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The future of mining machines
Posted by Heading Out on January 31, 2008 - 11:00am
Topic: Supply/Production
Tags: cavitation, energy needs, hydraulic mining, mining [list all tags]
Ugo Bardi produced a rather grim look into the future with his recent piece on the Universal Mining Machine, and the various considerations of what we are going to do as the major mining sources of the different ores that are required start to run out.
I would rather like to take another tack, and comment instead on the need that the mining industry will face, at some point soon, in having to significantly change the way in which it mines and processes ore. Whether it is in the mining of the large volumes of rock that yield the coal and oil from tar sands for the fuels industry, or the deeply won gold, from narrow veins found miles underground, the current energy cost of those operations is starting to come into conflict already with other needs, in a time of shorter energy supply. One has only to look at the stories that Leanan has been catching that have reported on the energy shortage in South Africa, to begin to see the start of the conflict. And although the current mine problems may have been overcome in South Africa itself, the “knock-on” effect in countries such as Botswana continues, with doubts as to where they will now get power.
There has been much discussion in the press and here, among other places, on the growing conflict between the growth of crops for food, and those for fuel. One now is starting to enter a time, when the energy cost of mining production may well fall under the same sort of scrutiny.
Charlie Hall has started a praiseworthy effort to look at the energy costs of various methods for producing fossil fuels, and I have, in the past, tried to explain that there are ways to look at getting rock out of the ground that change the energy cost depending on the way in which you actually mine the rock – mining it in very small pieces, for example, costs more energy than pulling it out of the ground in big bits.
But I think we have to go beyond that and look at the overall process, and consider that there might be alternate ways of mining that change the overall balance of the energy costs. Mining operations must consider many factors in choosing the equipment, and the mining methods that they use since they must plan on getting the most value from the operation, with a minimal cost. And in that regard, one might note, in passing, that when I visited the oil sand mining operations at Fort McMurray I stood beside the museum piece that was the bucket-wheel excavator (BWE) similar to the one that Ugo featured in the photo at the top of the page (and which was also featured in the picture of the Cat on the Catwalk , that occasionally crops up on the Internet). It is a museum piece up there (and its sisters have been sold) because when all your production is tied to one machine, when it goes down, then so does the mine (a point that Alistair McLean used in his book Athabasca which is based on mining up there).
Running the machines and keeping them going was a tough and expensive business, and in the end it proved more productive to break the mining operation into about a dozen large electric shovels , with truck haulage , rather than using the BWE and conveyors. Not that the shovels and trucks are that small. When the shovel takes a 100-ton bite out of the working face, and then loads three or four such scoops into a truck before it takes off for the pit floor crusher, we are not talking of stuff you can park in your garage. The middle of the tires is about head height, and, as has been noted, demand being up, it has been hard to get mining tires for over a year.
For large mining operations, shovel and truck operations will continue to dominate in the short term, since the process is very simple, and the large volumes of material that must be moved make the system practical, and it has the flexibility of operation that a BWE does not in terms of being able to do some selective mining (if the rock is barren it can be removed but not taken out of the mine). In the longer haul, however, technologies will need to change as the surface deposits start to diminish and more oil must be recovered from underground. It still may make economic sense to mine all the rock, however, since in this way all the oil can be stripped from the sand, rather than just a fraction.
In the more near term, the first victim to higher energy costs, and lower availability may be the valuable mineral and diamond operations, among the mines now being hit in South Africa. In these mines the ore is often found in narrower veins, that are more often at a steep angle to the horizontal, and where mining must, therefore, proceed in a different way. Depending on how valuable the mineral is that is being mined, and how widely it is disseminated through the host rock, different approaches can be undertaken. The fundamentals of the process, however remain the same regardless as to whether one is using vertical crater retreat or a room and pillar operation,
VCR is a method of blasting down successive layers of a thick deposit, into specially shaped underlying holes from which it can be fed into mine cars, or a conveyor that carries the ore to a mine shaft. (Slides 12 and 13 of this pdf Here it is raised to the surface, crushed down to the point where it is as fine as flour, and then the valuable minerals separated from the waste. And with the ore generally being relatively low in volumetric percentage terms in valuable mineral, that leaves the problem of disposal of this fine material at the surface, which can have environmental consequences.
