How long would a planet take to recover from a large asteroid impact?

Question

As part of my world's planetary history, an asteroid impact has delivered a sizable quantity of a previously unknown metal to the planet Earth. By sizable I mean a deposit large enough to sustain a mining programme for several years, possibly decades. This asteroid will land somewhere off the west coast of mainland England, presumably destroying Ireland and leaving a crater many miles across. Obviously this will be an extinction-level event.

The tales I intend to tell will document a technological society living on this altered Earth. My problem is how long would the Earth be rendered "uninhabitable" (i.e. impact winter making life on the surface very difficult, or even impossible) by such an impact? Are we talking thousands, tens of thousands, or even millions of years? And what sort of knock-on effect would that timescale have on a human population living underground?
Would it make more sense to have several smaller impacts or one massive impact? My plans involve one rather large deposit in a single place, but if this doesn't make much scientific sense then I have contingencies in place for that.

EDIT I'm now leaning toward a large-scale impact off the west coast of England, and two - or possibly three - smaller pieces of the same asteroid landing further west along its orbital track, assuming the asteroid came down in an east-to-west direction. So possibly one landing mid-Atlantic, another on either the east coast of America or the east coast of Canada, and a third in either Russia or China.

Answer 1

If the previously unknown "metal" was from the Island of Stability, that might make it resistant to vaporization prior to impact, leaving you with a large, mine-able deposit under the wreckage of its arrival.

However, being super-heavy as IOS elements are expected to be, its impact crater would probably be considerably large than is expected for a meteor of its size. So take a real world meteor crater and multiply its diameter a few times while holding the actual meteor size constant.

The Ice Limit is an excellent fictional story about exactly this kind of meteor and might be a good resource for the technical details of size, weight, crater size, etc.

As others have said, the recovery time for a society suffering a majro meteor will largely be a function of its size. I would suggest imposing environmental difficulties to the mining process (maybe it is in the artic or at the bottom of the ocean), that way the mining process can still take decades, even if the meteor itself is comparatively small.

Answer 2

Depending on the size of asteroid, we can talk about thousands of years, or even melting most of the earth surface. Better make it small.

Meteor Crater in AZ was caused by meteor about 50 meters across. Problem with that is - most of matter will vaporize before impact, leaving little to mine for. Tricky balancing act. Too small - will vaporize. Too big - will wipe out dinosaurs or other important living forms. Choose carefully!

Answer 3

Well the previous impacts were serious enough to cause extinction level events. Meaning years of global environmental havoc. Most of the surviving humans would likely be pushed back almost to the stone age with tech.

Another problem you would have to deal with is the actual impact. it will devastate the area for miles around and will have the worst kill zone. No one will survive for miles around. Also the meteor that hit the Yucatan sent debris up to 10,000 miles away.

No the size of the meteor can be modified some, depending. if humans are mining with picks and shovels, a fairly small meteor (150m after landing) could take decades to mine. It might also be small enough not to kill 90% of all life on earth.