1. I took the numbers from this industry report (pg 28): https://www1.eere.energy.gov/manufacturing/resources/aluminum/pdfs/al_theoretical.pdf
Its energy consumption was on the low end, but it serves the purpose for illustrating the point.
2. Solar lensing would be more energy efficient, but the amount of heat you get drops significantly from solar occlusion (even a light dust storm would inhibit it, and there are MANY on Mars). Solar panels and an electric furnace would be more consistent for a foundry.
Yeah, 390kWh/kg is the energy to heat to 960 C, without recapture. Counterflow type setup would greatly reduce this (may see this at Gigapress sites).