Geological environments and related Mineral Occurrences
Regional data compilations
West Greenland (66°-70°15') - the Palaeoproterozoic Nagssugtoqidian, Rinkian Orogen and the adjacent North Atlantic Craton
Background themes for Entire Greenland Geological Environments and related Mineral Occurrences
The main geological environments in Greenland and their mineral resources have been described in Stendal et al. (2005).
Greenland can be divided into four main geological environments, infracrustal regions, supracrustal regions, magmatic provinces, and sedimentary basins. Within these various geological environments characteristic, mineral deposits are presented. Four maps of the individual geological environments are produced as well as a combined map including all the geological environments.
Mineral occurrence data
In 2005, the Geological Survey of Denmark and Greenland (GEUS) completed a joint project with the Bureau of Minerals and
Petroleum, Greenland, about main geological environments in Greenland and their mineral resources. The project involved
definition of the four main geological environments and for each environment, the selection and description of characteristic
mineral occurrences (Stendal et al. 2005).
Not many mineral occurrences within infracrustal environments are recorded in Greenland but three types can be mentioned: Gold in gneiss, nickel and copper in mafic intrusions, and olivine in ultramafic rocks.
The supracrustal rocks include metasedimentary rocks, metavolcanics and banded magnetite-quartzite formation. The mafic
metavolcanic rocks are worth special attention because of their significant mineral potential, not the least for gold and base metal deposits. These deposits are often related to greenstone belts with mafic volcanics or mixed mafic volcanic and sedimentary rocks. Besides gold, other mineral occurrences are iron, copper, chromium, tungsten, as well as industrial minerals.
The mineral occurrences in the magmatic environment are the porphyry system related to Palaeogene alkalic intrusions in East
Greenland and associated vein systems with gold and silver; veins related to the Caledonian granite and the Julianehåb batholith, which carries tungsten, arsenic, antimony, and gold; the alkaline intrusions in the Gardar province have niobium, tantalum, zirconium, rare earth elements, and cryolite; carbonatite with niobium, tantalum, apatite and kimberlite-lamproite with diamonds are located within the Kangerlussuaq region of West Greenland.
Many of the globally known mineral occurrence types in sedimentary environments also occur in Greenland. Examples are copper in sandstones in Neoproterozoic and Triassic clastic sediments; lead and zinc in shale/carbonate sequences are widespread in the sedimentary basins; a fossil placer represents a placer deposit and celestite an evaporite deposit; lead-zinc veins in sediments occur in the Mesters Vig area including the now closed Blyklippen Pb-Zn mine, East Greenland.
Preliminary geological map 1:2 500 000
The base for drawing the geological environment map is the digital geological map at 1:2 500 000 scale based on the geological map of Greenland published by Escher & Pulvertaft (1995) and described by Henriksen et al. (2000).
Background themes for West Greenland 66°-70°15'
A selection of geo-themes is supplied as backdrops for the mineralisation data. Many more data images are available in Schjøth & Steenfelt (2004), Stendal et al. (2004), Nielsen & Rasmussen (2004) and Tukiainen & Krebs (2004). All reports can be ordered at costs from GEUS. In the environment of GMOM they are presented as images only.
Mineral occurrence data
In 2003, the Geological Survey of Denmark and Greenland (GEUS) completed a four-year project aimed at assessing the mineral potential of the Precambrian part of West Greenland between latitudes 66º and 70º15'N. The project involved compilation of existing geoscientific data, new geological mapping, field examinations of known and potential mineral occurrences, new chemical and isotope analyses, and data interpretation.
Exploration by commercial companies and government institutions has resulted in the identification of 160 mineral occurrences within the region. The reported information on the occurrences is stored at GEUS, in archived company reports and in a GEUS database (Greenmin). The mineral occurrences presented here for West Greenland comprises registration, classification and description of the occurrences together with an assessment of the mineral resource potential based on their geological setting, economic significance and genesis. Further details can be found in Stendal et al. (2004)
The data compilation, available on a DVD (Schjøth & Steenfelt 2004), comprises regional, systematically acquired data sets presented in a Geographical Information System (ArcView).
