* Former Amcor CEO to take over as chairman on Sept. 1
* Investors welcome appointment of Ken MacKenzie
* BHP under pressure to review structure, dump petroleum (Adds Elliott comment, updates shares)
SYDNEY/MELBOURNE, June 16 (Reuters) - Mining giant BHP on Friday named successful packaging executive Ken MacKenzie as its next chairman, handing him the job of tackling calls to dump its oil business and overhaul the board.
MacKenzie, 53, succeeds Jac Nasser as of Sept. 1 at a time when the world's biggest miner is being challenged by activist investors to revamp its structure and improve returns to shareholders.
Investors welcomed the appointment of MacKenzie, who was considered one of Australia's most successful chief executives in his 10 years running Amcor Ltd.
"It's an important first step in the right direction. Hopefully it creates a platform to be able to review what's amiss with the company in the eyes of some and address the concerns," said Brenton Saunders, an analyst at BT Investment Management, which owns shares in BHP.
Canadian-born MacKenzie presided over a long stretch of prosperity at Amcor, which makes packaging for food producers, industrial companies and pharmaceutical firms, that coincided with the end of a boom period for mining companies.
Hedge fund Elliott Management has fired a barrage of criticism at Nasser and BHP Chief Executive Andrew Mackenzie since publicly releasing a roadmap of changes it wants at the company, most notably an exit from U.S. oil and shale businesses.
Elliott also wants BHP to collapse its dual listing, and earlier this week called for a board shake-up, blaming long-tenured directors for bad investments and ill-timed share buybacks.
That could place MacKenzie, who joined BHP's board just last year, in good standing. Focused on capital discipline, he replaced 75 percent of Amcor's top 80 managers in his first two years at the company.
On Friday, Elliott said it supported the appointment of MacKenzie as a "constructive step in bringing much needed change to the direction of BHP."
Portfolio managers at another activist shareholder, Tribeca Investment Partners, were not immediately available to comment.
MacKenzie said he would meet with shareholders and others over the coming weeks to listen to their views.
"I am committed to the creation of long-term value for all of our shareholders and will work tirelessly with the board and management to achieve this," he said in a statement.
Nasser has defended the company's $20 billion investment in shale acquisitions in 2011 against Elliott's criticism.
BHP also faces a key juncture in the Samarco mine dam liability saga in Brazil, which is due to be settled in September.
A burst dam at Samarco, a joint venture between BHP and Brazil's Vale, killed 19 people and caused the country's worst ever environmental disaster in late 2015, when mud and waste destroyed a village and polluted the Rio Doce river.
Despite being the world's biggest mining house, BHP has a history of appointing executives from outside the sector as chairs. Since 1984 only two out of six chairmen had mining backgrounds.
BHP's shares were flat on Friday but have suffered a stretch of underperformance against arch rival Rio Tinto . The stock is down about 18 percent from its 2017 peak in late January. (Reporting by James Regan; Editing by Richard Pullin)