Few mineral deposits are easy pickings. Mining a diamond moves and processes tons of dirt. Before cheap energy, only those commanding the equivalent of slave labor mined diamonds, a legacy that lives on in African “blood diamond” controversies today.

Rare earth shortages have been a recent buzz. Rare earths are used in gizmos like cell phones and high efficiency electric generators. Chinese rare earth mines that have been the near-sole source of these things for 10 years appear to have peaked. Rare earth mines elsewhere are opening, but no one has hazarded a guess on the total global reserves.

Mining and refining rare earths is energy intensive and environmentally messy, but demand has grown rapidly because they are used in many exotic new, new things: flat screen TV, photovoltaic cells, electric cars, windmill generators.

For now, ingenuity is alleviating the pinch. Tesla’s induction motors in electric cars need no rare earths. Other industries have cut rare earth use or substituted. Prices of rare earths are dropping. But if normal market logic resumes and rare earth demand soars again, where will we be?

Like rare earths, all mineral reserves have ill-defined limits characterized by diminishing richness of ore. If growth consuming them continues to average 2% annually, we dig faster and deeper through known reserves on into less and less concentrated sources. For the punch line of this see the graph.  Question: If global return on energy (EROEI) is diminishing, and if the concentration of ores we mine is diminishing, where are we headed?

A 2% rate of growth over a period of 50 years racks up a 270% rise in annual use. Note that Diederen projects that at that growth rate we’d even exceed present proven reserves of iron ore (Fe), and be grubbing ever more rock to get less and less iron.

Diederen is also one of the few estimators that sees the dilemma of extracting more minerals from lower and lower grade deposits. See the next graph for his illustration of it.

Note that the X-axis is grade, not time. If one thinks time in mining (or extracting oil), it is apt to go from right to left. The graph illustrates starting with rich, concentrated sources and using more and more energy going right to left, hitting a peak rate, then declining as the ore quality decreases until finally, nothing can be gained by working further. As ore quality decreases or as sites become less accessible (like under a sea floor), better and better technology can increase the quantity extracted, but it takes more work to get it.

Finally, concentration is so low that trying to separate the molecules wanted from everything else is like boiling the ocean: can’t muster enough energy and would waste it if you did. Somewhere in this transition, entrepreneurs will conclude that a one-ton pile of used cell phones is far richer ore for many minerals than anything that can be found in nature.