Omar Prospect, Kiana Mining District, Northwest Arctic Borough, Alaska, USAi

Regional Level Types
Omar Prospect	Prospect
Kiana Mining District	Mining District
Northwest Arctic Borough	Borough
Alaska	State
USA	Country

Outcrops are rare at Omar and extensive frost-heaved rubble obscures most lithologic contacts.
Location: The main occurrences at the Omar prospect are centered approximately 0.5 mile northwest of Omar Mountain at an elevation of 1,500 to 2,000 feet. They are in sections 9 and 10, T. 24 N., R. 10 W., of the Kateel River Meridian. Grybeck (1977), location 8, and Schmidt and Allegro (1988), location 152.
Geology: The Omar deposit consists of copper and iron sulfides in discordant veinlets, blebs and stringers in Devonian carbonates. 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 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 range from 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% Cu. A sample from the southwest slope of hill 2455 contained 15.39% copper; other samples collected along the 3-kilometer trend ranged from 0.1% Cu to 9.6% Cu (Degenhart and others, 1978). High values of cobalt accompany the copper sulfides, along with minor zinc and silver. The thickest intercepts from two drill cores 300 feet apart were 25 to 30 feet of 9% Cu. These holes intersected two parallel shear zones (C.G. Bigelow, personal communication, 1975). Microscopic examination shows that the chalcopyrite forms coherent exsolution lamellae and non-coherent blebs and dots within bornite or tetrahedrite. Solution of the host dolostone created open spaces which were filled by dolomite, sulfide 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. The geologic setting and mineralization at Omar closely resemble those at Ruby Creek, 100 miles to the east in the Ambler quadrangle.
Workings: 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).
Age: Devonian.
Alteration: Hydrothermal dolomitization.
Reserves: Based on results of two drill holes, Bear Creek Exploration calculated possible reserves of 200,000 tons of ore containing 9% copper.

Commodities (Major) - Cu; (Minor) - Co
Development Status: None
Deposit Model: Kipushi Cu-Pb-Zn (Cox and Singer, 1986; model 32c).

Other Databases

Link to USGS - Alaska:	BM012

Other Regions, Features and Areas containing this locality

References