Mineralogy and Geochemistry of granitic pegmatite, Lichenhills, Outback Nunatak, North Victoria land, Antarctica

Abstract

Pegmatite is Macrocrystalline rock and composition of rock forming minerals is similar to granite. Tourmaline is boron-rich mineral which is much content in pegmatite. General chemical formula is XY3Z6Si6B3O27(OH,O,F)4. Tourmaline have useful information about the environment and conditions of deposition. And significance of petrogenetic indicator recently has gained more attention. Besides, variability in its crystal-chemistry reflects physical and chemical changes during crystallization.(Henry and Guidotti et al., 1985

Jolliff et al., 1986). The study area is located in Lichen hills and Outback Nunatak, North Victoria land, Antarctica. Lichenhills rocks are composed of granitoids, leucogranites and dolerites. Outback nunatak rocks are composed of granitic pegmatite and Precambrian schist. So, Igneous rocks of Outback Nunatak and igneous rock of Lichenhills are from same Granite habour Intrusive, but origin is little bit different. Lichen hills' rocks are more close to S-type rather than Outback nunataks. In Outback nunataks pegamatie, tourmaline is well discovered. Due to chemical difference, zoning is well developed on 001 side of macrocrystalline tourmaline. These tourmalines belong to schorl-elbaite solid solution and which indicate that Li, Mg contents is poor, Al, Fe contents is abundant when tourmaline were formed. Ferrischorl (ferric oxide)substitution (Fe3+Al-1) from core to rim occur. This means oxidation state of hydrothermal fluid increase at late period making rim of tourmaline. This can be done by mixture of hydrothermal fluid or supergene water which is more oxidizing fluid or boiling of hydrothermal fluid.