Winchester is a particularly valuable and large asteroid of near incalculable wealth. It is of the C type of carbonaceous asteroids. It has organic volatile compounds for fuels, water for crews, and a wide range of rare earth elements.
A 10 square mile claim would be enough for basic mining operations and local support structure. Hypothetical estimated value in 2017 USD $1 trillion. The number of available claims is limited to 5,200.
Image Credit: NASA / JPL-Caltech