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The sequential development of kaolin by progressive alteration of smectite, involving kaolin-smectite interstratifications as a genetic link is described from a red and black complex. Mineral compositions were studied using XRD, DTA and XRF techniques. The basaltderived soils are situated along a 600 m transect and grade in colour from dark grey (10 YR 3/1 ) to red (5 YR 3/3). The kaolin proportions in the interstratification increase almost linearly with increasing reddening up to ~80%. Whole-soil chemical analyses exhibit no significant variations in the major element composition, but dithionite extractable Fe increases along the transect from 1% to 4-16%. Hematite and goethite are the only secondary iron phases. Topographic differences are slight but sub-surface bedrock contours plus appreciable variations in sand content between red and black soils could be genetically significant.

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DepositsFor optimum bauxitisation conditions a relatively stable geomorphological history is essential. On the Gove and Mitchell Plateaux therefore, the adverse effects of land emergence and ensuing planation are counteracted by associated mild synclinal warping, so that the deposits constituted coastal hinge zones of at least two successive land (erosion) cycles. Nevertheless, following the main Cretaceous and Tertiary period of bauxitisation by leaching, the deposits were partially submerged by the sea and, particularly at Mitchell Plateau, extensively reworked. Assisted by quantitative heavy mineral studies distinct unconformities within several bauxite profiles can be established. Finally, the quantitative mineralogy of both deposits is discussed in some detail and an origin (supported by experimental studies) proposed.Die beste Voraussetzung fiir eine optimale Bauxitisation ist geomorphologische Stabilitfit. Auf den Gove-und Mitchell-Plateaus wirken den gegens~tzlichen Auswirkungen yon Landhebung (epirogenetischer Bewegung) und darauf folgender Abflachung (dutch Erosion) damit verbundene schwache synklinale Verzerrungen entgegen, so dab die Bauxit-Lager i3bergangszonen zweier Kiistengebiete von mindestens zwei aufeinanderfolgenden Erosions(gel~nde)zyklen bildeten. Nach der Kreide-und Terti~r-Periode der Bauxitisation dutch Eigenauslaugung lagen diese Gebiete teilweise unter dem Meeresspiegel und wurden vor allem am Mitchell Plateau weitgehend aufgearbeitet. Mit Hilfe yon quantitativen Analysen yon Schwermineralen k6nnen deutliche Diskordanzen zwischen mehreren Bauxitprofilen festgestellt werden. AbschlieBend wird die quantitative Mineralogie beider Lager detailliert diskutiert und deren Ursprung (gestiitzt auf experimentelle Untersuchungen) vorgeschlagen.