Li-BEARING ARFVEDSONITIC AMPHIBOLES FROM THE STRANGE LAKE PERALKALINE GRANITE, QUEBEC

The crystal structures of seven alkali amphiboles from the Strange Lake alkali intrusion have been refined to R values of 1–2% using single-crystal MoKa X-ray data. Crystals used in the collection of the intensity data were subsequently analyzed by electron- and ion-microprobe methods. Site occupancies were assigned by site-scattering refinement and stereochemical considerations, taking into account the electron- and ion-microprobe analysis of each crystal. These amphiboles are arfvedsonite and manganoan arfvedsonite, and have anomalously low X-ray scattering at the M(3) site. Ion-microprobe analysis shows the presence of significant Li in all of these amphiboles (up to 0.63 wt%, equivalent to 0.40 Li apfu), and the site-scattering refinement shows Li to be completely ordered at the M(3) site. Ion-microprobe analysis also shows some dehydrogenation that correlates with the amount of Ti in the amphibole. The amphiboles show several interesting chemical correlations: (1) the Mn and Zn contents show a very strong positive correlation; (2) the K and Al contents (0.02 < Al < 0.08 apfu are very strongly inversely correlated; (3) the Li and Ca contents show a strong negative correlation. The sample order in correlations (1) and (2) is the same, supporting the idea that these correlations are petrogenetic rather than crystal-chemical.