Abstract

Two 5-pound samples from the "hot spot" of the pyritic dump of the Wood mine, a past producer of pitchblende near Central City, Colo., showed Ra/U ratios that were abnormally high but nearly constant at about 150 times the equilibrium value for both samples in spite of a sevenfold difference in uranium contents. Analyses of oxidized but still black pitchblende from Katanga, in the Belgian Congo, before and after leaching in very dilute, dilute, and concentrated sulfuric acid solutions showed that: (1) UO 3 is preferentially leached with respect to UO 2 , Ra, and Pb in all three solutions, (2) the resulting residual concentration of both radium and lead effected in the process is proportional to the total amount of uranium leached except in concentrated H 2 SO 4 , and (3) after a sample has been leached in concentrated H 2 SO 4 the resulting increase in radium content relative to lead is much lower, as might be expected from data published by Lind, Underwood, and Whittemore in 1918 for the solubility of RaSO 4 . Under similar leaching conditions, unaltered pitchblende from Great Bear Lake, in Northwest Territory, Canada, lost only 1/10 to 1/15 as much uranium as the UO 3 -rich Katanga ore. Both laboratory and field results point to the same conclusion: in an oxidizing, highly acid environment uranium is rapidly leached and both radium and lead tend to be fixed about proportionally in the process. These results help to explain (1) why UO 3 -rich uranium minerals tend to give maximal Pb/U ages and (2) why the search for high-grade uranium ore in and around abandoned sulfide mines known to have produced pitchblende in the past has been consistently disappointing.

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