Gold bars? The ore cost 284gp ea, and a bar cost 101gp ea, so I don't know why they'd be profitable.
One way that is at a relatively good speed is making Iron Knives. Bars cost 330 ea, and to make 5 knives per bar, you basically get all your money back. If you buy bars at a lower price and/or sell the knives at a higher price, then better for you.

