Partial recursive functions and minimization

Hi all,

let's have partial recursive function F, which is not recursive. I
don't understand, why

G(x) = Min(y) (F(x,y) = 0)

(where Min(y) is just minimization operator or unrestricted mu-
recursion)

is not partial recursive function.

Could someone please explain this to me?

Thank you very much.
.