Strontium Isotopes and Trace Elements in Carbonatites and Limestones from Ice River, British Columbia

Abstract

HIGH in the westerly ranges of the Canadian Rockies the Ice River alkaline complex, described in a classic memoir by J. A. Allan¹, intrudes the Ottertail Limestones (of Cambrian age) forming an extensive metamorphic aureole of contact skarns and hornfels. In the heart of the complex, on Aquilla Ridge, is a large mass of carbonate rocks which Allan described as an “abnormally large xenolith” of metamorphosed Ottertail Limestone “at least ¾ mile long”, but which J. E. Rapson^2,3 has recently shown to be even more extensive and to consist of intrusive carbonatites. This locality is therefore a particularly favourable one in which to test certain isotopic and chemical criteria which are used to differentiate carbonatites from metamorphic limestones, and for this purpose we have examined a small series of specimens provided by J. E. Rapson. They comprise five carbonatites from Aquilla Ridge, three metamorphosed limestones from the contact of the nepheline syenites and ijolites with the Ottertail Limestone, and four specimens of unaltered Ottertail Limestone, one from nearby, and three from the Palliser River area 60 miles to the south-east, far from any possible effects of the intrusion. The Palliser River specimens, collected by Dr. G. B. Leach and donated by the Geological Survey of Canada, are from three well-spaced points in a stratigraphic section 1.450 ft. in thickness.