Your reminder of the history of oil discoveries in the US made me recall something quite similar regading diamonds. For hundreds of years, it was thought that commercial quantities of diamonds were only found in India. Then there were discoveries in South Africa, at which time it was believed diamonds only occured at two places on earth. Later still came discoveries in South America (alluvials), Australia, and later still in Russia.

By the 1990s, some few thought that Canada had the right geology for the presence of diamonds in commercial quantities, though a lot of people continued to dismiss the idea. Then, a persistent prospector decided to follow increasingly strong glacial deposits of indicator minerals "up ice" to logical points of origin, at which point drills proved his theory, making him and his backers very rich (as well as many others who searched in a few other of the different Canadian territories using mineral trains in glacial deposits).

In pioneering the glacial deposits theory for indicator minerals, Chuck Fipke outsmarted DeBeers who had by then a two or more years lead in prospecting for diamonds in Canada. They just did not know how to look, Fipke did, adding Canada to the list of world diamond producers, and breaking the DeBeers global marketing cartel in the process.

Earlier, Fipke had been though of by retail investors as one forever seeking grubstakes, living off gullible and poorly informed speculators. Today he's among the most famous prospectors of our time.

https://en.wikipedia.org/wiki/Charles_E._Fipke

http://geology.com/articles/canada-diamond-mines/

FWIW