There was a very interesting program on this topic on “The Daily Planet” a TV show on the Canadian Discovery channel, about eighteen months ago, that unfortunately I couldn’t find when I went back to look. It featured Lee Saperstein and he talked about the idea that he had been following, under Department of Energy funding, to look at the process with a new eye.
In essence his idea was that if the rock could be mined so that the different constituents were liberated into their separate grains, as part of the excavation process, then they could be separated at the mining machine, and, as a result, only the valuable mineral need be transported out of the mine, while the waste rock could be left near the excavation site, filling the holes that had been left, and not requiring the intense crushing, transport and surface disposal costs of current methods.
The idea of separating the rock into its mineral component grains was one of the advantages of early hydraulic mining in California, though that benefit turned rapidly into a disadvantage, when the water was not properly processed. In essence gold in the area around the Malakoff is found in a relatively soft sandstone. By using large monitors (water cannon) to wash out the rock, it was disintegrated so that the gold particles could be separated out and collected in the flumes into which the flow was directed. However, while the sand grains also settled out on the mine property, the rock also contained fine clay, and this was held in suspension until the water reached the Yuba, and other rivers, that carried it west to the sea. As the water speed slowed in the river, the clay settled out, and gradually filled the river bed. Thus when the rains came, or the snow melted, the river could no longer carry the volumes of water and the river overflowed its banks and flooded the farms and villages. This led to a legal battle, which the farmers won, and hydraulic mining has been a historical curiosity since. And I make no comment on that issue, but rather only point out that it illustrates that methods exist for breaking the rock into individual mineral grains, and it was the very efficiency of that process that led to its demise.
More recently, and as mentioned in the broadcast, it has been possible to use much smaller jets of water, at much higher pressures (waterjet cutting is one of the quiet revolutions going on in industry) in order to similarly break harder rock types. Because of the way that the water cuts into the rock, it penetrates along the individual grain boundaries of the individual rock components, breaking them out at the grain size scale, and eliminating the need to break the rock down to much smaller sizes to achieve liberation. The use of intensified cavitation as a secondary breakage tool for the particles not separated in the initial process, can also be provided in a very small envelope that can be included within the body of the machine. This rapidly disintegrates the rock particles into a smaller size, but again breaking along the boundaries of the rock particles that are weakest, to separate out the constituents. It thus provides, in combination, the means to locate both mining and separation equipment at the mining face, so that the ore can be separated there, and only the valuable mineral moved out of the mine. In doing so, and depending on the type of ore and method of mining, up to 50% of the energy used in moving and processing the unwanted waste rock can be saved.
I use this short example as an illustration of the ways that will have to be developed if the energy costs of mining are to be reduced. There are likely others, but in this particular case, the problems that I have cited previously about the future difficulty in developing new answers is illustrated by the fact that since the story came out Dr Saperstein has retired, and the office of DoE through which the project was funded has had its mission changed, and is no longer funding work of this type. (Which also makes it hard to find the reports on the research that was done).
Ah, well!
The true great frontier, though, is not mining but recycling. Assuming that sooner or later, we WILL transition to a renewables-based sustainable economy, we MUST figure out how to close all the circles and recycle all materials. We have just barely begun to do this.
What we'll really need to do is to develop whole systems. Goods will have to be made to be not merely durable and repairable, but also easily disassembled back into their component parts. Systems will need to be created to separate items for recycling by component material, and to aggregate them for reprocessing. We are going to have to figure out how to engineer products and processes so that they can utilize 100% recycled content.
Don't say that it is impossible - we're going to have to MAKE it possible. This is going to be one of the great technological challenges of the 21st century, and it will keep plenty of scientists, engineers, and entrepreneurs working.
The book "From Cradle to Cradle" talks about this.
I suspect it will not be possible to bring renewable energy systems on stream fast enough to halt the collapse of mine production rates.
From the little research I have done on this on the energy situation in UK, US, French, Japan I am relatively sure they are now past the point of no return.
Current net energy exporters may be able to build themselves a renewable energy infrastructure if they their energy resources are not seized/destroyed by war.
With ore grades dropping in many minerals over the last few decades we have been using greater and greater quantities of energy per unit resource. The Energy required to mine and process an ore rises exponentially with falling ore grade.
