The Aappaluttoq mine is underlain by an Archean aged anorthosite complex; this comprises multiple layers of mafic to ultramafic rocks that are orientated in a near vertical manner. The ruby and sapphire mineralization is located in a reaction zone between a melanogabbro and a leucogabbro. These rocks have undergone significant alteration and metasomatism at upper amphibolite to granulite facies; the gem corundum is hosted in two rocks – the first is a highly micaceous unit rich in Cr, the second is an altered leucocratic gabbro. These units form steeply dipping mineralized sheets that have been traced with drilling to depths of 230m; the deposit is open to depth and along strike.
A regional geological trend encompasses the rocks at Aappaluttoq; the so called ‘Ruby Island Line’ has multiple surface expressions of gem corundum mineralization within the same rock package as Aappaluttoq. This trend has a surface strike length of over 10kms, secondary trends exist at the advanced exploration sites Siggartartulik and Kigutilik; it is unclear if these lie on a continuation of the Ruby Island Line, or if multiple horizons within the layered anorthosite complex host corundum mineralization.
The phlogopitite primary ore at the Aappaluttoq mine contains corundum that is relatively free and easy to extract; the secondary gabbroic ore is stronger and this makes extraction without breaking the stones relatively difficult. Of the total corundum resource approximately 5% of the material extracted is high-end gem grade, approximately 20% is ‘near-gem’ this is material that contains inclusions, and roughly the remaining 75% of production is classed as ‘commercial’ quality goods.