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

Gold occurrences have Palaeoproterozoic Ketilidian Mobile Belt of South Gre enland within the past ten years. The mineralization occurs in various sett ings with different element associations: Au in the Archaean; Au in the Pal aeoproterozoic border zone; the association Au-Bi-(Ag-As-W-Cu-Mo) in the Ju lianehab batholith; the association Au-As in supracrustal rocks; and the as sociation Au-Cu within a volcano-sedimentary sequence at the edge of the Ju lianehab batholith. The emplacement of the juvenile I-type Julianehab batholith lasted from 185 0 to 1800 m.y. with late-stage intrusions until 1770 m.y. Emplacement of th e gold mineralization is considered to have taken place in the late stage o f formation of the batholith (1800-1770 m.y.) and during the regional defor mation and metamorphism before the intrusion of rapakivi granites. Local re mobilization 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 ma in stages of gold emplacement. The first was related to the Palaeoproterozo ic regional deformation and metamorphism (1792-1785 m.y.), during which sed iment-hosted gold was epigenetically remobilized into shear zones and vein systems. Pb in these occurrences is indicative of a ca 2000-m.y. source, wh ich is compatible with the direct basic host rocks to these occurrences. Th e second stage of gold deposition appears to have been temporally related t o late stages of emplacement of the Julianehab 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 th e host rocks may explain the scatter of data around a 1780-m.y. reference l ine.