Taxing is normal but not only tax. In other countries besides taxing a portion of ownership is taken back after discovery, definition of resource or at time of mine construction.
Most extreme example that I know of is Venezuela, now bankrupt? - Confiscated oil and metal resources.

I doubt that tax was the reason cliffs left. It must have been lowered revenues from depreciated iron prices and difficult negotiations with FNs.

Any how it is an old matter that should be put to bed ( politicians won't, no surprise) and we - Thank You Cliffs for the extra claims at a bargain price.

Ed