Mineralogy and genesis of the Skaergaard PGE-Au Mineralisation

The Skaergaard intrusion, East Greenland, hosts a large-tonnage but low-grade platinum-group element and gold mineralisation, and is a world-renowned laboratory for understanding igneous processes. GEUS actively collaborates with researchers at leading universities in the EU and US to advance the understanding of both this deposit and fundamental processes in layered mafic intrusions.

Minerals have been concentrated from many drill-core samples, photographed, measured and analysed to have a complete picture of the mineralogical and petrographic relations.

Gabbro Fjeld in the Skaergaard intrusion with three distinct leucocratic layers in the upper half of the mountain. The Skaergaard PGE-Au mineralisation is hosted in the gabbros that include the lower two leucograbbro layers. 

The mineralisation is modelled as the result of crystallisation and sulphide saturation in mush zones of the intrusion and concentration of precious metals in droplets of sulphides melt, followed by transportation to the floor of the magma chamber. At the floor, sulphides reacted with residing Fe-rich melt.

Re-dissolved precious metals were subsequently redistributed into a complex syn-magmatic structure. The structure of the mineralisation is based on identification and correlations of lithological, geochemical and mineralogical markers in up to forty-one drill cores and additional chip-line profiles.

The mineralogy is in central parts of the intrusion dominated by two minerals that compare in structure, tetra auricupride (AuCu) and skaergaardite (PdCu). The Skaergaard intrusion is the type locality for skaergaardite (PdCu) as well as nielsenite (PdCu3). The precious metal parageneses exhibit lateral variations with PGE sulphides on the western margin towards the Archaean basement and palladium plumbites (zvyagintsevite, Pd3Pb) on the margin to the contemporaneous Palaeogene lavas.

Detailed knowledge of the precious metal mineralogy is of major importance for the development of exploitation methods.

Cu-rich sulphide globule in titaniferous magnetite with precious metal telluride.
Euhedral crystal of Skaergaardite (sk, PdCu) in sulphide globule and euhedral crystal of tetra auricupride with Cu-sulphide. The two phases contain most of the precious metals contained in the Skaergaard PGE-Au mineralisation.

Troels F D Nielsen

Petrology and Economic Geology
Phone: +45 91333886