Anode mud contains metals like Ag, Au, Pt etc. Which are less reactive than Cu. Actually, they are not in a position to lose electrons though they constitue the electrode which acts as anode. All these metals are left as residue under anode (known as anode mud) while the entire copper present participates in the oxidation half reaction.
`Cu(s) to Cu^(2+)(aq)+2e^(-)`
