One of the rovers should confirm the composition one of these days. This could support a human mission and excavation machines for future mines. Maybe Mars is the new Eldorado. A very expensive one, at least for the moment.Mars is covered with iron compounds, and iron compounds can be very different colours depending on how the electrons between atoms are shared.
Mars normally gets its red colour from Iron (III) Oxide - aka rust - but I'd guess the above picture shows something like an accumulation of Iron (II) Sulphate, which is blue.
Or is it actually the opposite for them to have stayed (floated) above the surrounding material. Or maybe they just have to be larger particles; if you stir up a container of different sized gravel all of the same rock (and therefore density) don't the larger particles always end up on the surface?I found the dunes in the field near it even more interesting. They must be of a dense/heavy material to be so defined.