Rare earth element geochemistry as a prospecting tool

The recent development of inductively coupled plasma optical emission spectrometric methods for the rapid and cheap determination of rare earth elements (REE) has led to a realisation of the potential of REE geochemistry as a prospecting tool. Examples are given from the work in Southern Africa to illustrate some applications. The shape of chondrite-normalised REE profiles reflects the petrogenetic processes by which rock and ore samples are formed. Whereas igneous and hydrothermal processes fractionate REE, metamorphism and weathering have limited effects. REE geochemistry can be applied on both a regional and a detailed exploration level. On the regional scale it can be used to fingerprint ore-bearing formations or stratigraphic markers to delineate target areas. On the detailed scale of exploration the effects of hydrothermal alteration may be identified by a characteristic birdwing profile due to heavy REE enrichment, which accompanies both Cu-Zn massive sulphide and porphyry Au-Mo-W mineralization. Using this criterion, the genetic affinity of gossans may be tested and in other cases drilling targets may be selected by the delineation of hydrothermal conduits. 22 refs., 10 figs., 1 tab