Glencore Xstrata Plc, the biggest exporter of power station coal, is studying a plan to combine some of its Australian coal operations with mines run by Rio Tinto Group, according to two people familiar with the matter. Glencore and Rio own some of the largest thermal coal mines in the Hunter Valley region of New South Wales and have held initial talks on ways to share mines and infrastructure to cut costs, the people said, asking not to be identified as the discussions are confidential.