Yes it is feasible. There’s a long way from it being feasible in principle and an actual business, but plenty of possibilities to explore.

The main suggestions include volatiles from the poles - supplying water and the water split into hydrogen and oxygen as fuel, to LEO - where the Moon has the advantage that export is much easier than from Earth, precious metals for export to Earth such as platinum, which may be there as a result of impacts of iron rich meteorites and giant asteroids, and many resources suggested that could be used in situ on the Moon. We could also create solar panels on the Moon. It’s useful for fabricating electronics because of the hard vacuum. There are some processes you can do on the Moon easily which would be hard to do on Earth because it is so difficult to get a sufficiently hard vacuum to do them.

There are several books by Moon enthusiasts describing this in detail, how it would work. Paul Spudis is one, with his most recent book, The Value of the Moon: How to Explore, Live, and Prosper in Space Using the Moon's Resources. Another is Dennis Wingo, CEO of Skycorp, and author of Moonrush, see his recent paper, and appearance on the Space Show. Others include Madhu Thangavelu, David Schrunk, and other authors and contributors to The Moon: Resources, Future Development and Settlement. See also David Schrunk's paper Planet Moon Philosophy , and their appearance on The Space Show.

I did a summary of some of the main resources on the Moon for my Case for Moon first. The rest of this answer consists of extracts from the section The Moon is resource rich from my kindle book.

VOLATILE RESOURCES

We have pretty good evidence now of ice at the poles, in permanently shadowed craters, thought to be relatively pure and at least a couple of meters thick according to radar data from a NASA instrument flying on India's Chandrayaan-1 lunar orbiter.

It's not a direct detection however, so there is still room for scepticism about it, as rough material would have the same radar signature as radar transparent ice. But craters that are rough when new, are rough both inside and outside the crater rim. While these signatures are found only inside the craters and not outside the rims, which they interpret as meaning that they are caused by ice. The temperatures are also right for ice.

If it is ice, it could be "fluffy ice".

"We do not know the physical characteristics of this ice—solid, dense ice, or “fairy castle”—snow-like ice would have similar radar properties. In possible support of the latter, the low radar albedo and lower than typical CPR values for nonanomalous terrain near the polar craters are 0.2–0.3, somewhat lower than normal for the nonpolar highlands terrain of the Moon and are suggesting the presence of a low density, “fluffy” surface."
(page 13 of Evidence for water ice on the moon: Results for anomalous polar)

In either case, it is not just a little ice; if this is what they detected, there's estimated to be at least 600 million metric tons of this, and possibly much more.

It also contains other volatiles. We know for sure that there is some ice on the Moon, by the LCROSS impact experiment. Relative to H

2

O at 100% they found H2S at 16.75%, NH3 at 6.03% SO2 at 3.19%, C2H4 at 3.12%, CO2 at 2.17%.

So, if the rest of the ice at the poles has a similar constitution to the impact site that's a lot of nitrogen (in the ammonia) and CO

2

on the Moon at the poles.

On the other hand, caution is needed as this is not direct detection. The LEND results (searching for hydrogen through reduced emissions of neutrons of a particular type) are particularly puzzling, as there is almost no resemblance between their map and the miniSAR map.

LEND map - in this picture blue is reduced neutron emission and shows likely locations of hydrogen. 0 degrees longitude is at the top.

They did detect hydrogen, but puzzlingly, it was not correlated with the permanently shadowed regions - there was some hydrogen in permanently shadowed regions, and some also in illuminated regions. A recent paper suggests that ice mixed in the regolith in illuminated regions may be ancient ice that survived a minor shift of the lunar axis.According to one hypothesis, this may be ancient deposits from over three billion years ago before volcanic activity, which changed the polar axis slightly by shifting material.

A new LEND mission has been proposed involving low passes over the poles at altitudes as low as a few kilometers, for higher resolution results.

The Moon may also have ice at lower latitudes too, as there are permanently shaded regions up to 58 degrees from the poles (only 32 degrees from the equator). Though these regions are too warm to have ice on the surface, there may be ice there underground. See Ice may lurk in shadows beyond Moon's poles (Nature, 2012).

At any rate, the Moon does seem to have resources of ice at the poles (though memorably, Patrick Moore in one of the last Sky at Night programs that he did said that he'd believe there is ice at the poles when someone brought him a glass of water from the Moon). More research is needed to find out how much there is and where it is.

