Review of Greenland Avtivities 2001 - Geus

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67° Sisimiut • 53° 52° 51° 50° • Kangerlussuaq Inland Ice F G Søndre Strømfjord 66°30´ • H Itilleq C D E Sarfartoq J I B A 0 20 40 km Fig. 2. Distribution of kimberlitic and lamprophyric occurrences within the project area. A–J are localities mentioned in the text. Red triangles are kimberlitic and lamprophyric dykes known prior to the present study: lamproites predominate in the region between Sisimiut and Itilleq, kimberlites in the Sarfartoq region (Larsen & Rex 1992). Green triangles are observations from the present study. Heavy colouring represents in situ finds and light colouring represents boulders (float). were intruded into the Archaean gneisses prior to deformation and are now highly strained and boudinaged north of the boundary. The intrusion of alkaline dykes appears to have taken place during two events. Lamproite dykes in the Sisimiut region are around 1.2 Ga old, whereas the Sarfartoq complex (Fig. 2) and a swarm of associated kimberlitic dykes have ages of around 0.6 Ga (Larsen & Rex 1992). A precise spatial relationship between the two intrusive events has not been established. A project concerned with general scientific aspects of kimberlitic and related rocks in the Sisimiut– Kangerlussuaq region was established in 2000. The aim is to gather knowledge from companies’ exploration activities and to incorporate Survey expertise such as petrology, structural geology, isotope geology, geochemistry, geophysics and the geographic information system (GIS). Field work was carried out in 2000 and 2001, with the Kangerlussuaq International Science Support (KISS) centre at Kangerlussuaq airport as logistical base. A combination of daily reconnaissance covering large areas using a helicopter, and fly camps of 2–3 days duration was applied. The broad term ‘kimberlitic’ is used here in acknowledgement of the fact that the classification of the ultramafic dyke rocks of West Greenland is not resolved with unanimity. Many of the dyke rocks resemble kimberlites and have previously been described as such (Larsen 1980, 1991; Scott 1981; Larsen & Rex 1992). Mitchell et al. (1999), however, take the view that the dyke rocks are not ‘archetypal’ kimberlites, but ultramafic lamprophyres that should be termed melnoites or aillikites. In the light of the actual occurrence of diamonds in the West Greenland dyke rocks, Mitchell et al. (1999) consider them to represent one of the few examples of diamond-bearing ultramafic lamprophyres. One of the aims of the present project is to contribute to a generally accepted classification of the West Greenland kimberlitic and related rocks. Distribution of kimberlitic and related rocks Larsen’s (1991) compilation of Greenland’s kimberlite, lamproite and ultramafic lamprophyre occurrences proved to be a valuable initial guide to companies when the ongoing diamond exploration commenced in West Greenland in the mid-1990s (Olsen et al. 1999). The compilation includes data collected by earlier workers (e.g. Scott 1981), who typically operated by boat and thus were often restricted to working near the coast. As a 58
consequence, the known occurrences had an uneven distribution, and some areas appeared to be without occurrences. Many of the occurrences of in situ dykes and boulders (float) in the Sisimiut–Sarfartoq–Kangerlussuaq region known at present are indicated in Fig. 2. The approximately 600 occurrences include those from Larsen’s (1991) compilation and new localities added by exploration companies and recent field work by the Geological Survey of Denmark and Greenland (GEUS). It should be noted that the map does not include a large number of company localities that are at present confidential because they lie within active exclusive exploration licence areas. The map illustrates the concentration of occurrences in the vicinity of the Sarfartoq carbonatite complex, which Larsen (1980) interpreted as a swarm of kimberlitic cone-sheets centred on the carbonatite. Bedrock exposure is generally poor in the study region, and dykes and sills of kimberlite, lamproite and carbonatite can be difficult to trace because they are thin, easily eroded and often covered by overburden and vegetation. Therefore, both stream geochemical data and aeromagnetic data are investigated with the aim of identifying geochemical and geophysical signatures reflecting occurrences of kimberlitic and related dykes. Field activities Field work in 2000 consisted of one week’s reconnaissance and visits to new dyke occurrences discovered by exploration companies. The 2001 field work was focused on the spatial distribution of kimberlitic dyke rocks in areas with little or no previous information, and detailed studies on mantle xenoliths from the kimberlitic dykes. Studies of mantle xenolith-bearing rocks are described in a separate section below. The field work also included testing the ease of locating occurrences described in companies’ assessment reports using various Global Positioning System (GPS) equipment and GIS methods. Locality F (Fig. 2) provides an example of the density of new observations made in an area with no previously reported kimberlitic or lamproitic occurrences. Within the framed area 26 kimberlitic boulders and one new dyke were registered (Fig. 3). Three of the boulders measure about 1 x 1 x 1 m in size, indicating that the dyke or dykes from which they originated must be of substantial dimensions. Several large boulders were broken up into many smaller fragments, resulting in a much higher count of individual pieces of kimberlitic rock. The high number of kimberlitic boulders in this small area suggests they may have been derived from a nearby dyke outcrop. Similar observations were made at localities G and H (Fig. 2). Stream sediment geochemical anomalies reflecting alkaline rocks Geochemical reconnaissance-scale stream sediment surveys have been carried out over large parts of West Greenland, including the project region considered here. The chemical analyses have been compiled and Fig. 3. View of the area of locality F. A small outcrop of a new kimberlitic dyke (arrow) is located in the lineament marked by dotted line. Length of dotted line is approximately 200 m. 59
