"After defeating the Snowfield Slayers, Complete Crystallite Ingots will occasionally drop where they spawn."

Did the event on my elf next, this screenshot of the place they dropped, shows pretty clearly that the ores drop in a circle, the slayers spawned all over the place, died all over the place, and were rarely in that circle.

EDIT: After doing the event a few more times, it looks like they just spawn in a circle around where you start in the mission.