Eldorado Basin; Moose Jaw Mountain Prospect, Innoko Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Eldorado Basin; Moose Jaw Mountain Prospect	Prospect
Innoko Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

For more information, contact Ron Rosander, in McGrath, AK.
Location: 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.
Geology: 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.
Workings: 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).
Age: The igneous rocks inferred to be responsible for this deposit intrude Cretaceous strata of the Kuskowkwim Group.
Alteration: The headwater regions of Eldorado Creek contain limonite-stained, gossanous breccia (Avalon Development Corp., 1998).

Commodities (Major) - Au; (Minor) - Cu, Sb
Development Status: None
Deposit Model: Epithermal Au? (Cox and Singer, 1986; model 25b, 25c?)

Other Databases

Link to USGS - Alaska:	OP034

Other Regions, Features and Areas containing this locality

References