Geological overview and environments for mineral occurrences
Shield formation and cratonization occurred in Eo–Neoarchaean time in Greenland, typified by the formation of continental and oceanic crust, the amalgamation of oceanic crust (supracrustal and greenstone belts) and new arc-formed crust by emplacement of tonalite-trondhjemite-granodiorite plutons. This was succeeded by orogenic deformation and greenschist to granulite facies metamorphism. Contemporaneously with the Archaean period of huge crustal formation, major global mineral deposits of gold and banded iron formations formed worldwide in granite-greenstone terranes e.g. characterized in the terranes in southern West Greenland. Ultramafic to mafic intrusions in granite-greenstone belts occurs in Greenland as major carriers of Cr-Ni-V exemplified by the occurrence of chromitite (±PGE) in layered anorthositic complexes, as chromitite seams in dunite lenses and V-Ti in gabbro complexes.
The Palaeoproterozoic Era is globally characterised by growth of continental crust and amalgamation with formation of orogens centered on 2.0–1.9 Ga. These events were associated with the emplacement of major magmatic intrusives and formation of sedimentary basins. Orogenic mobile belts of Palaeoproterozoic age include the Ketilidian orogen in South Greenland, the Rinkian – Nagssugtoqidian orogen in central West Greenland, the Ammassalik mobile belt in East Greenland, and the Inglefield mobile belt in Northwest Greenland. Major sedimentary basins in Greenland formed at that time including the deposition of the Karrat Group, which occurs for 400 km along the west coast of central West and North-West Greenland. Other volcanogenic-sedimentary basins in the Palaoproterozoic Era include the Psammite and Pelite Zones in the Ketilidian orogen. Much smaller occurrences of supracrustal rocks occur within the Inglefield mobile belt and the Rinkian – Nagssugtoqidian orogen. The Ketilidian orogen represents a metallogenetic province for gold and hosts the Nalunaq gold mine. Elsewhere globally the accretionary orogenies were associated with the formation of volcanogenic massive sulphide Cu-Zn deposits (such as the Flin Flon in Canada or the Skellefte in Sweden). In Greenland similar deposits are known from the Rinkian – Nagssugtoqidian orogen; however, these are so far without economic significance concerning Cu-Zn. Sedimentary exhalative (SEDEX) lead-zinc deposits in large basins are also characteristic globally e.g. the former Black Angel mine within the Palaeoproterozoic marble of the Karrat Group. Stratiform occurrences of uranium in sedimentary basin also characterize this Era; this type occurs in South Greenland.
Globally the Mesoproterozoic Era started out with tectonic and continental stability, which lasted for several hundred million years. In Greenland, this is characterized by the formation of large sedimentary basins such as the Thule Group in Northwest Greenland, the Independence Fjord Group in North Greenland, the Krummedal sequence in East Greenland, and the Eriksfjord Formation in South Greenland. Stratiform Cu occurrences are known from these basins in Greenland. Anorogenic magmatism characterises the early Mesoproterozoic Era globally such as the Gardar Province in South Greenland. The Gardar Province hosts several major magmatic hosted mineral deposits, e.g. the Motzfeldt nepheline syenite complex, which is strongly enriched in Zr-Ta-Nb-REE-U-Th, the Ivittuut granite with the famous cryolite deposit mined from 1857–1987, and the Ilimaussaq intrusion, which is enriched in F-Zr-Zn-REE-Y-U-Th. The end of the Mesoproterozoic Era around 1000 Ma is characterized by the Grenvillian orogeny, which is expressed as reworking of basement rocks in Greenland.
The Neoproterozoic Era is globally characterized by tectonic and continental stability. Sedimentary basins, the Hagen Fjord Group and the Eleonore Bay Supergroup, were formed in North and East Greenland during that time. Anomalously high Cu concentration is known from many parts of the world as well as the Greenlandic basins with strata-bound copper occurrences. The 600 Ma Sarfartoq carbonatite intrusion hosts Nb and apatite occurrences. Associated with the carbonatite intrusion kimberlitic dykes are diamond-bearing in West Greenland. This event is related to the opening of the Iapetus Ocean and comprises the North Atlantic alkaline province.
The formation of the Iapetus Ocean between the Laurentia and the Baltica shield resulted in deposition of large Phanerozoic sedimentary basins on the shelf of the Laurentian shield; this is reflected in Greenland as the Lower Palaeozoic to Cretaceous basins in East Greenland, and the Late Neoproterozoic to Devonian Franklinian basin in North Greenland.
During the Phanerozoic time Greenland was affected by the Ellesmerian (365–345 Ma) and Caledonian orogenies (465–355 Ma) in North and East Greenland, respectively. The Ellesmerian orogeny closed sedimentation in the Franklinian basin and the Caledonian orogeny resulted in a compressional regime with associated magmatic activity. Globally, SEDEX and MVT deposits are widespread in the Late Palaeozoic – Early Mesozoic time; exemplified in Greenland with the Citronen Fjord SEDEX Zn-Pb deposit and Washington Land MVT Zn-Pb deposit in the Franklinian basin. Faulting in the Franklinian basin was associated with epigenetic Ba-Zn occurrences. The Caledonian event in East and North-East Greenland is associated with the intrusion of granites with related W-Sb-Au occurrences and extrusive felsic volcanic rocks with uraniferous hydrocarbons.
The North Atlantic region was in Palaeogene time characterized by continental break-up and initiation of sea-floor spreading; with the opening of the North Atlantic Ocean and the Davis Strait between Canada and Greenland. These events were associated with major volcanic and magmatic activity with the extrusion of 4–10 km thick plateau basalts covering Mesozoic – Early Palaeocene sedimentary basins and Precambrian basement in both central West and central East Greenland. The main flood basalt volcanism occurred between 61 Ma and 59 Ma in West Greenland and between 57 and 53 Ma ago in East Greenland. The magmatic activity in East Greenland also resulted in the formation of an extensive suite of Palaeogene intrusions and magmatic complexes. The Palaeogene extrusives and intrusives occur over more than 1000 km in East Greenland. The youngest felsic magmatic complex yields an age around 21 Ma, whereas the youngest basaltic volcanism in East Greenland took place around 13 Ma. The magmatism in East Greenland is associated with porphyry occurrences, e.g., Malmbjerg Mo deposit and the Flammefjeld Au-Ag-Cu-Pb-Mo deposit. Palaeogene layered tholeiitic gabbro complexes are also well-known from this part of Greenland; exemplified by the famous Skaergaard intrusion with Pd, Pt, Au and Cu reefs. In West Greenland the volcanic and magmatic activity is associated with the occurrence of native- iron and nickel-bearing sediment-contaminated dykes with affinities to Noril’sk style deposits.
Mineral occurrence map and main geological units in Greenland.
Further geological description can be found in the GEUS Bulletin 18 (2009) – Greenland from Archaean to Quaternary. The Bulletin includes the Geological map of Greenland 1:2,500,000. On the website of GEUS the Bulletin can be downloaded and the geological map can be seen interactive. See also www.greenmin.gl