If we take Gold production for example the historic production rate has grown exponentially following the energy curve. But now it may fall by the double exponential because both the easy to get at high grade ore is depleting and the available net energy will be collapsing.
I guess those of us who survive this transition will learn to live happier less material lives like Nate Hagens reindeer :)
Sorry to be so pessimistic. On the bright side we can make lots of money using our acknowledge of the resource sector. We may not live to spend it or enjoy it but it will be fun while it lasts :)
Personally I do not see much of a future in recycling even though I believe that in only a few years we will recycling almost everything. Simply because production will be falling exponentially.
There is a very real risk of a "disorderly" descent. I do not believe modern "capitalist" systems in the US/UK etc. will be sufficiently resilient to prevail.
I hope mining dose adapt to using new tools and techniques but I suspect much will simply be abandoned.
P.S. sorry for the lack of reference did not have time to include them.
Domestic consumption is only a thirdish of energy used. Demand destruction aka getting fired will free up plenty of demand, we will be able to sit at home and watch tv but that will be about it, but not when its too warm or too cold. Those times we will be asleep, otherwise people get kind of cranky
I have only researched UK electricity production to date. Within 3-5 years I suspect we here in the UK will not be watching TV due to the lack of electricity.
The UK is importing all it's Uranium, approx 3/4 of its Coal and by 2016 North Sea Oil and Gas will have collapsed to a fraction of its peak level in 1999, also by then coal production will be 5-8% of current consumption.
As for the US its importing 70-75% of its Crude oil consumption + importing refined products add the energy in imported manufactured products and out sourced services and that's a lot to loose when the imports dry up (export land model).
People will be happy because after labouring all day with their hands on the land they will be too tired to watch TV or worry or notice the hunger in their bellies ;)
Yup, your having one of those days... ;o)
On the brighter side we will may new Gas pipelines from Norway and Russia, a major expansion of LNG (although noted we will be competing for this resource with every other rich Nation not on the end of a local gas pipe).
Our new nukes won't come onstream till late/early 20s -most likely scenario is that the existing capacity will be eaked out till the very last second- by which time uncertain Gas and YellowCake at $1000/pound will have quadrupeled the electricity price (if anyone has some projections on this I would be interested in seeing them).
There will be windmills everywhere and a fair amount of solar heaters and solar PV on everyones house by then too which should take some of the strain off the grid. Bush is giving $1000 dollar checks out at the mo -how much NanaSolar type PV will that buy in 10 years?
Oil at $200/barrel would be ~£1.60/litre here in the UK -tough but its now £1.05 so it is at least thinkable...
Nick.
So true! was having one of those days, it's a problem of mine :)
My own view is that things will have to be standardized, that is, one or two versions of computers or home entertainment stuff, clothing, etc.. And, further, that parts be interchangable. For example, the parts in the mini-car are interchangeable with the 1 ton truck. Finally, that these things be produced for looong production runs - like, maybe, ten years until changes are made.
I know this undercuts the idea of introducing more energy efficient models as tech advances. But my guess is that it is more energy efficient to not have to replace an item for a moderate advance.
Todd
However, to be most effective, that will require that products be designed, from the beginning, so that they can be disassembled and reclaimed, and the contents reused. While there is a lot of logic in that approach, sometimes it is hard to get that into the heads of folk who are only designing for maximum efficiency in use, and a manufacturing process that keeps the price down far enough that you can sell the product.
Recycling sounds so green. It can be if it saves or creates more resources than it uses, but there are countless examples where this is ignored. Losing money recycling, is losing resources. A town government nearby where I live decided to be environmentally friendly by recycling plastics. Everyone though this was a wonderful idea, so collection of plastic containers began. It turned out that it cost much more to do this than they gained, but they kept on doing it because it was politically correct, when in reality it was like cutting down three trees to save one. They only looked at the benefit and not the cost.
As long as recycling is profitable, it is sound and of course should be done. I just don't see it as any great solution to resource acquisition since even when it is sound, it is marginal. It reminds me of corn ethanol where the return is at best 30% as compared to the current return for oil of near 500%; it may work marginally, but it is not going to come near replacing what we have today.
Well it's currently only marginally profitable because energy and commodities are cheap. If the price of oil rises dramatically, new plastic will become more expensive relative to recycled plastic. Even if a recycling program is currently uneconomical, it could make sense to implement it if you believe the economics are likely to change. You'll have your system in place and your people accustomed to the idea.
