Chinese President Hu Jintao's three-day visit to Denmark may ostensibly have been about signing billions worth of business deals, but a stake in Greenland's huge mineral wealth may have been the elephant in the room. Greenland, a self-governing dependency of Denmark, has some of the world's biggest deposits of rare earth elements, strategically important metals in which China has a near monopoly. The Atlantic island is also situated next to sea lanes that are increasingly important as the Arctic melts, and Washington has an air base in the northwest of the territory. That may explain why the leader of the...