METALS

Critics often say that the Moon is undifferentiated and doesn't have any processes to concentrate ores. Although the Moon doesn't have any liquid water so all the processes involving concentration of resources through water erosion won't work, it still has many processes that can concentrate ores. Including:

• Fractional crystallization - as a melt cools down, some minerals crystallize out at a higher temperature than others so form first. They then settle or float, so remove the chemical components that make them up from the mix, so changing its formula, leading to new crystals to form in a sequence.
• Gravitational settling, lower mass material floats to the top.
• Volcanic outgassing can concentrate materials such as iron, sulfur, chlorine, zinc, cadmium, gold, silver and lead.
• The processes that lead to volatiles condensing at the poles - which it seems can also concentrate silver too
• Processes unique to the Moon (perhaps electrostatic dust levitation may concentrate materials)?
• Volatiles brought in as part of the solar wind
• Asteroid and micrometeorite impacts bring materials from asteroids to the lunar surface such as iron and possibly platinum group metals etc.

The Moon has many valuable ores for metals. For instance, the highland regions (probably the original crust of th Moon) consists mainly of Anorthite (a form of feldspar, formula CaAl2Si2O8) which is 20% Aluminium, compared with 25% Aluminium for Bauxite on Earth. So aluminium ores are abundant on the Moon, indeed orders of magnitude more abundant than they are in typical asteroids, but it does require a lot of energy to extract the aluminium from the ore. Either a nuclear power plant or large areas of solar panels. Crawford, in his "Lunar Resources: a Review", says this about aluminium on the Moon:

"Aluminium (Al) is another potentially useful metal, with a concentration in lunar highland regoliths (typically10-18 wt%) that is orders of magnitude higher than occurs in likely asteroidal sources (i.e. ~1 wt% in carbonaceous and ordinary chondtites, and <0.01 wt% in iron meteorites; . It follows that, as for Ti, the Moon may become the preferred source for Al in cis-lunar space. Extraction of Al will require breaking down anorthitic plagioclase (CaAl2Si2O8), which is ubiquitous in the lunar highlands, but this will be energy intensive (e.g. via magma electrolysis or carbothermal reduction; Alternative, possibly less energy intensive, processes include the fluoridation process proposed by Landis , acid digestion of regolith to produce pure oxides followed by reduction of Al2O3 (Duke et al.), or a variant of the molten salt electrochemical process described by Schwandt et al."

Mining this for the aluminium would create calcium as a byproduct, which is useful as a conductor in vacuum conditions, a better conductor than copper weight for weight -you need half the mass for the same amount of electricity. (Copper does better than calcium on a per volume basis because it is 5.8 times denser, it is also of course much more practical in an atmosphere because calcium reacts vigorously with air, but that's not a problem for conductors that operate in a lunar vacuum, and in space applications the reduced mass may be an advantage).

"Calcium metal is not used as a conductor on Earth simply because calcium burns spontaneously when it comes in contact with oxygen (much like the pure magnesium metal in camera flashbulbs). But in vacuum environments in space, calcium becomes attractive.

"Calcium is a better electrical conductor than both aluminum and copper. Calcium's conductivity also holds up better against heating. A couple of figures mining engineer David Kuck pulled out of the scientific literature: "At [20C, 68F], calcium will conduct 16.7% more electricity than aluminum, and at [100C, 212F] it will conduct 21.6% more electricity through one centimeter length and one gram mass of the respective metal." Compared to copper, calcium will conduct two and a half times as much electricity at 20C, 68F, and 297% as much at 100C, 212F.

"Like copper, calcium metal is easy to work with. It is easily shaped and molded, machined, extruded into wire, pressed, and hammered.

"As would be expected of a highland element, calcium is lightweight, roughly half the density of aluminum. However, calcium is not a good construction material because it is not strong. Calcium also sublimes (evaporates) slowly in vacuum, so it may be necessary to coat calcium parts to prevent the calcium from slowly coating other important surfaces like mirrors. In fact, calcium is sometimes used to deoxidize some metal surfaces. Calcium doesn't melt until 845C (1553F).

"Utilization of lunar materials will see the introduction of industrial applications of calcium metal in space."

From the section on Mining the Moon in Permanent - by Mark Evan Prado, a physicist in the Washington, D.C., region working for the Pentagon in advanced planning in the space program.

The Moon is deficient in copper, at least on the basis of what is known so far, but as well as calcium, aluminium is a good conductor.

