Marble - Colorado Geological Survey

5"0
destroyed, although banding in some Conundrum
Creek marbles may relate back to
original bedding. Chemical analyses of marbles
conducted by CGS for this study reveal
CaC03 concentrations upwards of 95 percent
for marble sampled.
The pure calcific nature of marble units indicates
that metamorphism was not accompanied
by circulation of hydrothermal fluids. Metamorphism
of limestones, accompanied by exchange
of elements, would tend to produce
skarn and hornfels rather than chemically pure
marble. Marble units are, however, pyritized
locally. Alteration of marble is less extensive
and of decreased intensity to that of hornfels,
due to very low permeabilities in marble.
The Belden marbles are variable in color,
ranging from dark gray to white. Intermediate
colors exists, as do zones of alternating layers
of dark and light banding. The marbles are
composed of fairly large grained, euhedral to
subhedral crystals, although some zones of
more fine grained marble occur. All marbles
observed in the Conundrum Creek area are pyritized
to some degree. Small pyrite grains (less
than one mm) are aligned on fractures and
other permeable layers (Figures 6, 7, and 8).
12
Figure 5.
Hornfels from the
Conundrum-Colorado
Highland property. This
metamorphic rock is
interbedded with marble
and was produced
from a carbonaceous
sandy shale parent
rock. Hornfels at the
Colorado-Highland
property is of no
economic importance.
Note iron staining
caused by fine pyrite
inclusions in the rock.
Number corresponds to
sample number in
Appendix A.
Marble beds are of variable thickness due to
plastic deformation. Rift if present is generally
parallel to bedding. Folding of beds has tended
to align mineral grains in direction of deformation.
Some marble beds, especially the basal
sections of the gray marbles contain significant
quantities of chert. The white marbles have
some breccia zones.
Detailed descriptions of representative rock
samples from across the Colorado-Highland
claim block are reprinted in Appendix A of this
report. Locations of 65 collected samples are
shown on Plate 2. These samples are available
for inspection at the Colorado Geological
Survey offices.
STRUCTURAL GEOLOGY
Regional Setting
The Sawatch Range of central Colorado was
uplifted during the Laramide Orogeny. The
gentle eastern side of the Sawatch Range Uplift
has been truncated by a fault, emplaced along
the trend of the Rio Grande Trough, forming
the Upper Arkansas Valley. In the vicinity of
Aspen, the steeper and structurally more com-