Junction Mining District (Little Eightmile Mining District), Lemhi County, Idaho, USAi

Regional Level Types
Junction Mining District (Little Eightmile Mining District)	Mining District
Lemhi County	County
Idaho	State
USA	Country

The Junction District boundaries are loosely defined. According to Ross (194la) and Umpleby (1913, p. 112), the district extends to the McDevitt District on the northwest, to the Continental Divide on the northeast, to the crest of the Lemhi Range on the southwest, and into country with few mineral deposits on the southeast.

Most mines in the district explore lead-silver replacement deposits in Mississippian limestone. A few small mines explore deposits of secondary copper minerals in fractures and in thrust fault breccias and disseminated mineralization occurs in granitic rocks at two locations.

The Leadville and Kimmel mines are the only major producers in the district. Two east-trending ore shoots, as much as 4 feet thick, and separated by about 40 feet of barren, crushed limestone were mined at the Leadville. Primary ore minerals consisted mainly of fine-grained galena, less common pyrite, and rare sphalerite and chalcopyrite; secondary ore minerals, although rare, consisted of cerussite and anglesite. The eastern shoot also contained appreciable amounts of antimony, arsenic, and bismuth. Smelter analyses of the richest ore from the upper levels in the mine show that it contained about 55 percent lead, 0-1 percent zinc, 0.012 percent copper, 29- 35 ounces of silver per ton, and a trace of gold.

At the Kimmel mine, located just west of the Leadville mine, disseminated fine-grained pyrite and still finer grained galena occurs in hydrothermally altered and sericitized granite and limestone breccia. Assays indicate that the lead content averages about 1 percent and the silver content ranges from 0.05 to 0.5 ounce per ton (Rupple and Lopez, 1988, p. 90-100).

According to USBM records, the two mines produced at least 13,444 tons of ore containing significant amounts of lead and silver and lesser amounts of copper, zinc, and gold. Ruppel and Lopez (1988, p. 99) reported production of 4,000 to 4,500 tons.

Granodiorite and quartz monzonite at the Blue Jay contain vein, stockwork, and disseminated mineralization. Molybdenite and scheelite occur in an irregular quartz vein developed by the Mulkey adit. About 400 feet northwest of the adit, quartz, malachite, and azurite fill fractures, and chalcopyrite, molybdenite, and pyrite are in. quartz veinlets and disseminations in the altered intrusive rock. Between 1948 and 1950, more than 10,000 pounds of copper were recovered from 56 tons of ore (Gather and Rains, 1988).