| Summary: | This study investigates the distribution and characteristics of apatite and other REE-bearing phases within the Fabian ore body, part of the Malmberget apatite iron oxide (AIO) deposit. Six diamond drill cores intersecting the ore body were logged with a focus on apatite characteristics. Samples were then selected for further analyses, including optical microscopy, Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA) and Single Cell Inductively Coupled Plasma Mass Spectrometry (SC-ICPMS). Apatite in AIO deposits has long been recognised for its elevated LREE content. SC-ICPMS of the apatite from the Fabian ore body yields an average concentration of ΣREE (La-Lu) of 0.57%. The apatite in Fabian exhibits elevated Cl content in comparison to other AIO deposits in the Norrbotten ore district, possibly due to a higher metamorphic grade. Particularly high Cl contents were observed in larger apatite grains located within the wall rock, beyond the ore sections. Elevated Si and Na concentrations in apatite suggest a substitution trend, most pronounced in larger apatite grains (~0.1–0.5 cm) disseminated in the ore and in apatite within the wall rock. No discernible spatial correlation in LREE content for analytical points at the core and rims of apatite grains was observed, although variations within individual grains are evident. However, SC-ICPMS measurements revealed a tendency for most grains to be more enriched in REEs at the core compared to the rim. Monazite frequently occurs as inclusions within apatite or along the grain boundaries, averaging 56.6% (La-Lu). Titanite exhibits two distinct domains: an inner domain with ΣREE (La-Lu) content of 1.1% and an outer domain with 0.41%. The presence of these minerals, along with other likely REE-bearing phases, contributes to the overall REE enrichment in the Fabian ore body.
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