Targeting: Prospectivity mapping for orogenic gold in South-East Greenland

To support new activities in mineral exploration and to exploit the new knowledge from recently acquired geochemical and geophysical data from South-East Greenland, it was decided to carry out a regional reconnaissance-scale prospectivity analysis. For this a mineral system approach for orogenic gold mineralisation was used in an integration of geological-geochemical-geophysical studies carried out by fuzzy logic methods.

The study area in South-East Greenland encompasses the Archaean North Atlantic Craton (NAC; 62°–64°30’N) and the Palaeoproterozoic Nagssugtoqidian Orogen (also referred to as the Ammassalik Mobile Belt; 64°30’–66°N), including part of the northern Archaean foreland that mostly comprising rocks from the Rae Craton to the north. To the south, the study area is affected by deformation and intrusives of the Palaeoproterozoic Ketilidian Mobile Belt. The lower crustal, predominately mafic-ultramafic granulites, and the orthogneisses of the NAC are named the Thrym Complex. This complex is characterised by intrusions of the 2785–2664 Ma Skjoldungen Alkaline Province (SAP). The main deformation events and stages within the craton are named the Timmiarmiut (>2700 Ma) and Skjoldungen (2790-2700 Ma) Orogenies. The Palaeoproterozoic Nagssugtoqidian Orogen in southern East-Greenland comprises reworked Archaean rocks from both cratons, as well as slivers and belts of Palaeoproterozoic formed meta-volcanic, meta-sedimentary and intrusive rocks. Based on differences in lithologies and tectonometamorphic history, the orogen is divided into four terranes from south to the north. These are: the Isortoq Terrane, the Ammassalik Intrusive Complex (AIC), the Kuummiut Terrane and the Schweizerland Terrane. The orogenic events include subductions and magmatic arc-related magmatism as well as the formation of supracrustal successions. Later post-orogenic ~1670 to 1600 Ma granites and diorites occur within both the Kuummiut and Isortoq terranes. Nickel-copper±platinum group elements±gold sulphide mineralisation occurs in the Thrym Complex and within the AIC, and iron-vanadium-oxide mineralisation occur within mafic intrusions of the SAP. Graphite mineralisation occurs within the surpracrustal successions in the Kuummuit Terrane and gemstones in the form of corundum occur in association with ultramafic in the Isortoq Terrane. To date, no in-situ gold mineralisations have been found in the study area. However, for the Palaeoproterozoic orogenic part of the study area, a relatively high number of gold-bearing samples have been acquired within the public hunt for mineral program, Ujarassiorit, and a couple of areas stand as being anomalous in gold and pathfinder elements for gold. No indication of gold exists within the cratonic part of the study area.

In this prospectivity study, the mineral system models for orogenic gold were assessed and targeting elements, which may mirror certain geological processes of the gold mineralising system, were selected. The geological, geochemical and geophysical data were processed and a number of evidential datasets and maps believed to reflect the target elements was produced. The targeting maps were integrated by the use of a knowledge-driven fuzzy logic model. The results of the resulting prospectivity analysis were finally briefly discussed and the limitations, uncertainties and technical aspects of this work were summaries.