I've actually been wondering if artificial intelligence and robotics can significantly improve recycling. Currently, only certain relatively pure waste streams can be processed. We rely on the consumer to do the separating, a hassle for which he's not reimbursed. Then additional trucks and personnel to collect it. It doesn't seem unreasonable to equip a machine with a vision system, chemical sensors, etc, and a set of flexible robotic arms, and train it to do the sorting on a general municipal waste stream. It could permit a much larger number of categories, capturing a much larger fraction of what currently heads to landfills. And it wouldn't require household sorting or a separate collection infrastructure. Maybe the AI and robotics aren't quite good enough yet, but those fields are advancing fast....
peace,
lilnev
Hi HeadingOut. This figure is from chapter 4 of Limits to Growth: The 30 year update. It shows how energy requirements per ton take a very rapid increase as ore purity drops. Essentially it forms a kind of cliff, where increasing production is going to require exponentially more energy just to produce the same amount of ore, much less increase rate of extraction.
Do we have any idea where we are as a nation, and world wide, on the purity of our major metal supplies? Iron? Nickel? Platinum? Copper (for all those PHEV's)?
A quick googling turns up available ore in the following concentratiosn:
Al and Fe 65% to 75%
Ni 30% to 60%
Cu 30% to 45%
Platinum is basically available as a trace material in other ores.
Thanks! I think those might be maximum concentrations, because I know copper is down to less than 1% already. Here is the US geological survey. Time to dig in!
http://minerals.usgs.gov/minerals/pubs/commodity/
Copper can be somewhat different to other ores since I have been in a mine up in White Pine, Michigan, where the ore was, in places, thin sheets of copper lying between layers of shale. I had a sample in my office for quite a while.
As a student, I once worked in White Pine. A most unusual copper mine. Its use of the room-and-pillar underground mining technique resembled that in a coal mine. They were considering moving to longwall mining (continuous), also typical of coal mines (more difficult and expensive, but doesn't waste the 40% of the ore in the pillars). Although some native copper (and native silver) was present in the ore, most of the copper values were in Cu-sulfide, enriched in silver, within the shale. Native copper was far more typical of the so-called amygaloidal copper mines further up the Peninsula, in an older basalt horizon. These also were highly atypical deposits.
I was just looking at iron ore. All the North American reserves are expected to be exhausted by 2050. Many by 2025. Yikes! They are talking about a new 5 billion dollar steel mill in the iron range, but where will they get the ore?
Stated metal reserves are always limited (many states tax them, and exploration beyond immediate needs is generally not cost effective). Iron is an extremely abundant metal (why we use so much of it) and one that is relatively cheap to recover (why it is priced in dollars per ton rather than dollars per gram). One reason it is so cheap is that the oxide can be reduced to metallic form relatively easily, using only charcoal or coal. We are NEVER going to run out of that metal in particular, but it will become more expensive as energy costs increase, or as alternatives to fossil fuels are required by law. Quickly expanding production of any commodity can be difficult (and risky in case of a recession), as evidenced by present shortages. Steel may be in temporary short supply, but pass a strong magnet through almost any dry river or beach sand and you can convince yourself that magnetic iron oxide ore (magnetite) is nearly everywhere. (So-called black sands contain the most magnetite.)
That stated, and before Kayakguy gets on my case, I should mention that most of the high grade iron ore presently being mined, called iron formation or taconite, is something of a geological rarity. Like petroleum, it was formed over a limited time span under rather special conditions. This time span occurred 2.5 billion years ago, and the special conditions are thought to involve the very first oxygenation of the earth's atmosphere and uppermost ocean, by increasingly abundant single celled plants (photosynthesizing algae, similar to the ones that later dominated petroleum production). This oxygen pollution event (in terms of what the atmosphere had previously been like) progressively precipitated (as iron oxides) most of the reduced (ferrous) iron that had been dissolved in the oceans. After about 2 billion years ago, there was very little iron left (and the oceans have been rather deficient in iron ever since - why iron fertilization has been suggested to assist organic carbonate precipitation). Smaller iron oxide deposits, some quite high grade, form by many other processes, and variable amounts of iron oxide occur in most rocks and sediments. So iron won't run out, but once the taconite mines are exhausted, iron and steel costs should increase.
