See also: Blaine County Idaho Gold Production
Camas District
Commodity: gold
The Camas district (Hailey gold belt), served by a highway and a branch of the Union Pacific Railroad, produced some gold in the early days and has had intermittent prospecting since. Small veins of variable strike associated with lamprophyre dikes occur in granitic rocks of the Idaho batholith. The veins contain gold, pyrrhotite, pyrite, sphalerite, galena, chalcopyrite, quartz, calcite, and siderite. So far, the base metal ores have received little attention and appear less promising than those of other districts.
Galena District
Commodities: lead, silver
The Galena district, served by a highway and nearly 25 miles from the railroad at Ketchum, contains a few lead-bearing lodes formed by replacement in tabular shear zones in Paleozoic strata, probably similar to some of those in the well known Warm Springs district nearby. • Although known in the early days, none of the lodes has yet been developed to any extent, and there has been almost no activity in the district for many years. The 30-ton smelter erected at Galena in the eighties operated for only a short time and probably received much of its ore from the East Fork district which lies immediately to the north.
Little Wood River (Muldoon) District
Commodities: lead, silver, copper
Although numerous deposits are known in the Little Wood River district, most of the production has come from the Muldoon mine, after which the district is named by some. Muldoon is about 26 miles by road from a station on the Union Pacific Railroad, The Muldoon mine probably produced about $200,000 in silver-lead ore, mostly in 1881 to 1886, with intermittent activity and production in later years. Little except desultory prospecting has been done in the district for many years.
The part of the district containing known lodes is underlain by Paleozoic sedimentary rocks, cut by dikes of dioritic and granitic porphyry and aplite. In the Muldoon mine, the ore occurred as a replacement deposit along bedding in the Paleozoic strata with a porphyry hanging wall, locally mineralized. Argentiferous galena, pyrite, and some sphalerite and chalcopyrite are disseminated with quartz in altered rock of different kinds. In an area in the sedimentary rocks in which contact-metamorphic silicates are plentiful, there are deposits containing slightly oxidized galena and copper sulphides. Ore containing 6 per cent copper and small amounts of gold and silver are reported to have been found in these areas.
Mineral Hill (Hailey) District
Commodities: silver, lead, gold, copper, zinc, arsenic, quicksilver, barite
The Mineral Hill district (output about $20,000,000) is one of the most productive districts in Idaho. This district (sometimes called the Hailey district) and the Warm Springs district immediately north of it include most of the famous Wood River region which in common usage includes also the Galena and Camas districts. The district, which is served by a highway and by a branch of the Union Pacific Railroad, is best known for its lead-silver ore, but gold, copper, and zinc have also been produced, and arsenic, quicksilver, barite, and other valuable substances are present.
The first discovery is reported to have been made in 1864 and the principal development was in the period from 1879 to 1891 with several periods of revival since. Over 75 per cent of the total production was made prior to 1900. Many of the known shoots of lead-silver ore of good grade have been mined out, but, with few exceptions, development is confined to a depth of a few hundred feet. The future of the district lies in the discovery of new shoots at greater depth, although enough ore remains in sight in a number of the mines to permit profitable mining under favorable market conditions for years to come. A few new ore bodies have been found close to the surface in recent years.
The district is underlain mainly by the Wood River formation (Pennsylvanian) with the Milligen (Mississippian and Devonian (?)) locally exposed. The sedimentary rocks have been folded, intruded by several stocks (probably outliers of the Idaho batholith) and broken by thrust and normal faults. Large areas are covered by the Challis volcanics (Oligocene or Miocene).
Most of the lodes of commercial importance occur in shear zones in the sedimentary beds which locally extend into the igneous stocks. They contain argentiferous galena with some sphalerite and tetrahedrite and small amounts of pyrite and other sulphides in a gangue that consists of altered and crushed country rock, carbonates (principally siderite) and a little quartz. A few lodes, such as the War Dance, contain abundant arsenopyrite and others (in the southern part of the district) contain ruby silver.
There are also veins consisting of barite (of possible commercial value), and calcite or quartz with negligible amounts of metallic minerals. The Challis volcanics locally show the results of slight mineralization and in some of the lodes in the older rocks hisingerite, zeolites, and possibly some of the sulphides were deposited late, possibly in connection with Tertiary volcanism.
