Sorry I don't have time to write much about the history of mining, mining law, and treaties - it is an extensive topic. An introduction / stepping stone can be found in this Wikipedia Entry.

Mexico created enourmous wealth for Spain due to its extensive silver deposits. Most, if not all, of those deposits were known to the pre-colonial people. When the Spanish came they just took over. This glut of silver eventually caused finacial turmoil and depressed value for silver verses gold. (another chapter in the old saga between these two metals.) Because of this, the Spanish really didn't have to look for more silver, they were swimming in it.

It was very much the finacial structure of the early United States that led to the exploration and exploitation of the Western gold and silver deposits. With a constitution demanding gold and silver currency, the federal government became the buyer, and the mining biz boomed. That changed over the years and many booms and busts in the precious metal mining biz are directly related to the changes in the US finacial system.

In the early days of those mining camps it was pretty close to anarchy. Claims overlapping claims, underground battles (literally), and many other effects of people with gold fever and little or no enforcable law. That, and the mining technology was horrifingly destructive to the environment. Especially hydro-mining and dredging, both of which are now outlawed. Both processes destroyed rivers that impacted the economic development of fisheries and farming. So the mining industry was not only making money, it was removing the ability of other industries to do likewise. Basically, it is the destruction of another's property (a taking).

Another point is that the science of geology changed a lot over that time span. Some gold and silver minerals were never recognized as such until new milling, concentrating, and smelting techniques were developed. Telluride minerals are a good example, leading to new mines in the San Juan Mountains and Cripple Creek. Deposits near the surface are weathered and oxidized, making for easy mining and refining. But when the mine gets past the weathered zone, it is whole new problem.

BTW, I do agree with you that international treaties currently make mining the seafloor even less profitable than it already is. When we begin to run out of terrestrial sources for important commodities, those treaties will be modified to make it less expensive to exploit those resources. Maybe do it correctly from the beginning, and try best to avoid the destruction of other resources that we need.