Sulfur concrete is a mix of sulfur and aggregates that make a strong, quick-hardening concrete that is likely to be used for construction on Mars, which has a great deal of sulfur. Most experiments, however, seem to use commercial sulfur, which is relatively pure, while a great deal of sulfur on Mars is in the form of sulfate salts such as Ca-, Mg- and Fe-sulfates.
To get an initial structure built, are there any places on Mars:
With sulfur deposits having some pure or purifiable sulfur, or any form of sulfur that can be quickly and easily converted to at least moderately pure sulfur? (Aggregates in the mix is fine, they would just add less later.)
That are relatively easily accessible (no deep digging or apparent risk of life and limb).
Are near the Terra Meridiani or Arabia Terra area, where I'm hoping to place my proto-colony? It is one of the areas of Mars that is high in sulfur, although primarily in sulfate form, as seen in one of the images in this eurekalert article.