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GEOLOGY OF GREENLAND SURVEY BULLETI
Page 4:
Geology of Greenland Survey Bulleti
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Contents Numbers of articles corres
Page 9: ■ ■ ■ ■ ■ ■ ■ ■ ■
Page 12 and 13: Canada Pituffik O 1 Thule Air Base
Page 14 and 15: Publications A complete list of geo
Page 16 and 17: Canada Greenland Greenland Inland I
Page 18 and 19: northern Nagssugtoqidian orogen (SN
Page 20 and 21: western to the north-eastern corner
Page 22 and 23: group consists of conjugate sets of
Page 24 and 25: y pure shear. Coincidence of the or
Page 26 and 27: The Precambrian supracrustal rocks
Page 28 and 29: 68°25′ 52° 68°25′ BIF 0 3 km
Page 30 and 31: Fig. 4. Dolomitic marble in the sou
Page 32 and 33: Bugt (Fig. 1; Henderson 1969). The
Page 34 and 35: Keto, L. 1962: Aerial prospecting b
Page 36 and 37: ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲
Page 38 and 39: increases towards the south. We obs
Page 40 and 41: Kalsbeek, F. & Taylor, P.N. 1999: R
Page 42 and 43: Canada Nuussuaq 0 50 km PROTEROZOIC
Page 44 and 45: deposit. Descriptions of the differ
Page 46 and 47: Pegmatites The gneisses throughout
Page 48 and 49: tacts with quartzo-feldspathic coun
Page 50 and 51: Geological correlation of magnetic
Page 52 and 53: Fig. 2. The hand-held magnetic susc
Page 54 and 55: Susceptibility distribution (%) Sus
Page 56 and 57: have a reducing effect, which hinde
Page 58 and 59: ancy between the susceptibility val
Page 62 and 63: Table 1. Range of Nb concentrations
Page 64 and 65: chemical composition - may indicate
Page 66 and 67: Concentration/C1 chondrite 100.00 1
Page 68 and 69: Menzies, M.A. & Hawkesworth, C.J. (
Page 70 and 71: 72°30´ Aeromag 2001 50 km Upernav
Page 72 and 73: 56° 54° 52° 72° 72° nT 71°30
Page 74 and 75: Conclusions The aeromagnetic survey
Page 76 and 77: 53° 51° Inland Ice Greenland 72°
Page 78 and 79: On the south coast of Nuussuaq, wes
Page 80 and 81: Fig. 5. Blocks and boulders in the
Page 82 and 83: 2000 SW NE 1500 Surface trace 1985
Page 84 and 85: 1979). Along other sections of the
Page 86 and 87: Petroleum geological activities in
Page 88 and 89: Seismic acquisition during summer 2
Page 90 and 91: Other petroleum geological work Alt
Page 92 and 93: A multidisciplinary study of the Pa
Page 94 and 95: Seismic interpretation The grid of
Page 96 and 97: Middle Eocene Lower Eocene Upper Pa
Page 98 and 99: Chalmers, J.A., Dahl, J.T., Bate, K
Page 100 and 101: 95-06 ▲ ▲ 58° 95-12 95-10 56°
Page 102 and 103: 70° 71° 60° 2000 2000 2400 400 1
Page 104 and 105: Storey, M., Duncan, R.A., Pedersen,
Page 106 and 107: 24° 100 km 30° 27° 21 ° Jameson
Page 108 and 109: Oligocene Krabbedalen Fm Eocene Bop
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grading. Bivalve shell material is
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References Birkenmajer, K. 1972: Re
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B A 72° Palaeogene basalts Gl 50 k
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a b c d e f g h 20 µm i j k l Fig.
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offshore South-East Greenland, onsh
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▲ Albert Heim Bjerge Wordie Gletc
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T D A CW NS placed the lowermost c.
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is abundant and highly diverse, and
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The Heimbjerge Formation comprises
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Late Permian carbonate concretions
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m 25 20 15 B3 L2 B2 Fig. 3. Simplif
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(2001), who pointed out the restric
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Piasecki, S. 1984: Preliminary paly
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66° 68° • • • • • • 7
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absent at Tikeraussaq where a postu
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72° 70° 68° 66° Sample locality
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Table 2. Summary of selected elemen
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Concluding remarks Observations dur
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Lake-catchment interactions with cl
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lakes. As in earlier reports (e.g.
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Discussion Global climate models pr
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Glaciological investigations on ice
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Fig. 2. The new one-mast design of
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A B N 20 km 1993 1995 Fig. 5. Satel
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Krabill, W., Frederick, E., Manizad
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2001/47: Calibration of stream sedi
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Hanghøj, K., Kelemen, P., Bernstei
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Danmarks og Grønlands Geologiske U
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GEOLOGY OF GREENLAND SURVEY BULLETI
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