The Concentration and Distribution of Boron in the Keweenawan Metabasalts of Mamainse Point, Ontario

Abstract

<p> Nine rock samples from the mafic volcanics of Mamainse Point, Ontario were analysed for boron using Prompt Gamma Neutron Activation Analysis (PGNAA) and Alpha-Track Imaging (ATI). The mean concentration of boron in these rocks was 7.85 ppm with a maximum concentration of 15.5 ppm and a minimum concentration of 4.21 ppm. The Mamainse Point samples are therefore enriched in boron relative to fresh basalts (~ 2 ppm B) but depleted relative to basalts altered on the seafloor (30 - 60 ppm B). From ATI the boron was found to be most highly concentrated in iron oxides, chlorite, stilpnomelane and microscopic fractures throughout the rock. Plagioclase, clinopyroxene, quartz and calcite were all low in boron.</p> <p> These results led to the conclusion that the Mamainse Point Formation is of continental rather than marine origin. The addition of boron to the rock has resulted from penecontemporaneous burial and hydrothermal metamorphism in the zeolite and subgreenschist facies through the interaction of boron-bearing hydrothermal fluids. The source of the boron is thought to be from the surrounding Precambrian terrain (Canadian Shield), the lower continental crust and magmatic fluids associated with volcanism.</p>