INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
CATION PARTITIONING BETWEEN MINERALS OF THE TRIPHYLITE ± GRAFTONITE ± SARCOPSIDE ASSOCIATION IN GRANITIC PEGMATITES
RODA-ROBLES E.; GALLISKI M. A.; NIZAMOFF, J.; SIMMONS W.; KELLER P.; FALSTER A.; HATERT F.
Simposio; 5th International Symposium on Granitic Pegmatites; 2011
Phosphates of the graftonite-beusite (Fe2+,Mn2+,Ca)3(PO4)2, and the triphylite-lithiophiliteLi(Fe2+,Mn2+)PO4 solid-solution series, as well as sarcopside (Fe2+,Mn2+,Mg)3(PO4)2, are primary phases that frequently occur together in intimate intergrowths in some granitic pegmatites. These and other phosphates generally appear in the intermediate zones and/or core margin of the pegmatites, mainly in nodules that vary widely in size range, from a few millimeters up to ~ 2m in diameter. Most commonly, silicates are absent or scarce inside these nodules, with quartz, muscovite and plagioclase the most commonly observed. Nevertheless, it is not unusual to observe some Fe-Mn-Mg-rich silicates, such as tourmaline, biotite and/or garnet, in close contact with these phosphates. Despite studies on this phosphate association, which are relatively numerous, genetic relationships between these minerals are not fully understood. Consequently, phosphate assemblages from 11 pegmatites - Cañada, Pereña, La Fregeneda (Spain); Nossa Senhora de la Assunçao (Portugal); Cema, Santa Ana, La Empleada (Argentina); Boavista (Brasil); Palermo#1 (USA); and Tsaobismund, Abbabis (Namibia) - have been tested for cation partitioningof Fe-Mn-Mg by electron microprobe techniques, in order to determine some evidence for their genetic relationships, and for a discussion of pegmatite evolution in general. In this study we present the petrographic results and the preliminary data on partitioning of Fe-Mn-Mg between these phases.