Gold occurrences and lead isotopes in Ketilidian Mobile Belt, South Greenland

Abstract

at the edge of the Julianehåb batholith. The emplacement of the juvenile I-type Julianehåb batholith lasted from 1850 to 1800 m.y. with late-stage intrusions until 1770 m.y. Emplacement of the gold mineralization is considered to have taken place in the late stage of formation of the batholith (1800-1770 m.y.) and during the regional deformation and metamorphism before the intrusion of rapakivi granites. Local remobilization of metals, however, was caused by hydrothermal activity around some rapakivi granitoids. In essence, therefore, gold deposition in South Greenland is restricted to a quite narrow time interval. Lead isotopes from different occurrences in South Greenland indicate two main stages of gold emplacement. The first was related to the Palaeoproterozoic regional deformation and metamorphism (1792-1785 m.y.), during which sediment-hosted gold was epigenetically remobilized into shear zones and vein systems. Pb in these occurrences is indicative of a ca 2000-m.y. source, which is compatible with the direct basic host rocks to these occurrences. The second stage of gold deposition appears to have been temporally related to late stages of emplacement of the Julianehåb batholith. The source of the slightly more evolved Pb in these occurrences is difficult to assess, but a mixture of juvenile Pb from the batholith with some contributions from the host rocks may explain the scatter of data around a 1780-m.y. reference line. Gold occurrences have been found in the PalaeoproterozoicKetilidian Mobile Belt within the last ten years. This is due to the fact that the analytical methods used in the 1970s and 1980s did not include gold analyses as the commodities of interest at that time were U, Nb, Ta, Zr and rare-earth elements in the South Greenland uranium province. 2,3,24,29,43 At the beginning of the 1990s companies became interested in the gold potential of South Greenland. Nunaoil A/S carried out a gold exploration programme in the region, 30 which was followed by the SUPRASYD programme of the Geological Survey of Denmark and Greenland. 38 The results, with discoveries such as Nalunaq 15,32 and Kangerluluk,35 were impressive. The Nalunaq deposit has been through a feasibility study and Crew Development Corporation has announced the start of gold production from Nalunaq within two years.*The study reported here was undertaken with the objectives of characterizing the geological setting of the gold mineralization and the Pb-Pb isotope signature of these occurrences and suggesting the possible source rock of the gold and age of the gold formation.

Metallogeny of Greenland

“…Whole rock and sulfide Pb-isotope data indicate gold mineralization between ca. 1792 Ma and 1785 Ma, with a Paleoproterozoic Pb-source incompatible with regional granitic rocks (Stendal and Frei, 2000). Mass balance calculations show that the gold-stage is characterized by mass gain of Si and K and that the Au-rich fluids were enriched in Ag, As, Sb, Bi and W, which are elements that typically are enriched in orogenic gold deposits (Schlatter and Kolb, 2011).…”

Mineral exploration in Greenland in the 1990s

“…Drill-core information indicates a potential for more than 60 000 000 t at an average palladium concentration of 2.5-3 g/t. The best intersections show 5 g/t Pd over 1 m and more than 0.5 g/t over 10 m. 19 As an outcome of the SUPRASYD project in South Greenland 35,37,38,41 all the currently known gold occurrences in the Ketilidian Mobile Belt, e.g. at Nalunaq, Kangerluluk and Niaqornaarsuk (Fig.…”

“…These promising gold areas are well documented in the present issue. 31,39,40 Currently the most promising project is Nalunaq, which has been planned to go into production within two years. 9,10,14,39 A net present value of $U.S.…”

“…31,39,40 Currently the most promising project is Nalunaq, which has been planned to go into production within two years. 9,10,14,39 A net present value of $U.S. 39 800 000 and an internal rate of return of 51% for a 500 t/day operation were estimated in a pre-feasibility study.…”

Metallic mineral deposits in the Nordic countries

“…The juvenile Ketilidian orogen is considered to be a gold province with several prospects in different settings and the only gold mine in Greenland. The gold is thought to be related to the later stages of a batholith intrusion (1800-1770 Ma), but is found both in supracrustal rocks and granitoids (Stendal and Frei, 2000). The greenstone belts in the Paleoproterozoic domains outside South Greenland are at present considered to have a low potential for gold deposits.…”