The Hjelmkona ultramafic body crops out in upper amphibolite facies rocks of the Basal Gneiss Complex of western Norway, dated at 1,700 m.y., and it consists dominantly of carbonate-bearing harzburgites (sagvandites) with associated chromitites. The earliest recognisable mineral assemblages (olivine plus orthopyroxene) are metamorphic in origin and have undergone late stage CO2-metasomatism. Similar rocks are found in high-grade metamorphic gneisses elsewhere in west Norway. The proposal is made that these distinctive types of ultramafic rocks are characteristic of much of the Basal Gneiss Complex and may provide a basis for correlation.
The petrography and possible regional significance of the Hjelmkona ultramafic body (Sagvandite), Nordmøre, Norway