Provinces of ultramafic lamprophyre dykes, kimberlite dykes and carbonatite in West Greenland characterised by minerals and chemical components in surface media

This paper reports the results of studies undertaken to interpret the vast amount of chemical data for kimberlite indicator minerals in glacial overburden (ca. 96 000 grain analyses) acquired during diamond exploration within the Archaean craton of southern West Greenland. In particular, the studies and interpretations relate to the Neoproterozoic magmatic province, where abundant mineral grains from the diamond stability field have been recorded, but where the abundance and distribution patterns within the province were not readily understood in the light of known dyke distribution. Chemical data of indicator minerals from known dykes and from surrounding glacial overburden together with field observations allow us to conclude that the indicator minerals in the overburden are of local origin and that dyke emplacement patterns, local topography and glacial processes determine the efficiency of grain dispersal. Many new dyke occurrences were found during sampling and follow-up of kimberlite indicator minerals. Pronounced regional differences in the variation of chemical composition of indicator mineral grains from both overburden and rock are related to known differences in crustal lithology, magma compositions and lithosphere stratigraphy, and we argue that the latter is the main reason for chemical differences. The implication is that the mineral grains recovered from overburden samples, besides having proved their value in diamond exploration, contain much information of interest for investigations of the nature of the lithosphere.