Marble - Colorado Geological Survey

at or near the upper existing quarry face which
is close to the upper contact of the gray marble
and at its northern most outcrop. The minable
reserve here is limited by the steepness of the
topography and the inclusion of chert layers in
the lower portions of the unit. The volume of
this Phase 1 surface minable prism is 3,260,000
cubic feet. This is approximately 285,000 tons
at the assumed 175 pounds per cubic foot. The
Phase 2 operation here would be underground
to access the remaining two million tons of gray
marble. The southern area of the property is
composed of white marble outcropping in rugged
terrain. This area will require extensive
development prior to mining and will require
that all mining be underground. The development
there would include site preparation of a
service area, road building of 3,000 feet to the
main haulage road, and stripping to an adequate
area for an entry. In that area hornfels
units which overlie the marble are extremely
folded and would form an irregular back which
would be difficult to maintain.
The quarry operation must focus on the extraction
of blocks which are approximately 5.5
feet by 5.5 feet by seven to eight feet in length.
These blocks are small enough to ship easily and
will fit in all of the common saws used in fabrication.
It is the production of these larger blocks
that will represent the most economic product.
Quarrying operations generate considerable
quantities of waste material which either must
be disposed of or must be turned into some type
of by-product which could be sold at less than
the disposal cost. Such a by-product for this
marble quarry is crushed aggregate for use in
buffering acid mine drainage, as well as other
industrial applications. The operation will generate
approximately three tons of waste for
each ton of large quarry block material. Part of
this waste will be in the form of broken 5.5 feet
blocks especially those which fail because of
unseen joints. These smaller blocks represent
feed for the tile fabricating facilities.
Reserves
The minable reserves are usually far less than
the volume of the resource. CGS calculated the
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volumes based on surface mapping and on projection
without drill information into the hillsides
for 500 feet. The assumption is that both
quality and thickness will remain constant for
that distance. To support that assumption CGS
mapped a marble unit at the eastern most extent
of the subject property which closely resembles
the gray marble of the upper falls
bench. CGS believes that this marble is the exposed
eastern limb of a north plunging syncline
and projects some 2000 feet to the upper falls
unit. The projection of the white marble is less
due to the complexity of structures on the
southern property boundary.
The open quarry minable reserve was calculated
to be 3,260,000 cubic feet or 285,250
tons using SURFER Version 4, Golden Software.
Recovery will be a function of the ratio of
useable material to total material assuming a
waste loss. The recovery will be 50 percent of
the quarry material as follows:
Recovery of 5.5 feet by seven to eight feet
blocks will be 20 percent of reserves. Recovery
of tile blocks will be 10 percent of reserves,
Recovery of ashlar material will be 10 percent
of reserves, Recovery of useable CaCOs will be
10 percent of reserves. The remaining 50
percent will be unuseable waste.
The underground quarry will have a similar
recovery ratio of waste to ore with respect to
blocks but the resource will be further reduced
by the placement of ground control pillars. It is
assumed that pillars will have a height to
width ratio of unity and that the overlying beds
of white marble above the original quarry will
have sufficient strength to obviate leaving a
horizontal thickness of the mined gray marble.
This will require 20 percent to be left for roof
support allowing 80 percent of 1,421,875 tons
or 1,137,500 tons to be mined.
The white marble at the south property
boundary will have a lower extraction ratio
because the overlying hornfels is irregular,
broken, and severely folded. This will necessitate
leaving a substantial thickness of white
marble in the back. This is further complicated
by the existence of more non-vertical joints
which invariably reduce extraction ratios and