Reactions of Depressants
Ok, after having poked around a bit I doubt that $\ce{Pb(CN)2}$ forms. 

I'm guessing that you're collecting the froth to get a concentrate of the galena $\ce{PbS}$ out of some finely crushed ore. 

An aspect of the operation seems to be chemically reducing the concentration of $\ce{ZnS}$ by dissolving via the following reaction:

$$\ce{ZnS(s) + 4NaCN(l) -&gt; Zn(CN)4^{2-}(l) + 2Na2S }$$ 

Now there are two ways that $\ce{ZnS}$ could be mixed in with the $\ce{PbS}$. 

(1) The individual $\ce{Zn^{2+}}$ cations replace individual $\ce{Pb^{2+}}$ cations in the $\ce{PbS}$. In this case the random distribution of the $\ce{Zn^{2+}}$ cations wouldn't allow much extraction of $\ce{ZnS}$ as $\ce{Zn(CN)4^{2-}}$. The $\ce{Zn^{2+}}$ cations just are not going to diffuse through the solid galena particles to any appreciable extent. 

(2) There could be also be that the crushing creates a mixture of relatively pure $\ce{PbS}$ and $\ce{ZnS}$ particles which are mixed together. In this case an appreciable amount of the Zn impurity could be removed.  



Now for what seems to be the question. $\ce{PbS}$ is very insoluble with a $K_\mathrm{sp} = 9.04\times10^{−29}$. I couldn't find a solubility product for $\ce{Pb(CN)2}$ but it is doubtful that the solubility would be enough to cause the lead sulfide to dissolve and then form lead cyanide.