Marble - Colorado Geological Survey

closing of the Midnight Mine near Richmond
Hill in 1952.
A number of ore deposits are associated with
the Middle Tertiary plutons of the Elk Mountains.
Deposits of contact metasomatic iron,
disseminated sulfide, and fissure-vein leadzinc-silver
occur in and adjacent to granodiorite
intrusives. Except for iron produced by Pitkin
Iron Corporation during the 1960s, and possibly
some sporadic precious and base metal production
from fissure-veins, no significant metal
production can be attributed to the Middle
Tertiary deposits.
At the head of Cooper Creek in the southeast
corner of the Hayden Peak quadrangle, a
contact metasomatic deposit of iron has been
mined by open pit methods. The iron deposit
occurs in highly recrystallized limestones of the
Belden Formation adjacent to Tertiary intrusive
rocks. The ore was emplaced in steeply
dipping fractures which are most likely associated
with intrusion of the White Rock pluton.
The ore consists of massive magnetite with
some pyrite.
As previously mentioned, disseminated
sulfides are a common occurrence in granodiorites
of the White Rock pluton, as well as in adjacent
hornfels and to a lesser extent, marbles.
The deposits are mostly pyrite, but local occurrences
of disseminated molybdenum and copper
have been reported. There are no records of
metal production from altered granodiorite or
other pyritized units. CGS observed an old
prospect adit and dump which was developed
on an outcrop of pyritized hornfels unit at the
southern end of the California placer. Assay
results and panned concentrates from the
dump contained low metal values. These deposits
are not economically important.
Minor, non-extensive quartz-carbonatepyrite
veins cut red-beds, hornfels and other
strata above and adjacent to the White Rock
pluton remote from the subject property. These
fissure-veins locally contain sphalerite, silver
bearing galena, and very rarely gold. Fluid
inclusion data from veins of this type indicate
they are related to post-magmatic alteration
and mineralization associated with the intru
sion of granodiorite, as in disseminated deposits.
Production from these structures has been
minimal. The most noteworthy mine developed
on this type of deposit is the Montezuma mine
just northeast of Castle Peak. Records show a
total production of 6,700 tons of ore. No grades
are available for ore mined or shipped. Fissure
type veins have been reported to occur in the
upper Conundrum valley. The Cummings property,
on the west side of Conundrum gulch, has
been alleged to contain fair values in silver. CGS
did observe and sample a number of pieces of
'Vein float" which were picked up in the stream
bed. No veins were observed on the subject
property. Assay values on "vein float" were low
for both gold and silver (Plate 3, Table 1).
Geochemical analysis of samples taken in
"reconnaissance" fashion by CGS are documented
in (Plate 3, Table 1). Whole rock and
panned stream sediments were tested for multiple
elements. Fire assay and atomic absorption
analyses for gold and silver on select whole
rock samples gave low results. Several high
values for copper, both in pan concentrates and
rock samples are interesting, but are not considered
to be indicative of high mineral potential
within the claim boundary. Assay and
atomic absorption analyses mineralization from
the property were also consistently low.
Although Leadville Limestone represents
favorable host rock in known mining districts.
No Leadville rocks were observed on or immediately
adjacent to the property. This fact, combined
with the complex structure in the area
and the extreme variation in the thickness of
the Belden Formation, make accurate estimation
of depth to this horizon difficult.
Placer gold potential of the claim block was
tested by hand panning methods. This technique
will only test the immediate surface and
cannot lend insight into placer potential of deep
gravels or bedrock surface where most of the
gold would accumulate. The original placer
claims along Conundrum Creek extend for approximately
6,000 feet and from an elevation at
the north of 8,600 feet AMSL to 9,800 feet at
the southern end. The extreme southern end of
the claim block was considered by CGS to have
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