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Colorado Gossan

Occurrence in Alaska, United States with commodities Gold, Arsenic, Mercury, Antimony
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Geologic information

Identification information

Deposit ID 10307770
Record type Site
Current site name Colorado Gossan

Geographic coordinates

Geographic coordinates: -155.97701, 63.56046 (WGS84)
Relative position 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.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Gold Primary
Arsenic Secondary
Mercury Secondary
Antimony Secondary

Comments on the commodity information

  • Gangue = Ferricrete

Materials information

Materials Type of material
Arsenopyrite Ore
Tourmaline Gangue

Alteration

  • (Local) Extensive oxidation of original sulfide mineralization.

Mineral occurrence model information

Model code 72
USGS model code 19a
Deposit model name Polymetallic replacement
Mark3 model number 47

Host and associated rocks

  • Host or associated Associated
    Chronological age 71
    Stratigraphic age (youngest) Late Cretaceous

Nearby scientific data

(1) -155.97701, 63.56046
ListMap

Comments on the geologic information

  • 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).
  • Age = the Colorado Gossan prospect is inferred to be Late Cretaceous based on 71.0 Ma age of adjacent plutonic rocks (Moll and others, 1981).
  • Age = Chronological age is for adjacent plutonic rocks.

Economic information

Economic information about the deposit and operations

Development status Occurrence

Comments on exploration

  • Status = Inactive

Mining district

District name Innoko

Comments on the workings information

  • Workings / 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).

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF MD017

Bibliographic references

  • Deposit

    Mertie, J.B., Jr., 1936, Mineral deposits of the Ruby-Kuskokwim region, Alaska: U.S. Geological Survey Bulletin 864-C, 115-245.

  • Deposit

    Patton, W.W., Jr., Moll, E.J., Dutro, J.T., Jr., Silberman, M.L., and Chapman, R.M., 1980, Preliminary geologic map of Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811-A, 1 sheet, scale l:250,000.

  • Deposit

    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.

Comments on the references

  • Primary Reference = Bundtzen and others, 1997

General comments

Subject category Comment text
Deposit Model Name = Polymetallic replacement deposit (Cox and Singer, 1986; model no. 19a)
Deposit Other Comments = Similar morphological features at Won-North prospect (MD021) and Win prospect (MD060).

Reporter information

Type Date Name Affiliation Comment
Reporter 03-JUN-98 Bundtzen, T.K. Pacific Rim Geological Consulting