Yeah - I read somewhere (this board probably) that if there were gold bars, ready-refined to 100% purity, stacked for easy collection on the moon, it would not be economically viable to go get them.
I immediately thought of Iron Sky. Oh, wait. When you said “it” took place, I thought you meant the harvesting took place. But you probably meant the movie. So, no, Iron Sky didn’t take place entirely on the moon. Half the movie took place on Earth or in space between Earth and Luna.
I seem to recollect calculating for a thread on this forum a few years back that if you had a no-cost process to spin straw into gold, that only worked in microgravity, you still couldn’t put the ISS to that use profitably. The launch costs have probably gone down since then, so maybe it’s time to start researching it.
I saw a documentary about that called Space: 1999. Did not end well.
Why go and get them at all? They’d be even safer on the moon than in Fort Knox or the Federal Reserve! All you have to transfer is the ownership, right? 
My Scientific Intuition tells me that Lunar and Asteroid resources will be used in the next century. Too many technical difficulties to overcome.
Even that is far from being useful until Fusion Power is developed. How long will it take? Maybe many decades.
It was mentioned earlier, but it is worth repeating. The most valuable resource the Moon could offer us right now is it’s low gravity. There is enough material on the moon to construct large, massive space craft components for assembly in lunar orbit. Large refueling depots, stocked with rocket fuel produced on the surface of the moon, could be the first stop on a long-term space voyage or trip to Mars. Once scaled, creating the fuel (and other components) on the moon and launching it from the much lower gravity would be much more profitable than doing that from Earth.
As for mining the moon? All but one of the many valuable resources found on the moon are also found and more easily obtained here on Earth. As mentioned earlier, it’s Helium-3. Helium-3 has great potential as a fuel for fusion based nuclear power plants. Nuclear fusion using helium-3 could provide efficient, safe energy that produces zero waste or harmful radiation, but it is extremely rare on Earth.
The sun, a giant fusion reactor, creates helium by combining hydrogen atoms while producing energy. Some of this helium emitted by the sun comes in the form of an isotope missing a neutron and is known as helium-3. Both the Earth and the moon are constantly bombarded with this isotope, but it is repelled by the Earth’s magnetosphere. The moon, having no magnetic field, readily accepts the gas where it is absorbed in the regolith.
With reserves in the order of a million tons, and valued as high as $78,000 an ounce, perhaps nothing can match the potential profit (if any) from helium-3 mining. China is particularly interested in the presence of helium-3 on the moon. Professor Ouyang Ziyuan, chief scientist in charge of the Chinese Lunar Exploration Program believes helium-3 can solve the energy demands of the entire planet for at least 10,000 years. A mere 40 tons of helium-3 used as fuel in a nuclear fusion reactor could supply all of the United States with safe, clean energy for an entire year. Experts in the United States have estimated that a workable helium-3 project which includes the design and production of not only the necessary rockets, spacecraft and mining equipment, but also a functional fusion power plant, would cost around $20 billion over 20 years. However, at $3 billion a ton, helium-3 mining is considered by many to be the most economically viable lunar operation.
Not everyone believes the hype surrounding helium-3. Frank Close, a theoretical physicist at Oxford, goes so far as to call it “moonshine” and a complete fantasy. Chief among his criticism is the fact that deuterium reacts 100 times more slowly with helium-3 than tritium, and the temperatures required to utilize helium-3 are beyond the limits of present tokamak reactors. He also points out that within the plasma contained by the tokamak reactor, all of the nuclei in the fuel mix together. He believes deuterium will combine within the reactor to form a tritium nucleus anyway, which will result in the same standard deuterium-tritium reaction that “helium aficionados” are going through so much effort to avoid. By his calculations, using helium-3 is an exercise in futility. Despite his criticism, the potential profit of $300 billion per year is hard for many to ignore. Perhaps future reactor designs will overcome these obstacles. That will only happen through research and testing that can only occur with a ready supply of helium-3, which we simply do not have on Earth.
The most practical method for extracting helium-3 from the moon involves producing the gas on the lunar surface and ferrying it back to Earth in large storage containers. Moon dust would be scraped from the surface using large, solar powered machines and collected in a large processing facility. There, the regolith would be heated to 600 degrees Celsius to release the gas.
The facilities could be constructed on the Moon in situ. The moon contains enough resources to construct and sustain a permanent facility. Chemicals and materials located on the moon are useable for life support, construction, energy production and propellant fuel. Creating rocket fuel on the moon would drastically reduce the costs of a lunar facility. Launching the required mass of fuel from the Earth would be prohibitively expensive.
Useful minerals on the Moon include aluminum, calcium, potassium, phosphorus and iron. Also extremely useful, and much more valuable is the abundance of titanium (in the form of ilmenite), platinum-group metals, and the massive quantities of rare-Earth elements. The rare Earth elements on the Moon are of particular strategic importance as China currently controls 95% of that resource on Earth.
At Apollo prices, sure.
The SpaceX BFR will bring down costs by orders of magnitude. I sketched out a mission plan that could bring back 150 t from the lunar surface in roughly 10 launches (a ship, a tanker, and 8 refuelings). 150 t, in gold, is about $6B. That means an individual BFR launch would have to cost less than $600M to reach breakeven.
The target price for the BFR is $5M. Even if they are wrong by two orders of magnitude, picking up the gold bars would be profitable. It’s very likely that they’ll be within one order of magnitude, which would make the enterprise very valuable.
There are no gold bars, and I’m skeptical of He3 being a thing, but who knows. Perhaps some industrial process will work better at 1/6 g. Being a source for materials destined for space (including propellant) seems more plausible.