Johannesburg's nickname is ‘the city of gold'. What does the speaker mean when he refers to the gold as ‘judas' (line 2)?
The speaker is making a comparison to Judas Iscariot, a biblical figure who betrayed his Lord for money. Because of its betraying value, the gold is referred to as Judas here. The gold is untrustworthy, and it has the ability to turn its back on you or cause someone else to do so. Gold breeds greed, which leads to betrayal.
Deception and lying are common in Johanesburg because of its gold. People who come to Johannesburg to make a name for themselves should be aware that it is not a place for the faint hearted to make an honest living. Much of this is due to the gold, which has the ability to turn otherwise honorable people into criminals, conmen, and a variety of other vices that deal with deception and lying to others.