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Existing geochemical data on roll-type uranium deposits, their host rocks, and some related altered rocks in the Shirley and Powder River Basins of Wyoming and in rocks of the Oakville Formation and Whittset Formation of south Texas indicate differences in composition useful in examining possible modes of origin of the deposits. In addition to U and its radioactive daughter products, the elements enriched in the deposits of the Powder River Basin compared to unmineralized host rock include: Na, K, Ba, Co, ferrous iron, Ga, Al, Pb, Se, As, and V. In the Shirley Basin deposits, Ba, V, Fe, Al, Ga, Cr, Pb, Sr, and Cu are enriched along with U and eU. Ba, Ti, Y, Zr, V, Cr, Co, and Yb are enriched in the deposits in the Oakville Formation compared to nonmineralized rocks downdip of the ore. In the ores in the Whittset Formation, Na, K, Ca, Sr, Co, Ni, Mo, Y, Al, and radioactive decayproducts are enriched with U. The variation in the chemical characteristics of the roll-type uranium deposits probably reflects differences in the processes that formed the deposits and differences in the subsequent alteration of the deposits. INTRODUCTION The purposes of this study are to use existing geochemical data to determine which elements are enriched or depleted in various roll-type uranium deposits in Wyoming and Texas compared to background host rocks, and to compare the chemistry of the roll-type deposits in these districts to each other and to the chemistry of the roll-type (secondary or redistributed) deposits in the Ambrosia Lake district of New Mexico. Both the similarities and differences in the chemistry of these deposits are likely to add to our understanding of the genesis of roll-type uranium ores. Granger and Warren (1969) and Harshman (1974) discuss the genesis of roll-type uranium deposits. Harshman's paper also includes some data on the elements associated with roll-type deposits in Wyoming and Texas. Information used to characterize the secondary deposits of the Ambrosia Lake district was taken from Spirakis and others (1981). Additional chemical data used in this study was taken from published sources (Harshman, 1974; Santos, 1980) and from chemical analyses of samples included in the Survey's Rock Analysis Storage System (RASS); these samples were collected by A. Butler, J. Vine, F. Armstrong, D. Seeland, H. Dodge, K. Dickinson, and R. Reynolds of the U.S. Geological Survey. The only new data produced for this study were uranium analyses of 30 samples to confirm that the samples were not mineralized. ORGANIZATION OF THE DATA The data are organized into five groups: rocks of Tertiary age of the Shirley Basin and Powder River Basin of Wyoming, Oakville Formation and Whittset Formation of the Texas gulf coast, and Jurassic rocks of the Ambrosia Lake district of New Mexico. For each of these groups, data for a mineralized set of samples (arbitrarily defined as samples containing greater than 100 ppm uranium) and data for a background (nonmineralized) sample set were compiled. The background set in the Oakville Formation consisted of samples containing less than 100 ppm U and located downdip of the ore. (In table 2, this set is referred to as downdip.) Samples in the other background sets were selected on the basis of containing less than 100 ppm uranium or less than 100 ppm ell (equivalent uranium) for samples which were analyzed for eU but not U. Separate sets of samples were formed from those samples designated as altered by oxidizing solutions. These altered rocks are believed to represent former positions of the migrating, mineralized solution fronts. No data were available on altered rocks in the Ambrosia Lake district, and the number of analyses of altered rock in the Shirley Basin was too small for statistical treatment. The high average ell and selenium contents of our altered sets suggest that the altered sample sets are dominated by samples from very near the roll front; thus their chemical characteristics are not necessarily representative of altered rocks far from the deposits. Some of the samples from the Powder River Basin district were near-surface samples that are believed to have been oxidized by modern surficial processes. These samples were removed from the mineralized, altered, and background sets. Because of the lack of available drill core and the low relief in the Texas Gulf coast uranium district, most of our background samples for the Whittset Formation were taken from outcrops. These samples could have been affected by surficial processes but the extent of the effect on any sample cannot be determined. Consequently the background data set from the Whittset Formation is less than ideal and the results must be viewed skeptically. NATURE OF THE DATA The elements considered in this study, the limits of determination for each element and the analytical techniques used are shown in figure 1. Most of the data are from 3-step or 6-step semiquantitative emission spectrographic analysis. These data are presented as midpoints (.15, .3, and .7 for 3-step and .15, .2, .3, .5, .7, and 1.0 for 6-step) of geometric brackets whose boundaries are 0.12, 0.26, 0.56, and 1.2 for 3-step and 0.12, 0.18, 0.26, 0.38, 0.56, 0.83, and 1.2 for 6-step. Thus there are either three or six brackets for every order of magnitude; the boundaries and midpoints for higher or lower values are the same as these except for the position of the decimal. In 3-step data, about 60 percent of the results will be in the correct bracket. The precision of a reported value in 6-step data is approximately plus-or-minus one bracket at the 68-percent confidence level and plus-or-minus two brackets at the 95-percent confidence level (Motooka and Grimes, 1976). Large sets of spectrographic analytical data, such as these inevitably include results from samples that contain too little of certain elements to permit accurate determinations of their abundances. Data for such samples in Fi gu re I E le me nt s st ud ie d s L I 50 pp m S N a .0 5 % c K 0 .1 % s B e 1 p pm S M g .0 0 2 % S C a ,0 5 % S S r 2P pm S B a 2 p p m c V 7 p p m > « E le rr

Chemical characteristics of roll-type uranium deposits in Wyoming and Texas