What mineable Lunar mineral deposits are valuable enough to offset mission costs. I have read perhaps cobalt, titanium, lithium, helium and maybe obsidian?
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2$\begingroup$ Obsidian? Whilst it isn't worthless, it isn't really worth the effort to exploit it on Earth... $\endgroup$– Starfish PrimeCommented Jul 27, 2022 at 19:39
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1$\begingroup$ Yeah, obsidian is just volcanic glass. It forms from silica-rich lava (rare on the moon) that rapidly cools on exposure to air and water (nonexistent on the moon)...there's no shortage of it on Earth, and I'm not sure it can occur on the moon in any quantity. $\endgroup$– Christopher James HuffCommented Jul 28, 2022 at 15:05
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$\begingroup$ almost anything you can think of would be worth "mining", but not for its metal content but rather the oxygen. for an early moon base, the oxygen content will be far more valuable/useful. $\endgroup$– AlondaCommented Aug 1, 2022 at 16:50
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2 Answers
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From the title of the question I assume you are asking about underground mining on the Moon.
In terms of underground mining on the Moon we practically know nothing. There were very few holes drilled into the Moon during the Apollo era and the longest hole was less than 3 m long. I purposely write "long", not deep, because the holes were not drilled vertically. While useful in trying to examine lunar regolith below the surface the data from those holes is insufficient to give any indication of potential mining material from underground sources.
Satellite information has provided data on surface mineralization, but we don't know far below the surface any mineralization extends. Similarly we do not know the grade (how rich or poor) any mineralization is at depth (ie percentage of metal in the rock).
We do know that the grade of surface mineralization is generally less than what would be regarded as economic if mined on Earth. Unlike the Earth, the Moon has not experienced many of the mineral depletion and enrichment processes, such as actions by ground water - hydrothermal fluids and supergene processes.
As you state, cobalt, titanium, lithium and helium occur on the surface of the Moon. If they were to be mined and sent to Earth they would be uneconomic. If they were to be used on the Moon or in space, they may be economic.
Concerning helium-3, on the Moon. Until we can make a fusion reactor and particularly one that could use helium-3, helium on the Moon may be of interest, but it is uneconomic.
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2$\begingroup$ Helium-3 on the moon is a non-starter. The concentrations are waaaaaay too low... less than 50 parts per billion. You could manufacture the stuff on Earth more cheaply than you could mine it from the moon. If you already had a giant strip-mining operation, you might get useful amount of 3He from it, maybe, but that's the sort of thing you'd get with a mature industrial presence on the moon, long after you'd already offset your earlier mission costs. $\endgroup$ Commented Jul 27, 2022 at 19:46
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3$\begingroup$ We already produce helium-3, in fact, as a byproduct of our nuclear weapons program. From 1955 to 1996, the US produced 225 kg of tritium, and 150 kg of what we produced had decayed to helium-3 by the end of that time. That's equivalent to mining and processing 10 billion kg of lunar regolith, with helium-3 content toward the high end and no losses. We could make much more if we had a sufficient need for it. We'd probably be better off putting reactors and a tritium stockpile on the moon rather than trying to mine lunar helium-3. $\endgroup$ Commented Jul 27, 2022 at 22:58
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2$\begingroup$ "If they were to be used on the Moon or in space, they may be economic." – That's the fundamental problem with all the Moon, Mars, Asteroid, and whatever other heavenly body mining: even if there is a huge concentration of it just laying around on the surface to pick it up … you're still in friggin' space, nowhere near where the industry is that needs this stuff! $\endgroup$ Commented Jul 28, 2022 at 15:56
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$\begingroup$ “ In terms of underground mining on the Moon we practically know nothing.” Oh yes we do. For some TBD depth, meteor bombardment churns the “soil” (regolith) to some proportional amount, after some TBD time- “impact gardening.” The shallower the depth and the longer the time given, the more the regolith has been homogenized, as the flux of impactors scales exponentially with size (and therefore, kinetic energy). Trivial-to-low depths are both pulverized (“fines”) and homogenized, assuming enough time (no recent de-homogenization). Depths of ~meters imply big hits, and some millions of years. $\endgroup$ Commented Jul 30, 2022 at 12:34
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$\begingroup$ …given exposure of ~billion years, the lunar surface has been gardened to fair homogeneity, to fair (several meters) depth. The further you go, the more you get variation in the form of intact boulders (some thrown from other spots, some not), primordial condensations, intact impactors or their fragments, etc. $\endgroup$ Commented Jul 30, 2022 at 12:39
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“to offset mission costs”
You don’t really specify there: roundtrip mission costs? “tourist” (boots-on-the-ground) “missions”? uncrewed?
If you mean “valuable enough” back on Earth, the material value justifies basically nothing. Simply climbing out of the lunar gravity well eats all profit, via the propellant needed, including the landing propellant needed to gently set down the return propellant. If you use some sort of electric gun or catapult to get off the surface, now you’ve got an infrastructure problem. We can’t even get infrastructure on Earth approved and funded. If you mean non-material value, you might- might find souvenir or cultural Giffen or whatever value in “Moon rocks!”, but only some special examples. General lunar rock is available as lunar meteorites, recovered on Earth for a fraction- tiny fraction of the cost.
If you mean a mission stuck in the lunar gravity well, then the energy boondoggle isn’t a boondoggle. Even dumb rock has a use as shielding. The further you get from dumb rock, the more you need processing (some infrastructure issue again, varying), or prospecting/luck. But as a differentiated body, the lunar core is valuable; the lunar crust is basalt, and less valuable than Earth basalt. Aluminum, titanium, and other components of feldspathic ores are bound well, and not easily won.
If you mean a robotic mission, stuck on the Moon, then time is (mostly) out of the equation. The lunar night (extreme cold) has to be engineered away, but then some sort of low-rate, self-contained processor might work, financially. But you’ve still got the differentiation problem: a body’s crust is refrozen lava, and lavas lost many components to the core, or to space via outgassing.
I think Andy Weir put it best (paraphrasing, can’t find the link): people don’t want to hear economic arguments for the Moon- there aren’t any.
