Hydrothermal Overprint of the Chador-MaluKiruna-type Deposit (Bafq District, Central Iran) and Associated REE Mobilization: Evidence from Mineralogy and Geochemistry

This paper presents a discussion of possible mobilization of the apatite-hosted REE during hydrothermal overprint of the Chador-Malu Kiruna-type iron oxide-apatite deposit and their subsequent uptake by the adjacent actinolite-rich host rocks based on mineralogical and geochemical evidence. The formation of apatite-hosted monazite inclusions during apatite REE leaching is proposed to be a mineralogical control on REE mobility which would provide the HREE with a preferential opportunity for mobilization. Using a scanning electron microscope, it is shown that the apatite-hosted monazites are most abundant in the samples from the eastern periphery of the northern ore body having contact with a suite of actinolite-rich metasomatic rocks (metasomatites). The bulk REE patterns of the metasomatites closely associated with the monazite inclusion-rich ores shows elevated HREE patterns which would suggest the uptake of the mobilized HREE by these actinolite-rich host rocks. No significant LREE mobility could be interpreted from the REE patterns. The chloride-rich overprinting fluid compositions proposed by experimental studies and suggested for similar deposits at both the Kiruna and Bafq districts are consistent with the restricted REE mobility that could be interpreted from the bulk REE geochemistry of the host rock samples, and thus might be the case in the Chador-Malu iron oxide-apatite system.