21 Lutetia is one of the largest asteroids in the main belt, with properties that defy our current understanding of the formation of asteroids. It seems to have the kind of irregular shape which suggests one of the metallic asteroids, but by spectral properties and probe analysis, we know it to have a rocky surface. It could perhaps be an amalgamation of both metal and rocky material. In fact its high density seems to necessitate it.
A 10 square mile claim would be enough for basic mining operations and local support structure. Hypothetical estimated value in 2021 USD $1 trillion. The number of available claims is limited to 1,161.
Image Credit: ESA / NASA / JPL-Caltech