A bitter legal battle appears to be brewing between FTSE 100 mining firm Anglo American and the Chilean, state-owned copper miner Codelco.Anglo says it has received a letter from Codelco seeking to exercise an option to buy a 49% stake in Anglo American Sur, a huge copper mining plant in Chile that Anglo has spent billions upgrading.The dispute dates back to November when Codelco first announced its intention to exercise its option, a move which prompted Anglo to sell a 26.5% stake in the Sur project to investment firm Mitsubishi, as a defensive measure.On December 22 Anglo filed a legal complaint for breach of contract over what it describes as an "illegitimate premature attempt to exercise the option."Both firms say they are willing to work to a negotiated settlement.BS