Tourmaline concentrations in Proterozoic sediments of the southern Cordillera of Canada and their economic significance

Abstract

Local concentrations of tourmaline occur in the lower Proterozoic (Helikian) Aldridge Formation of southeastern British Columbia, 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:(1) A Proterozoic stock intruding the Aldridge Formation contains abundant schorl.(2) A tourmaline intermediate in composition between dravite and schorl is typical of Aldridge metasediments. Texturally this type occurs as (a) fine felted aggregates in the footwall of the Sullivan orebody, (b) disseminated through waste beds, and (c) in local concentrations removed from the Sullivan orebody.(3) Coarse-grained recrystallized tourmaline associated with the Sullivan ore is magnesiumrich. Recrystallization is erratic, and is probably related to uneven heat flow during metamorphism and to differences in bulk composition.The economic importance of tourmaline concentrations in the Aldridge Formation is their association in both space and time with stratiform sulfides.Des concentrations locales de tourmaline se rencontrent dans la formation d'Aldridge, datant du Proterozoique inferieur (Helikien), au sud-est de la Colombie-Britannique, assocites en certains endroits a des gisements stratiformes de mineralisation plomb-zinc comme les gites de Sullivan, de Stemwinder et de North Star. La teneur en bore de la roche atteint jusqu'a deux ordres de grandeur de plus au-dessus des teneurs moyennes rapportees pour la formation d' Aldridge ou d'autres types de roches ddimentaires semblables. Les concentrations ne sont pas dktritiques mais ont et6 causees par une teneur en bore anormalement elevke, localement, au moment de la sedimentation. L'apparition de tourmaline dans des galets fendus et en lamelles dans des cailloux est une preuve de l'introduction syngenetique de bore.On decrit dans cette region trois populations de tourmalines, en se basant sur leur composition telle que determinee par analyse a la microsonde:(1) Un stock proterozoique qui penetre la formation d'Aldridge contient de la shorlite en abondance.(2) Une tourmaline de composition intermediaire entre la dravite et la schorlite est typique des metasediments d'Aldridge. La texture de cette tourmaline se presente (a) sous forme d'agrkgats fins feutres dans le mur du gisement de Sullivan, (b) disseminee a travers les lits de roche sterile et (c) sous forme de concentrations locales eloignees du gisement de Sullivan.(3) Une tourmaline recristallisee agrain gros...

Coupled Substitutions in Schorl-Dravite Tourmaline: New Evidence from SE Ireland

“…Replicate analyses indicate reasonable agreement with the levels of precision and accuracy found for these instruments by Sweatman and Long (1969) and by Dunham and Wilkinson (1978). No evidence of beam damage (Reed, 1975;Ethier and Campbell, 1977) was observed during analyses.…”

Tourmalinites from Belgium and from SE Ireland—a discussion

“…In the quoted instance, and in others like it, it is probable that anomalously high boron levels, essentially of volcanic origin, existed at the time of original sedimentation (e.g. Ethier and Campbell, 1977;Slack, 1980). The spessartine quartzites of SE Ireland are coticules as originally defined by Renard (1878).…”

Tourmalinite from northern Guangxi, China

“…Metashale in the northern Guangxi, although rare, has an average boron abundance of 112 ppm Boron is a relatively mobile element. In aqueous solution it commonly occurs in the form of B(OH)s NaB(OH)g, HzBOg , and BO3 (Ethier and Campbell 1977). The abundance of tourmaline in ore deposits, to some extent, indicates a high activity of boron in hydrothermal fluids during mineralizing processes.…”