During the electrolytic refining of copper using acidified $\mathrm{CuSO}{}_4$ electrolyte with an impure copper anode, the metals that collect as anode mud are

Ag and Au are less reactive than copper and are not oxidised at the working potential; they fall from the anode as mud. Fe and Zn are more easily oxidised than Cu, go into solution as ions and are not deposited at the cathode.