Differentiation of the Elzevir magma into eight phases progressed with the concentration of radioactive elements in later, more acidic members, and culminated with relatively radioactive pegmatites and weakly active veins. The distribution of radioactivity in related rock types is such that it has correlative value. The results of several hundred determinations of radioactivity have shown a tendency for the heaviest elements to concentrate in the periphery of batholiths or stocks. In intrusives greater than 2 miles across, a core zone of lower than average radioactivity may be present if erosion has removed the roof.
Several variables must be considered if sampling for radioactivity research is to be representative. Regional differences in radioactivity suggest a steeper geothermal gradient in southeastern Ontario than in western Quebec. Local differences in the radioactivity of batholiths may be important in influencing the course of differentiation, syntexis, and refusion at depth.