Uncommon Nb-tantalate from the Cachoeira mine, Araçuaí pegmatite district (Minas Gerais)

Abstract

Important spodumene-rich pegmatites have been mined by CBL (Companhia Brasileira de Lítio, Brazilian Lithium Co.) at the Cachoeira mine (northeastern Minas Gerais state) since the 1990's. In this deposit, black platy crystals resembling columbitetantalite are also found; they were analyzed by electronic microprobe as part of the first author's master's degree dissertation. The Cachoeira pegmatite group comprises several spodumene-rich bodies that consist of pertitic microcline, spodumene (on average 23vol%), albite, quartz and muscovite, totalizing more than 95% of the bodies' volume. Analyses on 27 samples of supposedly Nb-tantalates showed a high variation of Ta, Nb and Sn contents, which has been observed inclusive in individual crystals, causing color variation on backscattered electrons images. Surprisingly, analyses on some grains also revealed the presence of ixiolite, a mineral species that has never been described in that region; it is characterized by high SnO 2 contents (up to ~16wt%). Columbite-(Fe) phase represents 42% of total Nb-tantalates analyzed samples, tantalite-(Fe) 19%, columbite-(Mn) 3% and ixiolite, 36%. Cassiterite, also observed, shows significant Ta 2 O 5 contents, probably indicating general exsolution processes.

Main mafic and accessory mineralogy in granites and greisens from selected occurrences in the A-type Graciosa Province, S-SE Brazil, and petrological implications

“…In Brazil, CGM are found in pegmatites from the Lourenço-Amapá Province (Melcher et al, 2015), Seridó Belt -Borborema Province (Beurlen et al, 2005;Baumgartner et al, 2006) and from São João do Rei and Araçuaí districts -Mina Gerais State (Francesconi, 1972 andDias andChaves, 2015, respectively). Abundant columbite was reported in the massive cryolite zone from the Pitinga Mine -Amazonas State (Minuzzi et al, 2006;Bastos Neto et al, 2009).…”