The LCROSS experiment found silver (a superb conductor) and mercury at the impact site, but the concentration is not known, except that it is far higher than the levels in the Apollo samples, and is probably in a layer below the surface, as the signal was delayed. See LCROSS mission may have struck silver on the moon.

It has abundant iron - in addition to ores (which would need a lot of power to extract), it actually has free iron metal

• From meteorite impacts
• Nanometer sized "blebs" released from the rock by the hydrogen in the solar wind reacting with iron oxides
• Particles of iron concentrated from the source materials for the regolith.

It's in powder form already, and naturally alloyed with nickel and cobalt. The blebs, or "nanophase iron" are found inside impact glass particles, so would be hard to extract. The rest though is made up of tiny particles of pure iron, so the obvious thing to try to do is to separate them out using powerful magnets. They are rather small though, most are less than a micron in diameter which could be a challenge. If we can separate them out, we can get five kilograms of iron, 300 grams of nickel and about half a gram of platinum, gold etc. (platinum group metals) in every cubic meter of regolith - as pure metal what's more. (This summarizes part of section 5, Metals from Crawford)

He bases that on a paper from 1980 by Morris and particularly its conclusion, which uses a model to interpret the data. Taylor and Meeks in the section Agglutinitic Glass versus Grain Size and Maturity (page 133) in their paper suggest that perhaps most of the iron is in nanophase form, mixed up with the glass and hard to extract.

However we don't need to speculate any more as Jayashree Sridhar et al of the NASA Johnson Space Center have done the experiment using actual samples of lunar regolith. See Extraction of meteoritic metals from lunar regolith, and they succeeded! The nanophase iron was a problem but they were able to work around it by varying the experimental setup. By varying on the size of particle they ground it down to, the strength of the magnets and details of the technique they could extract over 80% of the meteoritic iron in some of the tests. They conclude:

"Experimental results indicate promise for the extraction of meteoritic metals from lunar regolith. However, more work is needed to refine the technique and understand more about the variables that affected our results."

The iron is valuable for steel, and is also a conductor, though not nearly as good as Aluminium or Calcium. It would be useful for some applications such as electric railroads on Mars, and is a conductor easy to access in the early stages.

Also nickel and iron are useful for making nickel / iron batteries. These could be useful for making batteries on the Moon with in situ resources, for instance to help last through the lunar night.

"Iron-nickel batteries are very rugged. Their lifetimes which can exceed 20 years are not affected by heat, cold or deep cycling. They are not easily damaged by rapid discharging or over-charging. On the downside, they have poor performance at low temperatures but they can be kept warm with insulation (e.g. simple regolith) and thermal wadis. Also, they only have a charge to discharge efficiency of 65% and will self discharge at the rate of 20% to 40% per month. Despite these shortcomings, they might be the Moon-made power storage systems of choice due to their simplicity and the availability of their component materials on the Moon. Moreover, these materials are among the easiest of materials to produce on the Moon."
See Electrical Energy Storage Using Only Lunar Materials.

Then, you also have titanium. This is especially interesting as it is rare in asteroids. Apollo 17 samples are 20% high purity Ilmenite, a Titanium ore which is found in the lunar mare. And better than that, the Lunar Reconnaissance Orbiter, with its spectral mapping of the Moon, discovered deposits that are up to 10% titanium, more than ten times higher than titanium ores on Earth. (Phys.org report, NASA image). Titanium is an industrially desirable metal, stronger per unit weight than Aluminium (though it is a poor conductor).

Titanium is also widely used in medicine for hip replacements, dental implants, etc., as "one of the few metals human bone can grow around firmly", see also this new titanium / gold alloy four times tougher than titanium

Titanium is especially useful for medical applications because it

• Forms an inert and stable titanium oxide layer spontaneously
• Has a high strength to weight ratio
• Doesn't leach into blood and other aqueous environments because of its low rate of ion formation
• Is one of the few materials that can integrate directly into living bone tissues (osseointegration) without any soft tissue layers in between

Crawford writes (page 17):

"Therefore, in the context of a future space economy, the Moon may have a significant advantage over asteroids as a source of Ti. The fact that oxygen is also produced as a result of Ti production from ilmenite could make combined Ti/O2 production one of the more economically attractive future industries on the Moon.

For more on this, see major lunar minerals. And for an in depth study, read Crawford's review.

