Tysir IV

Tysir IV was a planet that was colonized by a mining corporation. During one of the digs, the robotic diggers were drawn to traces of metal, initially assuming a huge seam of ore. However, unearthed an ancient metallic structure which was later revealed to be a Cybermen base. The base contained a plague created by the Cybermen to be deadly to humans. (BFBS: Silver Lining)