Poland estimates that the planned mining tax will bring around 2 billion zlotys ($611.8 million) of budget revenue annually, finance ministry spokeswoman Malgorzata Brzoza said on Friday.

Earlier on Friday Deputy Finance Minister Maciej Grabowski told Reuters that Poland may implement a new mining tax as soon as the second quarter of next year.

The plans sent shares in Europe's No.2 copper producer KGHM down 13.5 percent on Friday.