GENERAL41483

• Permit No: M1995097
• IBM Index Class Name: General Documents
• Doc Name: BIBLIOGRAPHY WITH INTRODUCTION GLOSSARY OF TERMS AND LIST OF MINERALS
• Media Type: D
• Archive: No

Geology and Mining Methods
INTRODUCTION
Geologically, the mineral deposits of the Aspen district are
moderately complex, as compared to the relative simplicity of, for
example, the Gilman district, near Vail, Colorado, or the much more
complex deposits of the Leadville district, even though the host
rock in all three is the same (the Leadville Limestone; there are
other similarities as well). Mineralization is confined almost
entirely to upper Paleozoic sediments although some occurs
throughout the Paleozoic section.
Colorado Geologic Features
A map of the State of Colorado showing its major geologic
structural features is included at the end of this Introduction."
This map graphically ilustrates Aspen's location on the northwest
edge of the Sawatch uplift where it turns to the northeast as well
as melding into the White River uplift to the northwest. Stresses
ressulting from the turn in the Sawatch uplift at this point are
thought to be in part responsible for producing the folds and
faults that, in conjunction with suitable sedimentary host rocks,
controlled ore deposition in the Aspen mining district.
Most of the major structures shown (uplifts and basin), as
they are now defined, including the Sawatch, are of late Cretaceous
and early Tertiary age (75 to 60 million years old) and were
produced during the Laramide mountain-building period. Many of
these features are, however, reactivations of Pennslvanian-Permian
structures of the so-called ancestral Rocky Mountains. At least
some of these, including the Sawatch uplift, are probably related
to much older Precambrian fracture zones. The San Juan volcanic
field and the much smaller West Elk and Thirty-Nine Mile volcanic
fields, not shown but located at the southeast tip of the Piceance
basin and northwest of Canon City, respectively, are younger from
mid- to late-Tertiary. The current topographic expressions of
these features are, of course, much younger, virtually all being
Quaternary in age.
The so-called Colorado mineral belt extends from the
southwest boundary of the San Juan uplift northeast through that
uplift, the northwest part of the San Juan volcanic field, the
eastern two-thirds of the Gunnison uplift, the West Elk volcanic
field, much of the Sawatch uplift, the southern quarter of the
Sierra Madre-Park uplift, and the north-central part of the Front
Range to Boulder. While there are notable exceptions, the majority
of Colodrado's major mineral deposits occur with this belt.
11 Adapted from ROCKY MOUNTAIN As$Dc
2, p. 3 (H. C. KENT & K. W. PORTER, ED$,
OF GEOLOGISTS, COLORADO GEOLDOY, Flg.
Denver 1980).
BIUCe A. CO111nS - xxll - SMUGGLER BIBLIOGRAPHY