Comparison of the elemental abundances of six suites of ore-bearing sandstones from the Upper Jurassic Morrison Formation suggests that certain elements form haloes around these deposits. Field relations and uranium contents were used to classify approximately 700 samples of sandstone from the Morrison Formation in the Ambrosia Lake area, New Mexico, into the following groups: (1) primary U-V ore (prefault or trend), (2) secondary U-V ore (postfault or stack), (3) reduced rock adjacent to ore, and (4) oxidized rock adjacent to ore. The chemical characteristics of each of the groups were compared with each other and with the characteristics of two control groups of samples taken farther from ore deposits. One of these was a suite of 70 samples of Morrison sandstones from t e Thoreau area; the other consisted of approximately 200 samples of Morrison sandstones from various locations in the southern San Juan basin. Differences in the geometric means of the elemental abundances indicate that relative to the control groups, the primary ores are enriched in Fe, Mg(?), Ca, Mn, Ba, Be, Cu, Mo, Pb, U, V, Y(?), Na, Se, Sr, organic C, and carbonate C; the secondary ores are enriched in Fe, Ca, Mn, Ba, Cu, Na, Sr, U, V, and carbonate C. The data indicate that Ca, Ba, Sr, V, and carbonate C are more concentrated in

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the secondary ore than in the primary ore. Barren rocks adjacent to the ore are enriched in Ca, Ba, Cu(?), Sr, V, U, Na, Se, and carbonate C, compared with barren rock farther from the deposits. Both the enrichment of these elements in the vicinity of the deposits, and the better correlation of them (except for U) with eU than with U, suggest that these elements are mobile and form haloes that may be useful exploration guides. The data also suggest that Ga is depleted in and around the ore. Thus, a decrease in Ga might be an indication of proximity to a deposit.

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