Geology of the Lindenow Fjord - Kangerluluk area, South-East Greenland: preliminary results of Supresyd 1994

The Lindenow Fjord - Kangerluluk area in the southern part of South-East Greenland covers part of the early Proterozoic (c. 1.85-1.75 Ga) Ketilidian orogen. The map sheet area is underlain in the northwest by granodiorite s.l. of the Julianehåb batholith, and in the central and southeastern parts by supracrustal rocks consisting of migmatized metasediments (psammite, pelite, inch turbiditic sequences, minor conglomerate), subordinate mafic metavolcanic rocks (basalt-andesite, hyaloclastite, agglomeratic and tuffaceous rocks; with interleaved mafic greywacke), and graphitic schist horizons. Mafic and ultramafic dykes (’appinites’) occur throughout the sequence. Leucocratic autochthonous granite is common in larger volumes towards the east. Late stage rapakivi plutons (quartz monzonite, norite) intrude both the batholith and the supracrustal sequence. Granodiorite s.l. of the Julianehåb batholith contains a regional 060-trending foliation with local oblique sinistral and dextral shears, and was emplaced during sinistral transpression (Chadwick et al, 1994). Main boundaries between batholith and supracrustal rocks are vertical 060-trending mylonitic shear zones, but variably dipping intrusive and possible unconformable contacts are observed.

Supracrustal rocks record more complex deformation including early isoclinal-recumbent folds (overturned sequences), south-vergent recumbent folds and E to ENE-trending upright folds. All fold styles are associated with migmatization and neosome veins in axial planar orientation. Local late stage microfolds appear not to have influenced regional geometry. Batholith type granodiorite was emplaced into the supracrustal sequence during ENE-trending folding.

Regional low P metamorphism in the supracrustal rocks increases from lower amphibolite facies (epidote amphibolite) in a narrow zone along the batholith boundary to upper amphibolite facies throughout the remainder. Granulite facies rocks lie to the south of the map sheet. Preliminary observations in politic rocks indicate a very early high T peak metamorphic assemblage and a second lower T metamorphic event late during and/or after ENE-trending folding, possibly coincident with rapakivi emplacement.

Both batholith and supracrustal rocks are part of U and Au geochemical provinces. The migmatitic supracrustal sequence is also characterized by elevated As and Sb. Stratabound mineralization of the ’graphite-Fe sulphide-chemical sediment-amphibolite’ association include ’pelitic graphitic shale’, ’metalliferous black shale’ and mafic volcanic- dominated end-members. All these are characterized by variably elevated Au and As.
Epigenetic Au-Cu mineralization is noted in small veins in metabasalt and in small and large shear zones along the batholith - supracrustal boundary zone. Uranium mineralization, including the Illorsuit prospect, in migmatitic psammitic gneiss was remobilized during regional metamorphism and deformation.