Wallace reported in 1956 that the Bisbee district has been an important source of copper for many years and substantial amounts of lead and zinc ore and minor amounts of manganese ore have been mined during certain periods. The copper deposits occur both as low-grade disseminated ore in the Sacramento Hill stock and as massive sulfide (and secondary oxide and carbonate) replacement bodies in Paleozoic limestones that are intruded by the stock and related igneous bodies. The lead~zinc production
has come almost entirely from limestone replacement bodies.
The disseminated ore exhibits no anomalous radioactivity, and samples from the Lavender pit contain from 0.002 (20 ppm) to less than 0.001 percent equivalent uranium (10 ppm). The limestone replacement ores are distinctly radioactive and stopping areas can be readily distinguished from unminera1ized ground on the basis of radioactivity alone. The equivalent uranium content of the copper-replacement ores ranges from 0.002 (20 ppm) to 0.014 percent (140 ppm), and averages about 0.005 percent (50 ppm); the lead~zine replacement ores average more than 0.007 percent equivalent uranium (70 ppm).
Most of the uranium in the copper ores of the district is retained in the smelter slag as a residual concentrate; the slag contains about 0.009 percent equivalent uranium (90 ppm). Uranium carried off each day by acid mine drainage is roughly equal to 1 percent of that being added to the slag dump. Although the total amount of uranium in the district is large, no minable concentrations of ore~grade material are currently known or inferred; the samples of relatively high-grade material represent only small fractions o tons at any one locality.
There are many separate centers or source areas of mineralization in the Bisbee district~ and district-wide mineral zoning is poorly develped. In general, however, lead~zinc deposits are more abundant in the peripheral parts of the mineralized area, that is, those parts of the district farthest from the Sacramento Hill stock. Some composite ore bodies locally duplicate the district zoning. The total amount of uranium deposited with the copper and lead-zinc sulfide ores of the Bisbee district is large, but the concentration of uranium in the ores is low. The lead-zinc replacement ores are more uraniferous than the copper replacement ores, and these in turn contain a higher percentage of uranium than the low-grade disseminated copper ores of the Sacramento Hill stock; much of the uranium originally present in the pit ore has undoubtedly been leached by acid supergene waters.
Material containing more than ten percent uranium as primary uranium oxides is associated with both copper and lead-zinc sulfides; but known concentrations of ore-grade uranium material are not of economic interest because of their apparent small size. Although no uranium ores are currently known or inferred in the district, the radioactivity of the limestone replacement might prove a useful prospecting guide to base-metal ores in the district. The equivalent uranium content of manganese oxides sampled in various parts of the district, suggest that there is less. equivalent uranium in the wad in areas that, so far as is known, exhibit only very weak copper, lead, and zinc mineralization.
Most of the uranium in the copper ores being taken from the mines remains in the slag; some uranium is leached from the ore in-place by acid water and is discharged in the mine drainage. The uranium content of this groundwater suggests that there may be localities where concentration and flow are sufficient to encourage attempts to extract uranium from solution.
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