So, yes, there are plenty of metals on the Moon, but it might take a lot of power to extract them, apart from the iron, if that can be separated out using magnets.

And that's mainly based on the Apollo results which explored a small region of the lunar surface which has been found to be in some ways unrepresentative. The Moon may have many other surprises in store. Many ores on Earth would not be detected from orbit, and it seems the Moon has a fairly complex geology as well.

As an example of one way the Moon could surprise us - Earth is often hit by iron meteorites, so the Moon should be also. The main question is, how Dennis Wingo has hypothesized in his Moonrush book, that the Moon may also have valuable platinum group metals which could be mined, the result of the impacts of these iron meteorites.

Taking this further, there's a hypothesis by Wieczorek et al that magnetic anomalies on the Moon around the south pole Aitken basin may be from the remains of the metal core of a large 110 km diameter differentiated asteroid that hit the Moon to form the basin. If so, they could be useful sources for platinum, gold, etc.

From Wieczorek et al, the North and South poles are marked N and S. Notice the magnetic anomalies clustered around part of the rim of the South Pole Aitken Basin. This is thought to be the result of an impact by a 110 km diameter asteroid. Wieczorek et al hypothesize that the magnetic anomalies trace out the remains of the metal core of this asteroid. If so these could be rich ores, including iron, nickel, also platinum and other platinum group metals (gold, rhodium etc). See page 16 of Crawford's Lunar Resources: A Review

Platinum is a particularly useful metal. It is heavy, soft, malleable as gold and silver, easy to draw into wires, very unreactive, and has a high melting point. Out of gold, silver, platinum and copper, platinum is the densest and the hardest and the least reactive (the others are somewhat better in terms of electrical and thermal conductivity, and malleability, but it's not too bad at those either). So, it's not just useful for catalytic converters, fuel cells, dental fillings and jewelry. We'd probably use it a fair bit in other ways too if it didn't cost so much.

The platinum group metals might be valuable enough to return to Earth from the Moon, just as suggested for the asteroids, especially if there is water to split and use as fuel available on the Moon or once they set up a mass driver on the Moo

Of course, you can't just take the current market value of platinum, multiply by the amount of platinum available in a large meteorite - or on the Moon if Wingo and Wieczorek et al are right - and conclude that you'd get trillions of dollars by returning all that platinum to Earth and selling it here. You need to fulfill a need or eventually nobody will buy it. If it's just to replace copper, for instance, in wires, it wouldn't be worth returning unless you could reduce the transport cost back to Earth right down. Dennis Wingo suggested in Moonrush that it could be worth exporting it to Earth for use for fuel cells, as an application that could be high value and yet need a lot of platinum.

The gold could be useful too, on the Moon at least. You don't normally think of gold as more decorative than useful but it is used a fair bit in electronics Also combined with the abundant titanium on the Moon you get Ti3Au, an alloy with 70% less wear, four times the hardness and increased biocompatibility compared with pure titanium (and twice as hard as titanium / silver and titanium copper alloys). It's also 70% less wear than titanium, lower friction and four times harder with a hardness of 800 HV in the Vickers hardness test. Density about the same as steel.

(density of titanium: 4.43 g/cc. using the atomic masses of gold and titanium, multiplying by (196.96657+3*47.867)/(4*47.867)*4.43 = 7.88 approx. By comparison, density of steel is 7.75 g / cc).

The paper focuses on its medical applications, you can alloy titanium with copper or silver, which are twice as hard as pure titanium, but this is four times as hard. It's also 70% more resistant to wear which will make it last longer and lead to less debris. And has excellent biocompatibility properties. But I wonder if it might also have lunar applications, with the hardness especially and resistance to wear.

Probably only the platinum group metals would be worth returning to Earth, since it's going to be easier to mine the Near Earth Asteroids, especially the ones that consist almost entirely of pure metal. However, whether or not they are useful for Earth, they are well worth using on the lunar surface once you have industry there.

