Enrichment of heavy REE and Th in carbonatite-derived fenite breccia

Abstract Enrichment of the heavy rare earth elements (HREE) in carbonatites is as carbonatite petrogenesis favours light (L)REE. We describe HREE enrichment fenitized phonolite breccia, focusing on small satellite occurrences 1–2 km from Songwe Hill carbonatite, Malawi. Within breccia groundmass, a HREE-bearing mineral assemblage comprises xenotime, zircon, anatase/rutile and minor huttonite/thorite, well fluorite apatite. A genetic link between mineralization emplacement indicated by presence Sr-bearing carbonate veins, xenoliths extensive fenitization. propose that are retained hydrothermal fluids which residually derived after precipitation LREE minerals. Brecciation provides conduit for such fluids, enabling transport xenotime fenite. Continued fluid–rock interaction leads to dissolution minerals further huttonite/thorite. At maximum Y content 3100 µg g ?1 , concentrations presented example not sufficient constitute ore, but similar composition texture these rocks other cases carbonatite-related suggests all form via common mechanism linked Precipitation only occurs where pre-existing structure fenitizing reducing fluid – country-rock interaction. Th fenite serves an indicator expulsion may indicate within source body at depth.