The distribution and significance of the trace elements in the Braefoot Outer Sill, Fife

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Abstract
The Braefoot sill magma has been shown by Campbell, Day and Stenhouse (1933 and 1934) to have differentiated into picroteschenite, teschenite, dolerite pegmatite, dolerite, basalt and microsyenite. The trace-element contents of these rocks have now been determined by semi-quantitative methods in order to study the behaviour of the trace elements during the progress of differentiation. It is found that Cr and Ni concentrate in the early stage of crystallisation; Co, V, Cu and Sr in the intermediate stage; and Li, Rb, Ba, Ga, La, Y and Be in the late stage. Sc is enriched in the early and intermediate stages. Zr remains uniform in the early and intermediate stages but increases later. Ag is enriched in the early stage and Mo in both the early and late stages. The variations in Sn, Tl, Ge and In cannot be recognised by present methods because these elements occur only in amounts below their limits of sensitivity. The inter-relationships between certain trace elements are discussed. It is found that the rocks of the early and intermediate stages are characterised by the distribution Cr>Ni>Co and Sr>Ba, whereas the rocks of the late stage have Ni>Co>Cr and Ba>Sr. Certain ratios seem to furnish a guide to the degree of differentiation represented by a given rock. (Mg+Fe 2 +Fe 3 )/(Na+K+Ca) and (Cr+Co+Ni+V+Cu)/(Rb+Ba+Sr) decrease during the progress of the differentiation, while Li/Mg, Rb/Sr, Rb/Ba, Rb/K and Ga/Al increase. Fe 2 /Mg and (V+Co)/(Cr+Ni) reach their highest values in the intermediate stage.