Since no one else is around, here’s an interesting email which I am entirely unqualified to comment on intelligently:

Your reader is right except for one thing, there are some metals which are
finite and we are actually reaching the limits of.
Copper is the most glaring example but there are other exotic metals and
rare-earths which we can see the limit of.
Metals can’t be lumped under the same rules as looking for fossil fuels as
fossil fuels came from organic processes and built up over time in various
basins and regions while metals were deposited at the formation of the Solar
System and in ratios which we understand very well.
Furthermore, the reader’s comments that we can just go to the Asteroids
doesn’t work for everything because Asteroids don’t have the same sorts of
metals as the Earth does since they are more like the Core and Mantle of the
Earth while rare-earth and exotic metals like aluminum were lighter metals
and deposited after the asteroids and planets formed.
M-type asteroids are metallic asteroids; they are moderately bright (albedo
.10-.18) and made of nickel-iron, these won’t have rare-earths. S-types are
moderately bright (with an albedo of 0.10 to 0.22) and consist of metallic
nickel-iron mixed with iron- and magnesium-silicates. They are dominant in
the inner main belt within 2.2 AU, common in the central belt within about 3
AU, but become rare further out.
http://www.sciam.com/article.cfm?chanID=sa003&articleID=000CEA15-3272-13C8-9
BFE83414B7FFE87
Researchers estimated that 1.6 billion metric tons of copper exist that
could potentially be brought into use. This figure relies on the broadest
possible definition of available copper as well as a lack of energy
constraints and environmental concerns. In contrast, the U.S. Geological
Survey predicts there is only 950 million metric tons of the metal that
could be recovered.
Overall copper use in the U.S. climbed to a high of 238 kilograms per person
by 1999. Declines in areas like manufacturing and railroads were more than
offset by increases in areas like motor vehicles and domestic devices. In
fact, residents of Canada, Mexico and the U.S. required an average of 170
kilograms of copper per person. Multiply that by overall population
estimates of 10 billion people by 2100 and the world will require 1.7
billion metric tons of copper by that date.