TOURMALINE CONCENTRATIONS IN PROTEROZOIC SEDIMENTS OF SOUTHERN CORDILLERA OF CANADA AND THEIR ECONOMIC SIGNIFICANCE

Local concentrations of tourmaline occur in the lower Proterozoic (Helikian) Aldridge Formation of southeastern British Columbia, Canada, in some places in association with stratiform lead-zinc mineralization as at the Sullivan, Stemwinder, and North Star orebodies. The amount of boron in the rock is as much as two orders of magnitude above average levels reported for the Aldridge Formation or other similar types of sedimentary rocks. The concentrations are not detrital, but are caused by an anomalously high boron level, in a local area, at the time of sedimentation. The appearance of tourmaline within rip-up clasts, and in laminae within pebbles, is evidence of syngenetic introduction of boron. Three populations of tourmalines, on the basis of composition as determined by microprobe analyses, are described from the area. The economic importance of tourmaline concentrations in the Aldridge Formation is their association in both space and time with stratiform sulfides. Refs.