As of late, everyone has gone crazy over mines, which limits the new people's ability to actually progress as fast as they would want to, without having to get help from already settled players. Iron mines, especially, is the most important ressource of the game, along with high quality trees, as both are necessary to attain the superior stages of quality for the most used items.
Thinking about it, there always were alternatives to mines, even in the old days. It was possible to find mineral rocks lying around in forests, in water, etc. Therefore, I think it would make some sense that very few respawning mineral rocks should lie in forests and such. Also, along with that, it should be able to dig simple holes into the ground, just like mines, that gives access to semi-mines, which are full of soil/dirt, most of it at least, but contains a variety of ores, ranging from tin to gold. Since the ressource would be so common, in a way, the semi-mine that is, the chances of finding minerals into the semi-mines would be rather small, as to make it balanced against the effort it requires to prospect a mine.
An example of these minerals appearances would be something like that :
75% to find dirt/stone/soil
6% tin
12% copper
5% iron
1% silver
1% gold
Adding up with the smelting process, the chances that an ore becomes a bar, the chances for all of them is around 20% * (mining ratio). Those semi-mines could also have their own prospect window, or be merged with the current one, showing the % chances of finding any ores on a set spot, for example, you prospect on a spot and it says : ''10% iron, 5% tin'' which means that the semi-mine that would originate from that location would give 85% dirt and the shown ratios of iron and tin. Allowing the ressource to remain its status as a local ressource.
OR
Caves should be mines on their own, people being able to mine into cave walls with a pick and a miner's helm (or Pacho's Client). Either make the cave walls dissapear or simply make it like fishing with lures, once in a while, you get some type of ore. It could also be like clay, you can dig about 2-3 inventories of ores until it is depleted and needs to build up again (not in quality, but in quantity), which would need like 3-5 days to come back. As clay, some spots on the walls wouldn't give anything, ore deposits would need to be found in order to be minable.