Abstract
On the basis of their chemical composition, the Ilímaussaq ore minerals in pegmatites and hydrothermal veins have been subdivided into the following four associations: I Pb-Zn-Mo, II Cu-Sb (including two subtypes: IIA Cu-Sb and IIB Cu-Sb-S), III Fe-As and IV Fe-Ni-As-Sb. Accessory rock-forming ore minerals have been studied in heavy mineral concentrates isolated from the augite syenite and from the following agpaitic rocks: alkali granite, sodalite foyaite, naujaite, green lujavrite, medium- to coarse-grained lujavrite and black, red and white kakortokites. The ore minerals comprise sulphides (galena, sphalerite, molybdenite, pyrrhotite, troilite, marcasite, pyrite, chaIcopyrite and djerfisherite), native elements (tin, lead and iron), aIloys (seinäjokite [FeSb2] and unnamed Sn-Cu(-Pb)phase), arsenides (westerveldite and loeIlingite) and one antimonide (gudmundite). Oxides of iron, titanium and chromium have been identified. Native iron, native tin, unnamed Sn-Cu(-Pb)phase, decomposed wüstite and chromite may represent contaminated material. Some of the accessory rock forming ore minerals form two additional associations: V Fe-Cu and VI Fe-Ti-O. The accessory ore minerals in the agpaitic rocks crystallized relatively late compared to the silicate minerals. In the augite syenite the original pyrrhotite and associated chaIcopyrite crystallized from an immiscible sulphide phase. Correlation between accessory rock-forming ore minerals and bulk chemical composition of the major rocks is severely limited due to the lack of chemical data. The ore minerals in the rocks, pegmatites and veins crystallized at low sulphur and oxygen fugacities. The log αS2 and log fO2 ranges are semi-quantitatively estimated on the basis of published thermodynamic data.
Highlights
The Ilimaussaq intrusion, the Ivigtut cryolite deposit and the Grønnedal-Ika carbonatite complex in South Greenland belong, together with several other syenite, nepheline syenite and granite intrusions, to the Gardar igneous province
A relatively large number of ore minerals occur in pegmatites and pneumatolytic-hydrothermal veins within the Ilimaussaq intrusion
Examination of the heavy mineral concentrates extracted from several of the major rock types from the Ilimaussaq intrusion showed the existence of a large number of accessory ore minerals
Summary
The Ilimaussaq intrusion (fig. 1), the Ivigtut cryolite deposit and the Grønnedal-Ika carbonatite complex in South Greenland belong, together with several other syenite, nepheline syenite and granite intrusions, to the Gardar igneous province. A relatively large number of ore minerals occur in pegmatites and pneumatolytic-hydrothermal veins within the Ilimaussaq intrusion. The stratified rocks of the Ilimaussaq intrusion are nepheline syenites They comprise in ideal section from top to bottom (thickness in brackets has been taken from Sørensen, 1958): pulaskite and heterogeneous foyaite (2-40 m), sodalite foyaite 2-150 m), naujaite (400 m), lujavrites (up to 300 m) and kakortokites (minimum 400 m). Larsen (1976) assumes the existence of several intrusive magrnas: (1) an augite syenite magma, (2) a magma which produced the differentiation sequence: pulaskite ~ heterogeneous foyaite ~ sodalite foyaite ~ naujaite, (3) a magma from which the kakortokites crystallized and possibly (4) a magma from which the lujavrites developed. A large number of pneumatolytic-hydrothermal veins occur mainly in naujaite They are generally located near the contact between this rock type and lujavrites. The ore mineralogy of the four associations is summarized be1ow
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