AUTUNITE FROM MT. SPOKANE, WASHINGTON
Near Mt. Spokane, Washington, coarsely cry-stalline autunite is developed in vugs, fractures, and shear zones in granitic rock. With the exception of dispersed submicroscopic uraninite particles, autunite is the only ore mineral in the deposits. A study of associated granitic rocks revealed that apatite, the most abundant accessory constituent, was preferentially leached and corroded in mineraiized zones, suggesting that it may have provided a source of lime and phosphate for the formation of autunite. Leaching may have been effected partly by meteoric water, but is considered more probably due to the action of ascending connate solutions that may also have carried uranium from unoxidized, as yet undiscovered deposits, at depth. Autunite from the Daybreak mine was studied optically, chemically, and by x-ray diffraction. The autunite is commonly zoned from light-yellow margins to dark-green or black cores, and autunite from the inner zone has a higher gravity and higher refractive indices than peripheral light material. X-ray-powder-diffrtiction patterns of dark and light meta-autunite formed from this autunite show no significant differences in the d spacings; however, diffraction patterns of nine zoned samples each show uraninite to be present in the dark, and absent from the light, phase. UO/sub 2/ and UO/sub 3/ determinations range from 0.66 to 0.70% and 57.9 to 58.0%, respectively, for light autunite, whereas dark autunite showed a range (in seven determinations) of UO/sub 2/ from 1.2 to 4.0%, and UO/sub 3/ from 55.1 to 58.8%. The wide range of UO/sub 2/, values in dark autunite is tentatively attributed to nonuniform distribution of discrete uraninite particles, which may also account for the dark color and higher density. Thermogravintetric and differential therrmal analyses of autunite suggest discrete water losses at about 90, 145, and 220 deg C. The first water loss probably represents dehydration to meta-autunite II, also recognizable by marked changes in optical properties and the x-ray diffraction pattern. The form of the DTA curve above 90 deg C resembles that of montmorillonite. suggesting that the dehydrations at about 145 and 220 deg C may involve interlayer water as in montmorillonites, and the analogy with montmorillonite is further indicated by x-ray patterns of metaautunite II heated just above these temperatures .Autunite heated to red heat shoivs a diffraction pattern distinct from all others. The cation exchange capacity of autunite, about 2.5 milliequivalents per l0O grams,is substantially lower than that previously reported for artifical material. (auth)
- Research Organization:
- U.S. Geological Survey, Menlo Park, Calif.
- NSA Number:
- NSA-14-011800
- OSTI ID:
- 4178745
- Journal Information:
- Am. Mineralogist, Journal Name: Am. Mineralogist Vol. Vol: 45
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
APATITES
AUTUNITE
CALCIUM PHOSPHATES
COLOR
CONFIGURATION
CRYSTALS
DENSITY
DEPOSITS
DIFFRACTION
DISTRIBUTION
EVAPORATION
EXPANSION
GEOLOGY, MINERALOGY, AND METEOROLOGY
GRANITES
GROUND WATER
ION EXCHANGE
LATTICES
LEACHING
MONTMORILLONITE
OPTICAL PROPERTIES
PHASE DIAGRAMS
QUALITATIVE ANALYSIS
QUANTITY RATIO
RAIN
REFRACTION
ROCKS
SOLUTIONS
THERMAL ANALYSIS
THERMOGRAVIMETRY
TRANSPORT
URANINITES
URANIUM
URANIUM DIOXIDE
URANIUM MINERALS
URANIUM PHOSPHATES
URANIUM TRIOXIDE
WATER
WEIGHT
X RADIATION
ZONES