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B. F. Leonard

Publications and source records attributed to B. F. Leonard.

At least 19 recordsLinked to original sources
USGS1987

Residence of silver in mineral deposits of the Thunder Mountain caldera complex, Central Idaho, U.S.A.

Silver is an accessory element in gold, antimony, and tungsten deposits of the caldera complex. Most of the deposits are economically of low grade and genetically of xenothermal or epithermal character. Their gold- and silver-bearing minerals are usually disseminated, fine grained, and difficult to study. Sparsely disseminated pyrite and arsenoprite are common associates. Identified silver minerals are: native silver and electrum; the sulfides acanthite, argentite (the latter always inverted to acanthite), and members of the Silberkies group; the sulfosalts matildite, miargyrite, pyrargyrite, argentian tetrahedrite, and unnamed Ag-Sb-S and Ag-Fe-Sb-S minerals; the telluride hessite and the selenide naumannite; halides of the cerargyrite group; and the antimonate stetefeldtite. Suspected silver minerals include the sulfide uytenbogaardtite and the sulfosalts andorite, diaphorite, and polybasite. Electrum, acanthite, and argentian tetrahedrite are common, though nowhere abundant. The other silver minerals are rare. Silver is present as a minor element in the structure of some varieties of other minerals. These include arsenopyrite, chalcopyrite, chalcostibite, covelline, digenite, galena, sphalerite, and stibnite. The search for adventitious Ag in most of these minerals has been cursory. The results merely indicate that elemental silver is not confined to discrete silver minerals and is, therefore, an additional complication for the recovery of silver-bearing material from some deposits. Silver occurs cryptically in some plants of the region. At Red Mountain, for example, the ashed sapwood of Douglas-fir (Pseudotsuga menziesii) contains 2 to 300 ppm Ag. Silver in the ashed wood is roughly 100 times as abundant as it is in soil. The phenomenon, useful in biogeochemical exploration, deserves the attention of mineralogists. ?? 1987 Springer-Verlag.

Mineralogy and Petrology↗
USGS1983

Preliminary report on geology, geochemical exploration, and biogeochemical exploration of the Red Mountain stockwork, Yellow Pine District, Valley County, Idaho

New exploration targets for gold, molybdenum, tungsten, and tin are indicated by the systematic distribution of metals in soil and plants of the Red Mountain stockwork and its environs. The stockwork is built of countless quartz veins and veinlets, extensively argillized and containing sparsely disseminated gold, pyrite, arsenoDyrite, Dyrrhotite, fluorite, and other minerals. The stockwork developed along the outer ring-fracture zone of the Eocene Quartz Creek cauldron where subsidence strain, unrelieved by radial faulting, produced internal deformation and intense small-scale fracturing in rocks of the Idaho batholith. The stockwork, cropping out as a fault-bounded polygon 2,700 ft long and 2,000 ft wide, contains (underlies?) a large, virtually barren quartz body 1,350 ft long and 350 ft wide. Deformed, shattered granite flanks and presumably underlies the stockwork, which may plunge southward beneath inclusion-bearing granodiorite and alaskite of the Idaho batholith suite. Narrow dikes of rhyolite and latite radiate from two centers within the quartz body. Many dikes and small bosses of rhyolite and latite intrude stockwork and granite. The radial habit of some dikes and the high frequency of small intrusives concentrated within the sericite and kaolinite alteration zones suggest that a Tertiary porphyry is concealed beneath the mountain. Clay-mineral alteration zones mapped in residual soil extend far outward from the stockwork. Valleys filled with Quaternary deposits bound the stockwork-granite complex on the east, north, and west, effectively concealing elements of a crudely elliptical substructure that differs from the fault-dissected, mappable part of the complex. Metal anomalies in soil of the 3,600-ft x 8,400-ft gridded area are mostly weak and small. In contrast, metal anomalies in plants are strong, large, and consistent with the inference of a concealed elliptical substructure that may be hoodlike and may contain more than one mineralized zone. Gold in ashed sapwood of douglas-fir (Pseudotsuga menziesii) indicates a major gold anomaly, peak value 14.2 ppm Au, on inclusion-bearing granodiorite in an unprospected area south of the exposed stockwork. Locally, the gold anomaly is accompanied by a sizable tin anomaly, peak value 100 ppm Sn, in douglas-fir. Molybdenum in ashed leaves of beargrass (Xerophyllum tenax), peak value >500 ppm Mo, indicates extensive anomalies within a 2-milelong semi-elliptical belt of Mo values exceeding the 20 ppm median. Most of the belt is on valley fill, but the southern segment of it, near the major gold anomaly, is mainly on inclusion-bearing granodiorite. Here, where beargrass is sparse, the peak value of Mo in beargrass drops to 70 ppm. Where beargrass is absent, ashed leaves of sedge (Carex geyeri) have anomalous values of 100 ppm Mo. An additional target for molybdenum is indicated by molybdenite from the inaccessible Dart of the main adit. The molybdenite, seen only in dump specimens, is in weakly silicified granite that may underlie part of the stockwork. The source body of the molybdenite is blind, and no clue to it is given by samples of soil or plants. Just north of the major gold anomaly, 2 ppm values of W in beargrass coincide approximately with a tungsten anomaly in soil (peak value 22 ppm W) in an area of float containing disseminated scheelite in weakly silicified inclusion-bearing granodiorite. Other areas of 2 ppm W values in beargrass are nearly coextensive with the Moin-beargrass anomalies on Quaternary deposits of Quartz Creek valley. Some of the target areas for gold, molybdenum, tungsten, and tin have not been circumscribed by our sampling.

