a distance
of twelve hundred feet on the course of the channel, the width of which
was estimated at five hundred feet. The aggregate length of the
channel explorations was over two thousand feet. The samples of the
various drifts indicated a value of $2.01 per cubic yard. The actual
yield of 21,614 tons of gravel extracted from these drifts was
$33,-053.69, or $1.53 per ton, or about $2.75 per cubic yard.
The gross cost of the entire prospecting work, including the four shafts, was $63,956.20.
* " Geological Survey of Canada, Report of Progress, 1863-66," p. 36.
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