Romania's electoral office announced on Monday that two regional referendums on gold mine and shale gas projects were invalidated a day after too few people turned out to vote.

The referendums Sunday, which failed to meet the 50 percent turnout threshold, were held alongside general elections that saw the centre-left ruling coalition win a landslide victory.

But the referendums were not binding, with the decision left up to the new government as to whether to pursue the projects. Both referendums had a turnout of around 40 percent.

In Alba county in central Romania, Canadian firm Gabriel Resources plans to extract some 300 tonnes of gold and 1,600 tonnes of silver over 16 years using cyanide in the leaching process.

Local officials from both the governing party and the opposition initiated the project saying it would create jobs, but environmentalists, archaeologists and historians have opposed it.

The company is still waiting for a key permit from the government.

In Constanta county on the Black Sea coast in the southeast, American oil giant Chevron was hoping to drill the first shale gas exploration well in the second half of 2012.

But the governing Social-Liberal Union (USL) in power since May had imposed a moratorium of shale gas until the end of the year because of serious environmental and health risks associated with the drilling technique.

On Sunday, Prime Minister Victor Ponta's USL coalition took nearly 60 percent of the votes in a parliamentary poll also hit by low turnout.