Decades of research on the Skaergaard intrusion is now collected in two special editions of the GEUS Bulletin

Published 02-04-2024

All the latest data on the petrology and mineralogy of one of the most explored basaltic magma chambers in the world has now been compiled in two scientific publications.

The Skaergaard intrusion
The Skaergaard intrusion at the back with the characteristic ‘triple group’ – the three light layers of feldspar. (Photo: GEUS)

Continuous international collaboration, twenty tons of drill cores, decades of data collection and hundreds of scientific studies are behind two new monographs about mineral occurrence and petrology in the Skaergaard intrusion at the Kangerlussuaq fjord in East Greenland, published in the GEUS Bulletin.

“We have now collected so much data that we can make numerical modelling with a good degree of certainty and understand how the magma developed and the mineralisation was formed,” says one of the driving forces behind the research, Troels F.D. Nielsen, petrologist and emeritus at GEUS – Geological Survey of Denmark and Greenland.

The two special editions of the GEUS Bulletin consist of:

  • Modelling of the mineralisation in the Skaergaard intrusion
  • Descriptions and chemical data for minerals and rock types
  • Modelling of the petrogenetic development of the intrusion

Where did the gold and palladium come from?

Core samples from several decades of mineral exploration of the Skaergaard intrusion are the basis for the research that is now collected in the GEUS Bulletin. Drilling began properly in the mid-1980s, when a Canadian mining company was looking for precious metals in another intrusion 25 kilometres west of the Skaergaard intrusion, on the opposite side of the Kangerlussuaq fjord.

“One day there was fog in the fjord, and the helicopter couldn’t get over there. Instead, the geologists chose to collect samples in the Skaergaard intrusion. Two researchers from GEUS participated in the work,” recalls Troels F.D. Nielsen, who was head of the GEUS operations and has been doing research on the intrusion ever since.

The geologists collected small samples of sand and gravel – so-called ‘stream sediment samples’ – to analyse them.

“To everyone’s surprise, there was a high content of gold and palladium in one of the collected samples,” says Troels F.D. Nielsen

The question arose: Where did the precious metals come from?

“Most likely from a very special sequence of rocks characterised by three light layers filled with feldspar, also called ‘triple group’. The bright layers are visible on the mountainside from kilometres away,” says Troels F.D. Nielsen.

Concentrations of gold and palladium in the lower layers

The following year, the exploration company hired mountaineer geologists to collect samples. Secured with ropes, the geologists pounded small pieces of wood chips off the steep cliffs in continuous profiles.

Analyses of the chip samples confirmed that there is an unbroken layer of gold and palladium in the Skaergaard intrusion. And then the exploration took off: from 1989 to today, more and more cores have been drilled out. In some places, drilling has been done to a depth of approximately 1.3 kilometers to reach the mineralised layers.

The core samples are a large part of the basis for the petrological and mineralogical studies that are now collected in GEUS Bulletin’s special editions.

The mineralisation of gold and palladium is mapped

One of GEUS Bulletin’s special editions deals with the gold and palladium mineralisation in the Skaergaard intrusion.

For the past two decades, Troels F.D. Nielsen and his researcher colleagues collaborated with the company CNT Instruments LLC to investigate the precious metal minerals. The company has developed hydroseparator instruments and technologies that can concentrate the microscopic grains of precious metal found in the Skaergaard intrusion.

The publication ’The PGE-Au Mineralisation of the Skaergaard intrusion: precious metal minerals, petrography and ore genesis’ synthesises data from 30 mineralogical investigations. In addition, Troels F.D. Nielsen and the other authors are developing already published models for the mineralisation.

The researchers’ descriptions can be used in future exploration of precious metal deposits similar to the Skaergaard intrusion.

“When we know how the precious metals were formed in the Skaergaard intrusion, we know what to look for to find them elsewhere. All the processes that we describe leave footprints,” explains Troels F.D. Nielsen.

The petrology of the Skaergaard intrusion

The second of GEUS Bulletin’s special editions, ’Petrology of the Skaergaard Layered Series’, collects, interprets and models mineral and rock chemical analyses in a new standard profile up through the intrusion.

The first author is geologist Peter Thy, who is honorary professor at Aarhus Universit’s Department of Geosciences. He began his research in 2000.

“Previously, what we knew about the intrusion was poorly supported by data. With the work Peter Thy and his co-authors have carried out, the data base has been greatly increased and is much more detailed,” says Troels F.D. Nielsen.

The extensive amounts of data and background information have made it possible for Peter Thy and his co-authors to make a detailed record of crystallisation in the Skaergaard intrusion. Furthermore, they have managed to model the crystallisation processes in what is known in the world of geology as one of the most classic intrusions, says Troels F.D. Nielsen.

“The special edition also contains a large and very valuable appendix material with data and information about samples and other materials in museums and collections in Europe and North America,” he adds.

Troels F D Nielsen
Mapping and Mineral Resources
Anne Ringgaard
Communications Officer
Press and Communication

The scientific articles

GEUS Bulletin, volume 54; 2023: The PGE-Au Mineralisation of the Skaergaard intrusion: precious metal minerals, petrography and ore genesis

Authors: Nikolay S. Rudashevsky, Troels F.D. Nielsen, Vladimir N. Rudashevsky

Edited by Rune B.E. Larsen

GEUS Bulletin, volume 56; 2023: Petrology of the Skaergaard Layered Series

Authors: Peter Thy, Christian Tegner, Charles E. Lesher

Edited by Jakob K. Keiding

About the Skaergaard intrusion

The Skaergaard intrusion was formed around 56 million years ago and was discovered in 1931 by the British geologist Lawrence Wager. The intrusion consists of a suite of rock types from gabbro to ferrodiorite and finally granophyre.

In the past 80 years, investigations of the intrusion have set the tone and been central to the understanding of the petrology of igneous rocks, layering in intrusions, fractional crystallisation, magma differentiation and concentration of rare elements in magmatic systems.

The concentrations of gold and palladium are found through the lower of the three layers in the ‘triple group’ and are the result of a series of processes in the solidifying magma.

In addition to gold and palladium, the mineralisation contains titanium, copper and gallium. New minerals have also appeared in the Skaergaard intrusion, for example Skaergaardite (PdCu) and Nielsenite PdCu3, which is named after Troels F.D. Nielsen.