Rare earth element and isotopic evidence for the genesis of the Prieska massive sulfide deposit, South Africa

Abstract

The Prieska orebody is contained in high-grade metamorphic peraluminous rocks. Birdwing-shaped rare earth element profiles and high epsilon Nd values are observed in rocks under the ore. These characteristics are interpreted to reflect an early magmatic-dominated alteration stage during which heavy rare earth elements and highly radiogenic Nd were added to the rocks. Rocks studied above the ore display normal rare earth element profiles and country-rock epsilon Nd . The generally high Mg/Fe ratios of all the altered rocks are thought to indicate pervasive late alteration by seawater-derived fluids. The alteration processes appear to be linked to the cooling of a hypothetical high-level intrusion derived from the depleted mantle. The existence of this type of magmatism is also indicated by the occurrence of amphibolites higher up in the sequence which have flat rare earth element profiles and high epsilon Nd .