Natural analogue approaches to prediction of long-term behaviour of Ca<Subscript>2</Subscript>UO<Subscript>5</Subscript>∙2-3H<Subscript>2</Subscript>O X-phase: case study from Tulul Al Hammam site,Jordan

The Tulul Al Hammam area in central Jordan is an advantageous natural analogue site to study long-term U(VI) retention in ~?1 Ma old U-bearing combustion metamorphic marbles with clinker-like mineralogy exposed to prolonged supergene alteration for at least ~?100 kyr. The marbles contain abundant grains of high-temperature (ca. 800–850 °C) primary double Ca-U(VI) oxides (mainly Ca₃UO₆ and CaUO₄), which are commonly replaced by hydrated calcium uranates with various impurities (Si, Fe, Al and F). A more hydrous natural analogue of X-phase (Ca₂UO₅·2-3H₂O) occurs as a predominant secondary U compound after primary Ca-U(VI) oxides. The phase was studied by single-crystal XRD, SEM/EDX and electron microprobe (EPMA) analyses and Raman spectroscopy. It is a non-crystalline phase with a specific finger-like microtexture consisting of thin (no wider than 1–2 μm) lamellar particles. Its Raman spectrum shows a single strong band at 706–713 cm^?1, sometimes coexisting with up to three weak diffuse bands (ν ~?390, ~?540 and 1355–1400 cm^?1). The find of the natural X-phase (Ca₂UO₅·2-3H₂O) is evidence of its long-term stability in a natural environment. It proves explicitly that the compound Ca₂UO₅·nH₂O is a solubility-limiting phase in aged cements. The results have implications for geological disposal of radioactive wastes.     

Synthetic Gold Chalcogenides in the Au–Te–Se–S System and Their Natural Analogs

Doklady Earth Sciences - Quaternary chalcogenides of AuX (AuTe0.7Se0.2S0.1), Au3X10 (Au3Te6Se3S, Au3Te6Se2.5S1.5), and AuX2 (AuTe1.8Se0.2, AuTe1.8Se0.1S0.1) composition were synthesized for the...     

230Th/U Dating of Travertines Related to Paleoearthquakes in Gorny Altai: First Results

Doklady Earth Sciences - First 230Th/U-dating results have been obtained for six Quaternary travertine deposits from the southeastern Gorny Altai associated with zones of active faults that bound...     

Isotopic composition of pyritic sulfur from the mud volcanic ejecta in Azerbaijan

Geochemical studies of pyrite crystals from the mud volcanic ejecta in Azerbaijan were studied. It is shown that all of them have cubic shape. Determination of the sulfur isotope composition revealed a wide variation range of δ³⁴S values from–27.0 to +26.4‰. Signs of spatial zonation were recorded in the distribution of δ³⁴S values—lower values are confined to the present-day coastline of the Caspian Sea. Appearance of pyrite with a high share of ³⁴S is attributed to sulfate reduction that takes place in an environment with excess organic matter. It is supposed that the isotopically heavy sulfides represent the “neck” facies that are formed at the periphery of mud volcanic conduits at the contact of the hydrocarbon-rich mud volcanic fluids with stratal waters of host sediments.     

Gas reservoirs in the Dead Sea area: evidence from chemistry of combustion metamorphic rocks in Nabi Musa fossil mud volcano

Nabi Musa located at the northern tip of the Dead Sea at 31°48′ N, 35°25′ E is one of fifteen complexes of the Hatrurim Formation or the so-called “Mottled Zone” (MZ) which are fossil mud volcanoes. Self ignition of methane during their eruptions in the Middle–Late Pleistocene caused combustion metamorphism of sediments. Melting foci have been discovered in two craters of Nabi Musa volcano, with numerous veins of paralavas having particular calcic-silicic compositions (Ca₂SiO₄- and CaSiO₃-normative). Their major- and trace-element spectra bear signature of a mixed sedimentary protolith consisting of Cretaceous marine carbonates, marl, and quartz sand. The paralavas inherit high Sr, P, and U enrichments, positive La/La* and Y anomalies, and a negative Ce/Ce* anomaly from calcareous marine sediments, including bituminous and apatite-rich chalks. The presence of quartz arenite in the protolith is responsible for relatively high Ti, Nb, Zr, and Hf while the marl pelitic component accounts for MREE and LREE depletion. The suggested mixing models predict that the Nabi Musa paralavas result from combustion metamorphism of a sediment mixture with 53–60 wt.% chalk, 5–14 wt.% marl, and 27–44 wt.% quartz arenite. The history of mud volcanism at Nabi Musa began with small eruptions that mobilized gas and water from shallow (within 300 m) Turonian carbonate aquifers, and later explosive activity triggered violent gas blowouts from the older terrigenous reservoir of Aptian–Albian Nubian-type sandstone lying as deep as 1300–1500 m.