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Robert Hadley Moench

Publications and source records attributed to Robert Hadley Moench.

14 recordsLinked to original sources
USGS1966

Mines and prospects, Idaho Springs district, Clear Creek and Gilpin counties, Colorado -- Descriptions and maps

The Idaho Springs mining district forms an important segment of the Front Range mineral belt, a northeast-trending zone of coextensive intrusive rocks and hydrothermal ore deposits of early Tertiary age. This belt, which is about 50 miles long, extends from the region just west of Boulder southwestward across the Front Range. From 1859, when placer gold was discovered in Idaho Springs and lode gold in Central City, through 1959, ores valued at about $ 200 million were shipped from a 50-square-mile area that includes the Idaho Springs and adjacent districts to the north, west, and southwest. The adjacent Central City district, which produced ores valued at more than \$ 100 million, is clearly the most important district in the mineral belt. The Idaho Springs district from 1860 to 1959 produced ores valued at about $65 million, and the districts to the west and southwest produced smaller amounts. Gold has accounted for about 60 percent of the value of the ore, but in some areas silver provides the chief values, and copper, lead, and zinc add value to the ores in most areas. Mining activity in the Idaho Springs and adjacent districts was at its 'heyday' in the late 1800's, it declined sharply after 1914, it was somewhat renewed during the 1930's, and it greatly declined during World War II. In the 1950's uranium prospecting stimulated some mining activity. No uranium was produced, however, and at the close of the decade only one mine--the Bald Eagle--was being worked for its precious- and base-metal ores. In this report, 135 mines and prospects are described. The mines and prospects described are those that were accessible at the time of this study, as well as a few inaccessible properties for which some information was available. Most of the data for the inaccessible or unimportant properties were obtained from Bastin and Hill (1917) and Spurr, Garrey, and Ball (1908). The following list shows, in alphabetical order, the names of about 325 openings of mines and prospects, their coordinate location on the district map (fig. 1), the page of this report on which their description starts, and the number of the illustration, if any, referring to them.

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USGS1955

Geology of the Copper King uranium mine, Larimer County, Colorado

The Copper King mine in Larimer County, Colo., in the northern part of the Front Range of Colorado, was opened in World War I in an unsuccessful attempt to mine copper and zinc ore. In 1949, following the discovery of pitchblende on the dump, the mine was reopened, and it was worked until 1953 for uranium. A total of 652 tons of ore that contained an average of 0.28 percent U 3 O 8 was shipped. The bedrock consists predominantly of biotite granite, part of the Precamblian Log Cabin batholith, and minor metasedimentary rocks -- biotite-quartz-plagioclase gneiss, amphibole skarn, biotite schist, quartzite, amphibolite, and biotite sköls. The metasedimentary rocks occur as inclusions that trend northeast, essentially parallel to the prevailing foliation in the granite. In places the metasedimentary rocks are crosscut sharply by the granite and form angular, steep-walled blocks in the granite. Faults, confined to a narrow easterly-trending zone through the mine, cut all the Precambrian rocks. Mineral deposits of two types are present at the mines 1) sulfide-magnetite ore and 2) a uranium deposit in a filled fissure that cuts the skarn. The sulfide-magnetite deposits are small and consist of pyrite, sphalerite, chalcopyrite, pyrrhotite, and at places magnetite. Alpha-helium age determinations on ore magnetite by Hurley indicate that the mineral assemblage is late Precambrian in age. The deposits are pyrometasomatic in origin and possibly related to the granite. The uranium deposit consists of pitchblende and associated vein-forming minerals that occur in the Copper King fault and locally in pyrite boxwork adjacent to the fault. Three phases of black pitchblende have been identified -- uraninite, "coffinite", and UO 3 -rich pitchblend. Colored secondary minerals are absent. The pitchblende occurs in a steeply plunging, tabular shoot between 45 and 135 feet below the surface that has a horizontal length of about 50 feet. Within the shoot the pitchblende occurs in pods or layers generally only a few feet in height and length and as much as a foot thick that are separated by nearly barren vein. The grade of the ore within the pods ranges from 0.2 percent uranium to as much as 20 percent but averages about 1 to 2 percent. Age determinations by the Pb 206 /U 238 and Pb 207 /U 235 methods on two samples of hard pitchblende from the vein, not from the pyrite boxwork, gave ages by the two methods after suitable common lead corrections, ranging from 55 to 76 million years, corresponding to an early Tertiary age. Diamond core drilling and reconnaissance for radioactivity have not disclosed other uranium deposits the Prairie Divide region; nevertheless, it seems likely that other deposits are present.

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