Voga

Voga, also known as the Planet of Gold was a planet with an extremely high gold content. It contained more gold than in the rest of the known galaxy and with rocks being 50% gold, sometimes even higher. (DWN: Revenge of the Cybermen) The Doctor commented on the planet being worth more than a thousand 19th century sovereigns. (TDA: Wishing Well)

Voga was originally a full sized planet, inhabited by the Vogans. During the Cyber-Wars, the Vogans started supplying the gold dust which would be used in the manufacturing of glitterguns. The Cybermen tried to stop this by destroying the planet, but one emergency bunker survived, which started drifting in space. Centuries later, it was captured in Jupiter's orbit. The Cybermen later discovered the planet again and attempted to destroy the remaining gold. (DWN: Revenge of the Cybermen)