Does this mean there are high purity barely subsurface iron ore deposits on the moon with a X marks the spot... dig here? So assuming that, a large number of mirrors focused on a point would allow vacuum smelting and could be a game changer for a lunar base. So what if the lunar base was made out of pig iron at first. The thermal mass would help with the extreme sunlight and darkness temp fluctuations. Cast the domes a foot thick or thicker. No micrometeorite risks. With all the lunar dust easily available sacrificial casting after smelting.
How big are the lava tubes? Maybe they could be sealed off and used for habitat.