Eureka Mining District, Lemhi County, Idaho, USAi

Regional Level Types
Eureka Mining District	Mining District
Lemhi County	County
Idaho	State
USA	Country

In general terms, the Eureka District includes the north end of the Lemhi Range and a large area west of the Salmon River. The area west of the Salmon River extends from about Lake Creek on the south to the town of North Fork on the north. The ridge crest west of the Salmon River forms the district's western boundary with the exception of the Moose Creek drainage, which here is considered part of the Eureka District.

The first mining in the district began shortly after placer gold was discovered in the Moose Creek drainage during the 1860's. At first, mining was done by hand and hydraulic methods. Between 1899 and about 1919, several dredges were used to mine the gold-bearing gravel. By 1913, about $1 million in gold at a price of $20 per troy ounce had been recovered (Umpleby, 1913, p. 149).

In addition to the Moose Creek deposits, several lode mines in the district have produced significant amounts of metal. The Queen of the Hills deposit was located during the 1880's, but development did not start until 1898. By 1910, underground workings on five levels totalled over 9,000 feet. Mineralization consisted of three northeast striking, pyrite-, chalcopyrite-, and galena-bearing quartz veins in granite (Umpleby, 1913, p. 158). According to Mitchell (1995e, p. 8), production totalled 1,713 ounces of gold, 364 ounces of silver, 188 pounds of copper, and 6,993 pounds of lead.

The Pope Shenon, located near the north end of the Lemhi Range, developed veins along shear zones in quartzite and phyllite of the Yellowjacket Formation. The veins, generally less than 10 feet thick but up to 20 feet thick, contained quartz, chalcopyrite, pyrite, delafossite, and bornite (Anderson, 1956, p. 83). Between 1908 and 1975, recorded production totalled 4,594,951 pounds of copper, 24,725 ounces of silver, 500 ounces of gold, 22,107 pounds of lead, and 14,683 pounds of zinc (Mitchell, 1995d, p. 19). Most of the ore mined contained between 2.5 and 6 percent copper; some small bodies contained 10 to 20 percent copper (Anderson, 1956, p. 85).

The Harmony mine, located a few miles southeast of the Pope Shenon, also developed quartz veins and lenses along shear zones in quartzite. Ore minerals included chalcopyrite, chalcocite, and bornite (Anderson, 1956, p. 88; Gardner, 1930a, p. 2). Production between 1916 and 1931 totalled 47,826 tons of ore which yielded 1,815,353 pounds of copper, 2,050 ounces of silver, and 38 ounces of gold (Mitchell, 1995b).

Several distinct types of mineralization occur in the Eureka District. Near the north end of the district, a copper- and molybdenum-bearing stockwork/disseminated deposit (the Bobcat) formed where granitic stocks intruded quartzite. Ore minerals include chalcopyrite, chalcocite, and molybdenite. Resources at the Bobcat are estimated to be 60 million tons containing 0.2 to 0.3 percent copper (P. Nisbet, Formation Capital Corp., personal communication, 1994).

In a large area immediately to the south, gold-, silver-, lead-, and copper bearing quartz veins occur in quartzite and granite. At the King Solomon deposit, quartz veins, lenses, and silicified areas in shear zones in quartzite, phyllite, and granitic rock contain an estimated 3.3 million tons grading 0.037 ounce gold per ton (P. Nisbet, Formation Capital Corp., personal communication, 1994).

An area of thorium and rare-earth oxide mineralization also occurs near the north end of the district. Monazite and thorite, the principal minerals, occur in quartz veins in quartzite and granite.

Near the south end of the district, copper- and silver-bearing quartz veins and lenses occur along faults in quartzite. The Pope Shenon and Harmony mines are in this area. Resources are present, but tonnage and grade are confidential.