It has came to my attention that in Unofficial Patch it's author Arthmoor made a little mistake. While he removed ebony veins from Shor's Stone mine (which is fine by me, and i think it's justified) he deemed it necessary to change some other mine's iron veins into ebony veins to keep it even and balanced.

While i'm not entirely sure this game can ever be even and balanced (and that's what we love about it isn't it?) it was fair and justified idea to consider such side effect of ironifying Shor's Stone. However the mine he chose was Northwind Mine. In 2011 it was relatively unknown and unimportant place, but in 2013 ESO has provided bit more lore to it as a quest is happening inside. And in this lore we learn that it was 100% positively an iron mine. You can check it on UESP here: https://en.uesp.net/wiki/Online:Loading_Screens/The_Rift 

So what this minor ESL plugin does? Not much. It just ITMs 3 records from vanilla ESP about these 3 iron veins so if it is loaded after USSEP, it will re-ironify them. You don't even need USSEP, it isn't set to be a master. If any other mod makes this veins quicksilver ores, you can use this mod as well. However i'll still link USSEP as a requirement on this plugin's page, just to be fair to Arthmoor. I don't wanna jab at him or anything. I'm here just to provide small lore fix. If it ever get changed from Northwind to other place in USSEP, i'll remove this mod entirely.