Let them, mechanically at least.
If players are unhappy about a person or group having all of one resource (not that it is likely to happen (even on our starting continent)) let them take it through force I'll give two examples of a player describing what happened to the Iron Barons (a fictional alliance of Barons who 7 years from now own all the iron in the game and all the iron mines) decide which story sounds cooler.
The Devs slap them down
"Yeah so there was this group, the Iron Barons, who worked really hard over six years and managed to between them control all of the iron output in the game, over several continents. They really started hoarding it though and upping the price to ridiculous levels. This was making it hard for anyone without their favour to craft metal objects so Devs stopped them though, that's cool I guess."
Players do something
"Yeah so there was this group, the Iron Barons, who worked really hard over six years and managed to between them control all of the iron output in the game, over several continents. They really started hoarding it though and upping the price to ridiculous levels. This was making it hard for anyone without their favour to craft metal objects so an alliance formed to try and take back the iron supply - we ended up in a war between those who were loyal to the Iron Barons and those who weren't it was pretty cool some people even permadied. Let me tell you about the time we stormed Baron Stroud's mine it was pretty epic...."
EDIT: As an aside if there is a group who want's to control the iron mines of the game you're welcome for the name.