How efficient is iron smelting ?
Something really big is being missed.
Iron isn't worth much and transporting stuff back from Mars is really really expensive (so expensive it's never been done - everything that has gone to Mars is still there).
Getting the material from mars to low earth orbit would mean getting a vehicle to Mars with enough fuel and oxygen to lift it off the surface with a payload (the solid rocket boosters that the space shuttle uses won't work if there's no oxygen). I'm thinking you'll need a vehicle similar to the Saturn 5 for this.
Here's a link with info about the vehicle http://www.answers.com/topic/saturn-v (isn't google wonderful). Anyway you'll need a scaled down version of the vehicle because it's too big for your mass allowance. Anyway the ratio of vehicle mass to payload mass is about 50:1 for moon shots. Since Mars has a lower gravity than the earths, this ratio of vehicle mass to payload mass might be 20:1. Following this reasoning, a 200 000kg vehicle could transport 10 000kg of Iron which has a market value about US $2000.
So you send 500 tons of equipment to mars for a financle return of $2000 a couple of years later - I don't see the comercial potential.