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from the where-the-mother-lode-gives-birth? dept.
Geologists identify deep-earth structures that may signal hidden metal lodes
If the world is to maintain a sustainable economy and fend off the worst effects of climate change, at least one industry will soon have to ramp up dramatically: the mining of metals needed to create a vast infrastructure for renewable power generation, storage, transmission and usage. The problem is, demand for such metals is likely to far outstrip currently both known deposits and the existing technology used to find more ore bodies.
Now, in a new study, scientists have discovered previously unrecognized structural lines 100 miles or more down in the earth that appear to signal the locations of giant deposits of copper, lead, zinc and other vital metals lying close enough to the surface to be mined, but too far down to be found using current exploration methods. The discovery could greatly narrow down search areas, and reduce the footprint of future mines, the authors say. The study appears this week in the journal Nature Geoscience.
[...] The study found that 85 percent of all known base-metal deposits hosted in sediments-and 100 percent of all "giant" deposits (those holding more than 10 million tons of metal)-lie above deeply buried lines girdling the planet that mark the edges of ancient continents. Specifically, the deposits lie along boundaries where the earth's lithosphere-the rigid outermost cladding of the planet, comprising the crust and upper mantle-thins out to about 170 kilometers below the surface.
Up to now, all such deposits have been found pretty much at the surface, and their locations have seemed to be somewhat random. Most discoveries have been made basically by geologists combing the ground and whacking at rocks with hammers. Geophysical exploration methods using gravity and other parameters to find buried ore bodies have entered in recent decades, but the results have been underwhelming. The new study presents geologists with a new, high-tech treasure map telling them where to look.
Journal Reference:
Mark J. Hoggard, Karol Czarnota, Fred D. Richards, et al. Global distribution of sediment-hosted metals controlled by craton edge stability, Nature Geoscience (DOI: 10.1038/s41561-020-0593-2)
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(Score: 1) by khallow on Friday July 03 2020, @12:53PM (7 children)
Notice the key property here, energy transferred over great distances mechanically (such as a 100 km long stack). A lot of these problems go away, if the forces applied are incremental and local. That is, the drill bit isn't experiencing forces from the rest of the kilometers of stack on it because they are supported in some other way (near neutral buoyancy probably). All you really need is a drill (with a short stack) with sufficient greater density than the rock it's drilling into.
Similarly 100 km of fluid dynamics is much harder than 100 1 km stretches of fluid dynamics. There are ways to delink dynamics of a long pipe so you don't have to worry about large scale fluctuations breaking it. Also make sure the internal pressure is near equal to the external pressure.
The other big problem is heat. Rock isn't getting harder at those depths, but softer due to the heat. The problem is that the drill bit (assuming you continue to use a solid drill bit - there are other approaches like drilling with a pressurized fluid) is getting softer as well, also due to the heat. An ability to move massive amounts of heat to the surface would solve that problem because you could cool the bit to traditional working temperatures while not cooling the rock that is being drilled. The drill bit would experience greatly increased life span.
Further, drill bits have well understood lifespans. If it takes a while to transport a drill bit down, then why not transport numerous bits down so that you have a pool of bits to use when the current one fails? It's far quicker to transport a drill bit tens of meters than it is to transport it 100 km.
I think this really is not that hard aside from heat transport and maybe shear due to movement of the crust. A near neutral buoyancy structure (2.7-3 metric tons per cubic meter for crust [joidesresolution.org], somewhat greater for upper mantle, maybe around 3-3.3 [oup.com] metric tons per cubic meter?) is supported by the surrounding rock rather than having to support the mass of the structure. Pumping fluids or moving solid parts around can similarly be done incrementally.
(Score: 2) by Immerman on Friday July 03 2020, @02:07PM (6 children)
> If it takes a while to transport a drill bit down, then why not transport numerous bits down so that you have a pool of bits to use when the current one fails?
Where are you going to put them? The hole is the same size as the drill bit, and to use a new bit you must first remove the old bit. I suppose you could potentially design a "stacked bit" where you could disengage the dull front bit to let the next bit take over - but that next bit is going to have to either drill through the first one, or back up and drill around it.
(Score: 1) by khallow on Saturday July 04 2020, @03:23AM (5 children)
Well, sounds like we have another big challenge then. While it might be possible to assemble a drill bit wider than the hole it came in under the high performance conditions of 100 km down, we can also drill parallel holes and store stuff in them as well as use that for the space needed to swap out drills and such.
All I can say though is that if you're pulling drill bits all the way to the surface to replace them, then you're doing it wrong.
(Score: 2) by Immerman on Saturday July 04 2020, @09:23PM (4 children)
>All I can say though is that if you're pulling drill bits all the way to the surface to replace them, then you're doing it wrong.
If you're trying to dig a 100mile borehole, probably not. But if you're drilling, there's not a whole lot of other options - that shaft is transmitting a lot of torque, you'll be lucky if you can use a stack of bits that can break away on demand (rather than breaking away whenever you hit something hard). You're almost certainly not going to be able to park a bunch of replacement bits in a side hole and re-connect to them when needed - not in a semi-liquid environment of packed with mud and shattered stone.
(Score: 1) by khallow on Sunday July 05 2020, @01:51AM (3 children)
Why would it be transmitting any torque at all? The drill bit itself doesn't need to generate net torque. And the force needed to drill can be generated locally (rather than mechanically through a rotating shaft) meaning most of the pipe wouldn't be experiencing any force or torque from the drilling itself. And if you made most of the pipe near zero buoyancy, any segment wouldn't generate much force on the rest of the pipe.
Rather than be an impossible thing, this sounds like a way to implement things. The semi-liquid environment already moves things around. Stack of bits doesn't sound workable, but replacing a drill bit, by pulling back the assembly and replacing it, does sound to me like it would be viable.
My thinking is that in the long run, many decades down the road, one could create huge shafts and complex transportation systems capable of managing multiple drills at the same time at various levels of the system (to widen parts of the system or drill deeper), and vast underground infrastructure to mine these alleged deposits. And all of this could be a natural incremental improvement of technology we could deploy in the near future (well, have to make the stuff first).
(Score: 2) by Immerman on Sunday July 05 2020, @02:48AM (2 children)
Net torque is what lets the bit cut through rock - without it it your hole doesn't get any deeper.
Semi-liquid is fine - pieces of shattered stone are NOT. And inevitable.
(Score: 1) by khallow on Sunday July 05 2020, @03:51AM (1 child)
Torque not net torque is what lets the bit cut rock. You can, for example have two or more drill bits rotating counter to each other so that they are cutting rock, but generating zero net torque in the process.
Because?
(Score: 2) by Immerman on Sunday July 05 2020, @01:31PM
Because you're not plugging a connection together with a bunch of gravel in the way.