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Paul Kibler Sims

Publications and source records attributed to Paul Kibler Sims.

3 recordsLinked to original sources
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.

Colorado↗
USGS1952

Geology of the Copper King Mine area, Prairie Divide, Larimer County, Colorado (Part 1)

The Copper King mine, in Larimer County, Colo., in the northern part of the Front Range of Colorado, was operated for a short time prior to World War II for copper and zino, but since 1949, when pitchblende was discovered on the mine dump, it has been worked for uranium. The bedrock in the mine area consists predominantly of pre-Cambrian (Silver Plums) granite with minor migmatite and metasediments--biotite-quartz-plagioclase gneiss, biotite schist, quartzite, amphibolite, amphibole skarn, and biotite skols. The metasediments occur as inclusions that trend northeast in the granite. This trend is essentially parallel to the prevailing foliation in the granite. At places the metasediments are crosscut sharply by the granite to form angular, partly discordant, steep-walled bodies in the granite. Faults, confined to a narrow zone that extends through the mine, cut both the pre-Cambrian rocks and the contained sulfide deposits. The Copper King fault, a breccia zone, contains a deposit of pitchblende; the other faults are believed to be later than the ore. The two types of mineral deposits--massive sulfide and pitchblende deposits--in the mine area, are of widely different mineralogy, age, and origin. The massive sulfide deposits are small and consist of pyrite, sphalerite, chalcopyrite, pyrrhotite, and in places magnetite in amphibole skarn, mice skols, and quartzite. The deposit at the Copper King mine has yielded small quantities of high-grade sphalerite ore. The massive sulfides are pyrometasomatic deposits of pre-Cambrian age. The pitchblende at the Copper King mine is principally in the Copper King vein, a tight, hard breccia zone that cuts through both granite and the massive sulfide deposit. A small part of the pitchblende is in small fractures near the vein and in boxwork pyrite adjacent to the vein; the post-ore faults, close to their intersection with the Copper King vein, contain some radioactive material, but elsewhere, so far as is known, they are barren. The pitchblende in the deposit forms a steeply plunging ore shoot that has a horizontal length of more than 50 feet and a vertical height of about 85 feet. The thickness of the ore shoot averages about 2 feet, but it ranges from a feather edge to about 4 feet. The hard pitch-blende is intimately intergrown with siderite; other gangue minerals include pyrite, quartz, and finely comminuted fragments of the wall rocks. The vein was repeatedly reopened during mineral deposition as shown by several stages of brecciation and recommended by the vein matter. The pitchblende deposit probably formed at intermediate temperatures and depths and, according to the Pb/U ratio, is about 60 million years old--an early Tertiary age.

Colorado↗