March 23/14-The Flair Airlines Boeing 737-400 (C-FLEJ) was operating as flight FLE783 from Whitehorse, YT (CYXY) to Yellowknife, NT (CYZF). While taxiing for departure a fuel leak was noticed. The aircraft returned to the apron where a rapid deplanement was conducted. ARFF was called to attend to the spill. Company maintenance determined that the leak was isolated to the auxiliary fuel tank. The tank was emptied and locked out as per the maintenance manual. The auxiliary fuel tank was deferred in accordance with MEL 28-19 and the aircraft was returned to service.