Additionally, may only be coincidence, but the worlds largest
elemental copper deposits are found in Michigan south of the Sudbury
deposits perhaps are also of meteoric origin.
K
On Sun, Aug 16, 2020 at 1:53 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Sun, 16 Aug 2020, Ivan Vuletich wrote:
impacts.But the Sudbury mine is in fact mining a nickel-iron asteroid.
The nickel mines in New Caledonia are also apparently nickel iron
Don't know about New Caledonia, but no, alas, the Sudbury deposits are
*not* asteroidal metal.
There had long been some doubt about that, because the area has also been
volcanically active at times. In fact, it looks like it was active around
the time of the impact. (There was considerable speculation that the
impact had caused it, but there are now deep doubts about impact-caused
volcanism -- the proposed cases of it are all now thought questionable.)
There's no doubt that the Sudbury Basin is an old impact crater -- in fact
it's the third-largest confirmed crater on Earth -- but the metal ores are
not necessarily of extraterrestrial origin.
The most recent assessment I've seen,
<https://onlinelibrary.wiley.com/doi/full/10.1111/ter.12125> (beware,
you'll need a machete to chop your way through the geochemical jargon), in
fact comes to very much the opposite conclusion: the Sudbury impactor was
probably a comet! Assuming I've understood the paper correctly...
A very careful look at the geochemistry of the crater identified an
impactor-derived component, all right, but it's ordinary chondrite (or
maybe enstatite chondrite), not nickel-iron. Moreover, the amount of
platinum-group metals present is too small -- considering the size of the
impact -- for even a stony asteroid to be plausible, never mind an iron.
The best fit is a 15km comet nucleus, which could reasonably have a modest
fraction of chondrite rock in it. Much of the rest of the mass basically
wouldn't leave a detectable trace, and a comet could reasonably hit at
rather higher velocity than a typical asteroid.
In which case there should also be nickel iron impacts on the Moon,which in
the near-er term are likely to be more accessible than the asteroidbelt...
Nobody is seriously talking about mining the asteroid belt; most interest
in asteroid mining focuses on near-Earth asteroids, which are often closer
(in delta-V terms) than the lunar surface.
Sure, nickel-iron objects have undoubtedly hit the Moon, but there's still
the question of whether their remains can be found more or less in one
place. It helps that the Moon's weak gravity would reduce impact
velocity, but a good bit of that comes from relative orbital velocity and
won't go away.
My impression is that none of the known lunar mascons looks dense enough
to plausibly be a major nickel-iron body. Admittedly, the resolution of
the gravity maps isn't great, and small ones (still pretty sizable by
mining standards) could be missed.
I suspect that first generation mines are going to have to beeconomically
viable on a much smaller scale that ripping whole asteroids apart.
One problem with *any* scheme aimed at mining asteroids (or asteroidal
impact remains) for platinum-group metals and such is that they are
present as small impurities in a sea of nickel-iron. To the best of our
rather-limited ability to assess these things from a distance, there are
no platinum asteroids. Certainly there are no known platinum meteorites.
The nickel-iron would still qualify as quite a rich rare-metals ore, were
it on Earth, but that reflects how poor the current ores are. You still
have to rip apart and chemically process a whole lot of nickel-iron (which
is natural stainless steel, more or less) to collect your first ton of
rare metals.
Henry
