• Yamuna Singh

Articles written in Journal of Earth System Science

• Ianthinite: A rare hydrous uranium oxide mineral from Akkavaram, Andhra Pradesh, India

Ianthinite is the only known uranyl oxide hydrate mineral that contains both $U^{6+}$ and $U^{4+}$. For the first time, we report ianthinite from India (at Akkavaram, Andhra Pradesh), which is hosted in basement granitoids. The mineral occurs in the form of tiny grains, encrustations and coatings in intimate association with uraninite and uranophane. X-ray diffraction (XRD) data reveals that d-spacings of the investigated ianthinite are in close agreement with the corresponding values given for ianthinite standard in International Centre for Diffraction Data (ICDD) card no. 12-272. The crystallographic parameters of the studied ianthinite are: $a_{o} = 11.3$ (1) $Å, b_{o} = 7.19$ (3) Å and $c_{o} = 30.46$ (8) Å, with a unit cell volume of 2474 (27) Å3. The association of investigated ianthinite with uraninite suggests that the former has formed due to oxidation of the latter. Since a major part of the uraninite was exposed to oxidizing meteoric water, much of it has been transformed into hydrous uranium oxide (ianthinite) and very little part remained unaltered as uranium oxide (uraninite). Absence of schoepite in the investigated ianthinite suggests that after its formation it (ianthinite) was not exposed to oxygen/oxidizing meteoric water. As the oxidation was partial and short lived, some amount of primary uraninite is also preserved.

• Crystallochemical studies on davidite from Bichun, Jaipur District, Rajasthan, India

Crystallochemical data on metamict davidite from albitites and albitised rocks from the Bichun area (Jaipur district, Rajasthan, India) of Banded Gneissic Complex (BGC) are provided. Davidite occurs as euhedral, subhedral to anhedral crystals in the form of disseminated grains and also as fracture filled veins. The crystals of davidite are up to 8 cm in length and 6 cm in width. The powder X-ray diffraction (XRD) pattern of the heat-treated davidite (at 900◦C) reveals well-defined reflections of crystallographic planes. The calculated unit-cell parameters of the heat treated davidite are: a0 = b0 = 10.3556˚A and c0 = 20.9067˚A, with unit-cell volume (V) = 1941.6385˚A³; and α = β = 90◦ and γ = 120◦, which are in agreement with the values of davidite standard. Geochemical data reveals that the investigated davidite contains 51.5–52.6% TiO₂, 14.8–15.1% Fe₂O₃, 9.8–10.2% FeO, 6.97–7.12% U₃O₈, 6.72–6.92% RE₂O₃, 3.85–3.61% K₂O, 0.9–1.4% Al₂O₃, and 0.8–1.2% SiO₂. The calculated structural formulae of the two davidite crystals are: D-1: K0.0044/0.004Ba0.0044/0.005Ca0.20/0.20Na0.012/0.012Mn0.053/0.053Mg0.14/0.14Pb0.0076/0.008Fe2.675/2.675Fe1.59/1.59Y0.1175/0.118P0.053/0.053Nb0.008/0.008Sn0.001/0.001Zr0.033/0.033U0.468/0.468Th0.009/0.009REE0.6829/0.683)6.05/6.05(Ti12.15/12.15 Fe1.9022/1.903Si0.372/0.372 Al0.517/0.517 Cr0.018/0.018Co0.009/0.009Ni0.027/0.027)15/15O36/36(OH0.319/0.319[]1.681/1.681)2/2 and D-2: (K0.004/0.004Ba0.005/0.005Ca0.20/0.20Na0.012/0.012Mn0.05/0.05Mg0.094/0.094Pb0.007/0.007Fe2.58/2.58Fe1.71/1.71Y0.112/0.112P0.106/0.106Nb0.006/0.006Sn0.001/0.001Zr0.03/0.03U0.48/0.48Th0.009/0.009REE0.665/0.665)6.088/6.088(Ti12.48/12.48Fe1.87/1.87Si0.249/0.249Al0.334/0.334Cr0.019/0.019Co0.008/0.008Ni0.04/0.04)15/15O36/36(OH0.098/0.098[]1.90/1.90)2/2.The calculated structural formulae are not fully stoichiometric, which could be due to metamict nature of davidite. The characteristic feature of distribution pattern of REE in davidite is unusually high concentration of LREE and HREE and substantially low content of MREE. It may be due to the occupation of REEs in two distinct crystallographic sites in davidite structure, i.e., M(1) and M(O) sites. Chondrite-normalised plot of davidite reveals a pronounced negative Eu-anomaly (Eu/Eu∗ = 0.30−0.39), which suggests extremely fractionated nature of the metasomatising fluids from which davidite had crystallized. Metamict davidite-bearing U ores not only from Rajasthan, but also from other parts of India are likely to yield very high U leachability, thereby making them attractive sources of U, which otherwise are ignored by mineral engineers as uneconomic U ores.

• The first report on the chemical (Th–U–Pb) monazite age of the Mul granite pluton, Western Bastar craton, central India and its metallogenic significance

Petrography and the geochemical attributes of the studied Mul granite pluton reveal mixed characteristics of A-type and I-type within-plate granites consistent with an extensional tectonic environment. The dominance of the primary biotite over the primary muscovite suggests its meta-aluminous nature. The dating of monazite from the Mul granitoid pluton by the in situ Th–U–Pb electron probe micro analyser chemical method indicates the tectonomagmatic event around 1602 $\pm$ 27 Ma in the western Bastar craton, Chandrapur district, Maharashtra. The age data possibly represent the emplacement of large bodies of grey granite and attendant monazite crystallisation at $\sim$1600 Ma. This monazite age implies that Mesoproterozoic magmatism is coeval with the formation of the Pranhita Godavari rift in the eastern flank in Maharashtra and associated with the copper and barite mineralisation in Thanewasna and the adjoining areas.

• # Journal of Earth System Science

Current Issue
Volume 128 | Issue 8
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019