I want to add to the discussion of resource extraction by explaining what the effect of energy costs could be.
The premise is simple, mining takes energy. If players must make a comparison between the amount of energy spent on mining (in some kind of universal credit) tot he value in credits of the resources gained, and that balance doesn’t turn out well, the resource doesn’t get mined.
Thus, energy costs add room for several aspects of mining economics:
First of all, mining is no longer free. This will limit the problem of areas or planets being strip-mined; it has to be worthwile.
Second, it adds tot he economic balance of the game. As resources become scarce, prices will rise and mining becomes more profitable. This is easy enough for players to understand.
Moving along, mining itself can be made more complicated, or taking a bit more thinking than pointing some kind of harvesting beam anywhere. Different deposits could have different energy costs to recover. A deposit deeper underground could require more energy too. Add in the aforementioned option of diluting or contaminating your ores and mining becomes something more exiting altogether.
Dilution refers in this case to the concentration of valuable ore per cubic metre, contamination means the presence of undesirable or unexpected ores in otherwise valuabe deposits. Getting some nickel-contaminated iron could be workable for you if you know how to separate the ores.
It now becomes worthwile to specialize in mining and more apparent how to do so. You’d need the ability to mine at a lower energy cost than the competition, or be able to do so in areas where other players can’t, or be able to work with contaminated and/or diluted ores.
Finally, a consequence of this system is that there’d be an economic resource geography of sorts. By this I mean that virgin area’s get surface mined (costs little energy) first. Later on when players end up starved after the quick resource dump made by surface-mining players, more experienced miners can move in to make the investments necessary in profitably recovering deeper layers of ore.
Once this golden age of resource gathering has past, truly specialized players with exceptional abilities can gather the few valuable depositis remaining.
Adding in energy costs in general could have other consequences as well. Resources could get transported and sold where they can be converted into useful materials where the energy costs are lowest, necessitating transport.
Also, energy is necessary to recycle waste, be it broken up material or oxidized fuel.