Tyuyamunite

Quicksilver Pyromorphite SILICATES (Phyllosilicates) Alabaster Tyuyamunite... 

Tyuyamunite Ca(U02)2 (V04)2 5-8 (uranium calcium vanadate) Closely related to carnotite... 

Amethyst Galleries. 1995. The mineral tyuyamunite. Amethyst Galleries, Inc. httD //mineral.galIeries.com/minerals/DhosDhat/tvuvamun/tvuvamun.htm. 

Uranium U(VI) minerals are most often products of the oxidation and weathering of nearby primary U(IV) ore minerals such as uraninite [U02(c)I and coffinite [USi04(c)l (cf. Pearcy et al. 1994). They also form by evaporative concentration of dissolved U(VI), particulary under arid conditions. Schoepite (/J-UOj 2H2O) is fairly soluble and, therefore, is a rare mineral, whereas carnotite K2(U02)2(V04)2j and tyuyamunite (Ca(U02)2(V04)2j, which have lower solubilities (particularly above pH 5) are the chief oxidized ore minerals of uranium. The plots in Figs. 13.5 and 13.6 indicate that uranyl minerals are least soluble in I0W-CO2 waters, and, therefore, are most likely to precipitate from such waters. This is con.sistent with the occurrence of carnotite and tyuyamunite in oxidized arid environments with poor. soil development (Chap. 7), such as in the calcrete deposits in Western Australia (cf. Mann 1974 Dall Aglio et al. 1974), and in the sandstone-hosted uranium deposits of the arid southwestern United States (cf. Hostetler and Carrels 1962 Nash et al. 1981). The... 

The Eh-pH diagram in Fig. 13.12 shows the large stability field of carnotite under oxidizing conditions (the field of tyuyamunite is similar), consistent with its common occurrence in the weathered zone of U(IV) uranium deposits. The figure, which is from Langmuir (1978), is little changed by revisions in the thermodynamic data base in Table A 13.1. 

Recomputed from the empirical solubility data in Hostetler and Garrels (1962) consistent with the data in diis table and with corrections for ion activities and complexes. AG/ computed assuming AG/ for the tyuyamunite/carnotite exchange reaction equals its value for the autunite/K-autunite exchange reaction. 

Chemical equilibrium conditions are assumed for all reactions. The chemical model consists of eight components UOj"1", VO4-, CO2-, K+, Ca2+, H+, and HFO as the sorbent. Four minerals, carnotite (K2(U02)2(V04)2), tyuyamunite (Ca(U02)2(V04)2), calcite (CaC03), and gypsum (CaS04 2H2O), are allowed to participate in precipitation-dissolution reactions. The detailed chemical model (reactions and parameters) is presented in Morrison et al. (1995a). No ionic strength correction was made for activity coefficients. 

Camotite is a major ore of the Colorado plateau. Tyuyamunite occurs near Grants, New Mexico, in Utah, and in the Soviet Union. Autunite is found near Marysvale, Utah, and in Washington and Wyoming, Torbemite is found in the White Canyon district of Utah and in the upper zones of ore bodies in Zaire. 

The vanadate ion is a very effective precipitant for uranyl ions—as insoluble uranyl vanadate (carnotite, K2(U02)a(V04)2 and tyuyamunite, Ca(U02)2(V04)2). Precipitation of carnotite, according to... 

Colorado, is hosted in folded and brecciated Mississippian dolomite, shale, sandstone and coal, which is in fault contact with Precambrian gneiss. The Precambrian gneiss is anomalously enriched in uranium, and a Mesozoic or Caenozoic age of mineralization in the Mississippian host rocks, formed by downward percolation of uraniferous groundwater from the adjacent Precambrian terrain, is inferred. Mineralization in the Pryor Mountains region, Montana, is hosted in karsts developed with the Mississippian Madison limestone and consists of uraninite-tyuyamunite grading up to 7% UsOg associated with clay minerals and silicified collapse breccias. A Caenozoic age of mineralization, under conditions similar to those of Pitch mine, is favoured. 

All niarine phosphorites consist mostly of microcrystalline apatite (carbonate fluorapatite) in the form of laminae, pellets, oolites, nodules and skeletal or shell debris. Uranium, considered syngenetic, may be present in carbonate fluorapatite as a substitute for calcium. Uranium in sea water was probably incorporated during or shortly after precipitation, and it is usually disseminated rather uniformly throughout a given bed or horizon. Primary uranium minerals are rarely present, but secondary uranium minerals (tyuyamunite, autunite, torber-nite) have been identified in a few localities. 

Dominant ore minerals in the reduced zone are pitchblende and coffinite and, in some deposits, associated primary vanadium oxides—for example, montroseite. In oxidized zones the important uranium minerals are the uranyl vanadates (carnotite, tyuyamunite or francevillite). Accessory elements include Mo, Se and Cu. Average uranium content ranges from 0.01 to 0.40 7o U3O8. 

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