The scan shows nothing major beneath the ground, just the tectonic plates moving around. Something metallic was also down there beneath the earth, but it was easy to assume that it was an ore of some kind.
Over at the mineral clusters, as the Construction Drone collects the mineral shards, three of them rise up on their own, with two of them aiming at the Shade, and one at the Drone. They fly forward toward their targets, something guiding them toward their targets.
Several sections around each base had tunnels, possibly from natural burrowing predators. Although the Protoss and the Ser'vanar would not be able to make use of such tunnels, the Zerg creatures would be able make use of them.