During the process of electrolytic refining of copper, some metals present as impurity settle as 'anode mud'. These are:

In the electrolytic refining of copper, less reactive metals (noble metals) that are present as impurities do not get oxidized at the anode potential. As the anode dissolves, these metals fall to the bottom of the tank as anode mud. Common examples include $\text{Ag},\text{Au},\text{Pt}$, $\text{Se}$, and $\text{Te}$.