Chemical indication of Florencite-(Y) occurrence at Bom Sucesso (Minas Gerais, Brazil)

2014-12-01T03:40:53Z (GMT) by Alexandre de Oliveira Chaves
<p></p><p>Florencite-(Y), synonymous with the discredited koivinite-(Y), represents a mineral species not recognized by International Mineralogical Association. Based on electron microprobe analyses, there is a chemical indication of the apparent occurrence of such mineral at Bom Sucesso (Minas Gerais State, Brazil). This supposed mineral species has been found in association with churchite-(Y) in 2.7 Ga potassic peraluminous foliated granitoid from the Archean core of the southern portion of the São Francisco Craton. The formula obtained for this probable yttrium florencite is (Y0.402Nd0.213La0.171Ca0.086Dy0.044Gd0.032Ce0.029Sm0.029Pr0.018Fe0.017Pb0.008Th0.001U0.001)Σ1.051Al3.002(P0.959Si0.039O4)2(OH)6.073. Regarding churchite-(Y), its formula is (Y0.475La0.184Nd0.123Ca0.055Gd0.043Dy0.029Sm0.028Pr0.023Fe0.017Ce0.016Al0.007Pb0.007U0.002Th0.002)Σ1.011(P0.984Si0.021)O4.2H2O. Given that the Bom Sucesso peraluminous granitoid shows no signs of argillic weathering of feldspars, it is suggested a primary origin for the apparent florencite-(Y), i.e., it has been formed during crystallization (or recrystallization) of the rock</p><p></p>