There is firm Wolfden resources that has been trying to develop a similar to the Bald Mountain project in Pickett Mtn northeast of Baxter State Park. And another project in Pembrook Maine. The prior Maine governor who is running again and his supporters actually changed to mining laws in Maine for a short period but they were soon changed back. https://downeast.com/arts-leisure/battle-bald-mountain/
Gem grade minerals extraction has been going on in Western Maine for decades probably over 100 years with no acid mine drainage, but the concern is that any legislation to change the mining law to allow a pegmatite mining would open the door to sulfide mining. For those with their eyes on the relative short term, sulfide mines put a incredible amount of money and jobs into a local economy especially with the incredible demand for the proven reserves of copper that can be extracted relatively easily. The problem is along with the minerals are sulfides and that leads at a minimum to long term acid mine drainage which will trash a watershed. The methods used to separate the minerals from the waste product is also potentially very toxic. The temptation by developers and local politicians is to take the money and run while the mine is active leaving a toxic legacy.
Ultimately there is a huge demand for copper and the transformation to an electric economy is going to need more copper resources. It comes down to what country in the world is willing to host long term waste sites once the mining is over. Canada used to play it loose and arguably is still doing so with Crown lands but Wolden has been selling investors that Maine could be an easier regulatory structure to deal with.