BORON, Calif.

Some 75 percent of locked-out mine workers voted Saturday to approve a settlement with the operators of a huge borate mine in California’s Mojave Desert, ending an impasse that began in January, a union spokesman said.

Miners approved the six-year deal between their International Longshore Warehouse Union and Rio Tinto Borax that includes a $5, 000 bonus for each worker and a 2. 5 percent annual pay raise, union spokesman Craig Merrilees said in a statement.

The company said it won the right to base promotions and transfers on skills and performance rather than just seniority, to settle disputes through grievance and arbitration and to use contract workers during busy periods.

“We have reached a fair agreement that allows us to improve work practices and productivity so we can keep the business competitive throughout the life of the operation, potentially another 70 years,” General Manager of Boron Operations Dean Gehring said in a statement.

Negotiators had reached a tentative agreement Friday and needed ratification from the union’s 560 local members.

Workers will be paid starting Monday, the day the new contract takes effect, and planned to return to work Tuesday, Merrilees said. The company statement said workers would have three weeks to return.

Seniority protections rather than wages were the union’s major issues in the dispute that led to the Jan. 31 lockout at the huge open-pit mine in Boron, 75 miles northeast of Los Angeles.

The union had contended the company sought to convert full-time jobs into part-time positions, but the company denied this.

Rio Tinto Borax, part of the British-Australian Rio Tinto Group, did say it needed changes in work assignments and promotions to remain competitive in the global market for borates, which are used in manufacturing processes and numerous products ranging far beyond the well-known laundry booster, borax. The operation is the world’s second-largest producer of the world’s borates.

Rio Tinto spokeswoman Susan Keefe did not immediately return an e- mail message seeking comment, but after Friday’s agreement she said the company achieved “critical improvements that we had been looking for through the entire negotiations that allow us to remain competitive.”

The lockout hit hard in Boron, a tiny high-desert town that sprang up after a 1925 borate discovery.

Union workers staged a continuous protest at the mine’s entrances and the company brought in replacement workers to help salaried employees keep it running.

Union leaders said members had to file for unemployment, rely on working spouses’ health insurance and seek extensions on auto loans and mortgages.