I would love this as the amount of times I constantly get Copper spearheads or copper arrow parts makes me annoyed. It would lead to having over-powered copper, but make the cost of energy higher? As one part it would be useful, but it would lead to people wanting the parts vs. the nuggets. It's a case of I don't want overpowered smelting, but maybe require a higher temperature is the only good way to avoid the issue I guess?
Just somewhere between useful, but not overpowered. That's like the biggest concern for me.... I love this idea as it would one part make panning more useful, but it would lead to inevitable nerfs for it.