[Saulot]

@Sombre: Thanks.

These would be weapon flysprites (Table 5 in the modding.pdf), yes. (Though if I recall correctly they also appear to use some graphics from the explosion sprites (Table 4).)

To elaborate for anyone unsure, there are also weapon explosion sprites, spell flysprites, and spell explosion sprites, which all share the same group (Table 4 or FX 10000-10257).

Edit:
@llamabeast:
Well, AFAIK the explosion sprites for fireball are listed but I'm unsure of whether one can make a working fireball from scratch (Or a spell that looks like a fireball but does something different). Personally, I've found copyspell to be a much easier way to go, but is there any reason why using copyspell and editing from there wouldn't do the trick for you?