Imaging Archaean-age whole mineral systems

Structural fabrics that cause seismic wave anisotropy within the lithospheric mantle of the Slave craton of northwest Canada are interpreted as fluid conduits that form a macroscopic-scale stockworks of metasomatised peridotite dykes within depleted harzburgitic mantle. These metasomatised peridotite conduits probably are composed of rocks such as pyroxenite or wehrlite and must occupy 10% of the mantle in order to explain this distinct anisotropy where it is present. Reduced mantle shear-wave speeds associated with these stockworks may prove diagnostic of their presence deep in the sub-continental lithospheric mantle. The former (and present?) fluid conduits have been hypothesized as source regions for diamonds and kimberlite magmas, and may also be metal-enriched regions. In order to form a whole mineral system, such stockworks of metasomatised mantle conduits must communicate with crustal conduits leading to near-surface mineral deposits. Seismic evidence for these conduits at all levels has been observed beneath a few major mining camps.

► Significant parts of subcontinental mantle lithosphere are carbonated and metasomatised.
► Seismic anisotropy and reduced wave speeds map metasomatism.
► Carbonated regions source kimberlites, host diamonds and may source metallogenic minerals.