"I know of no other thing in space which is minable. "

There could be other ways of getting rocket fuel or rocket propellent. And in terms making rocket fuel one is mostly looking for some way to get oxygen. 40% of the mass of the lunar surface is oxygen. And oxygen is very abundance in space- after Hydrogen and Helium, it's the most abundant element in the universe.

One could also look at different ways of getting around in space- such as using beamed power. And/or using lasers to get stuff off earth and beyond. Maybe one could some business of delivering power to locations in space.

Or if you have govt willing to throw hundreds of billions of dollars at something there other things one might do, such as:
One could build a mass driver on the Moon.
One have a govt project of moving a space rock into the Earth/system.

Iron on the Moon is probably minable if a govt would simply buy enough of it say for around $100 per lb.
So, 10 billion dollar worth of lunar iron gets you 50,000 tons of iron. You could look at kind of like gold reserves.

So the US or China or UK, or some other country or all other countries do something like this.
Suppose as reserves one had 10 billion dollar worth of Iron.
You could use that iron for making a govt mass driver or other projects or have it collect dust as gold reserves do.
You don't get rid gold reserves, but could a part of them- instead buying more gold, buy Lunar iron.

You have other strategic metal, such Lunar aluminum, titanium, pure silicon, etc.

So companies mining these things would have as a "waste product", oxygen, which could use for their operational needs and they sell it as rocket fuel. The oxygen would worth more per lb than Iron and from an mining operation one could be getting more money from the oxygen than Iron- therefore "waste product" is in quotes. But with iron one could fairly easily harvest iron ore and doesn't require much energy to make pure iron.

It might possible to forget all of the above, and instead of mining water, mine iron to make rocket fuel, in similar model [not requiring huge govt subsidies] in which one could mine lunar ice

"All the approaches produced water by reaction of the hydrogen with the soil. On the Moon, this water could be used for life support. Most important, it could be split into hydrogen and oxygen to use as rocket fuel. The experiments also produced metallic iron. That could be used as a building material or for electrical cables, if we could figure out an efficient way to separate it from the rest of the dirt."
http://www.psrd.hawaii.edu/Nov00/mining.html

But if one has the oxidizer, one still needs the fuel. Is it possible to use iron as the fuel? Or you could look at as way to merely lower costs by providing a fraction of the rocket fuel and bring say kerosene from Earth.

As said before for water to be minable, it would have be priced around $500 per lb at the lunar surface. If water is worth 500 per lb, Oxygen is worth as much.

If you split 9 lbs of water you get 8 lb of oxygen and 1 lb of Hydrogen. Hydrogen per lb would be priced higher than oxygen- there is no doubt about that.

If rocket fuel is selling at $2000 per lb at lunar surface,
9 lbs is $18000, if oxygen sells at $500 per lb then $4000 of the $18000 is for oxygen and $12000 for the lb of hydrogen. It seems hydrogen would not be priced much higher than that nor oxygen much lower. And it might instead be around 1000 per lb for oxygen and 4000 per lb for hydrogen

So, if instead of mining water that sells at $500, if mine something like iron ore and be able to sell the oxygen for $500 per lb, it similar to mining water as far making rocket fuel.

I think a very significant aspect of making any kind of rocket fuel on the Moon is being able to sell it in lunar orbit/L-points/or High earth orbit. And if one could buy oxygen for say $1000 and hydrogen for $4000 per lb and lunar rocket fuel costs about $2000 per lb, oxygen could have more margin for profit as compared to the higher price Hydrogen.
Or said differently it could be said that in the "lunar water mining and making rocket fuel" business one could focus on exporting lunar oxygen and water and sell domestically the Hydrogen.

So, say iron mining sells oxygen $500 per lb and imports from Earth to lunar surface hydrogen, in the form of kerosene, methane, or some hydrocarbon- which result in a cost of H2 so it $20,000 per lb.
So, rocket fuel costs for 9 lb is 24,000 lb or $2667 per lb.
Shipped O2 to lunar orbit is roughly, 500 + 2667,
so one could charge around $4000 per lb for O2 in orbit.

If one can get H2 [or other fuel] at Lunar orbit, etc, for about $8000 per lb and O2 for $4000 per lb
Rocket fuel for 9 lbs is 40,000 or 4444 per lb.
So the cost get the H2 [in whatever form] to the lunar surface from orbit is 4444 + 8000 so 12444- and say one charges 16000 per lb [which is cheaper than the 24000 I started with as the price paid for H2 at the lunar surface.

So, if instead of using 20,000 per lb as the price of H2 at the lunar surface. I plug in 16,000 lb:
Rocket fuel cost for 9 lbs is $20000 or $2222 per lb.

So, if iron mining can sell their "waste oxygen" at $500 or less it seems to roughly work out that it would lower their costs- and lower the cost of anyone getting to the moon or needs rocket fuel in high earth orbit. It may not be particularly important what they sell their iron for but obviously it has uses and could be something which has value.