Why are old mines sometimes reopened What factors may have influenced the reopening of old mines?

mines close when the ore is not producing enough minerals to pay for the expenses of the mine and not making a profit. They reopen if the price of the mineral in the ore goes up enough so that the mine makes a profit. Example: a mine produces $100 of gold per ton back in 1900. But extracting it costs $500 so the mine closes. Now with gold prices today it would be $1900 of gold per ton and an extracting cost of $700. So it reopens.