SANTIAGO (Reuters) - Chilean miner Codelco has requested an environmental permit to extend the life of its Gabriela Mistral copper mine by more than 25 years with an $800 million investment, the state-run company said on Monday.

The world's biggest copper miner aims to extend the mine's lifespan beyond 2028 to 2055 and end its use of domestic land-based water in 2035.

Water is essential for multiple copper mining processes and many mines in Chile, the world's leading copper producer, increasingly pump seawater directly to their operations to move away from using water from lakes, rivers and reservoirs.

Codelco said it will provide the same amount of water used by Gabriela Mistral to the northern Chilean region of Antofagasta, where the mine is located, switching from land-based water to third-party sources that meet environmental standards.

The company did not specify what sources would provide the alternative water supply.

Gabriela Mistral, one of Codelco's smallest mines, began operations in 2008, employs almost 4,000 people and produces about 110,000 metric tons of copper a year, the company says.

To extend the mine's lifespan, Codelco plans to extract copper oxides and then move on to sulfides, incorporating salt in the chlorinated leaching process to improve recovery rates.

The miner has been struggling to boost production after quarter-century lows in the past two years, hit by delays at major expansion projects.