Uranium distribution and geology in the Fish Lake surficial uranium deposit, Esmerelda County, Nevada

Fish Lake Valley, in southern Nevada and California, contains about 675 acres of uranium-enriched lacustrine and marsh sediments in an arid alluvial-fan environment. A change in the trend of the Silver Peak Range, which forms the valley's eastern margin, and bedrock spurs that divert clastic sediments away from the marsh have allowed a large deposit of lacustrine and marsh sediment to accumulate. Section lines across the deposit were sampled at 0.3-m intervals to a maximum depth of 6.5 m. All samples were dried and analyzed for uranium and organic matter content. Uranium concentrations in the sediments ranged from 6 to 800 ppm and averaged 64.3 ppm (253 samples). Uranium values correlate with organic content of the samples. The marsh is fed by ground water and surface runoff derived from the Silver Peak Range. Tertiary volcanic rocks of the Silver Peak Range supply uranium to the base of the deposit in upwelling ground water. The uranium is concentrated in organic-rich layers in the marsh sediments. Water migrating laterally through the marsh sediments at the edge of the permanent pond in the southern part of the area may also contribute uranium to the sediments. Reconnaissance sampling in the surrounding valley and mountain areas showed minor enrichment of uranium (as much as 150 ppm) in wetland areas and localized accumulations of organic-rich sediments.