Paul, did your research also show that it is the States who own the minerals and have the right to charge rent (royalties)? They enter a contract with the miners and have, up until now, abided by the terms of those contracts.
How often have you doubled the rent on a property while a valid lease is still in place?
The only reason it doesn't happen is because as an individual can't do this legally. I can't say "the rent you are paying us is too low we are getting a bad deal, therefore I as landlord will increase your taxes to make up for it". If people could do that, they would. There is all sorts of things governments can do "for the greater good" that I can't do. I don't think the mining industry can really be surprised by a change of rules by the government when so much money is being made from government owned assets.