Indonesia will impose a 20% export tax on 14 metal ores on May 6 in an effort to boost downstream industries, Energy Minister Jero Wacik said here on Thursday.

The minister said that mining companies should propose plans to build smelters, meet their tax obligation and commitment of environmental preservation, otherwise they would be banned from shipping their unprocessed mining products.

If the miners meet all the requirement, Jero said that they may export the metal ores with export tax on average of 20%. "The miners should calm down, it is not aimed to stop their operation," Jero told a press conference after a cabinet meeting.

The minister suggested that small firms whose financial capability is weak join other firms in building smelters.

Indonesia wants to ban exportation of unprocessed metal ores, including nickel, bauxite, copper among others in 2014 to boost downstream industry.

But the planned ban has pushed miners to exploit more metal ores and their output have risen by 500 to 800%, according to Industry Minister MS. Hidayat.

Thereby the government need to slow down the over-exploitation.

The government also plan to require foreign miners to divest shares equal to 51% or greater to local investors.