Hornet Creek District
Commodities: copper, lead, gold, silver
This district, also called the Galena, is near the crest of the Cuddy Mountains, 22 miles from the Pacific, Idaho, and Northern Railroad at Council and is accessible only by trail. Thus far, it has been only superficially prospected. At one place, there is an area of altered rhyolite with some chalcopyrite that may be similar in genesis to the Red Ledge (see Seven Devils district, p. 7 of this pamphlet), and elsewhere there are bunches of lead-silver ore in lime- stone. Apparently a little placer mining has been done in the general vicinity as mention of a Placer Basin mine near Council is made on Page 207 of the Minerals Yearbook, 1936, pt. 2.
Meadows Placer District
Commodity: gold
The placer deposits on Goose Creek, about 4 miles east of Meadows, have yielded a little gold and are reported to contain sapphire, diamond, corundum, and other uncommon minerals.
Mountain View District
Commodity: gold
This little known district (also termed the Black Lake and Rapid River) is now included in the Seven Devils district for the purpose of filing claims. It is near Rapid River, about 12 miles northeast of Landore, and contains some gold-bearing quartz veins. It is reported that $200,000 or more have been produced, but at costs in excess of the value of the ore.
Seven Devils District
Commodity: copper
This district is the best known in western Idaho south of the "Panhandle", and its name is sometimes extended to include all the mountainous area in Idaho bordering the Snake River from Reiser to Lewiston. The district has been under development intermittently since about 1894, with some prior placer and lode mining, and has a total output roughly estimated at about $1,000,000 in copper with some gold and silver. This district is relatively inaccessible. Many of the prospects are reached only by trail and none has received extensive development.
About 1925, attention was attracted to the district by the activities of the Idaho Copper Company and Idaho Copper Corporation, controlled by George Graham Rice and associates, but it appears from press accounts and the reports of the State Inspector of Mines that most of the work accomplished on the ground was in road-building and the installation of a surface plant. On December 14, 1928, Rice and the corporation were convicted of using the mails to defraud in connection with this promotion.
The area is mostly underlain by altered andesitic and rhyolitic flows and pyroclastics with interbedded limestone, all largely or entirely of Permian age, cut by granitic rock that is probably either a projecting part of the Idaho batholith or a closely related stock. Extensive areas are overlain by the Columbia River basalt.
The lodes that have been most productive are copper deposits of contact-metamorphic origin that replace blocks of limestone enclosed in granitic rock and extend out into the latter as well. Lime silicates such as are usually associated with contact-metamorphic deposits are abundant and the granitic rock is sericitized. In some deposits, the principal hypogene (primary) metallic mineral is chalcopyrite; in others, bornite. Some molybdenite and other sulphides are locally present. The deepest workings have not reached ore unaffected by supergene (secondary) processes.
Relatively complete oxidation is confined to a zone of variable depth, apparently nowhere more than 75 feet below the surface but secondary sulphides persist to the deepest workings of record, about 300 feet below the surface. It appears that much of the readily accessible high-grade ore (containing over 30 per cent copper and a little silver and gold) has been picked out and shipped, but that in several prospects considerable ore containing 5 to 7 per cent copper remains in sight. Like other deposits of this type, the contact metamorphic deposits of the district are irregular in size, shape, and tenor, so that extensive development is required to determine their value.
A few of the mines of the district, particularly the Red Ledge, are in deposits of pyrite sparsely disseminated through rhyolitic and andesitic rocks, largely tuffaceous, that have undergone widespread hydrothermal metamorphism. The valuable parts of the deposits consist of slips and fracture zones along which chalcopyrite and smaller amounts of sphalerite, galena, and other sulphides have formed in a gangue of quartz, barite, calcite, hematite, and the hydrothermally altered rock.
In the ore so far developed, there has been supergene (secondary) enrichment which has caused the formation of chalcocite, covellite, and rarely bornite. It appears from the incomplete data available that some of the zones of fracture and ore deposition are 60 to 150 feet wide and contain 1.5 to nearly 2.5 per cent copper and small amounts of silver and gold.
Several prospects have been opened on small and apparently nonpersistent fractures in andesite and andesitic tuff in which there has been irregular deposition of chalcocite and other sulphides in a sparse gangue of quartz and epidote. The brilliant colors of the oxidized copper minerals that stain the rocks around such fractures make them conspicuous, but the amount of ore in sight appears to be very small.
In addition there are some fissure veins containing quarts with gold and some sulphides, and others containing copper sulphides in which feldspar (mainly orthoclase) and muscovite are so abundant in the quartz that the vein material resembles pegmatite. So far as recorded development goes, all the ore shoots in the fissure veins are relatively small and of low to moderate grade. A little placer mining has been done.
