Copper isotope ratios are an important tool in tracing the sources and pathways of base metal forming fluids in the crust. Copper in Earth’s crust ultimately comes from the mantle, yet, our understanding of the distribution and concentration of copper and its isotopes within the lithospheric mantle, a source of ore forming fluids, is limited.
We present a study of copper concentration and isotope compositions from mantle xenoliths sampled on the Slave Craton (Diavik) and the Superior Craton (Kirkland Lake and Wawa), allowing us to characterize Cu values in peridotites formed in the Meso- to Neoarchean that were affected by subsequent metasomatism. Cu concentrations were measured in olivine by LA-ICPMS, whereas Cu isotopes were determined from bulk rock powders via solution MC-ICPMS.
Olivine copper contents show a strong temperature dependence (0.4 to 10.5 ppm), while the isotope ratios vary significantly, between -0.59 and 0.56 ‰. A distinct correlation of copper content with depth is observed in both cratons, where the highest concentrations occur at the base of the lithosphere. Initial results also suggest that the Cu isotope ratios exceed the known range for non metasomatized peridotites and are positively correlated with the Cu concentration, as well as 187Os/186Os.