Decision comes two weeks after the country's top court kept in place a more than 14-month suspension of operations at the company's Escobal silver mine.
A company owned by Russian billionaire Alisher Usmanov is in talks to raise $1.25 billion from Russian banks by the start of 2019 to build a massive mining and metallurgical plant at Russia's biggest untapped copper deposit.
Eskom said on Monday that it had fewer than 20 days of coal supplies at 10 of its 15 coal-fired power stations, posing a threat to national power supplies.
The project, which would become the European Union's only open-cast uranium mine if given the go-ahead, has faced local opposition since it was proposed.
Hydro, which is not interested in acquiring aluminium plants that use coal-fired power, was hoping the deal would be part of efforts to make its output as green as possible.