The Moon has some advantages over Mars indeed for metals, such as the pure nanophase iron mixed in with the regolith, which can only exist in oxidized form on Mars except for rare metal meteorites. Also, it's unlikely it will be commercially worthwhile to return metals from Mars while there are definite possibilities of returning metals from the Moon. See Exporting materials from the Moon for future suggested low cost methods for export from the Moon. For discussion of whether anything physical could be worth the expense of export from Mars, see Commercial value for Mars

LUNAR GLASS

This is a beneficial side effect of all the micrometeorite impacts on the Moon (which you don't get so much on Mars with its thin atmosphere, just enough to filter out micrometeorites). The Moon's "soil" or regolith contains large quantities of glass, created during the impacts. It also has free iron, as we saw, at half of one percent of the soil, in tiny micro beads of iron (nanophase iron) which concentrate the microwave energy. Again, you don't have this on Mars.

As a result, it is really fast to melt the regolith using microwaves. It took only 30 seconds to melt small lunar sample at 250 watts (typical of a domestic microwave). You can melt the soil to glass as easily as you can boil water using the microwave in your kitchen. See lunar lawnmower. This only works with genuine lunar soil and not the simulants. We have nothing analogous to lunar soil on Earth, as Larry Taylor, principle author of this paper found: Microwave Sintering of Lunar Soil: Properties, Theory, and Practice. He says the microstructure of the genuine lunar regolith, with nanophase iron beads scattered throughout, would be almost impossible to simulate.

His idea (see Products from Microwave Processing of Lunar Soil on page 194 of the paper) is to run a "lunar lawnmower" over the soil with two rows of magnetrons (such as generate microwaves in a microwave cooker). The first row would sinter it to a depth of half a meter using microwaves. Then the second row completely melts the top 3-5 cm of the soil, which then crystallizes to glass. As it does this, it will heat up and release most of the solar wind particles notably hydrogen, helium, carbon and nitrogen. So it could also capture these assets as it goes along, including the Helium 3, if this turns out to be of economic value.

See also The Lunar Dust Problem: From Liability to Asset. This could also be useful, for instance, for a solar panel paving robot to make solar panels, and other applications.

Then, there's Behrokh Khoshnevis' idea for making a landing pad on the Moon using tiles made of lunar glass in situ. The idea is to make the surface into lots of tiles by injecting a material that can't be sintered easily using microwaves into the soil first to outline the edges of the tiles, then use microwaves to melt the soil in between.

This would make a tiled flat surface for supply vessels to land on. It would also help with the problem of lunar dust by removing dust from the landing area. You can read the details here. He used lunar regolith simulant, so presumably by Larry Taylor's results, it would work even better with genuine lunar samples.

SOLAR CELLS FROM LUNAR MATERIALS - SOLAR PANEL PAVING ROBOT

Once you have glass, it might not be such a big step to make photovoltaic cells on the Moon. And here the Moon has one big advantage, the high grade vacuum so you could use vacuum deposition to make the cells in situ. To start with you'd make the cells themselves from materials sent from Earth, later on mine them on the Moon.

This is a report from the Center for Advanced Materials at the University of Houston, suggesting the possibility of an autonomous solar powered lunar photovoltaic cell production rover

It would use silicon extracted from lunar materials to make the cells themselves. Of the various methods you could use, magma electrolysis may be best. He uses low efficiency silicon cells which are vacuum deposited on glass, something that is not easy to do on Earth but would be possible in the ultra high vacuum conditions on the Moon. Techy details of this suggestion are here.

It would require transporting a small mass to the Moon in the form of the rover which then over several years of driving could build a 1 MW facility on the Moon.s

Idea for a robot to drive over the surface of the Moon leaving solar panels in its wake wherever it goes, using only indigenous lunar materials to make the panels. The panels would be only 1% efficient, but given that there is no shortage of real estate on the Moon, that might not matter. It might be more important to make the panels in situ without any imports from Earth than to make them highly efficient

Structure of the panels

For making glass on the Moon see the section above: Lunar glass

BASALT (LIKE GLASS FIBER)

The basalt itself is a natural resource. If reasonably pure and consistent in composition, it's ideal for making basalt fibre, which is like glass wool, but much better in some ways. The regolith consists mainly of powdered basalt. So might well be ideal for making basalt fibre. See:

• Basalt Fiber Properties

HELIUM 3

I should mention this, since the topic is brought up so often in discussions of lunar settlement. However I don't see this as a major plus point for the Moon at present.

The Moon is a source for helium 3, deposited in the regolith by the solar wind, and some say that helium 3 will be of value for fusion power in the future because it is not radioactive and doesn't produce radioactive waste products. If so, small amounts of helium 3 from the Moon could be worth a lot on Earth and be a useful commodity to export. Apollo 17's Harrison Schmidt is a keen advocate of helium 3 mining on at a reasonable rate at a reasonable rate the Moon.

