Abstract
Two new occurrences of sapphirine from West Greenland are described. In the first of them (from Sukkertoppen District) sapphirine is present as rims of reaction around grains of corundum in patches of anorthite in small lenses of hornblendite. The hornblendites are found in a hydrid zone around a bronzititic ultrabasite. The second occurrence of sapphirine is a boulder of hornblendite found in the Qorqut branch of the Godthaab Fiord. Sapphirine is here found in a similar way as in the first-mentioned occurrence, namely as rims between corundum/spinel and anorthite. New observations from the Fiskenæsset occurrence are published. It is shown that the sapphirine-bearing rock has been formed by retrograde metamorphism of a spinel-bearing bronzitite. Sapphirine is formed at the expense of spinel ; gedrite, hornblende and phlogopite at the expense of the bronzite. Corundum has also been found in this occurrence. Irregular replacement veins are found in the sapphirine-bearing rock. They consist of basic plagioclase, hornblende, biotite and cordierite. It is suggested that this cordierite (and possibly the kornerupine) has been formed at the expense of the sapphirine. The occurrences of sapphirine at Sukkertoppen and at Auvaitsersarfik are briefly mentioned. Corundum in ultrabasic rocks is discussed. The parageneses with sapphirine mentioned in the literature are reviewed and the stability relations of sapphirine are discussed. It is concluded that sapphirine most often appears to be formed at the expense of spinel and corundum and that it often is associated with ultrabasic rocks. Sapphirine is regarded to be formed where concentrations of Al in a milieu rich in Mg and poor in Si have been metamorphosed in a "closed system" under conditions of P,T corresponding to high amphibolite low granulite facies.
Highlights
Two new occurrences of sapphirine have been found during the expeditions of GRØNLANDS GEOLOGISKE UNDERSØGELSE (1'he Geological Survey of Groenland) to vVest Greenland, in 1949 and 1951, respectively
Nodetailed mineralogical examination of the sapphirine from the two localities has been undertakon and the scarce material did not allow any chemical analyses to bo carried out. 1'he identity of the minerals have been checkod by means of powder diagrams taken in the X-ray laboratories of the Geological Museum, Oslo
NEm'lA~N for this valuable help. 1'he occurrences are compared with the occurrences of sapphirino to which references have been found in the literature. In this connection specimens from the classie locality at Fiskenæsset have been examined. 1'he examination has been based on material collected by the writer and on samples from the collections of the Mineralogical Museum in Copenhagen
Summary
Two new occurrences of sapphirine have been found during the expeditions of GRØNLANDS GEOLOGISKE UNDERSØGELSE (1'he Geological Survey of Groenland) to vVest Greenland, in 1949 and 1951, respectively. 13570 a collected by the writer and three sections from the collections of the Museum This type of rock has sapphirine of a paIe blue colour occurring in thin plates Ol' in aggregates of plates so that grains more than one centimetre across may be seen. It is clearly in a process of dissolution One of these rocks examined in thin section had the components biotite, sapphirine, basic plagioclase (almost pure anorthite), cordierite, chlorite, tiny grains of corundum and a few small spots af ares. Dierite has been identified in powder from the outer part of the white patch so that it appears as if the corundum-plagioclase rock is separated from the sapphirine-bearing complex by cordierite and biotite. The writer did not examine this problem when visiting the occurrence in 1949
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