ORIGIN OF RARE-EARTH ELEMENT-ENRICHED HEMATITE BRECCIAS AT THE OLYMPIC-DAM CU-U-AU-AG DEPOSIT, ROXBY DOWNS, SOUTH AUSTRALIA

Hematite breccias, the host rocks to Cu-U-Au-Ag ore at the Olympic Dam deposit, occur as steeply dipping, northwest-striking, dikelike bodies within fractured granite. The breccia complex has a strike length of over 5 km and extends to depths greater than 1 km. Both the deposit as a whole and the individual breccia bodies are zoned from weakly brecciated, sericitized and hematized granite on the margins, through heterolithic breccias, to hematite-quartz microbreccia at the center. The breccias are highly enriched in light (LREE) and heavy rare earth elements (HREE) (avg = ~5000 ppm REE in hematite-rich rocks). Five hydrothermal REE phases have been identified: bastnaesite, florencite, monazite, xenotime, and britholite(?). The hematite breccias formed by progressive hydrothermal brecciation and iron metasomatism of the granite host. -from Authors