It's a good feedstock for making hydrocarbons and petrochemicals and also as good a reducing agent as hydrogen for making metals. In fact you could use the CO to make, say, iron, producing CO2 which gets cycled back into the above reactor.
CO as rocket fuel isn't as effective as Hydrogen or Methane, but for the lower gravity of Mars it can still be useful for Mars-Mars transport or even returning to orbit.
? but iron is an element?
https://en.wikipedia.org/wiki/Blast_furnace
since it partially burns coke to make CO which reduces FeO to Fe producing CO2. An alternate approach is to reduce FeO with hydrogen producing H2O. Either way this is likely to be a circular process in a space economy since volatiles like H2O and CO2 are precious.
[1] https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/...
With that in mind, any metal ores had plenty of time to oxidize just like on earth. But metal from asteroids that impacted over the last two billion years or so should be unoxidized.
https://factorio.com/blog/post/fff-365