[Arkcon]

Free metallic copper, which is occasionally found native, (you will have to check, perhaps microscopically, in your particular ore sample) only reacts with hot concentrated nitric, and evolves many nitrogen oxides, not just NO₂ (and it's equally nasty nasty partner N₂O₂) but even N₂O (hey, no fooling around, you have lots of work to do).  The safe way to dissolve copper is with sulfuric and oxygen.  For certain definitions of the word, "safe."

More important, can you see another, quantitative problem with your switch?

[FIFOkid]

I would first determine if the ore is an oxide or a sulphide? In commercial applications oxides tend to be leached with sulfuric acid and sulphides with cyanide before it goes through the circuit.

[cloomis]

goldrefiningforum.com has all the info and explains how to do these processes