The uranium ore sample used in this study occurs as hand-pickable lumps and grains in the Jogipalle pegmatite, Nellore Schist Belt, Andhra Pradesh. Powder X-ray diffraction (XRD) studies on separated uranium minerals (UMs) have revealed the presence of both primary (uraninite) and secondary (ianthinite, clarkeite, curite and â-uranophane) uranium minerals, which are mostly characterised by their sharply-defined reflections. The crystallographic parameters of various UMs are: Uraninite-1and 2 unit cell dimension (ao) = 5.4758 and 5.4422 Å and unit cell volume (V) = 164.08 and 161.18 Å3; clarkeite a0 = 3.9473 Å, b0 = 3.9473 Å, c0 = 17.6835 Å, α = β = 90°, γ = 120°, V = 238.628 Å3; curite a0 = 12.6292 Å, b0 = 13.2035 Å, c0 = 8.3646 Å, V = 1394.81 Å3; and βuranophane a0 = 13.9481 Å, b0 = 15.4688 Å, c0 = 6.6362 Å, α = γ = 90°, β = 91.3°, V = 1430.90 Å3. Out of two, one uraninite has ao of 5.4758 Å, which is more than the value given for the uraninite standard (5.4645 Å), suggesting its anomalous nature and formation of uraninite (primary) under high temperature condition (∼500–550°C). In contrast, another uraninite has ao = 5.4422 Å, reflecting its oxidized nature. It, thus, suggests that after their formation, the uraninites have been subjected to oxidation leading to the formation of secondary uranium minerals (SUMs) with a relict core of black mineral (uraninite) encircled by successive zones of SUMs, namely, black (ianthinite, in traces), orange (clarkeite-curite) and yellow (β-uranophane). Based on available mineralogical data, the inferred paragenetic sequence of the investigated uranium minerals is: Uranium oxide (primary uraninite) > uranium oxide (altered uraninite) > uranium oxide hydrate (ianthinite) > sodium-potassium uranium oxide (clarkeite) - lead-uranium oxide hydrate (curite) > calcium uranyl silicate hydroxide hydrate (β-uranophane). Uraninite-1 contains high U3O8 (74.25%), ThO2 (7.96%), PbO (7.73%) and rare earth elements (16214 ppm), whereas, SiO2 (1.03%), CaO (0.82%) and Fe2O3 (0.33%) contents are low. Chemically, â-uranophane analysed 47.42% U3O8, 4.75% CaO, and 19.15% SiO2.
X-ray diffraction, Mineralogy, Uraninite, Ianthinite, Clarkeite, Curite, β-Uranophane, Nellore Schist Belt, Andhra Pradesh, Paragenesis.
