THE GEOLOGY OF THE AAPPALUTTOQ RUBY AND PINK SAPPHIRE DEPOSIT, SW GREENLAND

The gem corundum deposits of southwest Greenland lie within the Archean (2970 Ma) aged Fiskenaesset Anorthosite Complex. This layered igneous intrusion spans several hundred kilometres across southwest Greenland and forms part of the North Atlantic Craton. The gem corundum deposits are stratigraphically located within the Middle Gabbro layered sequences, and lie in a contact zone between an ultramafic unit, a meta-leucogabbro and a meta-melanogabbro. Each unit is distinctive in its mineralogy and structure, with the essential corundum chromophore (Cr) most likely mobilized from the ultramafic units. Regional prograde granulite facies metamorphism and the metasomatism connected to the amphibolite facies retrogressive cooling can be observed in the mineral assemblages throughout the area. A metamorphic-metasomatic aureole developed along the outer contacts of the ultramafic unit, creating a 5-10 m thick sheet of phlogopite-biotite rich rock grading over 350 g/T corundum.

Aappaluttoq is believed to be the largest geologically defined ruby and pink sapphire deposit in the world at this time, with over 400 million carats of corundum within 65 m of the surface. The mine recently received permission to open from the Greenland Government, and formal gemstone production is expected in late 2014 or early 2015. The use of modern geological exploration and 3D modelling has enabled the reasonable prediction of ruby and sapphire distribution, grade and tonnage within the deposit as it moves into production.

This study presents the first geological characterization of the Aappaluttoq deposit and will outline the deposit lithologies, structures and mineralization along with the major and trace element geochemical and geochronological results. The host rocks and the mineralization within the deposits are rare and unusual, and are unlike the traditional gem corundum deposits in the rest of the world. Studies continue to evaluate and understand the link between the regional metamorphism and the formation of the gem corundum, as well as investigating the geology of the other deposits that lie directly along strike from Aappaluttoq.