I ask this question because I don't know if we can enchant a guilgate, like a boros guildgate as example, with Chained to the Rocks.
"Mountain" can mean two things:
- An object whose name is "Mountain". e.g. Mountain
- An object which has the land (sub)type "Mountain". e.g. Mountain and Steam Vents
When a card refers to something that can be a name or a type, it always refers to the type. As such, Chained to the Rocks looks for objects with the land type "Mountain".
- A Mountain does have that type. It can be enchanted by Chained to the Rocks.
- A Mountain enchanted by Contaminated Ground does not have that type. It is a Land, it is a Basic, and it is a Swamp, but it is not a Mountain (despite having that for name). It cannot be enchanted by Chained to the Rocks.
- A Steam Vents does have that type. It can be enchanted by Chained to the Rocks.
- A Boros Guildgate does not have that type. It is a Land, and it is a Gate, but it is not a Mountain. It cannot be enchanted by Chained to the Rocks.
For references to permanents, this is covered by 109.2.
109.2. If a spell or ability uses a description of an object that includes a card type or subtype, but doesn’t include the word “card,” “spell,” “source,” or “scheme,” it means a permanent of that card type or subtype on the battlefield.
The same is understood to apply for references to non-permanents, though this is not explicitly stated in the rules.