HISTORY OF THE ROCKS

Greenland is the world’s largest island. It covers 2,186,00 sq. km. The vast inland ice blankets roughly 80% of the total area. The surface geology can only be studied in the ice-free zone, as much as to 250 km. wide, skirting the ice cap. This coastal strip of virtually bare rock (roughly 75% remains exposed) covers 383,600 sq. km., approximately the area of the British Isles.

Geologically, Greenland likely is a break-away fragment of the North American continent. The dominant rocks consist of gneisses and granites that make up the stable continental core, or craton. In places, the craton has a cover of flat-lying, layered sedimentary and volcanic rocks. The gneisses and granites are often interbanded with layers of metamorphosed sediments and volcanics.

After the craton was formed in Precambrian time, a succession of younger rock formations was deposited, mainly in sedimentary basins near the margins of the continent.

Continuous subsidence of the basins (1.2 to 0.4 billion years) led to extensive accumulations of sediments many kilometres in thickness in some regions. A younger group of basins (380 to 60 million years) contain marine and fluvial sediments.

North and East Greenland contain continental margin fold belts (420 to 350 million years). In these fold belts, the mountain-building processes affected not only the young sediments but also parts of the Precambrian crystalline rock units. These new crustal belts were welded onto the old Precambrian craton.

The subsequent geological history was one of relative stability, characterized by shallow marine sedimentation. These sediments are preserved in the present coastal areas of East and central West Greenland and extend offshore on to the shelf regions surrounding Greenland.

During the separation of Greenland from North America and Europe 60 million years ago, enormous volumes of basaltic lavas were extruded in the rift zones. Parts of these lavas make up the several-kilometre-thick lava sequences now found in central East and central West Greenland.

Previous mining activity has taken place at Ivittuut, where cryolite was mined from Proterozoic rocks in southern Greenland by open pit from 1858 to 1987. The famous Black Angel mine on the west coast of Maarmorilik was in operation from 1973 to 1990 and produced, from a Proterozoic marble host, more than 11 million tons of ore grading 16.6% zinc/lead combined. On the east coast, the Blyklippen produced more than half a million tons grading 19% lead/zinc from Palaeozoic veins. Significant occurrences of a wide range of metallic and industrial minerals are known scattered through the full suite of rocks in Greenland.