Re-assessment of diamond potential for South Greenland

Johan Dahl Land in South Greenland is regarded to hold a potential for diamond prospecting based on its suitable geology that includes carbonatite-related (s.l.) intrusions, and previous findings of diamond-indicator minerals in sediment samples. Work in the mid-1990’s by ’Quadrant Resources’ and ’Major General Resources’ revealed some samples with diamond indicator minerals, primarily Cr-rich garnets and spinel, but also chrome-diopside, olivine, Mg-rich ilmenite and orthopyroxene. The positive indications from stream and lake sediments were not followed up on since the 1990’s, nor was an attempt made to tie indicator minerals to specific outcrops of carbonatite/lamprophyre/kimberlite intrusions.

This report summarises the results of new field work in 2021 by GEUS/MMR to the Johan Dahl Land area with the following tasks: (1) to re-collect and supplement sediment samples for diamond-indicator minerals, (2) to conduct reconnaissance with the aim to identify rocks of potential source character for indicator minerals, i.e., ultramafic lamprophyre-related intrusions, either in-situ or as floats, and (3) to visit the dykes and breccias in the island of Illutalik, to collect samples for laboratory testing – which would involve identification of possible mantle xenoliths or their alteration products and the possible occurrence of diamond indicator minerals.

The newly collected sediment samples were analysed for their content of diamond-indicator minerals. The samples were processing at SRC, Geoanalytical Laboratories Diamond Services in Saskatoon, Canada, followed by analysis at GEUS using Automated Quantitative Mineralogy maps to obtain the proportions and chemical compositions of the minerals. Out of 265 hand-picked mineral grains, none could be classified as diamond-indicator minerals: garnet (3 grains) classifies as G0 type; ilmenite (82 grains) is Mg-poor and plot away from the kimberlite field; diopside (16 grains) is Cr-absent; olivine (112 grains) is generally relatively Mg-poor (Mg# <76).

The present study does not confirm previous positive findings regarding diamond prospectivity in Johan Dahl Land, South Greenland. However, this does not invalidate the previously established potential due to several factors, including the limited sample size, small investigation area, intense rock alteration, and evidence of past magmatic activity. Despite challenges, South Greenland's tectonic setting and geological history indicate an underexplored but promising diamond potential. Future exploration should focus on identifying primary sources, such as lamprophyre or kimberlite intrusions, to assess economic viability.