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Colorado Gossan

Occurrence, Inactive

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Commodities and mineralogy

Main commodities Au
Other commodities As; Hg; Sb
Ore minerals arsenopyrite
Gangue minerals ferricrete; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale MD
Quadrangle map, 1:63,360-scale C-6
Latitude 63.561
Longitude -155.974
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Colorado Gossan occurrence is located on a south-facing slope overlooking the broad saddle that contains the Montana Saddle prospect (MD018). The occurrence is at an elevation of 1,870 feet (570 m) in Section 28, T. 22 S., R. 15 E., of the Kateel River Meridian. The occurrence is precisely located as the reporter visited the site in 1996.

Geologic setting

Geologic description

The Colorado Gossan is a rectangular shaped, 1,500 feet by 950 feet (457 m by 290 m) zone of iron rich ferricrete-tourmaline flooding in hornfels adjacent to the Cripple Creek Mountains pluton. Most of the zone is rubble crop with only a few outcrops observed. Disseminated arsenopyrite grains were seen in selected hand specimens but most samples are extensively oxidized. The gossan area is approximately 2,500 feet (762 m) away from the contact between the hornfels and plutonic phases of the Cripple Creek Mountains stock. The Colorado Gossan prospect is inferred to be Late Cretaceous based on 71.0 Ma age of adjacent plutonic rocks (Moll and others, 1981).
Three large, continuous, chip-channel samples taken across 700 feet (213 m) of the long axis of the zone averaged 1,815 ppm arsenic, 80 ppb gold, 3,540 ppb mercury, and 154 ppm antimony (Bundtzen and others, 1997).
Geologic map unit (-155.976375869205, 63.5603897043124)
Mineral deposit model Polymetallic replacement deposit (Cox and Singer, 1986; model 19a).
Mineral deposit model number 19a
Age of mineralization The Colorado Gossan prospect is inferred to be Late Cretaceous based on 71.0 Ma age of adjacent plutonic rocks (Moll and others, 1981).
Alteration of deposit Extensive oxidation of original sulfide mineralization.

Production and reserves

Workings or exploration No previous surface working were detected in 1996. Three large, continuous, chip-channel samples taken across 700 feet (213 m) of the long axis of the zone averaged 1,815 ppm arsenic, 80 ppb gold, 3,540 ppb mercury, and 154 ppm antimony (Bundtzen and others, 1997).
Indication of production None
Reserve estimates None.

Additional comments

Similar morphological features at Won-North prospect (MD021) and Win prospect (MD060).

References

MRDS Number 10307770

References

Bundtzen, T.K., Pinney, D.S., and Laird, G.M., 1997, Preliminary geologic map and descriptive data tables from the Ophir C-1 and western Medfra C-6 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File Report 97-46, 10 p., 1 sheet, scale 1:63,360.
Mertie, J.B., Jr., 1936, Mineral deposits of the Ruby-Kuskokwim region, Alaska: U.S. Geological Survey Bulletin 864-C, p. 115-245.
Patton, W.W. Jr., Moll, E.J., Dutro, J.T., Jr., Silberman, M.L., and Chapman, R.M., 1980, Preliminary geologic map of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811-A, one sheet at 1:250,000 scale.
Reporters Bundtzen, T.K. (Pacific Rim Geological Consulting)
Last report date 6/3/1998