However, we don't yet have fusion power plants at all, and one able to use helium 3 is a tougher challenge. Frank Close wrote an article in 2007 describing this idea as "moonshine" saying it wouldn't work anyway. Frank Close says that in a deuterium - helium 3 tokamak, at normal temperatures for a tokamak, the deuterium helium 3 reaction proceeds so slowly that the deuterium would instead fuse with itself producing tritium and then fuse with the tritium (the original article is here, but it's behind a paywall). For a critical discussion see also the Space Review article The helium-3 incantation

See also Mining the Moon by Mark Williams Pontin. If you can use much higher temperatures, six times the temperature at the centre of the sun by some calculations, the helium 3 will fuse at a reasonable rate, but these are temperatures way beyond what is practical in a tokamak at present. The reason such high temperatures are needed for a tokamak is because the plasma is in thermal equilibrium and has a maxwellian distribution which means that to achieve a few particles at very high temperatures you have to heat up a lot of particles to lower temperatures to fill up the maxwellian distribution so that just a few will react. This is potentially feasible for the lower temperatures of DT but not feasible for the higher temperatures of 3He 3He.

However if you use electrostatic confinement, a bit like a spherical cathode ray tube with the fusion happening at the center where the negatively charged "virtual cathode" is, then the particles are all at the same high energy and the result is much more feasible with lower power requirements. This is the approach of Gerald Kulcinsky who achieves helium 3 fusion in a reactor 10 cm in diameter. However though it does produce power, it produces only one milliwatt of power for each kW of power input so is a long way from break even at present.

Gerald Kulcinski who has developed a small demonstration electrostatic 3He 3He reactor 10 cm in diameter. It is far from break-even at present, producing 1 milliwatt of power output for each kilowatt of input. See A fascinating hour with Gerald Kulcinski

Perhaps this line of development will come to something. Perhaps one way or another we will achieve helium 3 fusion as the enthusiasts for helium 3 mining on the Moon hope. However it is early days yet, and we can't yet depend on this based on a future technology that doesn't exist yet.

However even if we do achieve helium 3 fusion, it might not be such a game changer for the lunar economy as you might think. Crawford says (page 25) that to supply all of our energy from Helium 3 would mean mining 5000 square kilometers a year on the Moon, which seems ambitious (and would mean the whole Moon would only last 200 years). So, even if we develop Helium 3 based fusion, and it turns out to be a valuable export, it's probably not going to be a major part of the energy mix.

Even more telling, he also calculates that covering a given area of the Moon with solar panels would generate as much energy in 7 years as you'd get from extracting all the Helium 3 from that region to a depth of three meters.

Also - there are many other ideas being developed for nuclear fusion, such as laser fusion, and the polywell which has the same advantage that no significant radiation is produced when it uses fusion of boron and hydrogen. I think it is far too soon to know whether or not the helium 3 on the Moon will be an asset in the future when we achieve nuclear fusion power. For a summary, see ESA: Helium-3 mining on the lunar surface.

This doesn't mean that there is no point in helium 3 mining however. As Crawford suggests (page 26), Helium 3 is useful for other things, not just for fusion power. It's used for cryogenics, neutron detection, and MRI scanners, amongst other applications, so some Helium 3 from the Moon could be a valuable export right away, even if it doesn't scale up to the huge quantities you'd need for Helium 3 based power generation on Earth. You'd get it automatically as a byproduct while extracting the more abundant volatiles from the solar wind in the regolith, so it might well be a useful side-line to help support lunar manufacturing economically as part of the mix along with everything else.

THORIUM AND KREEP (POTASSIUM, PHOSPHORUS AND RARE EARTH ELEMENTS) ,AND SOME URANIUM

The Moon has some uranium, which is a bit of a surprise for such a heavy element, but when bound with oxygen it is rather lighter and can occur in the lunar crust as on Earth. It is especially rich in Thorium, in the lunar Mare. This is useful as a fuel for nuclear fission reactors, which have to be designed to burn thorium instead of uranium to use it. It's not likely to be worth returning to Earth as thorium is abundant here. But it could be very useful in space, at some point in the future.

Nuclear power stations built on the Moon wouldn't have the same pollution hazards and hazardous waste issues as stations on the Earth. Perhaps this may be a way to power space colonies, and interplanetary ships fueled from the Moon, so avoiding the need to launch nuclear power plants from Earth to orbit.

