The U.S. issued a $20 gold coin from 1850 until 1907. The amount of gold in the $20 gold coin did not change during that time. The face value never changed.
During that same time period the U.S. issued a $1 silver coin. The amount of silver in the $1 silver coin did not change until 1935 when the mint stopped making silver dollars. The face value never changed.
At any time from 1850 until 1933 you could exchange 20 - $1 silver coins for one - $20 gold coin or one - $20 gold coin for 20 - $1 silver coins. Their relative values and weights never changed.
As you can see the 0.9675 ounces of gold in the $20 gold coin always equaled 20 silver coins with .76 ounces of silver each until 1933 when gold coin was removed from circulation.
You will see that same gold/silver/dollar ratio no matter what the coin size was. A $10 gold piece was always worth 10 silver dollars etc.
As you can see there was no way to change the face value on the silver and gold coins. That's because the
ratio between silver and gold was the only factor that Congress could control. (U.S. Constitution Article I Section 8 #5). There was no paper debt money permitted in the U.S. until the North ran out of silver and gold during the civil war. To keep funding the war they created paper "Greenback" notes that were supposed to be redeemable in gold at some later date.
There was no drop in value of gold to promote the closing of mines before 1933. And that was my point, you need to look for another reason why that lead mine was closed. It certainly wasn't because gold dropped in value. I'm guessing the deposit "pinched out" at depth just like 97% of all other hardrock mines do. Only research into the mine history itself can answer that question.
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