We have damaged white macabaus. From the time of putting down a deposit, to install day, the slabs sat out in the rain. I noticed that they acquired alot of iron staining around the edges. It was orange/brown. It was def from being left outside. The pics I took a year prior did not show these stains. They assured me they would 'cut off' the stained edges. They did, and you could not see the staining once installed. However, if I had not seen the stone prior to staining, I might have thought it was natural as there are parts of the stone that are iron in color(a few iron colored veins). However...once installed, the stone began to develop dark water or oil looking stains along all of the edges, and the stain began to creep over time. From what I gather, they applied a wax to the edges during fabrication, and the wax absorbed and continues to seep deeper into stone...it will not come out. ALL of this is to say that quartzite(atleast mine) is more porous than I had assumed, it easily sucks things up, but won't evaporate them back out...so with my experience with my stone, those veins may have sucked in something from its environment(or during fabrication along what karin says) and is now seeping... IMO it is going to continue to seep, so I would def try to get it resolved the best you can. It is still a beautiful stone! Good luck!
Q