The Fiskenaesset anorthosite complex was emplaced ~2970 Ma ago as multiple sills of magma and crystal mush into oceanic crust (tholeiitic basalts and gabbros), forming an association of ~550 m thick anorthosite, leucogabbro, gabbro and peridotite layers. The complex has a present strike length of ~200 km. It has been partly broken up during multiple deformations, and suffered amphibolite- to granulite facies metamorphism. Chromite-rich bands are common throughout the complex; sulphide-rich layers are generally rare.
In 2007, a joint project between Bureau of Minerals and Petroleum (BMP), Nuuk and GEUS with the purpose of evaluating the PGE potential of the Fiskenaesset anorthosite complex was initiated and field work has been carried out in 2008 and 2009. The project revealed elevated PGE contents in different parts of the complex. Seven profiles revealed PGEs in small but significant amounts throughout the ultrabasic rocks with a significant enrichment in a ~5 m thick reef, named Ghisler Reef, grading 690 ppb Pt, Pd and Au over 5 m with best values within the Reef of 2 ppm Pt, Pd and Au with 20 ppb Rh over 1 m. The PGE-bearing unit can be traced with intervals for ~5 km and an exposed thickness up to 50 m.
Ghisler Reef displays an unusual geochemical signature with near perfect correlation of Pt, Pd, Au and Cu with Bi. This geochemical signature is in good accordance with the observed presence of PGE-Bi bearing minerals such as froodite PdBi2, sobolevskite (Pd, Pt) Bi, insizwaite PtBi2, maslovite PtTeBi, michenerite (Pd, Pt) TeBi, keithconnite Pd1-x (Te, Bi), unnamed Cu3Pt3Bi4S10, electrum AuAg, native Ag, parkerite Ni3Bi2S2 and native Bi. Ghisler Reef has low contents of sulphur.
The association of PGE with bismuth is seen in deposits such as Sudbury, Great Dyke and Monchegorsk intrusion on Kola Peninsula.
The discovery of ultrabasic rocks highly enriched in PGE has opened up parts of the 200 km long Fiskenaesset anorthosite complex for finding economic PGE deposits. The investigated area is situated next to the sea with excellent access for larger vessels.
A comprehensive report on the available data can be purchased from GEUS.
Discovery of new PGE mineralization in the Precambrian Fiskenaesset anorthosite complex, West Greenland. By P. W. U. Appel, O. Dahl, P. Kalvig & A. Polat. Danmarks og Grønlands Geologiske Undersøgelse Rapport 2010/29, 42 pp. + CD-rom.
For further information please contact Peter Appel pa@geus.dk