ST. PAUL — Gov. Mark Dayton says he intends to visit up to four mining operations after Labor Day as he weighs how his administration will proceed with the proposed PolyMet copper-nickel mine in northeastern Minnesota.

Dayton said Tuesday he potentially travel to two sites around the country suggested by project supporters and two by opponents. The PolyMet Mining Corp. project has been under environmental review for years but is nearing a critical point.

The Democratic governor says he is studying a 3,000-page preliminary environmental impact statement and reviewing financial information for the company involved. He says whether to let the first-of-its-kind Iron Range project advance “will be the most momentous, difficult and consequential decision I’ll make as governor.”