UPDATE 1-Antofagasta to buy 40 pct of Chilean power plant

* Buys stake in power plant from GDF Suez

* Plant to provide power to Antofagasta's Esperanza mine

* Antofagasta to pay 40 percent of $400 mln building costs

(Adds detail)

LONDON, July 13 (Reuters) - Chilean copper miner Antofagasta Plc (ANTO.L) is buying a 40 percent stake in a thermo-electric power plant which will supply electricity to its Esperanza copper-gold mine project.

London-listed Antofagasta said on Monday it had exercised an option from France's GDF Suez (GSZ.PA) for the interest in Inversiones Hornitos S.A., the owner of the 150 megawatt power plant project.

GDF Suez granted the option to Antofagasta when a long-term agreement was signed in late 2007 to provide power to Esperanza.

"This power plant will use circulating fluidised bed technology and will be able to burn biomass and other fuels," Antofagasta said.

Under the option, Antofagasta will be responsible for its 40 percent share of the estimated $400 million development costs of the power plant, it said.

On June 10, Antofagasta said it was on track with expansion plans under which output will jump 60 percent by 2011. [ID:nLA1031161] (Reporting by Eric Onstad; Editing by Dan Lalor)