Omar

Prospect, Active

Commodities and mineralogy

Main commodities Cu
Other commodities Ag; Co; Zn
Ore minerals bornite; chalcopyrite; covellite; malachite; pyrite; tetrahedrite
Gangue minerals calcite; dolomite; iron oxides; quartz

Geographic location

Quadrangle map, 1:250,000-scale BM
Quadrangle map, 1:63,360-scale B-4
Latitude 67.4898
Longitude -160.8834
Nearby scientific data Find additional scientific data near this location
Location and accuracy The main occurrences at the Omar prospect are centered approximately 0.5 mile northwest of what is informally called Omar Mountain. They are mostly in the lower portions of sections 9 and 10, T. 24 N., R. 10 W., of the Kateel River Meridian. The location is accurate.

Geologic setting

Geologic description

The Omar deposit was discovered by Bear Creek Exploration in 1962 as a result of a regional geochemical reconnaissance program. Work done on the prospect into the 1980s includes geologic mapping, soil, silt and rock sampling, hand trenching, ATM and EM surveys, and 19 cored drill holes. The geophysical surveys produced indifferent results even though they were in areas of known mineralization (C.G. Bigelow, personal communication, 1975).
The Omar deposit consists of copper and iron sulfides in discordant veinlets, blebs and stringers in Devonian carbonates. Outcrops are rare at Omar and extensive frost-heaved rubble obscures most lithologic contacts. A 3-kilometer-long, complex fracture zone trends north-northwest across the prospect and hosts the deposit. Highly leached gossans are in the southern and central areas of the prospect. Three samples of gossan contained 1,070 parts per million (ppm) copper, greater than 20,000 ppm copper, and 13,400 ppm copper. Mineralized zones containing chalcopyrite, bornite, covellite and malachite in breccias and fracture fillings are 300 to 1,000 meters long and up to 30 meters wide. Bornite and chalcopyrite are the dominant copper sulfides. Typical samples of sulfide-bearing talus contain 9.6 percent copper. A sample from the southwest slope of hill 2455 contained 15.39 percent copper; other samples collected along the 3-kilometer trend varied from 0.1 to 9.6 percent copper (Degenhart and others, 1978). High values of cobalt accompany the copper sulfides, as well as minor zinc and silver. The best intercepts from two drill cores 300 feet apart were 25 to 30 feet of 9 percent copper. These holes intersected two parallel shear zones (C.G. Bigelow, personal communication, 1975).
Microscopic examination shows that the chalcopyrite forms coherent exsolution lamellae and noncoherent blebs and dots in bornite or tetrahedrite. Solution of the host dolostone created open spaces which were filled by dolomite, sulfides, and quartz. The mineralizing event occurred prior to metamorphism and deformation associated with the middle Jurassic to Cretaceous Brooks Range orogeny (Folger and Schmidt, 1986). The carbonate sequences at Omar have been folded into broad anticlines and synclines. Most rock units at Omar strike north-northeast to northwest. Dips vary from 6 degrees to vertical.
In 2006, NovaGold began working in the region, staked a large block of claims, and subsequently acquired the Omar property (TintinaGold, 2010). In 2007, NovaGold carried out extensive field work in the area, emphasizing geologic mapping and geochemical sampling. Their work indicates that the Omar prospects are part of a north-northwest-trending belt of mineralization three kilometers long and up to a half kilometer wide. Rock samples contained up to 34.3 percent copper, 0.85 percent zinc, and 0.4 percent cobalt. NovaGold subsequently passed the property to TintinaGold who did considerable field work in the area in 2009. See also the similar Frost (BM011), Deadfall (BM010), and Peak (BM022) prospects nearby that were also studied by NovaGold and TintinaGold.
Geologic map unit (-160.886269129461, 67.4891776714873)
Mineral deposit model Kipushi Cu-Pb-Zn (Cox and Singer, 1986; model 32c).
Mineral deposit model number 32c
Age of mineralization Devonian or younger based on the age of the host rocks.
Alteration of deposit Hydrothermal dolomitization.

Production and reserves

Workings or exploration
The Omar deposit was discovered by Bear Creek Exploration in 1962 as a result of a regional geochemical reconnaissance program. Work done on the prospect includes geologic mapping, soil, silt and rock sampling, hand trenching, ATM and EM surveys, and 19 core drill holes. The geophysical surveys produced indifferent results even though they were run in areas of known mineralization (C.G. Bigelow, personal communication, 1975).
In 2006, NovaGold began working in the region, staked a large block of claims, and subsequently acquired the Omar property (TintinaGold, 2010). In 2007, NovaGold carried out extensive field work in the area emphasizing geologic mapping and geochemical sampling. TintinaGold Resources Inc. continued the NovaGold work and did considerable field work in the area in 2009. See also the similar Frost (BM011), Deadfall (BM010) and Peak (BM022) prospects nearby that were also studied by NovaGold and TintinaGold.
Indication of production None
Reserve estimates Based on results of two drill holes, Bear Creek Exploration calculated possible reserves of 200,000 tons of ore containing 9 percent copper.

References

MRDS Number A015621

References

WGM Staff, 1980, Non-fuel mineral resources of Alaska: Anchorage, Alaska, WGM, Inc. Unpublished report for Phillips Petroleum Company, 320 p. (Report held by NANA Regional Corporation, Anchorage, Alaska).
Reporters Anita Williams (Anchorage, AK); D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/2/2010