There is this theory that I read and makes sense-during the Bronze age - tin was such a rare commodity that Phoenicians and other tin searchers travled long and far in search of this commodity. They kept such routes secert from mouth to mouth. When the bronze age came to an end, the value of tin for making bronze evaporated and the routes were forgotten except in some half remembered tales by the Phoenicians that the Greeks picked up on and wrote about. That age probably saw limited colonization maybe a trading fort or something-no women but local Indian women. Some slaves - probably Celtic slaves and or Negro slaves to the Phoenicians? This would explain the cocaine and tobacco found in Egyptian mummies. They were Phoenician trading goods and these Phoenicians lept such routes a trade secret.
I think that is a reasonable overview and good assumption.