Li-bearing arfvedsonitic amphiboles from the Strange Lake peralkaline granite, Quebec

The crystal structures of seven sodic amphiboles from the Strange Lake pera lkaline granite, on the Quebec-Labrador border, have been refined to R valu es of 1.3-1.7% using single-crystal MoK alpha 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-scatte ring refinement and stereochemical considerations, taking into account the electron- and ion-microprobe data for each crystal. These amphiboles are li thian arfvedsonite and lithian manganoan arfvedsonite, and have anomalously low X-ray scattering at the M(3) site. Ion-microprobe analysis shows the p resence of significant Li in all of these samples (up to 0.63 wt%, equivale nt to 0.40 Li apfu), and the site-scattering refinement shows Li to be comp letely ordered at the M(3) site. Ion-microprobe analysis also shows evidenc e of limited dehydrogenation that correlates with the amount of Ti in the a mphibole. 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 inversely correlated; (3) the Li and Ca contents show a strong negative correlation. The sample order in co rrelations (1) and (2) is the same, supporting the idea that these correlat ions are petrogenetic rather than crystal-chemical. Moreover, similar corre lations occur in similar amphiboles from the Virgin Canyon pluton, New Mexi co.