Enceladus is certainly a promising moon for a mining operation, with its small size and high density indicating that the moon has a large silicate core, which may contain useful materials, though it would certainly be a risky trip due to the high-pressure subsurface ocean, a global feature of this tiny moon.
The rest of the moons in the Saturn system left unclaimed are pretty much iceballs, with Tethys being the worst offender of all.
Meanwhile, further out, Phoebe is composed of a wide variety of materials, and possibly lots of heavy elements, too. With low gravity, it sounds like a great place for a mining operation.