Chemical and mineralogical characterization of cassiterite and columbite-(Fe) associated to the São Miguel Granite, Biguaçu Region, Santa Catarina State, Brazil

Columbite-(Fe) and cassiterite are associated with the Biguaçu facies of the São Miguel Granite, which is enriched in rare metals. Two sources are proposed for the generation of these minerals: one directly associated with greizenized granite, responsible for the formation of crystals ≤ 0.25 mm and another considered as derived from greisens and/or small greizenized quartz veins that would produce grains ~ 2.0 mm. Columbite-(Fe) disseminated in rock, with and without evidence of deformation, points to two stages of crystallization of the mineral: magmatic and hydrothermal-metasomatic, the latter being post-tectonic. Variations in chemical composition and types of inclusions in cassiterite and columbite reinforce the hypothesis of more than one mineralizing phase and source. In terms of spatial distribution, it was observed that the cassiterite crystals in the northern part of the region present lower SnO₂ and higher FeO compared to those found in the southern part. The contents of Nb₂O₅ (~ 66.0%) and Ta₂O₅ (~ 12.8%) of columbite-(Fe) in the northern part differ from those in the southern part (Nb₂O₅ ~ 61.3% and Ta₂O₅ ~ 18.0%). The mineral inclusions in cassiterite are the same in both areas, except for the ilmenite and hafniferous zircon in the crystals of the northern and southern sector respectively. Although the cassiterite analyses do not accurately indicate the genesis of the mineral, the presence of crystals directly derived from the Biguaçu facies with Ta₂O₅ contents < 1.0% with inclusions of ilmenite and hafnium-rich zircon are likely indicators of a hydrothermal/metasomatic origin related to greisens. (author)