Rule 605.1a

An activated ability is a mana ability if it meets all of the following criteria: it doesn’t require a target (see rule 115.6), it could add mana to a player’s mana pool when it resolves, it’s not a loyalty ability (see rule 606, “Loyalty Abilities”), and its cost and effect don’t move any card to or from a library. Do not take into account replacement effects that may apply, other than self-replacement effects, when evaluating these criteria.