Formation of baotite in alcaline rocks of a moraine of Dara-i-Pioz glacier, Tadjikistan
Karpenko, Vladimir; Pautov, Leonid
published: Oct 21, 2002
Unusual baotite aggregates were found among boulders, bearing alcaline mineralization at a moraine of the Dara-i-Pioz glacier, Tadjikistan. Baotite forms intergrowths with barylite and berezanskite (association #1) and with quartz in tienshanite (Tn), as well as radial needle splitted crystals in tienshanite voids (association #2). Electron microprobe analysis gives (wt %, assoc. #1/assoc. #2): SiO2 15.65/15.80, TiO2 41.05/36.97, Nb2O5 0.72/2.70, Fe2O3 0.33/1.21, Al2O3 0.14/1.21, PbO 1.39/-, BaO 37.96/38.14, Cl 2.46/2.29, MnO, CaO, Na2O, K2O - traces, total 99.24/98.17. Optically uniaxial, positive, ω = 1.940(5), ε > 2.00. Six strongest lines in the X-ray powder diffraction pattern are (dobs., I): 3.73(6), 3.52(6), 3.32(8), 2.92(5), 2.236(10), 1.334(4). The origin of the baotite (Baot), associated with tienshanite (Tn) appears to result from the hydrothermal alteration. A possible reaction is:8Tn + Cl- = 1Baot + 44Qv + 8(2Na+, Mn+2, 2B+3, 5.5O-2).