Colorado’s placer and lode sources of gold, which gave first impetus to
the series of mining booms in the state, were fantastically rich. Summit
and Lake Counties, for instance, each produced more than $5,000,000 in
placer gold between 1859 and 1867. During the same nine-year period,
more than $9,000,000 in lode gold was produced from Gregory Gulch, a
tiny canyon between Central City and Black Hawk. Other districts
rivalled or surpassed these figures.
Early in the game it was recognized that almost all the deposits
occurred along what came to be known as the “mineral belt,” a
fifty-mile-wide zone extending southwest from the Boulder region. Most
of the metals mined in the state come from this belt, but there are
three notable exceptions: Cripple Creek, Silver Cliff, and western
Colorado vanadium and uranium districts. In the first few years of the
Colorado rush, gold ores and placer gold were discovered only in the
northeastern part of the mineral belt. Gradually the belt was found to
extend further and further southwest: Tincup was discovered in 1861,
Silverton in 1870, Lake City in 1871, and Telluride in 1875. Aspen, on
the western edge of the belt, was not discovered until 1879, perhaps
because the area was difficult of access and lacked the easily
recognizable native gold.
In the northeast part of the mineral belt, gold and other minerals occur
in veins in Precambrian granite and gneiss. In the Leadville and Aspen
areas, ores are associated with altered Paleozoic limestones. At the
southwest end of the mineral belt, in the San Juan Mountains, ore veins
are found near or in Tertiary volcanic rocks. Native gold, gold-bearing
compounds, and other metallic ores in these veins originated where
mineral-rich solutions from deep within the earth penetrated fissures
and joints in the surrounding rock. Regardless of the age of the host
rock, almost all the ores of Colorado were deposited in the early or
middle Tertiary Period, about 35 to 70 million years ago.
Gold and silver are no longer mined extensively in Colorado, although
any summer Sunday will see weekend operators panning near mountain
streams or trundling rock from one-man mines. The recent rise in the
price of silver has encouraged many miners to reopen old shafts. The
most active mines in the state today are those producing molybdenum,
lead, zinc, and vanadium. (Vanadium, although a metal, usually occurs in
Colorado with radioactive minerals, and so is discussed with them rather
than with the metals.)
[Illustration: The Colorado mineral belt extends from Boulder County on
the northeast to San Juan County on the southwest. Almost all of the
prominent mining districts in Colorado lie along this belt. Cripple
Creek and Silver Cliff, however, lie far to the east of the general
trend.]
Telluride
Denver
Colorado Springs
Alamosa
BOULDER
Ward
Gold Hill
Boulder
Nederland
GILPIN
Central City
Black Hawk
JEFFERSON
Golden
CLEAR CREEK
Empire
Georgetown
Silver Plume
Idaho Springs
SUMMIT
Breckenridge
EAGLE
PITKIN
Aspen
GUNNISON
Tincup
CHAFFEE
PARK
Climax
Alma
Como
Fairplay
TELLER
Cripple Creek
FREMONT
OURAY
Ouray
Camp Bird
Ironton
SAN JUAN
Silverton
HINSDALE
Lake City
LA PLATA
Durango
MINERAL
Creede
CUSTER
Silver Cliff
All told, some 430 metal mining districts have been established as legal
entities in the state of Colorado. Each of these districts had the right
to draw up its own regulations concerning prospecting, claims, and
mining rights, within a framework established by the Federal government.
Only a few of the districts ever became really significant producers.
The geology and history of several of the leading areas are presented in
the pages that follow.