Characterisation of the Nickel Sulphide Mineralisation between Graah Fjord and Bernstoff Isfjord, South-East Greenland. South-East Greenland Mineral Endowment Task Project, SEGMENT 2009-2014 [BSc thesis]

Laterally extensive mafic bands, hosting Ni-Cu sulphide mineralisation can be found throughout the orthogneiss which dominates the relatively unexplored region between Graah Fjord and Bernstorff Isfjord in South-East Greenland. The mafic bands are volatile-rich and are dominantly gabbroic in composition but they do show large variation, ranging from gabbros to pyroxene hornblende norites. The mafic bands display some similarities with the mafic complex of the Ivrea-Verbano Zone (IVZ) in Italy which is thought to represent lower crustal material. Amphibole-bearing ultramafic bodies can be found locally within the mafic bands. The ultramafic rocks are dominantly peridotites with a smaller volume of pegmatitic pyroxenites. It seems most likely that the mafic bands of this study represent lower crustal material intruded by mantle-sourced ultramafic magmas.

The ultramafic rocks can be subdivided into two generations based on their trace-element geochemistry. One generation was most likely sourced from a deep, relatively undepleted mantle source, while the other was sourced from a depleted shallow mantle source. The shallow sourced ultramafic rocks host the majority of the mineralisation and display evidence for having interacted with a volatile, incompatible element, S, Cu and Ni bearing fluid. This fluid is interpreted as a key factor in the formation of the mineralisation.

All of the rocks comprising the mafic bands show enrichment of incompatible elements with Nb depleted relative to K and La. This is interpreted as evidence that all of the lithotypes in the mafic bands have interacted with a second, incompatible element bearing, Nb depleted fluid.

The mineralisation in the study area most likely does not represent a typical orthomagmatic Ni sulphide system, which are usually controlled by processes at the site of emplacement including interaction with crustal material. Rather, this mineralisation is controlled by mantle fluid processes. Work is ongoing for the determination of the economic viability of this mineralisation.