THE TOPAZ-ALBITE GRANITE AND RELATED ROCKS FROM THE SN-IN MINERALIZED ZONE OF MANGABEIRA GRANITIC MASSIF (GO, BRASIL)

MÁRCIA ABRAHÃO MOURA, NILSON FRANCISQUINI BOTELHO

Resumo


The Mangabeira Massif is part of the Goiás Tin Province and is constituted of an A-type Paleoproterozoic biotite granite, evolved granites and greisens. The Main Greisenized Zone of the massif (MGZ) is composed of the less evolved Li-siderophyllite g2d granite, the topaz-albite granite (TAG), Sn-mineralized greisens and a quartz-topaz rock, with anomalous indium contents (up to 0.4 wt%). Micas are important for the characterization of each facies and define a phengite-zinnwaldite series, so far only described in the Paranã Subprovince rocks. Late/post-magmatic processes affected the MGZ rocks, causing the mobility of many elements, except TiO2 , Ta and Th . The topaz-albite granite (TAG) is similar to the rare topaz granites and has derived from g2d granite by magmatic differentiation. TAG is subsolvus, leucocratic, equigranular, medium-grained and contains essential quartz, albite, topaz, microcline and zinnwaldite. Topaz occurs either as inclusions (20mm) in albite or as large subhedral grains. The accessory minerals are monazite, cassiterite, zircon and magnetite. In the Qz-Ab-Or system, TAG samples plot near the minimum for 0 wt. %F. Chemically TAG is characterized by molar Na/K mainly >1, A/CNK ratio between 1.3 and 1.5, high contents of F, Li, Al2 O3 , Rb, Zn and Sn and low TiO2 , MgO, P2 O5 , CaO, Zr, Ba and Sr. The granites REE pattern is flat with a pronounced Eu anomaly. The quartz-topaz rock occurs associated with the TAG and resembles topazites, interpreted as magmatic rocks in the literature, but it can also be the product of topaz-albite granite hydrothermal alteration. The rock also contains sphalerite, wolframite, löllingite, chalcopyrite, bismutinite, galena, stannite, tennantite, In minerals (yanomamite, roquesite and dzhalindite) and hydrated arsenates of Sn, U, Ba, K, Pb and Bi.

Palavras-chave


Topaz-albite granite; Topazite; Indium; Geochemistry; Goiás Tin Province.

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