# Why would you reasonably expect cadmium to be a contaminant in zinc but not in silver?

Well, cadmium commonly forms a $C {d}^{2 +}$ ion as does $Z {n}^{2 +}$.
Silver commonly forms the univalent, $A {g}^{+}$ ion, so it could not directly replace $Z {n}^{2 +}$ in ores. As I recall, and you will have to read up on this, most heavy metal mining firms have silver, lead, zinc operations; these are a very common mixture of ores.