ocesses of weathering and transportation
everywhere operative on the surface of the earth tend to separate quartz
from other materials, and to concentrate it into deposits of sand.
Katamorphism is primarily responsible for most of the deposits of silica
which are commercially used. Anamorphism--cementing and hardening the
sands into sandstones and quartzites--has created additional value for
certain uses, as in refractories, building stones, and abrasives (see
pp. 84, 267).

FOOTNOTES:

[31] Report of the Royal Ontario Nickel Commission. Printed by order of
the Legislative Assembly of Ontario, Toronto, 1917.

[32] Campbell, J. Morrow, Tungsten deposits of Burma and their origin,
_Econ. Geol._, vol. 15, 1920, p. 511.

CHAPTER X

COPPER, LEAD, AND ZINC MINERALS

COPPER ORES

ECONOMIC FEATURES

The electrical industry is the largest consumer of copper. The
manufacture of brass, bronze, and other copper alloys constitutes
another chief use for the metal. Considerable quantities of copper
sheets, tubes, and other wares are used outside of the electrical
industry, as for instance in roofing, plumbing, and ship bottoms. Copper
is also used in coinage, particularly in China, where it is the money
standard of the working population.

The average grade of all copper ores mined in the United States in
recent years has been about 1.7 per cent metallic copper. Ores
containing as low as 0.6 per cent have been mined in the Lake Superior
country, and bonanza deposits containing 20 to 60 per cent have been
found and worked in some places, notably in Alaska and Wyoming. The
lower-grade ores, carrying 1 to 3 per cent copper, are usually
concentrated before smelting, while the richer ores, carrying 3 to 5 per
cent or more, are generally smelted direct. Many of the ores contain
values in gold and silver, and also in lead and zinc. An average of
about 40c. worth of gold and silver per ton is obtained from all the
copper ores of the United States.

In other countries the average grade of copper ores mined is somewhat
higher than in the United States,--where large scale operations,
particularly the use of steam-shovel methods on extensive bodies of
disseminated or "porphyry" copper ores, as well as improvements in
concentrating and metallurgical processes, have made possible the use of
low-grade ore.

The principal sources of copper are the North American continent, Chile
and Peru, Japan, south and central Africa, Aus