The first map combines the three elements in the best possible way to preserve their individual intensities. Fe is rendered as Red, Th as blue and Si as green.

The second includes an additional layer that preserves the topographic contours so that you can see where things are on the map (but it mucks up the intensities and gives too much white).

My analysis: Fe and Si should not be too soluble - they represent bedrock type. We see moderate Fe enrichments around some of the flatter volcanic constructs such as Syrtis Major. Also High Fe in the stealth terrain and in the lowland basins west of Elysium.

High Si and Fe in Tharsis - implies basic volcanism. An interesting patch of high Fe in the outwash plains where V1 and Pathfinder landed - could be all those boulders?

Th, OTOH is potentially solube or transportable in a fine phase. There are some odd areas of Th enrichment in the northern plains that may be related to transport of Th to further distances than Fe.

ANd a huge Fe-Th anomaly in eastern Hellas that is south of those two prominent valleys.

This is the best I can do right now - I only downloaded the jpeg images and they are inconsistent sizes and poor quality. I probably have to redo the whole exercise with better quality stuff...