I have tackled a couple of perspectives on this very broad question over the years, and while you're waiting for new, focused answers, you might like to review those:

Conditions in Wallachian salt mines in the 13th-15th centuries

Scotland's early modern mining serfs

Some earlier threads cover aspects of the development of mining in this period, as well:

How did iron mining differ from bog iron harvesting?, with u/wotan_weevil

I'm a castle blacksmith in 12th century England - where is my iron coming from? How does it go from mine to, presumably, ingot?, with u/AshkenazeeYankee

In the Ancient world tin was an extremely rare (and important) resource and England was famous for being a source of the metal. What was life like for those miners before the advent of modern mining techniques? How did they mine and transport tin?, with u/itsallfolklore

One answer might be that, possibly, the metal did not come from mines, and another, that some societies did not produce texts.

Without any deeper knowledge, it is easy to guess that we should expect to find many different conditions and methods, given the size of the geographical area, and the many hundred years of history in question.

Also, not all mines are born equal, some are minuscule, and some are gigantic. A mine like the Falun copper mine, was so huge that some years 2/3rds of the total world production came from it.

Before we have a look at metal mining, it should be mentioned that there were also other types of mines. Since I mentioned Falun, it might be interesting to have a look at one on the other end of the spectrum.

One such mine is the garnet mine in Sjönevad in Halland, Sweden. As far as I know, we don't even have any traces of the mining activity; possibly because it was in use as late as during the 30-40s. But what we do have are raw garnets, found at the central places Slöinge and Slafsinge some kms from the mine. The garnets were possibly an important source for the elite there. They would manufacture jewellery and trade for "money" and influence. The Slöinge central place existed about 400-1000 AD, and possibly the mine was not in use later on. Presumably, Sjönevad, was an open cast mine with very few miners, if any. It is possible that those mining were also the jewellers, and that they would go mining for garnets only when they needed them.

But about metals, and the most common one, iron. It is quite probable that the source for the iron ore was red soil (what is probably also called iron sand), bog ore, and lake ore. Such sources were in use as late as the 19th century.

Red soil is a surprisingly rich source, with up to 40 % pure iron, and also easy to collect. It, and the other sources mentioned above, have been used since Europeans started making iron. In Sweden we have dated manufacturing from the 8th century BC, and from the 6th. The oldest finds are from a place aptly named, Röda Jorden (the red soil).

Commonly with these sources are that, even though they are rich, the "veins" are pretty thin. You would be lucky to find metres of red soil. What happens is that an iron producing area will have hundreds of ovens spread out over the whole area. They would have been worked by many persons, which might have created a less stratified society. Such sources were exploited in the middle ages, and for nations without mines, they could be quite important.

The individual "miner" would often be a farmer-miner. Luckily we have an extant text from the high middle ages showing us how common it was for a farm to make iron. It is Raven von Barnekow's bookkeeping. Raven controlled Södermanland around 1366, and in the book we can see that many farms paid some of their taxes in iron. Those farmers would not only make iron for to pay taxes, they often lived on marginal lands, where they made iron for the market, so that they could buy what they needed.

It must have been somewhat similar in many places, and for example, Denmark had a sort of medieval iron making centre in Halland, close to traditional iron making centres in Småland and Västergötland.

But, so here we have some of the answer, namely that iron making was very common in some areas, and that the average farmer there would create a surplus every year.

I'll stop there and continue tomorrow.