Does Unbridled Growth provide two mana or one?
You don't get two mana. If you enchant a basic land (mountain, forest, etc.) then it now essentially has two abilities. For example, if you enchant a mountain, then it's as if that mountain now reads:


  {T}: Add {R} to your mana pool.
  {T}: Add one mana of any color to your mana pool.


So you can tap it for the first ability, or the second. You don't get to do both (just like you can't tap a creature to attack and use an activated ability).

Alternatively, you might enchant a non-basic land. For example, also from Aether Revolt is the land Spire of Industry. If you enchant it with Unbridled Growth, then it's as if the card now reads:


  {T}: Add ◊ to your mana pool.
  {T}, Pay 1 life: Add one mana of any color to your mana pool. Activate this ability only if you control an artifact.
  {T}: Add one mana of any color to your mana pool.