Fluorapatite from alkaline pegmatites of the Kerala Khondalite Belt: A petrologic and fluid inclusion study

We report the occurrence of primary apatite crystals in association with graphite within alkaline pegmatite dykes in the Kerala Khondalite Belt (KKB). Petrologic and X-ray diffraction studies identify the mineral to be fluorapatite. Fluid inclusion studies show that the fluorapatites contain abundant CO₂-rich inclusions with densities in the range of 0.85-0.72 gcm^-3. A subsequent generation of trail-bound CO₂-H₂O inclusions with low salinity were entrapped along hydraulic cracks. The abundance of CO₂-rich inclusions, and the intimate association of fluorapatite with fluid-precipitated graphite suggest that the pegmatite dykes hosting fluorapatite were rich in CO₂-dominated fluids. We identify that among the magmatic conduits proposed for the transfer of CO₂-rich fluids in granulite processes in the KKB, the fluorapatite and graphite bearing pegmatites reported in this study form important examples.