i have my own answer here but I'm not 100% sure so might as well ask
Gambanteinn has 25% chance of +200% elemental damage.. that proc elemental damage should also apply to spells right since it's from an artifact? like ice shard, volcanic orb, eruption?
actually even if it's from a weapon i think it should apply also to spells because it's also %elemental damage, just a proc