On the colonization of space

Dave Logsdon wrote:
>
> The NEOs offer resources the Moon doesn't have. A carbonaceous chondrite
> asteroid (the most common variety) contains from 5% to 20% water: an easier
> source of oxygen, as well as hydrogen that's not available on the Moon. The
> total amount of volatile materials from the asteroid ranges from 20% to 40%,
> including nitrogen: needed for creating viable atmospheres in habitats, as
> well as for fertilizer. Lunar regolith, by comparison, contains between .01%
> and .02%, some two *thousand* times less. The asteroidal material left over
> after these volatiles are extracted is of considerable value itself. Using
> autoreduction to extract the organic carbon from the magnetite will leave a
> residue of about 30% ferrous metal alloy. Lunar regolith, by comparison, has
> about 0.1% free metal. This time, the asteroid is *only* three hundred
> times richer! Now, let's take what's left of our asteroid, and use
> some of the water we already extracted to leach out a wide array of
> water-soluble salts, rich in sodium, potassium, halogens, and sulphates.
> These can be used to produce valuable industrial chemicals: acids, bases,
> halogens, sulphur, etc. The residual `slag' left over after all this is a
> dry silicate that's very similar to average Lunar regolith! That's right;
> the stuff you throw away from asteroid mining is what you'd *start with*
> mining the Moon. The slag could then be used for radiation shielding for
> space habitats, and/or ablative material for aerobraking material to the
> Earth's surface.
>

Dang, Dave, those are impressive numbers! And here I thought
carbonaceous chondrites were the black sheep of the asteroid family ...

Just out of curiosity, how were those values determined?

Steve