Several hundred clay mineral and whole rock samples of ores and barren rocks from the Grants mineral belt have been analyzed by instrumental neutron activation analysis (INAA) and delayed neutron activation analysis (DNAA). The DNAA method allows high precision and accuracy for uranium and thorium determination, whereas the INAA method allows determination of 20 to 30 trace elements. The trace-element data can only be interpreted properly if the clay-mineral (—2μ) fraction is compared directly with whole-rock samples. The INAA data support mineralization of trend ore as due to southeast-flowing solutions; the DNAA determination of uranium suggests that the source of uranium in the Westwater Canyon Member of the Jurassic was not from the overlying Brushy Basin Formation. Local zonation of trace elements, especially the rare earth elements (REE), indicates fixation of many trace elements when uranium mineralization occurred. Thus, REE-depleted, oxidized ground can, with caution, be used for exploration purposes. Vanadium originally precipitated as V3+ in chlorites remains in the original sites after oxidation to V5+ and is thus also valuable as a pathfinder. Data for antimony suggest that it, too, may be useful. In general, trend-ore deposits are characterized by a high chlorite + illite, illite + illite-montmorillonite, or illite + chlorite + illite-montmorillonite, whereas ore near the redox front may contain primary kaolinite. The REE are concentrated greatly in all types of ore, primary or secondary, and, coupled with uranium haloes, are useful as ore guides.