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SR-I I (Ike #1 Mine) Designated Mining Operation <br /> January 31, 1995 - Page 5 <br /> very insoluble minerals carnotite or tyuyamunite (depending on the <br /> amount of K or Ca also in solution) . Weeks, et.al. (U. S.G.S. Prof. <br /> Paper 320) have shown that the precipitation of carnotite takes <br /> place following three stages of oxidation of Salt Wash ore bodies. <br /> The most common primary vanadium mineral in the Salt Wash ores is <br /> montroseite VO(OH) which readily oxidizes to paramontroseite, V021 <br /> when exposed to air. This can happen in a few months time. Other <br /> V+° minerals are possibly early alteration products of montroseite, <br /> including doloresite, duttonite, and simplotite. <br /> The silicate vanadium minerals (vanadium-bearing chlorites, clays, <br /> and hydrous micas) oxidize much slower, if at all. Coffinite and <br /> uraninite will be oxidizing at the same time. However, as <br /> previously mentioned, early states of uraninite oxidation do not <br /> produce much soluble uranium. Therefore, "considerable oxidation <br /> of vanadium takes place between the time of alteration of uraninite <br /> and coffinite and the appearance of uranyl vanadates in corvusite <br /> ore. " <br /> Further oxidation of the ore results in the second stage, <br /> corvusite, which is characterized by a blue-black color. The V+4 <br /> minerals formed in the early stage will alter to compounds <br /> containing both V+4 and V+5 and available Ca, Fe, Na, or K. The <br /> liberated V+5 will combine with any available U+6 to form the <br /> poorly-defined mineral rauvite, Ca0.2UO2.6V205.20H2O. Several other, <br /> relatively stable uranyl minerals can form at this stage if the <br /> vanadium has not reached the V+5 state, including phosphates, <br /> arsenates, and silicates. "Depending on the relative abundance of <br /> calcite with respect to pyrite in primary ore, a wide range of pH <br /> is possible. . . and the solutions may remain acid or be neutralized <br /> by calcite. Part of the calcite gangue and cement may be dissolved <br /> and the sandstone partly recemented by gypsum and iron oxides. " <br /> This will liberate Ca to the solution. <br /> "As oxidation progresses, carnotite, K2(UO2)2 V20801-3 H2O and <br /> tyuyamunite, Ca(UO2) V205.5-8 H2O develop from rauvite. . . Once <br /> crystallized, carnotite is remarkably stable and fixes the uranium <br /> very effectively. The minerals containing V+4 and V+5 of the <br /> corvusite stage oxidize to form V+5 minerals. The specific ones <br /> depend on pH conditions, on the presence of certain cations, and on <br /> several other factors. Vanadium fixes all available uranium in <br /> uranyl vanadates, and the excess vanadium. . . combines with other <br /> elements - these include Ca to form hewettite, pascoite, and <br /> rossite, K and Mg to form hummerite, " Na, Al, Fe and Cu. Some of <br /> the original vanadium silicates probably remain unchanged whereas <br /> some of the interstitial clay may become impregnated with vanadium <br /> solutions migrating during oxidation. <br /> As can be seen on accompanying Eh-pH diagrams, carnotite is most <br /> stable at low CO2 pressure near neutral pHs, as is the case of <br /> surface and shallow ground water in a semi-arid climate such as the <br />