Preliminary geological map 1:2 500 000
Investigations by the Danish Lithosphere Centre, 1994 to 1997 (van Gool et al. 2002b), together with geological mapping by GEUS, 2001 to 2003, at 1:100 000 scale (van Gool et al. 2002a) in the central part of the assessed region
(between latitudes 67° and 69° N) have demonstrated a need for revising the published geological maps.
The digital geological map presents a preliminary version of the study region at 1:2 500 000 scale based on the geological
map of Greenland published by Escher & Pulvertaft (1995) and described by Henriksen et al. (2000). The outline of the
carbonatite complex has been digitised from Secher (1986), and it reflects the outer boundary of the fenitised zone sur-rounding a core of carbonatite. The revised map only portrays regional scale features as it is intended for presentation in publications, but it reflects the present perception of the re-gional geology. Notice that the copyright of the topographic base for this map is 'G/2.5 M Vector, copyright KMS/GEUS 1997.
The digital terrain model (DTM) with 50-metre pixel size covering the entire region her pre-sented as an image file.
The regional DTM is made using ArcInfo Workstation TIN-extension (TIN = Triangulated Irregular Network) in command line mode. The topographic data set at 1:100 000 scale, including all valid 100-metre contour lines, is used to create this model. The input lines and polygons are generalised to 50-metre vertex length. The altitude of the lakes is used and the rivers are used as hard break-line. The sea-polygon is added as a hard erase area to improve the visual display of the land area. The TIN-output is then converted to a grid with a cell-size of 50 metres using the ArcView GIS extension Spatial Analyst. A hillshade relief with a simulated light source from 315°N and 45° declination is computed. The grid and the hillshade are then converted to an image using a free ArcView GIS extension.
Regional magnetic surveys
Ten maps of processed regional aeromagnetic data showing different aspects of the data are available as for the region in West Greenland (66°-70°15'). The aeromagnetic data originates from regional airborne surveys 'Aeromag 1992', 'Aeromag 1997' and 'Aeromag 1999', funded by the Bureau of Minerals and Petroleum, Government of Greenland, and supervised by GEUS (Thorning 1993; Rasmussen and van Gool 2000). The original data are available and may be purchased at cost from GEUS.
Survey specifications for the three surveys are given in the here below.
||Aeromag 1999 |
||Lersletten, central West Greenland
||Disko-Nuussuaq region, central West Greenland
||Southern West Greenland |
||Magnetic total field
||Magnetic total field
||Magnetic total field |
|Orientation of regular survey lines:
|Spacing between regular survey lines:
||500 m over land, 1000 m over sea
||500 m |
|Orientation of tie-lines:
|Spacing between tie-lines:
||5 km |
|Total line kilometres:
||141009 km2 |
||300 m |
||61292 km2 |
||Sander Geophysics Ltd.
||Sander Geophysics Ltd. |
||The Government of Denmark with a contribution from Nunaoil A/S
||The Government of Greenland
||The Government of Greenland |
||(Schacht 1992; Thorning 1993)
||(Murphy & Coyle 1997)
||(O'Connor 1999; Rasmussen & van Gool 2000) |
The data from the three surveys have been merged and processed to produce maps displaying variations in the magnetic total field, supplemented by maps of eight calculated parameters listed below.
The maps are based on interpolated data (100 m grid) using a minimum curvature method for the interpolation. They appear as colour images (geo-referenced TIFF files). The shaded image has a simulated light source from NW with an inclination of 45 degrees. The Cretaceous-Palaeogene strata on Disko and Nuussuaq were surveyed in Aeromag 97, but this part of the image has been hidden because the mineral resource assessment programme for West Greenland (66°-70°15') reported here is limited to the Precambrian shield.
