An autoradiographic examination of rocks and minerals from the Ilímaussaq batholith, South West Greenland

Abstract

Rocks and minerals from the lower part of the Ilímaussaq complex have been examined by means of the nuclear emulsion method. It was found that the radioactivity of the rocks increases from the early naujaite to the later lujavrite and hydrothermal veins. The eudialyte is very weakly radioactive in the naujaite, naujaite pegmatites and in the kakortokites, but is more radioactive in the lujavrites which according to the field relations are the youngest nepheline syenites of the complex. The altered eudialyte may be strongly radioactive. The radioactivities of lovozerite and rinkite are of the size of order of that of the eudialyte of the lujavrite. Isotropic parts of the grains of rinkite may be strongly radioactive. The epistolite is very weakly radioactive, but flakes of a murmanite-like mineral in lujavrite were found to be fairly radioactive. There are small strongly radioactive grains of thorianite in some vein steenstrupines. Apatite is rare and very weakly radioactive; the rare earth-apatite, britholite is generally rather weakly radioactive. The monazite of the lujavrites may, as mentioned in 8, be very weakly radioactive, but strongly radioactive monazite has been found in a few rocks. Several types of steenstrupine have been found in lujavrites and hydrothermal veins. The radioactivity varies from rather weak to strong; the weakly radioactive grains being anisotropic and the strongly radioactive ones isotropic. The crystals may be zoned with isotropic, strongly radioactive central parts and anisotropic, weakly radioactive marginal zones. The cause of this distribution is discussed. The results of the autoradiographical and chemical examinations of steenstrupine are compared and the agreement is found to be satisfactory.