Yep. Yogg-Saron. Not Y'Shaarj. Yogg-Saron. I remember when Cataclysm was announced and they showed pictures of the new Orgrimmar, that was rebuild with steel and iron, that Afrasiabi said, that we should recognize the black iron he uses - "it's from somewhere". Now I always took it as, it's from Northrend, and it's Saronite. And Saronite is the black blood of Yogg-Saron. http://www.wowwiki.com/Quest:Black_Blood_of_Yogg-Saron
So I'm pretty sure the Horde took it and build the new Orgrimmar out of this. The metal is even said to breathe. Is it possible that Garrosh and the orcs are under the influence of Yogg-Saron since the end of Wrath of the Lich King?