Eldorado Basin

Prospect in Alaska, United States with commodities Gold, Copper, Antimony

Geologic information

Identification information

Deposit ID 10308034
Record type Site
Current site name Eldorado Basin
Alternate or previous names Moose Jaw Mountain

Geographic coordinates

Geographic coordinates: -156.009, 63.53606 (WGS84)
Relative position The Eldorado Basin prospect is located in the headwaters of Eldorado Creek, which flows into Colorado Creek. The coordinates are for the midpoint of a 2200-meter-long, northeast-trending mineralized zone that crosses Eldorado Creek at an elevation of approximately 2000 feet. The location is accurate within 200 feet. This zone extends northeast into the Medfra quadrangle, where the Nerod East (MD020) and Bear Paw prospects are located.. The Moose Jaw Mountain prospect described in this record is different from the Moose Jaw prospect (OP033). The Moose Jaw Mountain prospect is in the Medfra quadrangle, but is part of the northeast-trending mineralized zone that begins in the Ophir quadrangle. The Moose Jaw prospect (OP033) is on the western flank of Moose Jaw mountain, in the Ophir quadrangle.
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Geographic areas

Country State
United States Alaska


Commodity Importance
Gold Primary
Copper Secondary
Antimony Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Chalcopyrite Ore
Stibnite Ore
Actinolite Gangue
Epidote Gangue
Quartz Gangue


  • (Local) The headwater regions of Eldorado Creek contain limonite-stained, gossanous breccia (Avalon Development Corp., 1998).

Mineral occurrence model information

Model code 106
USGS model code 25b
Deposit model name Epithermal vein, Creede
Mark3 model number 58
Model code 150
USGS model code 25c
Deposit model name Epithermal vein, Comstock
Mark3 model number 16

Nearby scientific data

(1) -156.009, 63.53606

Comments on the geologic information

  • Geologic Description = The rocks in the vicinity of Eldorado Creek consist of intermediate to mafic volcanic and volcaniclastic rocks, and of Cretaceous Kuskokwim Group black shale, limestone, graywacke, and conglomerate intruded by Cripple Mountain monzonite (McGinnis, 1997; Avalon Development Corp., 1998; Duncan, 1999). The headwaters of Eldorado Creek contain limonite-stained, gossanous breccia (Avalon Development Corp., 1998). The Eldorado Basin prospect is on a mineralized zone that trends northeast across the headwaters of the Eldorado Creek for 2200 meters. This zone extends northeast into the Medfra quadrangle and terminates at Colorado Creek, northeast of the summit of Moose Jaw Mountain. At the Eldorado Basin prospect, the zone contains scattered, thin veins of quartz and stibnite, of arsenopyrite and quartz, and locally of actinolite, chalcopyrite, or epidote. Soil samples collected from the Eldorado Basin contain up to 674 ppm copper, 2250 ppb gold, 2818 ppm arsenic, 945 ppm antimony, and 12 ppm bismuth (Avalon Development Corp., 1998). The northeast extension of this zone is defined by soil samples on Moose Jaw Mountain. Two mineralized areas have been identified: a NW-SE-trending, 400-meter by 50-meter area; and an adjacent area 1400 meters long by 200 to 400 meters wide. The 1400-meter-long area is open to the south (Duncan, 1999). Soil samples from these areas contain up to 515 ppb gold, 2770 ppm arsenic, 2942 ppm antimony, and 9 ppm bismuth (Avalon Development, 1998). Hypabyssal, porphyryritic rock at the top of Moose Jaw Mountain is cut by veins less than 5 centimeters thick of crystalline quartz, stibnite, arsenopyrite, and scorodite (Avalon Development, 1998). Exploration in the Eldorado Basin includes geologic mapping and sampling by Barker during 1994, 1995, and 1996; soil sampling, rock sampling, and geologic mapping by NovaGold during 1998; and mobile-metallic-ion (MMI) sampling by Poseidon Minerals Ltd. during 1999 (Barker, 1996; Avalon Development Corp., 1998; Duncan, 1999). Also see OP002 and OP031-033.
  • Age = the igneous rocks inferred to be responsible for this deposit intrude Cretaceous strata of the Kuskowkwim Group.

Economic information

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Active

Mining district

District name Innoko

Comments on the workings information

  • Workings / Exploration = During 1994, 1995, and 1996, claimholder Ron Rosander contracted geologist James Barker to evaluate the lode sources of placer gold in the Colorado Creek area. Barker collecteed 254 soil samples, 93 rock samples, and 12 samples of placer gold for scanning-electron microscope and trace element analysis. Geologic mapping and a ground-based magnetometer survey were also carried out (Barker, 1996; McGinnis, 1997). In 1996, the Alaska Division of Geological and Geophysical Surveys conducted geologic mapping in the Cripple Creek Mountains and Placer Dome Exploration flew an east-west-oriented aeromagnetic survey over the Cripple Creek Mountains. Nova Gold conducted geologic mapping, rock sampling, and soil sampling during the summer of 1998 (Avalon Development, 1998). During 1999, Poseidon Minerals, Ltd. carried out soil sampling in the Colorado Creek area, and used mobile-metallic-ion (MMI) analyses (Duncan, 1999).

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF OP034

Bibliographic references

  • Deposit

    Barker, J.C., 1996, Geologic evaluation of the Colorado Creek prospect area, Alaska: Summary report prepared for Placer Dome Exploration, San Franscisco, California, 73 p.

  • Deposit

    McGinnis, M.F., McCoy, M.E., Nerup, M.R., and Barnett, D., 1997, Colorado Creek project Alaska, 1997 summary report: unpublished Placer Dome Exploration Inc. report, 37 p.

  • Deposit

    Avalon Development Corp., 1998, Colorado Creek project, Ophir and Medfra quadrangles, southwest Alaska: report prepared for NovaGold Resources Inc., 9 p.

  • Deposit

    Duncan, R.G., 1999, Colorado Creek project, Alaska, interim report: unpublished report for Poseidon Minerals Ltd., 22 p.

  • Deposit

    Dashevsky, S.S., 2000, Colorado Creek project (Au) Innoko district, Alaska: unpublished report for Rosander Mining Company, 7 p.

Comments on the references

  • Primary Reference = Duncan, 1999

General comments

Subject category Comment text
Deposit Model Name = Epithermal Au? (Cox and Singer, 1986; model 25b, 25c?)
Deposit Model Number = 25b, 25c?
Deposit Other Comments = For more information, contact Ron Rosander, in McGrath, AK.

Reporter information

Type Date Name Affiliation Comment
Reporter 07-AUG-01 Cameron, C.E. Northern Associates Inc.