URANIUM DEPOSITS IN THE ESPAÑOLA BASIN, SANTA FE COUNTY, NEW MEXICO. Shaw No. 2 prospect. Oxidized uranium-bearing layer with clay galls. Note clay lense below oxidized layer (Oxide Butte, NMSF-158). Sketch of the formation of roll-front uranium deposit. S=sulfur, Se=selenium, U=uranium.
Shaw No. 2 prospect.
Oxidized uranium-bearing layer with clay galls. Note clay lense below oxidized layer (Oxide Butte, NMSF-158).
Sketch of the formation of roll-front uranium deposit. S=sulfur, Se=selenium, U=uranium.
VIRGINIA T.McLEMORE, 1, DENNIS McQUILLAN2, PATRICK LONGMIRE3, AND DAVID VANIMAN3
1New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, [email protected];
2 New Mexico Environment Department, 525 Camino de los Marquez, Suite 1, Santa Fe, New Mexico 87505,[email protected];
TYPES OF URANIUM DEPOSITS
Uranium mineralization in the Española Basin is not of sufficient quantity and quality to justify mining. However, many private water wells in the region produce water with concentrations of uranium (up to 1,820 g/L) that exceed the safe drinking water standard of 30 g/L. Therefore, it is important to understand the source of the uranium in the groundwater and the processes involved. Potential sources for uranium in the groundwater include 1) uranium occurrences in the Tesuque Formation (San Jose mining district); 2) veins, replacements, and pegmatites in Proterozoic rocks (San Jose and Nambe mining districts); 3) Proterozoic granitic rocks in the Sangre de Cristo Formation; and 4) rhyolitic ash beds found interbedded within the Tesuque Formation.
Three types of sandstone uranium deposits are found in the San Jose district: 1) medium-grained sandstone with uranium associated with clay galls and carbonaceous material, 2) poorly consolidated fine- to medium-grained sandstone with disseminated uranium and little carbonaceous material, and 3) coarse-grained sandstone to conglomerate with abundant uranium associated with carbonaceous material. Carnotite, schroeckingerite, and meta-autunite coat fractures and bedding surfaces in sandstone, siltstone and shale within the Tesuque Formation, especially near clay galls and carbonaceous material. Uranium also occurs as coatings around opal and chert grains, with organic debris, and in clay zones. One property, the San Jose No. 13 (NMSF0033), produced 12 lbs (5kg) of U3O8 at a grade of 0.05%U3O8 in 1957.
The uranium occurrences in the Tesuque Formation probably represent natural precipitation and concentration from uraniferous groundwaters, likely derived from 1) the Sangre de Cristo Mountains to the east, 2) ash beds within the Tesuque Formation, and/or 3) the alteration of granitic and/or volcanic detritus in the sedimentary host rocks. The occurrence of uranium in the waters in this area is most likely a result of weathering of uranium from rocks in the adjoining mountains and subsequent migration of uranium (VI)-carbonate complexes and radon in the groundwater. Uranium then precipitated from the waters to form the geochemical anomalies found in the stream sediments and prospects.
URANIUM IN PROTEROZOIC VEINS, REPLACEMENTS, AND PEGMATITES
SANDSTONE URANIUM DEPOSITS
Uranium with clay galls and
organic material, San Jose mine.
Shaw No. 2 adit.
Uranium is found in veins, shear zones, and pegmatites in Proterozoic rocks in the San Jose and Nambe mining district. At the Shaw No. 2 prospect (NMSF0034) in section 7, T20N, R10E (35.9827424°N, 105.9221679°W), pits and 2 short adits expose Precambrian vein and replacement deposits consisting of secondary uranium minerals disseminated along a shear zone (N20°E), approximately 1 m thick, in Proterozoic amphibolite schist intruded by simple quartz-feldspar-biotite pegmatites and granite. The uranium minerals are reported associated with secondary copper minerals. Hematite, quartz, biotite, feldspar, and uranium minerals are found along fractures within the shear zone. Radioactivity was approximately 50 times background reading (background 30 cps, high 1500 cps). Reid et al. (1982) reported a sample contained 47 ppm U and a sample collected for this report contained 48 ppm U.
Three types of sandstone uranium deposits are found in the San Jose mining district: 1) medium-grained sandstone with uranium associated with clay galls and carbonaceous material, 2) poorly consolidated fine- to medium-grained sandstone with disseminated uranium and little carbonaceous material, and 3) coarse-grained sandstone to conglomerate with abundant uranium associated with carbonaceous material. Carnotite, schroekingerite, and meta-autunite coat fractures and bedding surfaces in sandstone, siltstone and shale within the Tesuque Formation, especially near clay galls and carbonaceous material (Chenoweth, 1979). Uranium also occurs as coatings around opal and chert grains, with organic debris, and in clay zones. One property, the San Jose No. 13 (NMSF0033), yielded 12 lbs (5kg) of U3O8 at a grade of 0.05%U3O8 in 1957(U.S. Atomic Energy Commission file data; McLemore, 1983). Samples assay as much as 800 ppm U.
