It's one of those situations where if you have to ask ..... you shouldn't be doing it.

If you were to set your sights a little lower:

Most of the boards have the copper plating. Once in awhile you'll see a board with a thin gold plating but they're not that common. Seems like you could take a few scratchings and test for the presence of gold or copper using established standard lab procedures under the direct supervision of someone with a degree in chemistry. ( A teacher or professor ?)

After it's all said and done you might come to the conclusion that the extraction needs to be done on an industrial scale in order for it to be profitable. We've had guys here that have sent loads out to be refined and the returns are generally pretty dismal.

You might check out Apple computer company's recycling program too.

Best of luck in your search !