Hydrothermal and metamorphic berthierine from the Kidd Creek volcanogenic massive sulfide deposit, Timmins, Ontario

Berthierine, a 7 Å Fe-Al member of the serpentine group, occurs in the footwall stringer zone of the Archean Kidd Creek massive sulfide deposit, associated with quartz, muscovite, chlorite, pyrite, sphalerite, chalcopyrite, and local tourmaline, cassiterite, and halloysite. Petrographic and scanning electron microscopic (SEM) studies reveal different types of berthierine occurrences, including interlayers within the rims on deformed chlorite, intergrowths with muscovite and halloysite, and discrete coarse grains. This is the first reported occurrence of berthierine from volcanogenic massive sulfide deposits. Textural relations suggest that most of the berthierine formed as a primary hydrothermal mineral at relatively high temperatures (~350°C) in the footwall stringer zone, probably by the replacement of a pre-existing aluminous phase such as muscovite or chlorite. However, the intergrowth textures observed by SEM and TEM suggest that some of the berthierine originated by syn- or post-metamorphic replacement of chlorite. -from Authors