There is no reason to suppose that original ore deposition was confined to the shallow zone in which nearly all the mining has so far been done. The shear zones are much larger and more continuous than the valuable ore shoots within them. The original fracturing appears, locally at least, to have been of the reverse type, and the ore shoots are thought to be in large part localized at places where buckling relieved the pressure and facilitated deposition. However, with present data, it is ordinarily impossible to predict much in advance of development where such shoots are to be found. As many of the known shoots are in steep segments of the shear zones, increase in dip is to be regarded as a favorable indication.
Repeated fracturing occurred during and subsequent to the mineralization. Much of the movement was approximately in the plane of the lodes, but locally, as in the Minnie Moore, complex transverse faulting made the problem of finding ore more difficult. In general, post-mineral movements have not been as widespread nor as potent in interfering with mining as is popularly supposed. No evidence exists to support the idea, held by some, that a great fault, the "Wood River fault", underlies the region and cuts off the lodes at shallow depth.
Vienna and Sawtooth Districts
Commodities: silver, lead
The Vienna and Sawtooth districts adjoin each other near the southern end of Stanley Basin, about 40 miles by road from Ketchum at the end of a branch of the Union Pacific Railroad. The districts have been intermittently worked since the eighties. Each district produced roughly $1,000,000, mostly from silver ore in the first few years after discovery. The lodes contain some lead and zinc which have only recently become of interest because of improved transportation facil- ities, Since 1925, there has been renewed activity in the two districts and some production has been reported.
These districts are mainly underlain by the Idaho batholith which is cut by a few dikes of a pink silicic porphyritic rock, dioritic porphyry, and lamprophyre. Patches of sedimentary rocks and Challis volcanics in places overlie the batholith. All lodes are in the granite, in part associated with the dikes. They consist of quartz and altered granite with some siderite, with scattered galena and other sulphides, in part in shear zones, in part in minor fractures. The ore shoots are thus irregular and generally small.
Warm Spring District
Commodities: silver, lead, gold, copper, iron
This district contains the principal modern producers of the Wood River region. It produced over $3,000,000 from 1880 to 1902, and has a recorded output of $6, 162, 747 from 1902 to 1931. In the latter period, nearly 59 per cent of the total was produced in 1917 to 1923, largely from the Independence, and about 37 per cent in 1927 to 1931, largely from the Triumph. In later years, the Triumph has continued to be one of the district’s principal producers.
The rocks of the district include intricately folded and faulted sedimentary beds of preCambrian (?), Ordovician, Silurian, Devonian (?), Mississippian, and Pennsylvanian age, cut by several granitic masses and dikes of different kinds.
Most of the ore deposits, including all with notable production, are roughly tabular replacements along shear zones, mainly in Carboniferous rocks, broadly similar to many of the lodes of the Mineral Hill district. They differ from the latter in having somewhat more calcite and distinctly less siderite in the gangue, relatively more abundant boulangerite and stibnite, and in the fact that some of the ore is an exceedingly fine-grained, intricate mixture of sulphides of lead, zinc, antimony, and iron, requiring special treatment for successful separation.
Much of the production in the early days came from the Parker and other mines near Xctchum, whose ore was rich in silver because of the abundance of tetrahedrite and polybasite. There are also a number of irregular replacement deposits characterized by the presence of lime-silicate minerals. Some of these contain gold ore, others copper, and some were worked for ferruginous flux to supply local smelters, now long abandoned. Although some production was obtained from each of several varieties of lime-silicate ores, none of these deposits is large, and few have received any attention recently.
The problems pertaining to the discovery of ore shoots in the Warm Spring district, although similar to those in the Mineral Hill district, are less acute because of the fact that a number of the mines still have considerable known ore and because several are deeper than the average for the Wood River region. One of the essential factors in future development is the successful treatment of the complex ore referred to above. The refractory nature of this ore retarded development in the early days and its treatment by what is reported to be a special kind of oil flotation is responsible for the recent production from the Triumph mine.
The district contains beds of impure graphitic anthracite of possible future value as a source of low-grade graphite for paints and other uses. Chalcedonic masses in the Challis volcanics have been sought to some extent to be cut and polished for ornaments.
