Tysir IV

Tysir IV was a planet that was colonised 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, they unearthed an ancient metallic structure which turned out to be a Cybermen base. The base contained a plague created by the Cybermen that was deadly to humans. (BFBS: Silver Lining)