Over a large area of the Plateau Province in western Colorado, Mesozoic
sedimentary rocks are locally stained bright yellow, orange, or green.
Such staining suggests mineralization, and radioactive compounds were
recognized here before 1900. At that time, however, there was little or
no market for them or for the vanadium frequently associated with them.
When Marie Curie required radium for experiments with her newly
discovered element, the raw materials were sent from western Colorado;
by and large, though, production of radium from these ores was
prohibitively expensive.
In 1905, vanadium was found to be effective in toughening steel. The
Vanadium Corporation of America was formed to mine the Colorado ore.
This company mines a rich zone in the Jurassic Entrada Sandstone, where
vanadinite occurs with carnotite and other uranium ores. In the early
days of vanadium mining, the uranium ores were discarded with other
gangue materials; now, of course, uranium is produced from them.
Since 1945, uranium production has been an important Colorado industry;
in 1969 about $17,500,000 worth was produced. Uranium occurs in the
state in two very different situations. In the Plateau Province, where
it was first discovered, it occurs in sedimentary rocks as patches of
pitchblende, carnotite, and a greenish yellow mineral called
schroekingerite. It is most abundant in the Triassic Chinle Formation
and the Jurassic Entrada and Morrison Formations, where it was probably
deposited by downward movement of rainwater from overlying uranium-rich
Tertiary volcanic rocks. Concentrations of uranium often occur in or
near organic matter such as coal, fossil bone, or petrified wood, so
mines tend to be located along rock layers carrying abundant organic
material.
Another type of uranium ore is found in the Mountain Province. Veins in
Precambrian rocks of the Front Range and several other ranges contain
pitchblende which seems to have been deposited by hot groundwater rising
through broken and fissured Precambrian rocks. Often exceedingly rich,
such ore is mined in the manner of most of Colorado’s metals. The
Schwartzwalder Mine, a few miles northwest of Golden, has produced more
ore of this type than any other mine in Colorado.