Cuddy Mountain District
Commodities: gold, silver, copper, lead
This district is also known as the Heath district, after the town of Heath which is its principal settlement. This town is about 20 miles by road from Cambridge on the Pacific and Idaho Northern Railroad,and several of the prospects are even closer to the railroad. Desultory mining has been carried on here for the last 30 or 40 years and a number of lodes containing gold, silver, copper, and lead have been prospected, but the production so far is small.
The district is underlain by sedimentary and volcanic strata of probable Triassic and Permian age overlain by extensive areas of Tertiary basalt flows and cut by monzonite, granodiorite, quartz porphyry, and basalt. According to Livingston's tentative interpretation, the monzonfte and granodiorite, which are interrelated, are of pre-Triassic age, the quartz porphyry Tertiary or Cretaceous, and the basalt Miocene.
The deposit at the I.X.L. mine consists of pyrite, chalcopyrite, and pyrrhotite irregularly disseminated through fractured and altered monzonite over an oval area approximately 8,000 feet long and 4,000 feet wide, covered by a shallow gossan. Apparently the sulphide ore in the principal tunnel contains little more than 1 per cent copper, but parts of the deposit may be of higher grade. Livingston suggests that the quartz porphyry may be the source of mineralization and may itself contain undiscovered ore bodies.
At the Climax and Railroad mines and others, the deposits are limestone lenses in the Permian strata that have been replaced by garnet and other silicates with chalcopyrite and other sulphides. Some high-grade, silver-copper ore is reported to have been mined.
There are also several silver-lead veins and replacements in Triassic (?) rhyolite and Permian andesite, most of which were inaccessible at the time of Livingston’s visit, although some had formerly been productive.
Mineral District
Commodities: silver, copper
The mines of this district (which is also termed the Washington) are reached by short roads from the Mineral ferry across the Snake River to the branch railroad on the Oregon side. At one time, there were two small smelting furnaces in the district. Prior to 1900, about 600,000 ounces of silver had been produced, but comparatively little has been done since.
The area is underlain by Permian andesite and Triassic rhyolite, schist, slate, and limestone, cut by small pre-Triassic (?) granitic masses and Miocene basalt dikes. There is much faulting.
Some of the veins are replacements striking northwest and commonly associated with basalt dikes. They contain quartz, calcite, pyrite, chalcopyrite, galena, sphalerite, and tennantite (or tetrahedrite). These veins are locally 20 feet or more wide. They include all the deposits which have yielded silver ore.
A second set strikes northeast and consists largely of chalcopyrite and pyrite in quartz, with little silver. They are reported to range in width from 4 to 68 feet. These veins are associated with granodiorite, but do not appear to out the Triassic strata, a fact which led Livingston to the suggestion that the granodiorite of this part of Idaho may be comparatively old.
Monroe District
Commodity: gold
This district (also termed the Weiser), about 10 miles north of Weiser, contains the Modoc gold lode, which is a network of quartz seams in a volcanic breccia. Fuller's earth also occurs here. No further data are available.
Weiser Quicksilver District
Commodity: quicksilver
The Idaho Almaden mine, 11 miles east of Weiser, was first developed in 1937. By August, 1939, it had produced a total of 469 flasks and since then has continued to be actively productive. The ore is in parts of sandy and shaly beds supposed to belong to the Payette formation (Miocene) that has been replaced by chalcedony and opal.
