. Bulletin of the British Museum (Natural History), Geology. /P° "SPILOSITES + DESMOSITES" Fe203 + MgO+CaO MC11 SC21 MC10 Fig. 5 Ternary diagram (modified after Agrell, 1939) delineating fields for 'adinole', 'spilosites + desmosites' and 'slate'. Samples plotted are all the Dinas Head sediments, and those labelled are referred to in the text. field, albite is a major mineral phase, whereas mica and chlorite are predominant in sediments from the 'slate' field. It is also noteworthy that true 'adinoles' occur in all 4 sections sampled, illustrating the extensive distributio
. Bulletin of the British Museum (Natural History), Geology. /P° "SPILOSITES + DESMOSITES" Fe203 + MgO+CaO MC11 SC21 MC10 Fig. 5 Ternary diagram (modified after Agrell, 1939) delineating fields for 'adinole', 'spilosites + desmosites' and 'slate'. Samples plotted are all the Dinas Head sediments, and those labelled are referred to in the text. field, albite is a major mineral phase, whereas mica and chlorite are predominant in sediments from the 'slate' field. It is also noteworthy that true 'adinoles' occur in all 4 sections sampled, illustrating the extensive distribution of adinoles at Dinas Head. Samples rich in C02 plot towards the (Fe203+FeO+MgO+MnO+CaO) apex of the ternary dia- gram. Sediments from the Stinking Cove section appear to differ from those of the other sections in that they plot either as true adinoles ( SC11 and SC16), or in the 'slate' field of the ternary diagram ( SC20A, Fig. 5). All of the samples in the 'slate' field are boron-rich, although some adinoles at Stinking Cove are also boron-rich ( SC21, NA20 = , B = 550 ppm), but with lower boron concentration levels. It appears likely that the introduction of boron was concomitant with removal of sodium. The sample of unaltered fissile slate collected from the Stinking Cove section (SC6) plots well within the 'slate' field. Slate samples collected well away from the intrusive dolerites at Stepper Point (ST5) and Trevone Bay (TR3), also plot very close to the Dinas Head slate sample on all the geochemical diagrams presented ( Figs 6, 10 and 11). +AI203 A Dolerites (GROUP 2) *B>400ppm (GROUP 3) + Other Samples (GROUP 4) TR2 SEDIMENT TR3 SLATE ST1 SEDIMENT ST5 SLATE SC6 SLATE CAT2 SEDIMENT "ADINOLES "SLATES" PC5 SEDIMENT "SPILOSITES - DESMOSITES" Fe203 + MgO+CaO Fig. 6 Apices as for Fig. 5. Samples plotted are: dolerites — GROUP 2 (filled triangles): sediments with B>400 ppm — GROUP 3 (stars); sedime
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