The Deep Mine is the unique faction structure for the Gorons. It is a superior mine with much higher income than its regular equivalent. A Deep Mine costs 5000 Rupees and requires at least a City-level Settlement to construct.
The Gorons are undoubtedly some of the best miners in all of Hyrule. Their natural affinity for dwelling under the earth has allowed them to dig deeper then any other race could ever hope to. A Deep Mine can be constructed in any Goron city to tap into valuable resources in the ground, even if there are no resources visible in the area.