Man's physical universe

xanabras

186 THE EARTH AS MAN'S ABODE

ore (bauxite) by the action of water containing cari)on dioxide on

feldspar.

Tin was early found to alloy with copper to form bronze.

Tin does

not occur widely. England has some tin mines in Cornwall, but the

most important mines lie in a region extending southward from Burma

and Siam to the Islands of the Dutch East Indies. There is also a rich

deposit 16,000 feet high in the Bolivian Andes.

Lead and zinc are two other important metals that man uses today.

Deposits of many other metals have been found, and man is constantly

seeking new uses for them.

Platinum and gold are heavy metals usually found in an uncombined

condition in veins where they were deposited or in the bottom of

streams where they have settled below the less dense gravel as a result

of the erosion of the original lodes.

Both gold and silver are deposited

in fissures from solutions working upwards from lower deposits.

The original "mother lode" in California, about a mile wide and a

hundred miles long, contains gold-bearing veins whose content per ton

is worth about $3.00 or $4.00 or more; but the disintegration of large

portions of this mother lode, followed by the sorting-out processes of

erosion, produced fabulous gold deposits, some of which were worth

$200 to $300 per shovelful.

Today man is working the richer mother-lode veins, duplicating the

processes of nature. The ore is crushed to a fine powder in stamp mills;

and then it is either mixed with water and run over concentrating

tables, where the heavier gold and silver minerals separate out by

gravity, or it is mixed with chemicals which cause these minerals to

float ofif in a froth. Frequently the powder from the stamp mills is

mixed with water and run over a sloping copper plate coated with

mercury, which retains the gold as it settles out of the mixture.

Man sometimes even resorts to the chemical-decomposition processes

and dissolves the gold with cyanide. The gold is then precipitated from

the cyanide solution by adding finely divided zinc.

Colin G. Fink has predicted that the next age will be that of aluminum.

It is the most abundant metal in the earth's crust. There are

8 pounds of aluminum for every 5 pounds of iron and every 0.002 pound

of copper. The known supplies of copper at the 1929 rate of consumption

will last only 40 or 50 years.

The history of man is closely tied up with that of the prospector in

his search for new deposits of metals.

Vast Deposits of Useful Salts Have Been Found.

Some of the salt deposits were formed under conditions which caused

the different salts in the ocean water to separate out one at-a time.

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