* CEO says aspirational goal for "gender balance" at all levels
* Chairman led push for productivity, efficiency
* Samarco victims stage protest (Adds Nasser, BHP board details)
By Barbara Lewis
LONDON, Oct 20 (Reuters) - BHP Billiton BLT.L BHP.AX Chairman Jac Nasser, one of the most powerful figures in the mining industry, will retire at next year's shareholder meeting, telling investors on Thursday that after a decade on the board, it was time to step down.
The former Ford Motor (NYSE:F) Co F.N chief, nicknamed Jac the knife after extensive cost-cutting efforts there, said he had intended to leave BHP last year, but agreed to stay on to provide stability as the world's biggest miner responded to the deadly Samarco dam disaster in Brazil.
Now that the "basic structure of the Samarco response is in place," Nasser said in a speech at this year's Annual General Meeting, he would not seek re-election. He will carry on leading the board in the interim, while a replacement is found.
Brazilian prosecutors on Thursday charged 21 people with "qualified homicide" for their roles in the disaster, including the former chief executive of Samarco. move marks a generational shift in the mining industry, which over the past decade has seen an unprecedented boom, frenzied M&A and draconian cost cuts.
Rio Tinto RIO.AX RIO.L , the world's second-largest miner, is also expected to replace its chairman, South African Jan du Plessis, in the coming months.
"(Nasser) was ready to go but then Samarco happened ... so it's not coming as a surprise," said Macquarie Bank mining analyst Hayden Bairstow.
Both miners could look within their ranks or outside for a successor. Both will also consider an appointment that would diversify traditionally male-heavy boards.
BHP's Chief Executive Andrew Mackenzie, in a separate speech, said the company had set a 2025 goal of achieving "gender balance at all levels of the organisation".
The target is higher than that set by the Australian Institute of Directors, which is calling for 30 percent female representation on boards by 2018.
BHP's 12-person board has three women members: Anita Frew, Carolyn Hewson and Shriti Vadera.
Frew is chairman designate of Croda International Plc CRDA.L , the speciality chemicals group, and deputy chairman of Lloyds Banking Group Plc. LLOY.L
Hewson is a former investment banker and an executive director of Schroders (LON:SDR) Australia Ltd. Shriti is chairman of Santander (MC:SAN) UK.
Asked whether the new chairman might be a chairwoman, Nasser said "why not?", but added gender balance would take time.
Growing up in suburban Melbourne, Australia, Nasser, 68, said he had never expected to lead global companies.
He joined the BHP board as a non-executive director in 2006 and was named chairman in August 2009.
At BHP, Nasser rode the China-led commodities boom and its bust, which the company had weathered better than peers, he said. BHP still lost $6.4 billion in the last financial year.
"We kept a solid A credit rating through the valley of the commodity price death," he said.
His last year has been what he described as "one of the most challenging periods" in BHP's history, largely because of the Samarco dam burst in which 19 people died. Samarco is a 50/50 joint venture between BHP and Brazil's Vale. VALE5.SA displayed a softer side last year at the Australian annual meeting in Perth when he vowed to "find out what went wrong" at Samarco, as Mackenzie teared up by his side.
Brazilians impacted by what Brazil says is its worst environmental disaster were among those who staged a protest outside Thursday's AGM in central London.