There is a fundamental limit of power... I get that. The Perseverance Mars Rover has one experiment that requires 180 watts of power, (The Oxygen Generator experiment) and it has a 110 watt RTG powering everything. They charge up some lithium batteries during down time, and use them to make up the difference.
In the limit, If something takes 5,000 watts, you could run it for a few minutes/day, with that same RTG, provided you had suitable energy storage.
Perhaps they could gather grains of material, and just sort them, one at a time, only keeping the iron rich material, or use a permanent magnet to gather ferrous material. You could sinter the grains together using a microwave or laser pulse.
The results don't need great quality, just enough tensile and compressive strength to be mechanically stable during additive or subtractive manufacture.
Lots of minds have been thinking about refining metals for a very long time, but they haven't been thinking about doing it on Mars, with limited power, and very far outside the box of normal constraints, like cost.
This is one time capitalism doesn't apply at all... and most solutions assume capitalist incentives and costs, instead of going back to first principles thinking.
