UNUSUAL URANIUM MINERALS OF COMBUSTED PHOSPHORUS-RICH BITUMINOUS MARL , CENTRAL JORDAN

Secondary yellow uranium minerals (uranyl vanadates) together with unique green smectites (Cr-rich smectite/volkonskoite) are hosted in altered varicolored marble and chalk marl/travertine, and/or calcrete/top soil (saprolite) of central Jordan. Tyuyamunite Ca(UO₂)₂V⁵⁺₂O₈•3(H₂O) - strelkinite Na₂(UO₂)₂V₂O₈•6(H₂O) solid solution series (uranmica) are the major components and their composition reflects changes in the Ca /Na ratio of the circulating water. The Ca-end member tyuyamunite is also common in the secondary veins of the altered varicolored marble. The Na-rich member (strelkinite) is dominant in the calcrete/top soil (saprolite) and its precipitation is related to continuous evaporation during seasonal dry periods.

Tyuyamunite- strelkinite phases are intermixed with the porous fine grained matrix (>50 um to < 2 um). The uranium phases have two stages of crystallization. The earlier stage is composed of very fine crystallites (less than 1 μm) intermixed with the matrix. The coarser later stage (up to >50μm) fills pores and weakness zones. The matrix is composed of U-F-bearing aggregates of intermixed calcite, carbonate-fluorapatite, and variable amounts of clay minerals dominated by smectite (montmorillonite), gypsum, barite, halite and fluorite. The porosity of the host rock controls tyuyamunite- strelkinite distribution. The green smectite fills voids and cavities of the altered marble, chalk marl/travertine and Recent calcrete/top soil deposits.

New primary calcium uranate phases (restricted to the varicolored marble) were also identified. The calculated structural formulae were CaUO₄, Ca₂UO₅, Ca₃UO₆, Ca₃U₂O_9, Ca₄UO₇, Ca₅UO₈, and Ca₆UO₉. Crystallization of calcium uranate phases is the result of oxidation of U⁺⁴ at high temperature as a result of combustion of phosphorus-rich bituminous marl into U⁺⁶under high oxygen fugacity.