Anomalous ‘Common Strontium’ in Granite

Abstract

THE term ‘common strontium’ is customarily used to denote the element as found in minerals with high ratios of strontium to rubidium. These include strontium-rich minerals such as celestite and also many common rock-forming minerals containing strontium in the parts per million concentration range. All analyses reported so far, with the single exception of meteoritic strontium, indicate that the isotopic abundances of common strontium are constant to within a few per cent. In particular, no significant increase has been found in the world-wide strontium-87 abundance due to the continual addition of radiogenic strontium with time¹, nor has any case been previously reported of strontium-87 enrichment due to local mixing with radiogenic strontium. In this communication, we wish to cite an instance of local strontium-87 enrichment: two common strontium minerals isolated from a Precambrian granite at Boya near Perth, Western Australia, show strontium-87 abundances some 8 per cent higher than the ‘normal’ value, while the common strontium for the granite as a whole is apparently some 15 per cent higher.