Many residents in the Española Basin in Santa Fe County have high concentrations of uranium and radon in their drinking water and high concentrations of uranium are found in both NURE water and stream-sediment samples (McLemore, 2010a, b). Uranium has been detected in approximately 50% of the water supply wells in this area at concentrations exceeding the drinking water standard of 30 ug/L. At least 27 wells serving 19 public water systems, and 209 private domestic wells, produce water with excessive uranium. Concentrations range from less than 1 μg/L to a maximum of 1820 μg/L. High uranium in drinking water can cause kidney toxicity. In addition, high levels of indoor radon are widespread in this region. EPA’s recommended action level for indoor radon is 4 pCi/L to protect against lung cancer. Radon concentrations in excess of 20 pCi/L have been measured in buildings in the area, and abatement measures have been taken at many locations. Since some of the uranium concentrations in groundwater exceed safe drinking water standards and some homes in the area have excessive indoor radon, it is important to understand the source of the uranium in the groundwater and the processes involved.
SOURCES OF URANIUM
Typical rhyolite ash can contain 10-20 ppm U and this uranium is easily leached.
The sandstone uranium occurrences in the Tesuque Formation probably represent natural precipitation and concentration from uraniferous groundwaters, likely derived from 1) Proterozoic rocks in the Sangre de Cristo Mountains to the east, 2) volcanic ash beds within the Tesuque Formation, 3) the alteration of granitic and/or volcanic detritus within the sedimentary host rocks, and 4) uranium-bearing waters rising along the faults along the eastern boundary of the basin. Uranium in modern groundwaters likely was derived from the same sources, as well as from leaching and oxidation of older uranium occurrences in the Tesuque Formation. Green clay lenses in the Tesuque Formation could have formed from the alteration of leaching of volcanic ash beds. Volcanic ash beds are a well known source of uranium in sandstones (Zielinski, 1978; Walton et al., 1981; Kizis and Runnels, 1984).
Green clay beds.
Reworked ash beds.
Volcanic ash beds in the Tesuque Formation.
Typical granites contain 5-10 ppm U and pegmatites can contain as much as several percent U. Uranium-bearing minerals are found in many pegmatites deposits in the Sangre de Cristo Mountains (McLemore, 1983).
Typical Proterozoic pegmatite intruding granite.
DISTRIBUTION OF URANIUM IN THE SAN JOSE AND NAMBE MINING DISTRICTS
DEPOSITION MODEL FOR URANIUM DEPOSITS
Anderson, O.J.,1980, Abandoned or inactive uranium mines in New Mexico: New Mexico Bureau Mines Mineral Resources, Open-file Report 148, 778 p.
Chenoweth, W.L., 1979, Uranium in the Santa Fe area, New Mexico: New Mexico Geological Society, Guidebook 30, p. 261-264.
Collins, G.E., and Freeland, R.E., 1956, A report in the airborne radiometric survey and ground geologic reconnaissance in the Espanola area New Mexico: U.S.Atomic Energy Commission, Report RME-1075, 16 p.
Devoto, R.H., 1978, Uranium in Phanerozoic sandstone and volcanic rock, in Short course in uranium deposits; their mineralogy and origin: American Geological Institute, Short Course Handbook 3, p. 293-305.
Green, M.W., and others, 1980, Uranium resource evaluation, Aztec NTMS 1- by 2-degree quadrangle, New Mexico and Colorado: U.S. Department of Energy, Report PGJ/F-012(82), 79 p.
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Kizis, J.A., Jr., and Runnels, D.D., 1984, The mobility of uranium and associated trace elements in the Bates Mountain Tuff, central Nevada: Economic Geology, v. 79, p. 558-564.
Koning, D.J., 2002, Preliminary geologic map of the Espanola 7.5-minute quadrangle, Rio Arriba and Santa Fe Counties, New Mexico: New Mexico Bureau of Geology and Mineral Resources, Geologic Open-file Report OF-GM 54, scale 1:24,000
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McLemore, V.T., 1983, Uranium and thorium occurrences in New Mexico: distribution, geology, production, and resources; with selected bibliography: New Mexico Bureau of Mines and Mineral Resources, Open-file Report OF-182, 950 p., also U.S. Department of Energy Report GJBX-11(83).
McLemore, V.T., 2010a, Use of the New Mexico Mines Database and ArcMap in Uranium Reclamation Studies: Society of Mining, Metallurgy and Exploration Annual Convention, Phoenix, Feb 2010, Preprint 10-125
McLemore, V.T., 2010b, Use of the New Mexico Mines Database and ArcMap in Uranium Reclamation Studies: Society of Mining, Metallurgy and Exploration Transactions, in press.
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Uranium migrated in the groundwater down dip and precipitated from the groundwaters to form the roll-front sandstone uranium deposits. Uranium precipitated at reduced zones formed by clay, organic material, and possibly at the interface of reduced basin waters.
Continued oxidation and leaching of uranium from the uranium sources and from older uranium deposits in the Tesuque Formation and Proterozoic rocks then formed the modern geochemical anomalies found today in the stream sediments and groundwater. Radon results from the decay of uranium-bearing minerals in the rocks.
This area warrants continued examination to understand the significance of these geochemical anomalies and to determine if public health is at risk.
Location of uranium mining districts, mines, prospects, NURE stream-sediment samples, and NURE water samples in the San Jose and Nambe mining districts, Santa Fe County, New Mexico (T19-21N, R8, 9E; McLemore, 2010a, b). Note that high uranium concentrations also are found in the Proterozoic terrain (Nambe district), which are related to radioactive shear zones and pegmatites that intruded Proterozoic granitic and metamorphic rocks. Stream-sediment samples containing greater than 12 ppm U are considered anomalously high and water samples containing greater than 30 ppb are considered anomalously high (McLemore, 2010a, b).