Uranium-niobium-rich alteration products after “pisekite”, an intimate mixture of Y,REE,Nb,Ta,Ti-oxide minerals from the Obrazek I pegmatite, Pisek, Czech Republic

摘要: An improperly described association, further called "pisekite" aggregate, of fine-grained, mostly metamict U, Th-enriched Y, REE, Nb, Ta, Ti-oxide minerals from Obrazek I pegmatite, Pisek, forms an intimate mixture polycrase-(Y), samarskite-(Y) and fergusonite-(Y). It underwent a low-temperature hydrothermal alteration the products which are depleted in Y REE>U significantly enriched Si, As P. Two distinct assemblages secondary phases were recognized to be associated with namely (i) that developed within central parts aggregate (ii) pocket assemblage albite adjacent it. Both dominated by Fe-rich smectite. "Pisekite" is intensively replaced Ti, Fe, As, P-rich variable chemical composition: phase A (Nb>Ti>Fe>U>As) first assemblage, as well B (U similar Nb>Ti>As>P>Fe) C (U>Nb>As>Fe>Ti) second assemblage. Associated pharmacosiderite kahlerite/metakahlerite smectite indicate low temperature processes (less than 150-200 degrees C). Whereas was likely source Nb arsenopyrite host pegmatite yielded Fe. The textural features show replacement Nb-rich A, took place on micrometer scale, these highly heterogeneous represent nanoscale, possibly amorphous hydrated oxides, phosphates-arsenates silicates Fe Ca.