605.1 Some activated abilities and some triggered abilities are mana abilities, which are subject to special rules. Only abilities that meet either of the following two sets of criteria are mana abilities, regardless of what other effects they may generate or what timing restrictions (such as “Activate only as an instant”) they may have.
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.
(refs: 115.6, 606)
605.1b
A triggered ability is a mana ability if it meets all of the following criteria: it doesn’t require a target (see rule 115.6), it triggers from the activation or resolution of an activated mana ability (see rule 605.1a) or from mana being added to a player’s mana pool, and it could add mana to a player’s mana pool when it resolves.
(refs: 115.6, 605.1a)