It has some double meaning. I'd say effectively both; there were temporary riches from seemingly abundant tin and copper, some mining spin off industries like steam engines for pumps/transport but none of it has brought lasting prosperity. These town's are now poorer due to other's riches, with wealthy non-locals buying Cornish houses just to use as holiday homes hence depressing the local economy and driving up property prices, displacing local communities.

It could be either or both actually, it’s really not clear!

Yes rich is correct . Abundant means plenty or quantity of something. Wealthy indicates possession Rich is correct indicating (been) - mining area

Abundant in resources with a large number of mining sites. This may lead to wealth but not necessarily. Such areas are often inhibited by the lower class workers.

Hi there! I would have to disagree and say abundant! The adverb is describiing the mining area as rich in material, the mining area itself is not wealthy.