The ice cap - made of solid carbon dioxide at temperatures as low as -143 - 'boils' every summer (or, more correctly, 'sublimates' directly from solid form to gas), leaving huge pits in the Martian polar ice.
The 'gold' lining these pits isn't likely to be ferried back to Earth, though - scientists remain unsure of the chemical composition of the yelllow, shimmering dust that lines the pit walls every 'summer'.
Martian summers are rather chilly in comparison to our own - the temperature usually remains below zero degrees centigrade. It's still 'warm' enough, relatively speaking, to make the 'dry ice' of the polar ice caps boil off.
Part of the fascination of Mars for both scientists and writers has always been how similar the planet's weather is to ours - with seasons, currents, and polar ice caps.
Mars has no surface water, however.
Scientists often study Mars's weather in the hope of better understanding our own. There have also been academic studies into the feasibility of 'mining' Mars for precious metals - but the academics concluded glumly that it was unlikely we would ever find enough to make it worth the trip.
The picture here was taken by HiRise - the High Resolution Imaging Science Experiment, one of the largest telescopes in deep space. It is mapping the surface of Mars from an altitude of 300km from the safety of the Mars Orbiter - and has even taken 3D pictures of the surface of the planet.