Despite the name, this company isn't digging for the blue-green stone popular in Southwest art and jewelry. Turquoise Hill Resources  explores for and develops mineral properties (copper, gold, and coal), mostly in Asia. Its main assets include its Mongolian interests: controlling stakes in the Oyu Tolgoi copper/gold project, which began producing gold in 2013, and in Mongolian coal miner SouthGobi Resources. Turquoise Hill, which exports coal and gold to China, also has exploration projects in Mongolia and Indonesia. Giant mining group Rio Tinto holds a 51% stake in Turquoise Hill, which changed its name from Ivanhoe Mines in mid-2012.