The Secret Martians by Jack Sharkey

Marsport, the largest -- if you excluded the prospecting encampments within a hundred-mile radius of the place -- city on the Planet, had grown fast, from the time of its founding in 2014. Originally simply a mining site for the Tri-Planet Refining Corporation, it had spread backward from the area of the original mines in a rough circle, beginning with the monotonous quonset huts of the miners, and modulating in its move toward the perimeter to smart iron-and-adobe structures. Some of these, thanks to the less-than-half Earth's normal gravity, as high as fifteen stories.

The planet, barely half the diameter of Earth and a tenth of Earth's mass, was a minerologist's paradise. The rusty red sands of the Martian desert were almost pure ferrous oxide, a source of both iron for the profitable refineries and oxygen for the inhabitants of Marsport.