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III.—What is Laterite?

Published online by Cambridge University Press:  01 May 2009

L. Leigh Fermor
L. Leigh Fermor
Affiliation:
Geological Survey of India.1
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Extract

Few natural mineral products have aroused more general interest or been more provocative of discussion amongst geologists than that superficial rock-formation so typical of the tropics known as laterite. This material excites interest not only because of its chemical composition, but also on account of its wide distribution. It has been recorded, for instance, from tropical South America (e.g. the Guianas and Brazil), Central Africa (e.g. Guinea and East Africa), the Seychelles, India, the Malay Peninsula, the East Indies, and Western Australia. Many papers have been published dealing with its distribution, composition, and also its origin, to explain which many hypotheses have been invented.

Type
Original Articles
Information
Geological Magazine , Volume 8 , Issue 10 , October 1911 , pp. 454 - 462
Copyright
Copyright © Cambridge University Press 1911

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References

page 454 note 2 To prevent this casual allusion to the subject of Indian manganese-ores giving rise to one of those misconceptions which, once formed, are so difficult to eradicate, I must state at once that the lateritic manganese-ores are, as a rule, of small importance compared with those of the Archæan areas.

page 455 note 1 Mem. Geol. Surv. India, xxxvii, ch. xix, pp. 370–89, 1909.Google Scholar

page 455 note 2 Bauer, , Neues Jahrb. Für Min., etc., ii, p. 163, 1898.Google Scholar

page 455 note 3 Holland, GEOL. MAG., Dec. IV, Vol. X, pp. 59–69, 1903.Google Scholar

page 455 note 4 Trans. Inst. Min. Met., xix, pp. 432–57, 1910.Google Scholar

page 456 note 1 Geol. Mag., 1909, p. 431.Google Scholar

page 456 note 2 Mem. Geol. Surv. India, xxxvii, p. 381, 1909, and infra.Google Scholar

page 456 note 3 Op. cit., p. 524.Google Scholar

page 457 note 1 GEOL. MAG., 1909 p. 574.Google Scholar

page 457 note 2 Op. cit., 1906, p. 546.Google Scholar

page 457 note 3 Op. cit., 1909, p. 350.Google Scholar

page 457 note 4 Op. cit., 1908, p. 539.Google Scholar

page 457 note 5 Op. cit., 1910, p. 139.Google Scholar

page 457 note 6 Op. cit., p. 189.Google Scholar

page 457 note 7 Op. cit., 1910, p. 234.Google Scholar

page 457 note 8 Op. cit., p. 336.Google Scholar

page 458 note 1 Geol. Mag., 1910, p. 382.Google Scholar

page 458 note 2 Op. cit., p. 384.Google Scholar

page 458 note 3 1910, pp. 439–52, 488–95, 553–62.Google Scholar

page 459 note 1 i.e. clays formed in situ, as distinguished from those deposited as aqueous sediments.

page 459 note 2 Clarke, F. W. holds similar views, as may be judged from the following quotation from his Data of Geochemistry, pp. 417–18 (1908)Google Scholar: “Whatever its derivation may be, whether from rocks in place or as a transported sediment, true laterite [my italics] is essentially a mixture of ferric hydroxide, aluminium hydroxide, and free silica in varying proportions. To laterite in situ this statement applies very closely; detrital laterite is usually contaminated by admixtures of clay. Just as in the formation of kaolin, the process of laterization may be complete or partial, the typical product appears only when the alteration of the parent rock has gone to the end. Then the silicates seem to be completely broken down, whereas in kaolinization a stable, hydrous silicate remains.” MrCampbell's, J. M. definition (loc. cit., p. 437)Google Scholar is also similar; he mentions manganese, titanium, and phosphorus, in addition to the constituents named by Clarke.

page 459 note 3 Other related oxides, such as Cr2 O3, have been found in laterite, and are to be regarded as true lateritic constituents. See Mem. Geol. Surv. India, xxxvii, p. 378Google Scholar, and infra of this paper.

page 460 note 1 The Indian manganiferous laterites have been discussed elsewhere (Mem. Geol. Surv. Ind., xxxvii, pp. 380–9)Google Scholar, and they need not enter further into the discussion here, although they are probably of greater importance and wider distribution than is generally recognized.

page 460 note 2 I use this word in a petrographical sense, concerning which see Section IV of this paper, infra.

page 460 note 3 “The Occurrence of Bauxite in India”: Rec. Geol. Surv. Ind., xxxii, pp. 178–80, 1905.Google Scholar

page 460 note 4 “Report on Laterites from the Central Provinces”: Ibid., xxxvii, pp. 215, 216, 1909.

page 460 note 5 The third group of analyses by H. and F. J. Warth shows, however, three true laterites containing 47 per cent to 56 per cent of Fe2 O3, with 33 per cent to 26 per cent of Al2 O3. See infra.

page 461 note 1 An analogous expression is bauxitic clay used by Watson, T. L. in his account of the “Bauxite Deposits in Georgia”, Bull. No. 11, Geol. Surv. Georgia, p. 52, 1904.Google Scholar

page 461 note 2 Mem. G.S.I., xxxvii, p. 381, 1909; and infra.Google Scholar

page 461 note 3 See infra for the use of the term laterite in a stratigraphical sense.

page 461 note 4 Mallet, , Rec. G.S.I., xvi, p. 103, 1883.Google Scholar

page 461 note 5 Mem. G.S.I., xxxvii, p. 375.Google Scholar

page 462 note 1 I must point out here the logical sequence of the adoption of this term lake laterite. If one is to apply the term to pisolitic iron-ores that have been deposited by chemical precipitation from a body of water, and are, in addition, associated with bodies of typical laterite, it is difficult to avoid its extension to include those deposits of iron-ore, manganese-ore, and bauxite that have been formed in an identical manner, but are not associated with lateritic rocks. All the deposits classed as bog iron-ores and lake ores in textbooks on ore-deposits could then be called lake laterites, and also the sedimentary manganese-ore deposits. The lake iron-ores of Sweden, the bog iron-ores of various parts of Northern Europe, the manganese deposits of the Caucasus, and perhaps the iron-ores and bauxites of Antrim, must then all be classed as lake laterites of various ages. Further than this, if my theory of the origin of the manganese-ore deposits of the gondite series of the Central Province is correct (loc. cit., pp. 308–19, 365), they are to be regarded as in part (the primary ores) the product of metamorphism of a series of manganese-oxide sediments, chemically deposited in lake basins, and interlaminated with mechanically deposited sands and clays, the whole series representing a metamorphosed Caucasus (as has been noticed by Launay, De in his recent work La Géeologie et les Richesses, Minérales de l'Asie, p. 698, 1911)Google Scholar. These Indian deposits are therefore metamorphosed lake laterites. However, I do not wish to give this extended meaning to the term, but insert this footnote merely to draw attention to the real significance of the existence of the lake laterites, if any such can be proved to exist. There is to me nothing objectionable in this term lake laterite, nor in its possible wide extension as outlined above, if fellow - geologists think it desirable. This possibility merely serves to point out the inherent chemical relationship between the typical laterites and many deposits of iron, manganese, and aluminium ores all over the world, which, whilst differing from true laterites in mode of occurrence and formation, are yet related to them through the lake laterites as denned in the body of this paper.