In Pathfinder, a lich has a natural touch attack that deals negative energy damage. If a lich casts Chill Touch and touches an enemy, does he deal his normal touch attack damage plus the 1d6 damage from Chill Touch, or does the 1d6 damage from Chill Touch replace his normal touch attack damage?

In Pathfinder, a lich has a natural touch attack that deals negative energy damage. If a lich casts Chill Touch and touches an enemy, does he deal his normal touch attack damage plus the 1d6 damage from Chill Touch, or does the 1d6 damage from Chill Touch replace his normal touch attack damage?

Note: The question is inspired by this character from the Kingmaker adventure path, an unusually low-level lich who has Chill Touch as one of his few damaging prepared spells (his published tactics seem to think that he can deal damage by channeling negative energy, forgetting that necromancers can only do that to Turn/Control Undead).