The sign read anniversary mine LLC. Lots of equipment in the immediate area, back hoe, trailers, etc. we though they were opening the mine. That's what it looked like, but who knows. They may be blasting the entrance shut again, but like you said that's a quick operation. Who knows. I know it sucks either way, it was a cool mine to explore too. Someone may have gotten hurt inside too, there was a wooded ladder and people are dumb!
The difference between stupidity and ignorance. Ignorance is doing something wrong and not knowing better. Stupidity is knowing better, but doing it anyway. Don't be stupid!