Prospecting for gold and silver by Lakes Arthur 1844-1917

Author:Lakes, Arthur, 1844-1917
Language: eng
Format: epub, pdf
Tags: Gold mines and mining, Prospecting, Silver mines and mining
Publisher: Scranton, Pa., Colliery engineering
Published: 1895-03-25T05:00:00+00:00

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means. Sometimes it happens that more gold is obtained from " leader " veins that had been overlooked, than from the main worked vein.

Quite commonly, especially in the lower part of a placer, the pebbles and sand are firmly cemented together into a coarse conglomerate by infiltration of iron oxide and clay. This may consolidate into a false-bottom and not be true " bed rock." Generally two or three such false-bottoms, with intervening strata of greater richness, alternate with barren ones. So, many old diggings, thus supposed to have been exhausted, may be worked again, the true bottom not having been reached. These conglomerate bottoms may lie just upon bed-rock, with a white clay rich in gold beneath them. Gold occurs also in the conglomerate and must be stamped out.

Modern rivers frequently cross in their course old river courses, and redistribute their golden sands.

Placers are richer in their richer parts, than the veins from which their gold was derived.

When shallow placers are due to the wearing down of quartz veins, no placer will be found above these veins, or above the point where the vein crosses the placer. In the Sierra Nevada there is but little alluvium, the gold comes from veins near by.

Gold placers may sometimes occur below silver mines. Thus.the Comstock vein was discovered by following up placer gold to its source. This vein has produced a gold-bearing silver-ore, the silver rapidly disappearing and leaving the gold behind.

EXAMPLE OF A PLACER.

In Ballarat, Australia, the " wash-dirt'' runs in a series of " leads " of varying width, starting from the same point, and trending in different directions towards the " deep leads." The "reef wash" is about 100 feet deep, the "pay dirt" 5 feet. The barren drift wash overlying the "pay dirt " is of black clay. The reef itself is of green slate, the bed-rock is sandstone. Gold lies sometimes on thin layers of sand or " pipe clay " on the surface of the "bed-rock," more often in crevices of the bed-rock itself, which is more or less rotten. This bed-rock is broken up for some 12 to 20 inches and the gold is found in "pot-holes " in it 15 to 18 inches in diameter and 6 to 10 inches deep, cut out of the solid rock. The alluvial gold is found chiefly in bed-rock of slate, dip-

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