Mineralogy and geochemistry of pegmatites rich in REE, F and alkali metals associated with albite granite facies in the deposit of Sn-Nb-Ta- (F, REE, U, Th) Madeira (Pitinga mine, AM, Brazil)

According to the literature, the pegmatites of Madeira granite, located in the mining district of Pitinga (Amazonas, Brazil), belong to the albite granite facies. Previous studies have proposed that these pegmatitic bodies are associated with N320/60SW oriented faults and are rich in rare earth elements (REE). Due to this, the characterization of these pegmatites was carried out based on mineral chemistry and whole rock geochemistry. The paragenesis is composed of albite, microcline, quartz, polylithionite, riebeckite, fluoro-arfvedsonite, fluoro-eckermannite, cryolite, xenotime, gagarinite-(Y), hematite, zircon, pyrochlore, cassiterite, thorite, zircon, columbite, magnetite, galena, sphalerite and native bismuth. Based on the chemical composition and typical minerals, they were divided into: PEG ANF (medium K and Na, riebeckite and genthelvite), PEG POL (high K, polylithionite and xenotime) and PEG CRIO [high K, very rich in F; cryolite and gagarinite- (Y)]. Mineral chemistry data and structure of the major minerals of the pegmatites are presented and compared with those of the albite granite. The integration of mineralogical data with the geochemistry of the three types of pegmatites characterizes the hosting rock as the parent rock, records the enrichment in F, REE and elements of group 1 and allows following the chemical-mineralogical evolution of the albite granite giving rise to the late residual facies (PEG CRIO). (author)