You should check out what they do in South Africa with their PGM ores.Yes, copper is also good but if there is au, and if its ag/au then lead is batter than copper.
When its about PGM , then copper is ok but iron is much more batter option.
Only some more research required to adjust the ingredients. Iron is good to collect from slag with magnet.
Copper is only good that its easy to refine and low boiling point. , than iron,
I do not think they smelt at the high temperatures you aim at, and I believe they are using fluxes to thin the smelt so the metals easier aggregate and coalesce to a button or into the matte in the bottom.
This is done while they sparge with Oxygen to remove most of the Iron and base metals as Oxides in the slag.
After it is concentrated this way, they pressure leach it with HCl-Cl in closed reactors.
At least as to what I saw in one documentary from the mining industry in South Africa.