MG-FE-CS-NA AQUAMARINE BERYL FROM REVELSTOKE, BRITISH COLUMBIA, CANADA: DISCOVERY OF UNUSUAL MINERAL CHEMISTRY, AND IMPLICATIONS FOR CRYSTALLIZATION OF MELTS AND FLUIDS OF THE HOST LEUCOGRANITE

An aquamarine of unusual chemistry from Revelstoke, British Columbia, Canada, was uncovered while investigating beryl crystal-chemistry using 113 samples from around the world. The identification as anomalous was possible due to analysis of a large chemical data sets, which allowed differentiation between what is standard mineral crystallization and what is unusual. It has high Mg, Fe, Cs, and Na, a combination which is exceedingly rare, and has only been previously documented in one other locality.

The rim of this aquamarine has Mg > Fe, which occurs predominantly in emerald, and no other beryl variety. The Fe content is higher than most other aquamarine recorded, especially for one in a granitic environment. Additionally, it has high Cs content, which tends to occur in Li-bearing beryl like goshenite and morganite. The core zones of the aquamarine are less elevated in Mg, Fe, and Cs than most other aquamarine, but maintain high proportions of Mg to Fe.

These aquamarine occur in peraluminous leucogranite boulders downhill from Twin Butte and Llewlyn W5, peaks immediately east of Revelstoke, BC, which display early fractionation and pegmatitic tendencies via presence of beryl and fine lines and occurrences of garnet. The aquamarine in particular is useful in documenting the change in melt/fluid due to the prominent chemical zonation. The host granite does not display anomalous enrichment in Mg, Fe, or Cs in other minerals. Spessartine-almandine garnets occur as inclusions in beryl, at the rims, and within the host rock outside of beryl, and appear to be the primary sink for Mn and Fe. Other accessory minerals also display chemistry of interest, including zircon with elevated Sc. The composition of the aquamarine here also differs from beryl recorded on neighboring mountains of Boulder Mountain and Mount Begbie, immediately west of Revelstoke, demonstrating that beryl from the same region cannot reliably be considered the same, and could be hold subtle clues about regional geology.