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

VAN DERWILT REPORT
dipping 30° southwest. Fault displacements vary from 0 to
over 200 ft. Faults are commonly indicated by shattered
zones over 100 ft, across. Beds in the footwall are
invariably offset to the west. Pronounced brecciation
occurred at the intersection of these cross-faults with the
contact between Devonian [Dyer] or Mississippian [Leadville]
dolomite and Pennsylvanian shaly limestone [Belden]. Some
of the most important orebodies have been found in these
areas, and in addition the breccias have been cited as
evidence for bedding faults.2L Brecciation along the
dolomite-shale contact diminishes away from the cross-
faults. Ore and breccia are virtually concurrent, but
neither are continuous along the contact between adjacent
parallel cross-faults except locally where the faults are
close together. "The obvious relation of this breccia to
the cross-faults refutes the idea that they resulted from
faulting parallel to bedding."
Breccia parallel to beddino, pp. 236-237. Brecciation of
dolomite is far more common than of limestone. Brecciated
beds of dolomite in [otherwise undisturbed] dolomite is
common, and in some cases dolomite beds within limestone are
strongly brecciated without detectable disturbance of the
enclosing limestone. Vanderwilt believes this style of
brecciation was caused by shearing stresses produced by
close folding, and that relative movements amounted to
[only] a few inches. "Since the brecciation took place
along cross-faults where total displacement was unimportant,
the breccia parallel to bedding cannot be accepted as
evidence of important movement."
Relation of breccia to ore deposition, pp. 237-238. The
direct relationship of breccia to the ore deposits is the
relatively large percentage of open space through which the
[mineralized] solutions can circulate. On Smuggler
mountain, ore is virtually confined to breccia (whereas
there is significant limestone replacement on Aspen
mountain); the interbedded shales, dolomites and limestones,
and sandstones of the Pennsylvanian Weber [Belden] are more
brecciated than the underlying dolomite, and the amount of
ore obtained from the dolomite is relatively unimportant.
Bearina_of revision on future of the district, pp. 240-241.
The general opinion at time of writing [1935] is that the
Aspen district is mined out, except possibly at greater
depths. Important orebodies on Smuggler mountain have been
_` SPDRR MONOGRAPH, 71-72, 74, 88-89, 106, 120-122, 128, 144-145; SPURR
REPORT, 306-315. See also, among others, S. F. EHHONS, PRELIMINARY NOTES ON
ASPEN, COLO.; A. LAKES, GEOLOGY OF THE ASPEN MINING REGION, PITHIN COUNTY, COLORADO; AND
W. E. NEWBERRY, NOTES ON THE GEOLOGY OF THE ASPEN MINING DISTRICT (COLORADO], as cited
previously, Part I, ante, pp. 11 and 13, respectively.
Bruce A. Collins - 15 - BIaLIGGRAPHx