If the two mines produce the same ore and are located in the same society/market, the value of the same amount of ore is the same between them (ignoring transportation). The rich mine would be more profitable if all other variables were the same.

The value of labor is not very relevant to what a worker is paid, except as a kind of upper limit. Workers are paid relative to the value of their labor-power, which is a concept that will be introduced in chapter 6. The value of labor power varies across the globe, so a relatively poor mine can be profitable in a country with cheap labor-power and a rich mine can be unprofitable in a country with expensive labor-power.

Maybe oversimplified here, but what about particularly difficult, dangerous, or unpleasant jobs? An hour in the mines is surely worth more than an hour driving trains. I can think of a lot of ways to properly value different jobs without resorting to trying to value the product, but it's odd it's not mentioned here when the next quote is.

I believe the quote that immediately follows is partially addressing this, insofar as it argues that it's most reasonable to express all labor as a modified quantity of an abstract "mean unskilled labor in a given society." Skilled and otherwise difficult labor might be "worth" a multiple of unskilled labor but you are expressing the same social reality by just referring to it in terms of the unskilled mean. My copy also has a note to remind the reader that we aren't talking about wages yet, we are trying to understand what it means to express that commodities are interchangeable in a consistent way. Eventually we will get to money and wages but I think those are all logically dependent on what Marx means here with value in commodities as a social reality.

If you emphasize the this in the phrase this value, I think we are meant to distinguish the kind of value at play from other kinds, such as the usefulness of what is produced or the material substance of it as a potentially useful thing.

difficult, dangerous, or unpleasant jobs

We intuitively think about commodities from the perspective of single units because we deal with unit prices when we enter the market. So the natural first question is: how much does this single banana cost? What is its value?

In Capital you should think about it from the aggregate level and not the individual level. What is the total social labor required to produce all bananas for society? Let's say it is 1 million labor-hours to produce 1 billion bananas. Then, on average, each banana contains in it 1/1,000 of a labor-hour, or 3.6 labor-seconds¹. Nowhere in this procedure did there arise a consideration for how it makes the producers feel, or what they ought to earn, or whether society should produce that many bananas.

Value is independent of supply and demand. Value depends only on the labor time needed to produce a commodity, or in other words, it depends on the state of technology at a given time and place.

So the value of one banana is 3.6 seconds, but that does not guarantee that the supply will meet the demand. The price of a banana may therefore exceed its value. It is quite possible that, say, there are not enough laborers willing to tame lions or clean shark tanks, and the prices for those labor-powers exceed their values.

¹Important caveat: You cannot directly compute value in terms of physical labor like this because value consists of abstract labor, not concrete labor.

I feel the same way about a lot of this, the reader on soundcloud I'm listening to with us says that he's considering a fairly simple society with mostly "unskilled" labour and slowly adding things in (e.g. he starts with only a relationship between linen and coats), and he glosses over stuff that he briefly mentions here. I haven't read this before so idk if he goes over stuff like that in more detail though. But for this hyper-idealised economy with linen, coats, workers, and producers (capitalists, I guess) and no foreign trade, this is how linen, coats, and labour time is compared in relation to each other (at least by the producer).

I am pretty sure he's describing the bourgeois economy specifically with its flattening of the perception of workers (that, in an idealised bourgeois economy, sees all workers labour as the same, which means they're replacable and can be slotted in and out as the tides vary, again without the added complexity of education etc.).

(this is my guess, I'm pretty stoned and read this a few hours before you did)

A poor mine yielding less than a rich mine

The proper question is: How much labor-time does it take each mine to produce ore, relative to the social average? In a simple scenario, if the poor mine cannot profit, then the mine will close, or the owner will redirect their money to the richer mine that returns a larger profit. (This latter mechanism is a major point in volume 3.) In real-world scenarios, you have to factor in international exploitation, which complicates the analysis; but suffice it to say that laborers in the imperial periphery (aka global south) are indeed exploited harder than laborers within the imperial core.

experience/training/knowledge is a form of capital [...] ways of rewarding craftsmanship and experience

Reward is an immaterial moral judgement about what things "ought" to cost.

In future chapters, the value of labor-power will be discussed. I don't want to spoil that but it is quite important. Necessary training does impact the value of labor-power.