Thorium is a tracer for KREEP - potassium, phosphorus and rare earth elements. Also associated with chlorine, fluorine, sodium, uranium, thorium, and zirconium, so KREEP ores could be sources for all those elements on the Moon.

When the Moon cooled down from the original molten state, then olivine and pyroxene crystals form first, and sink to the bottom of the magma ocean (both made of iron and/or magnesium plus silicon and oxygen). Meanwhile anorthite also forms (made of calcium, aluminum, silicon, and oxygen), which is less dense and floats to the top (forming the lunar highlands). Some of the other elements like nickel are able to squeeze into the crystal lattice and get removed at the same time. But the larger elements can't, and are left in liquid state. They are last to solidify and form the KREEP deposits. It forms in between the olivine and pyroxene deep down, and the floating anorthite on top and may have been liquid for a long time.

For some reason, not fully understood, then KREEP deposits on the surface of the Moon are concentrated on the near side of the Moon near the Imbrium basin, with a small amount also in a separate concentration on the far side. The Imbrium impactor probably excavated the KREEP deposits on the near side. But it's puzzling that the much larger Aitken basin didn't lead to large deposits on the far side. Perhaps for some reason KREEP is concentrated on the near side of the Moon. For more about this see The Moon is a KREEPy place by the planetary geologist Emily Lakdwalla which I summarized here.

The abundances of rare earth elements on the Moon are much less than rare earth ores on Earth, and despite the name, they aren't very rare here on Earth. So it's not likely that they'll be worth returning. However the most concentrated spots - the ones marked white in this figure - haven't been sampled on the surface and the spatial resolution is low, tens of kilometers. So it's possible we'll find more concentrated ores on the Moon.

It's a similar situation for uranium and thorium. The abundances on the Moon from this map are too low to count even as a low grade ore on Earth. But with such low resolution, there could be richer ore deposits when we look at it closely. (Here I'm summarizing what Crawford says about lunar KREEP ores in his survey, see section 7, Rare earth elements and following)

POSSIBILITY OF USING LUNAR SOLAR POWER FOR EARTH

This is a bit further ahead, but it is worth thinking about, whether solar power for the Moon could actually be useful for Earth also. Some scientists think it could be.

The advantage of doing this on the Moon is that you can use indigenous materials to make the solar panels. For a small amount of launch mass to the Moon you could have a rover that travels over the surface leaving solar panels in its wake. See Lunar glass and Solar cells from lunar materials - solar panel paving robot (above)

It's easy to see this working to supply power to the Moon, but some have suggested it could also be used to generate power on Earth. So, taking this even further, with a large scale operation of this type, using only 1% of the surface area of the Moon, you could supply 2 kilowatts of continuous power per person to a population of 10 billion on the Earth. See Solar Power via the Moon. More details here.

Or, further ahead, maybe this is more interesting as a talking point than a likely near future concept, the Japanese Shingzu corporation has suggested we could build solar panels in a band around the Moon - at the equator

See Shimizu dream - Lunar Solar Power Generation - Luna Ring.

Earth would get solar power only half the day, so they send the power to satellites in orbit around Earth, which then beam it down to the other side of Earth. Of course they need large receivers to collect the power from the Moon, but only 1% of what they'd need to collect it directly from the sun - that could be worth doing if it is significantly easier to make solar panels on the Moon.

On the other hand there are ideas to use large thin film solar panels in space or large thin film mirrors to concentrate the light onto solar panels or furnaces, launched from Earth to LEO. So would the lunar solar plants be a major saving compared to those?

Another way that the Moon could help the Earth though, with solar power, is to make the solar cells from lunar materials, and then ship them to GEO or lower orbit. The idea of using lunar materials to make solar power satellites goes back at least to the 1970s, see Construction of Satellite Solar Power Stations from Nonterrestrial Materials

For more on this see the The Moon is resource rich section of my Case for Moon First

Whether it is useful off planet depends a lot on how easy it is to export the materials from the Moon, and one of the most promising ways to do that is Hoyt’s cislunar tether system which exploits the Moon’s position as higher in the gravitational well than Earth to basically “roll the goods down hill” from the Moon to Earth through a system of rotating tethers.

See

• Exporting materials from the Moon
• Ballutes - return of high value resources such as platinum to Earth

in my Case For Moon First