Rare Earth Element Mineralisation in Apatite-Magnetite Veins of Kanyaluka Area, East Singhbhum District, Jharkhand: Insights from Petro-Mineralogy and Mineral Chemistry

ABSTRACT Iron-Oxide Apatite (IOA) deposits are a lesser known, yet significant source of Rare Earth Elements (REE), which occur in different geological settings of the world, temporally distributed from Archaean (e.g., Carajas province, Brazil) to Pliocene (e.g., El Laco, Chile). The most significant occurrence of IOA deposit in India is in the form of apatite-magnetite intrusions, along the Singhbhum Shear Zone (SSZ), located in the eastern part of the country. Apatite-magnetite veins, which host REE minerals such as xenotime, monazite and allanite, concordantly intrude the foliation planes of sericite-biotite-quartz schist of Chaibasa Formation of Singhbhum Group of rocks in Kanyaluka, located at the eastern part of SSZ. Paragenetic sequence derived from textural analysis indicates that the initial mineralisation episodes were dominated by REE minerals, while apatite and magnetite crystallised in the subsequent stages. Trace element concentration of magnetite was used to determine its formation environment, which revealed that they have a high temperature hydrothermal origin. Geothermometry carried out on monazite coexisting with xenotime indicated a mean formation temperature of 570° C, further reiterating the high temperature hydrothermal origin of the deposit. A possible mode of origin for the fluid can be attributed to a liquid immiscibility process. Earlier experiments have proved that it is possible to create two immiscible liquids, one rich in Fe-P, crystallises to form apatitemagnetite, and the other having a felsic composition from an originally Fe-rich parent magma under high oxygen fugacity conditions. The Fe-P-rich immiscible liquid can incorporate a relatively higher amount of REE from the parent magma due to its depolymerised nature compared to its felsic counterpart. An Fe-P-REE rich high temperature hydrothermal fluid formed by this process intruded the foliation planes of schistose rocks of Kanyaluka, which acted as pathways, forming the vein-type apatite-magnetite deposits.