The distribution of Cu across three basaltic lava flows from the Faeroe Islands

The distribution of Cu across lava flows has been investigated by using a combination of several different analytical methods on samples taken along two profiles across each of three flows: one from the lower series, one from the middle series, and one from the upper series of the Faeroe Islands basalts. The profiles comprise 97 samples, all of which have been investigated by X-ray fluorescence analysis, atomic absorption analysis, and microscopic analysis. Furthermore some of the samples have been investigated by microchemical analysis, spectral analysis, and electron microprobe analysis. Spectral analysis has also been carried out on separates from selected samples. The total amount of Cu present in the samples has been determined by X-ray fluorescence analysis. The amount of Cu lattice-bound in Fe-Ti-oxides, pyroxenes and plagioclases has been determined as the difference between total Cu and Cu values obtained by atomic absorption analysis carried out on solutions obtained by using weak solvents which do not dissolve lattice-bound Cu in minerals not having Cu as a major element. Electron microprobe analysis has shown that the amount of Cu lattice-bound in Fe-Ti-oxides, pyroxenes and plagioclases increases with increasing oxidation, with an abrupt increase coincident with the formation of pseudobrookite. Where pseudobrookite is present most of the Cu is lattice-bound, but where the oxidation during initial cooling has not resulted in the formation of pseudobrookite, most of the Cu ends up loosely held in the rock in the same manner as cations in zeolites, but in many of the samples a smaller part of the Cu forms native copper and Cu-bearing sulphides.