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The Heavy Mineral Correlation of Intrusive Igneous Rocks

Published online by Cambridge University Press:  01 May 2009

A. Kingsley Wells
A. Kingsley Wells
Affiliation:
King's College, London.
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Extract

Over a period of some three years Dr. A. W. Groves has been working on the correlation of intrusions by their heavy mineral content, and the results have been published in three papers which have appeared in recent volumes of the GeologicalMagazine. The three papers read seriatim provide an interesting study of the evolution of an hypothesis which, if substantiated, would remove much, and in certain favourable cases, all of the uncertainty that usually shrouds the age of an intrusive rock-body.

Type
Original Articles
Information
Geological Magazine , Volume 68 , Issue 6 , June 1931 , pp. 255 - 262
Copyright
Copyright © Cambridge University Press 1931

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References

page 255 note 1 Geol. Mag., LXIV, 1927, 241–51.Google Scholar

page 255 note 2 See, for example, Plymen, G. H., Proc. Geol. Assoc., xxxiii, 1921, 163.Google Scholar

page 255 note 3 In Text Book of Petrology, vol. i, The Igneous Rocks, 1926, 433.Google Scholar

page 255 note 4 Geol. Mag., LXVII, 1930, 218–40.Google Scholar

page 256 note 1 “On the Significance of the Accessory Minerals in Igneous Rocks” title only, in Report of the Brit. Assoc., South African Meeting, 1930.Google Scholar

page 260 note 1 It is indeed difficult to reconcile the statements concerning the stoping of granite into shale at l'Étacq, Jersey, with what is at present known of this process, in other localities. The sequence of rock types mentioned, viz., normal granite→muscovite granite→muscovite-pegmatite, cannot be admitted as a series showing progressive contamination; rather it seems clear that the magma was not contaminated with the shale, but had reached its present position too late to react with the country rock. The sequence illustrates the influence upon a cooling granite magma of an increasing concentration of flux, giving an abnormally high muscovite content, and an unduly coarse texture.… Although andalusite, etc., are absent from the specimens supplied to Dr. Groves (which is itself evidence of the relative purity of the rock), my own specimens show that this mineral does occur in xenoliths more or less completely assimilated by the granite magma, as at Les Rouaux; and also frequently in the numerous aplite veins in the granite. In both cases the andalusite is a highly pleochroic type and quite unmistakable.

page 262 note 1 The writer is strongly of the opinion that precise nomenclature is essential in describing these crystals; the terminal faces should be referred to as bi-pyramids (not pyramids, which belong to Class 9, the Hemimorphic Class); while distinction should be made between tetragonal bi-pyramids and ditetragonal bi-pyramids. For example, Dr. Groves speaks of “the simple combination of prism and unit pyramid(111). The steeper pyramid (311) is generally absent.” From its context, one cannot help wondering whether this is a misprint for “steeper (bi)pyramid 331 ”, a common zircon form; but so is the ditetragonal bi-pyramid 311, and so one is left guessing, as the drawings do not help.