I agree that the original mining is too powerful, but now is it too weak?
Consider that you have gone from a card that can boost a set of gold, gems, silver, bronze, or iron to a card that gives you a 6 card. (Either a bronze, silver, or disaster)
That's a huge change.
Example 1:
You have a set of 3 gems. Before, you could exchange that for 128 points. Now you can exchange that for 78 (72 points + 6 points for bronze) - or find someone who will trade you a gems for a bronze.
Example 2:
You have a set of 3 silver. Before, you could exchange that for 96 points. Now you can exchange that for 60 (54 points + 6 for bronze) - or find someone willing to trade you silver for bronze.
Example 3:
You have a set of 3 bronze. Before, you could exchange that for 96 points. Now you can exchange that for 96 points.
Generally mining increased the points values of the sets that you trade in as well as the frequency that larger point sets we traded in.
Don't foret that the more people who have mining (old style) the more people are after metals and the less likely you are to get them. I have had turns (when I have had mining) that no-one would trade any metals to me. I couldn't even get any iron.
Some thoughts to consider for the new mining:
* Having people being able to buy in the six stack will mean that it's possible (maybe even probable) that you will empty the six stack.
- Other people miss out on cards (double if they have mining)
- Disasters will come out more frequently.
* Benefits of mining is limited / concentrated to bronze and silver, making them worth more, and the other metals worth less.
* I have no fear of slave revolt, slave revolt is weak. Even Earthquake picks on slave revolt in the playground.

* Maybe civil war could be move to the 6 stack, or slave revolt (see last comment)