Over 2,700 separate analyses were made on 22 different geologic samples selected to cover wide concentration ranges for the 30 elements studied. The precision for low, medium, and high concentrations of each element determined is represented by superimposed frequency diagrams and displays the frequency of reported values occurring within one-sixth order reporting intervals about the mean.Results are derived from mixed analyst and instrument conditions with no controls enforced other than randomization of samples. The precision of the six-step (one-sixth order) semiquantitative spectrographic analysis utilized by the Denver-based mobile laboratories exceeds that which is necessary for exploration geochemistry. Disallowing results obtained near the detection levels, the repeatability of the method, in general, is shown to be within on adjoining reporting interval on each side of the mean, 83 percent of the time, and within two adjoining reporting intervals on each side of the mean 96 percent of the time.

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USGS1976

Mineral resources of the proposed additions to the Scapegoat Wilderness, Powell and Lewis and Clark Counties, Montana

The proposed additions to the Scapegoat Wilderness include the Silver King-Falls Creek and Arrastra-Stonewall units. They cover about 84 square miles (218 km 2 ) south and southeast of the wilderness in the Helena and Lewis and Clark National Forests, northwest Montana. Their mineral resources were evaluated as part of a study by the U.S. Forest Service to determine their suitability for addition to the wilderness. The additions have copper resources, which may also contain some silver, some lead, and possibly zinc and gold. Stone and sand and gravel deposits are present, but deposits of equal or better quality are available closer to major markets. The Silver King-Falls Creek addition may have a potential for the discovery of oil and gas, but detailed studies, including seismic surveys and drilling, would be required to adequately determine the potential. The additions have a low potential for geothermal resources. The geology is structurally complex and consists of sedimentary rocks that range from Precambrian Y to Holocene in age. Precambrian rocks are locally intruded by sills of intermediate composition. The mineral resource evaluation is based ongpological, geochemical, economic, and geophysical studies. A total of 480 rock samples and 120 stream-sediment samples were collected during geologic mapping; 86 lode samples and two placer samples were collected during the examination of mines and prospects. Results from these samples delineate areas that are anomalously high in base metals, precious metals, and mercury. The geophysical investigations indicate small magnetic and gravity anomalies, which mostly appear to be unrelated to mineralized areas. More than 60 recorded mining claims have been located in theadditions. Except for a small amount of copper shipped from StonewallMountain, no record of mineral production exists for the additions.Gold has been mined from placer deposits near the southern boundary ofthe Arrastra-Stonewall unit, and small amounts of copper have beenextracted from deposits near the northern boundary. A copper deposit in Cotter basin, adjacent to the northern boundary of the Arrastra-Stonewall unit, was being explored and developed by industry during the present investigations, and minor production has resulted. This deposit, a carbonate vein system, is estimated to contain 1 million tons (910,000 t) of paramarginal resource averaging0.85 percent copper and 0.2 ounce byproduct silver per ton (6.9 g/t) with selected areas of higher grade that may be presently economic. Similar copper deposits may occur in this carbonate vein system in the northern and eastern parts of the Arrastra-Stonewall unit. Smaller and lower grade copper deposits occur near the mouth of Byrnes Creek and near the head of Alice Creek, in the Silver King-Falls Creek unit.

Montana↗

USGS1976

Mineral resources of the Scotchman Peak Wilderness study area, Lincoln and Sanders Counties, Montana, and Bonner County, Idaho

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Open-File Report↗

USGS1975

Geochemical soil studies in the Cotter Basin area, Lewis and Clark County, Montana

Geochemical sampling in an area of abnormal vegetation in the Cotter basin area, Lewis and Clark County, Montana, shows anomalously high concentrations of Cu, Pb, Ag, Zn, and Au in the soil. The singular presence of a particular plant species growing in the highly anomalous zone merits further investigation for its potential use as an indicator plant for base-metal deposits, buried at shallow depth.

Open-File Report↗

USGS1970

Mineralogy and geochemistry of some Belt rocks, Montana and Idaho

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Bulletin↗

USGS1968

Direct-current arc and alternating-current spark emission spectrographic field methods for the semiquantitative analysis of geologic materials

Two spectrographic methods are used in mobile field laboratories of the U. S. Geological Survey. In the direct-current arc method, the ground sample is mixed with graphite powder, packed into an electrode crater, and burned to completion. Thirty elements are determined. In the spark method, the sample, ground to pass a 150-mesh screen, is digested in hydrofluoric acid followed by evaporation to dryness and dissolution in aqua regia. The solution is fed into the spark gap by means of a rotating-disk electrode arrangement and is excited with an alternating-current spark discharge. Fourteen elements are determined. In both techniques, light is recorded on Spectrum Analysis No. 1, 35-millimeter film, and the spectra are compared visually with those of standard films.

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