Marble - Colorado Geological Survey

Figure 8: Close-up of handed marble. Note
variable grain size and alternating
coloration. Brown staining is due to the
weathering of fine pyrite located between
grains. Banded marble beds are generally
too thin and too folded to be of economic
importance.
plastically deformed, structurally complex lower
plate rocks (Plate 1).
Site Setting
Lower plate rocks of the Elk Range Thrust, have
been exposed in the Conundrum Creek window
in the area of the study. On the east side of the
valley, deformed and interbedded marble and
hornfels of the Belden Formation crop out in an
eliptical shaped zone where erosion has proceeded
below the plane of the Elk Range Thrust
Fault (Figure 10). The fault plane, which is
high on the west slope of Hayden Peak, is not
14
recognizable because of a large intrusive mass
which occupies the fault zone. The plane of the
thrust fault is recognizable on the west wall of
the valley where it brings rocks of the Maroon
Formation above into contact with upper
Belden rocks below. A sill of granodiorite was
emplaced just above the thrust plane in rocks
of the Maroon Formation.
Detailed mapping by CGS of lower plate
rocks exposed on the east side of Conundrum
Creek reveals complicated structure characterized
by intense folding and plastic deformation.
Alternating beds of marble and hornfels
have been in some places overturned, with
thinning and thickening of beds common (Plate
2). Exposure of the stratigraphic section is
locally sufficient enough to make estimates of
bedding thicknesses. Projection of structures
and bedding contacts is subjective due to complex
structure. Folding of beds has not been
accompanied by major faulting due to plastic
deformation. The jointing pattern is highly
variable throughout the exposed marble area.
Belden rocks in outcrop above creek level on
the Conundrum Creek property manifest as a
dissected view of the east limb of an asymetrical,
plunging syncline in gross aspect (see Figure
11 and Plates 1 and 2). Appreciable thickening
of strata is evident in the "waterfall
zone", at the north end of the outcrop, where
the black marble unit of the lower bench is estimated
to be 80 feet thick (see Figures 12 and
13 and Plate 2). This same unit was measured
at 20 feet thick at the south end of the outcrop.
Intense folding and thinning of "waterfall zone"
marbles to the south limit the southern progression
of quarrying of these marble (See
Figures 14, 15 and 16 and Plate 2).
Belden rocks exposed on the west side of
Conundrum Creek are postulated to be higher
stratigraphically than marble and hornfels of
the east wall (Plate 1). No major beds of marble
were observed on the west wall, suggesting
that marble units which outcrop on the east
side of the valley may be found at depth if they
persist. Projection of marble and hornfels units
beneath the west side of the valley is consistent
with our observations and corroborates the map