“Yet lithium is a metal, and state regulations passed in 2017 prohibit mining for metals in open pits of more than three acres, which would be the only way to cost-effectively extract lithium at Plumbago North. “I don’t know of any underground and manganese or lithium mines in the world,” said Dr. John Slack, a geologist who co-authored a separate upcoming paper on critical minerals in Maine. “Because those metals have a relatively low cost, in terms of their concentration per ton or per ounce, you need to excavate large volumes of rock cheaply in order to economically and profitably produce the metal you’re interested in.””
Basically, Maine demands that whatever mining is done, is done underground, like coal. But open carrier mining is cheaper. If all this lithium is so important, someone will find a way to mine it properly underground, I guess.