Open-File Report↗
USGS1974

Antimony and other metal anomalies south of Stibnite, Valley County, Idaho

Results of geochemical investigations south of Stibnite, Valley County, Idaho, show that the distribution of Sb, As, Au, Zn, Ag, and Mo in mull ash and of Hg, in soil forms a highly anomalous area which is more than 1.5 km long and 1 km wide along the trace of the Meadow Creek fault, a major northstriking fault zone. In the report area the Meadow Creek fault is covered by deposits of Quaternary glacial debris ranging in thickness from several meters to more than 30 meters. Two other highly anomalous areas--one of Au, Zn, and Hg, and one of Zn, Ag, Hg, and Mo--correlate with silicified granodiorite along the trace of the Meadow Creek fault. These anomalies are not related to hnown Ore deponits and merit further investigation. The enrichment of metals in mull ash in the area of thick glacial debris suggests that the metals migrate from bedrock upward through the glacial debris, are taken up by the forest vegetation, and are concentrated in the mull as the litter from the vegetation-decays. The findings indicate that mull is the most useful geochemical sampling medium in the stibnite area because the bedrock is deeply buried beneath deposits of transported material such as colluvium or glacial debris.

Open-File Report↗
USGS1973

Gold anomaly in soil of the West End Creek area, Yellow Pine District, Valley County, Idaho

A gold anomaly recently found by soil sampling near the Yellow Pine mine is accompanied by a silver anomaly and by conspicuous though minor mercury, antimony, arsenic, and tungsten anomalies. The anomalies are not completely delimited by the sampling, but preliminary results indicate that a gold anomaly extends 600 feet along one fault and 500 feet along a fault that intersects it. The gold content of 128 soil samples ranges from less than 0.05 ppm (part per million) to 8.0 ppm; the median value is 0.70 ppm. Within the area in which gold in the soil samples is equal to or greater than 1 ppm, 23 samples have as the mean 2.91 ppm, equivalent to 0.085 troy ounce of gold per ton. The gold anomaly in soil helps define an attractive exploration target for low-grade gold ore in this area, which overlaps that of the West End Creek gold prospects described by J. R. Cooper in 1951 in U.S. Geological Survey Bulletin 969-F (p. 151-197).

Circular↗