Gold

Gold is a chemical element much prized by Humans, and a major weakness of Mondasian Cybermen. Owing to its non-corrossive nature, gold essentially choked their respiratory systems. The glittergun, a weapon used during the Cyber-Wars, fired gold dust at its targets to exploit this weakness.

Gold appeared to affect some varieties of Cybermen in the way that silver affected werewolves, so that gold coins or gold-tipped arrows fired at them had the same effect. (DW: Silver Nemesis)

Other weaknesses of Cybermen included solvents and excessive levels of radiation.

During a time period in which Cybermen had been reduced to small remnant groups wandering around the galaxy, one group tried to take revenge by making a desperate attempt to blow up the remnants of the planet Voga, a planetoid of pure gold that had wandered into the Sol system and become a moon of Jupiter. They hoped that this would disrupt their enemy's supply of the metal. (DW: Revenge of the Cybermen)