The ten map images presented in the view for West Greenland (66°-70°15') are:
||· Magnetic total field |
||· Magnetic total field, shaded image |
||· Vertical gradient of magnetic total field |
||· Horizontal gradient in N-direction of the magnetic total field |
||· Horizontal gradient in NE-direction of the magnetic total field |
||· Horizontal gradient in E-direction of the magnetic total field |
||· Horizontal gradient in SE-direction of the magnetic total field |
||· Amplitude of horizontal gradient vector of the magnetic total field |
||· Amplitude of analytic signal of the magnetic total field |
||· Pseudo gravity field calculated from the magnetic total field |
Details of the calculation and interpretation of the processed data used in this presentation may be found in Nielsen, B.M. and Rasmussen, T.M. (2004) and references therein. The above text is partly a modified version of Rasmussen and Nielsen (2004).
Regional stream sediment geochemistry (fine fraction)
Three contoured grid images of Au, As and Cu content in stream sediments (fine fraction) and a combined grids of As-Sb-Rb are included in the presentation of West Greenland (66°-70°15') with a special map showing sample locations, also included below. The low-density coverage with stream sediment samples in the region has been accomplished during several sampling campaigns, but the chemical analyses have been calibrated as described here.
Stream sediment sample sites of individual stream
sediment surveys/batch within the region in West
Greenland (66°-70°15'). Map from Schjøth & Steenfelt (2004).
Suitable sample sites with an even distribution have been selected by stereoscopic inspection of aerial photographs prior to the fieldwork. Second or third order streams with catchments areas less than 20 km2 are preferred. Two man teams supported by helicopter undertook the actual sampling. In certain low-relief landscapes, proper streams were absent, and samples have been collected from sediment on the shores of small lakes instead. At each sampling site, c. 500 g of stream sediment was collected in a paper bag and a short site description made. The stream sediment sample was composed of subsamples from three to fifteen sediment deposits along 10 to 50 m of the stream course. Samples were preferably collected among stones and gravel on the streambed, with the consideration that the resultant sample should contain a sufficient amount of fine material. Deficiency of suitable stream sediment has been met in streams with high water flow or streams in low-relief, vegetated terrain. In such places, a sample was collected from sediment trapped in moss or other vegetation between stones or along the banks.
Until 1992, the sample locations were noted on aerial photographs, transferred to topographic maps at scale 1:250 000, and then digitised. From 1992 onwards, the Global Positioning System (GPS) was used. As streams and lakes are variably offset from their location in the old topographic base (scale 1:250 000) all stream sediment sample sites have been adjusted to a new topographic in scale 1:500 000 base by manually moving the sample location to the proper new stream position.
Sample preparation and analysis: Sample bags were provisionally dried in the field before they were wrapped, packed and shipped to GEUS, Copenhagen. Samples were then oven-dried at 60°C and dry-sieved using two polyethylene screens. The fraction above 1 mm grain size was discarded, the 0.1 to 1 mm size fraction stored, and the
The record of analytical treatment of samples throughout the long period of surveying is given in Steenfelt (1999). This report also gives a short description of each of the laboratories and analytical methods employed.
Quality control: The low-density stream sediment data presented here are extracted from the quality controlled and calibrated data used to produce a geochemical atlas of West and South Greenland (Steenfelt 2001). Steenfelt (1999) describes the methods used for selection of valid data and correction of analytical bias.
Theme presentation: Au, As and Cu distributions are illustrated by coloured grid images using software (Oasis Montaj) provided by Geosoft Inc. The gridding was performed with the kriging method using a power model, a grid cell size of 5x5 km and a blanking distance of 5 km. The square outline of individual grid cells is seen at the margin of the grid image only. The software has a default interpolation procedure for smoothing boundaries between differently coloured cells similar to contouring. The colour scale giving class intervals for grid colours is constructed individually for each element and is guided by percentiles of the frequency distribution. The distribution of As, Sb and Rb is illustrated by combined grids – as a triplot grid.
Additional images of other geochemical elements and sample locations are available in Schjøth, F. & Steenfelt, A. (2004).Analytical data can be acquired from GEUS at cost.