By Sarah McFarlane LONDON -- Royal Dutch Shell PLC has appointed Andrew Mackenzie as its new chairman, tapping a mining veteran to oversee the oil and gas giant as it navigates the transition to low-carbon energy. The Anglo-Dutch company said Thursday that Mr. Mackenzie, who joined its board as a nonexecutive director in October, would succeed outgoing chairman Chad Holliday in May. A Scottish-born geologist, Mr. Mackenzie is best known as the former chief executive of BHP Group Ltd., one of the world's largest mining companies, which he ran for six years to 2019. During his tenure at BHP, he is credited with simplifying its business, overseeing the sale of its U.S. shale-gas assets and carving out several mining operations into a new company called South32 Ltd.