New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/32 Uranium in the Gunnison County, Colorado Craig S. Goodknight, 1981, pp. 183-190 in: Western Slope (Western Colorado), Epis, R. C.; Callender, J. F.; [eds.], New Mexico Geological Society 32nd Annual Fall Field Conference Guidebook, 337 p. This is one of many related papers that were included in the 1981 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks. Copyright Information Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States. No material from the NMGS website, or printed and electronic publications, may be reprinted or redistributed without NMGS permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. New Mexico Geological Society Guidebook, 32nd Field Conference, Western Slope Colorado, 1981 183 URANIUM IN THE GUNNISON COUNTRY, COLORADO* CRAIG S. GOODKNIGHT Bendix Field Engineering Corporation P.O. Box 1569 Grand Junction, Colorado 81502 INTRODUCTION rences are in pegmatites and shear zones in Precambrian rocks, Uranium prospecting spread eastward from the Colorado Pla- Cambrian vein material, and sandstones of early Tertiary age. teau in the middle and late 1950s to a more hard-rock environ- Much of the information and basic data on the various uranium ment in the area surrounding Gunnison. Two major uranium dis- occurrences for this paper were collected from 1977-1979 during tricts (Cochetopa and Marshall Pass) were discovered during that the evaluation of the Montrose (1°x2°) quadrangle by Bendix time, as were numerous uranium occurrences elsewhere in the Field Engineering Corporation, under contract to the U.S. Depart- area. More recently, in the late 1970s, the Gunnison country ex- ment of Energy for the National Uranium Resource Evaluation perienced renewed and more intense uranium exploration and (NURE) program. The reader is referred to the Montrose quadran- development. gle evaluation report (folio) for additional information on uranium Approximately 1.2 million kg of L.1308 have been produced from occurrences (many others having less than 0.01 percent U308) and the Gunnison country; over 99 percent of this has come from the favorability (Goodknight and Ludlam, 1981). Cochetopa and Marshall Pass districts. Uranium in both districts The area of Gunnison country for this paper is somewhat re- and many of the other occurrences is associated closely with fault stricted to within the Montrose 1°x2° quadrangle boundary, and and shear zones which cut brittle host formations (dolomites and also excludes the area around Lake City; the boundary of the area sandstones) of Paleozoic and Mesozoic age. Minor uranium occur- described in this paper is shown in Figure 1. An index map (fig. 1) shows all the known occurrences of material containing at least *Publication authorized by the U.S. Department of Energy, Grand Junction Office. 0.01 percent U308. 184 GOODKNIGHT DESCRIPTION OF URANIUM OCCURRENCES IN AREAS developed stream channel systems that trend west or northwest. (OR DISTRICTS) Samples of mineralized rock taken during quadrangle evaluation Ruby-Irwin District contain up to 0.035 percent U308; no uranium minerals have been Uranium has been found in the southeastern part of the Piceance identified. Creek basin in the Ruby-Irwin base- and precious-metal mining The uranium occurrence at the Standard mine is in gray, fine- district. In this district, centered about 10 km west of Crested grained sandstone with clay and carbonaceous clasts, probably Butte, uranium is in the Ruby Anthracite Creek area and at the from a fluvial channel. A sample of radioactive material taken dur- Standard mine. Prospectors in the mid-1950s found uranium in the ing quadrangle evaluation from the mine dump contained 0.59 lower part of the Eocene Wasatch Formation along Ruby Anthra- percent U308 and uranium (uraninite?) is associated with car- cite Creek at the Yellowdog and Pearl B claims (locality 1, fig. 1 and bonaceous material which composes about two percent of the Table 1). Workings on the claims in the E1/2 sec. 4, T. 14S., R. 87W. rock. The mine is within the body of base-metal mineralization consist of several prospect pits and one short adit; no uranium was related to the Redwell Basin intrusive complex of Oligocene age, produced. During quadrangle evaluation (Goodknight and Ludlam, centered about 2-3 km to the east. Uranium was probably em- 1981) in 1978, high radioactivity was found in some dump material placed by groundwaters in the carbonaceous sandstone before from the abandoned Standard mine in the SE% sec. 25, T. 13 S., R. the episode of base-metal mineralization which provided pyrite, 87 W. (loc. 2). The anomalously radioactive dump material came sphalerite, argentiferous galena, chalcopyrite, and pyrrhotite. from the Paleocene Ohio Creek Formation and/or the Eocene Wasatch Formation; the exact location of the material was uncer- Elk Mountains tain because the entrance to the mine (formerly a large producer The part of the Elk Mountains shown in Figure 1 extends from of lead, zinc, and silver) was caved. Gothic on the west to the Taylor River on the south and east. Four Uranium mineralization in the Ruby Anthracite Creek area is in areas of uranium cocurrences have been found in this (southern) iron-stained, fine- to medium-grained feldspathic sandstone that part of the Elk Mountains. contains a moderate amount (up to several percent) of carbona- On the west side of Virginia Basin about 2.5 km north of Gothic ceous material and minor pyrite along bedding. Uranium is associ- in the NW% NE% sec. 34, T. 12 S., R. 86W. (loc. 3), low-grade strati- ated with carbonaceous material, mainly near the base of poorly form uranium enrichment occurs in a thin, gray, freshwater lime- URANIUM IN THE GUNNISON COUNTRY 185 stone bed in the lower part of the Morrison Formation. This oc- small, widely scattered pods of uranium-bearing minerals. The sim- currence was discovered in the mid-1950s and was investigated in ple and zoned pegmatites in the district are related to the Wood 1978 by Goodknight and Ludlam (1981). A sample from the lime- Gulch Granite of Precambrian X age exposed to the south. stone bed contained 0.01 percent U308; the highest radioactivity Pegmatite No. 783, named on the map by Staatz and Trites was along fractures or joint surfaces. The occurrence is probably (1955), was sampled by Goodknight and Ludlam (1981) in 1979 epigenetic and may be either an efflorescent or a peneconcordant and found to contain the thorium minerals brockite and greyite deposit. and 0.011 percent L.1308; no uranium minerals were identified. This Near the head of Cement Creek on the north side of Mt. Tilton in microcline-quartz-pegmatite is in the E1/2 sec. 32, T. 50 N., R. 3 E. the SPA sec. 28, T. 12 S., R. 84W. (loc. 4), another low-grade strati- (loc. 7). form uranium enrichment occurs—this time in the lowr part of the The Brown Derby mine in the NE% sec. 3, T. 49 N., R. 3 E. (loc. 8) Parting Sandstone of the Chaffee Group. This occurrence was produced about 110 kg of U308 from 365 metric tons of lepidolite found in 1978 during quadrangle evaluation (Goodknight and Lud- and microlite mined during World War II (Nelson-Moore and lam, 1981); a sample of the Parting contained 0.017 percent radio- others, 1978). Chip samples taken during quadrangle evaluation in metric uranium. High radioactivity occurs in a thin bed of dark 1978 from the margin of the Brown Derby No. 1 pegmatite con- brown, quartzose, medium- to fine-grained sandstone in the Part- tained several percent U308 from the minerals pyrochlore and ing, which represents a marginal-marine environment during trans- uranopyrochlore. gression of a sea in Late Devonian time. A sample taken during quadrangle evaluation in 1978 from a ra- On the south side of Star Basin near the head of Italian Creek in dioactive part of the Bucky pegmatite at the Willow Creek mine secs. 1 and 12, T. 13 S., R. 84 W. are three closely-separated (loc. 9) contained 0.084 percent U308. This mine is near the north- uranium occurrences (all shown by loc. 5, fig. 1). All three oc- ern end of the district in the NE1/4 sec.