Magmatic platinum-nickel occurrences in the Tertiary West Greenland Basalt Province: prospecting by Greenex A/S in 1985-1988

Mafic and ultramafic magmas, which are potential carriers of Co, Ni and Cu and platinum group elements (PGE), were erupted in vast volumes in the West Greenland Basalt Province. Part of the magmas reacted with sulphur-rich carbonaceous sediments precipitating sulphide-rich liquid and metallic iron and produced Co, Ni, Cu and PGE bearing metallic iron and sulphide deposits which have been found in lavas and subvolcanic intrusions.

With this background Greenex A/S prospected for PGE ore deposits in 1985-1988. The prospecting comprised geophysical surveys, a panning programme and traditional geological field work. Traditional field work proved the most efficient to localize contaminated rocks in this generally well-exposed area: five contaminated lava sequences were traced throughout a large part of the Nugssuaq peninsula and some contaminated dykes were discovered. Ten new occurrences of metallic iron and sulphides were discovered - two in a lava on Nugssuaq and eight in dykes and subvolcanic intrusions on Disko. Among the geophysical methods employed, electromagnetic ground surveying was the most efficient for tracing subsurface mineralization.

A total of 288 grab and chip samples were analysed for Cr, Co, Ni, Cu and precious metals (Pt, Pd, Os, Ir, Ag and Au) which lead to identification of 16 Pt-Pd anomalies (>15 ppb Pt and >10 ppb Pd). Analyses from the most prominent and most intensely sampled occurrence, the Hammers Dal Complex, have a Pt/Ni ratio that is more than a factor 10 lower than previous records. This suggests that serious problems may be connected with sampling, preparation or analysis of the metallic iron bearing rocks.

Partial analyses (for TiO₂, MgO, Cr, Cu and Ni) of 314 rock samples from 26 profiles on Nugssuaq indicate a total volume of at least 200 km³ of contaminated lava. More than 50% of the samples are depleted for more than half of their initial Ni and Cu content by precipitation of sulphide or metallic iron. Because only a few samples are enriched in these elements, most of the extracted metals (PGE and more than 10 million tons of Ni) must occur at depth.