Mineralogy and petrology of the petalite-subtype Prof pegmatite, Revelstoke, British Columbia, Canada

Abstract The Prof pegmatite is located NW of Revelstoke, British Columbia, Canada on Boulder Mountain. Due to the abundance of petalite, the pegmatite is classified as a petalite subtype Li-Cs-Ta pegmatite or a Group one pegmatite. The Prof pegmatite contains a suite of minerals indicative of a highly evolved pegmatite melt including petalite, elbaite, lepidolite and Nb–Ta oxides. Four textural zones are present: (1) border; (2) intermediate, including (2.1) graphic texture dominant and (2.2) overgrowth dominant, where diverse minerals form rims around one another; (3) central; and (4) quartz. The border zone has a similar mineralogy to the intermediate zone and is interpreted to represent a chilled margin. The intermediate zone has a feldspar, mica, garnet and dravite–schorl dominant composition. The central zone hosts an evolved pegmatite core, which contains the majority of the lithium mineralisation composed of petalite, elbaite and lepidolite. The tourmaline, Nb–Ta oxides and mica within the pegmatite record the geochemical evolution of the melt from more primitive Fe- and Mg-rich minerals to a Li-, Mn- and Nb-rich assemblage indicative of a highly evolved geochemical system. The various pegmatitic textures and extremely fractionated geochemical composition of the pegmatite indicate that the melt was undercooled and crystallised rapidly. Three phases of metasomatism are recognised in the Prof pegmatite: an albitisation event observed cutting primary orthoclase; followed by a transition to a Na–Li–F-rich event mostly containing secondary albite, trilithionite and elbaites; and a sericitisation event. The Prof pegmatite has a similar mineralogy to known pegmatites at Mount Begbie, 15 km to the south, in particular the notable presence of the rare mineral qitianlingite, petalite, lepidolite and elbaite. Together, these pegmatite bodies form part of an extensive, poorly mapped pegmatite field. Additional work is required to assess the extent and nature of mineralisation within this field.