Taconite itself has only been the preferred source for iron relatively recently. Previously, nearly pure iron oxide (red rust or hematite), locally formed at the surface by weathering of taconite, was the preferred ore. Incipient exhaustion of these hematite ores led to investigation of much lower grade siliceous taconite. It was discovered that grinding and roasting of taconite made its iron minerals alter to magnetite, which could easily be upgraded with a magnet. Thus the iron industry was reborn.
Economists apparently assume that some similar miracle involving tar sands or oil shale will happen to save the oil industry, a possiblility that many here delight in discounting. Using energy to produce valuable metals (for, e.g., tools, weapons, or structures) is not quite the same math as using energy simply to produce energy.
It is interesting that you mention this because it has been proposed that most technological innovation involves using more energy to overcome problems. And here is a perfect example, grinding and heat replace a depleted ore type. I have been in the closed Sudan Mine where they mined, well, basically rust. It is a neat place.
The graph above shows energy per kilogram. The real question to me is where are we as a whole on that graph. I don't worry that we will "run out". I worry that as we move left on that graph in ore purity our standard of living (based on mined metals) is going to suddenly be cut in half or 1/10th by crossing that cliff of energy requirement.
That graph may be somewhat deceptive. Go back to the source to read the underlying assumptions, and find out what is actually being plotted. For iron, for example, is it the energy required to pull 1% magnetite out of dry beach sand using a magnet (very low), or is it the energy required to grind up a solid granite rock containing 1% magnetite and then use a magnet on that product (very high). No one is even mining iron from laterites yet, AFAIK, nor aluminum from clays, so I'm not sure how one could obtain the energy cost involved, unless it was just based on thermodynamic calculation (energy needed to break the metal-oxygen bonds). The general trends are clear, but such graphs alone might not be a reliable indicator of closeness to any sort of cliff.
Also, as for, say, small plastic beverage bottles, so also for metal cans. Such uses are not essential and are a symptom of undervalued energy resources. Usage could be cut way back (as it was during the Second World War) without much affecting essential uses. Reusable glass bottles are an obvious replacement. You do pay in convenience and flexibility, but we're probably going to have to get used to that.
According to this EPA site, the energy inputs required for production from recycled aluminum is 95% less, and betwen 60-74% less for recycled steel. (I don't know what level of ore purity they are basing these figures upon, but probably not the lowest ones.) This probably holds true for most other metals as well.
I suspect that there will be considerable quantities of minerals that will remain in the ground and never be mined, because the energy inputs will just be too high and too costly. There will come a point where just recycling what we already have will make more sense (if we are not there already).
"I suspect that there will be considerable quantities of minerals that will remain in the ground and never be mined, because the energy inputs will just be too high and too costly. There will come a point where just recycling what we already have will make more sense (if we are not there already)."
oil is at $90 but with higher prices they are opening all types of old mines around the world. minerals stay in the ground when prices are low. less mining activity will eventually drive up prices and we'll have more mining.
The issue is the cost of mining will go up exponentially, as the ore bodies hit that cliff in energy demand while energy supplies are in decline. Prices will rapidly outpace demand, forcing curtailed usage, and the economy contracts. This is the whole issue with peak oil. Resource decline = economic decline.
In order to document this claim you would need to evaluate what proportion of mining and smelting costs was represented by energy, and what by other costs, such as labor. For steel, energy is a relatively small part of the total, whereas for aluminium, it is large (owing to competely different technologies). So increasing energy prices should yield increasing substitution of steel or ceramics for aluminum, for applications such as beverage containers (steel and glass containers were universal prior to about 1950), as well as increased recycling. Demand destruction is far more likely, as you note - people will drink tap water or keg beer.
Having been a Consultant to the Steel Industry myself and, after being inside almost every mill (Mini Mills included) north of Mexico during the Prime of the 70's and 80's, I would ask you to please substantiate your claim that "energy is only a small part of the total", in reference to Steel.
Do you really have any idea what it takes to reduce Iron Oxide to liquid steel, and the energy input that must go on before it can be used in any way whatsoever?
Ever walked a Coke Oven Roof? Ever read "The Making and Shaping of Steel", put out by US Steel?
BZ
Um, sorry, I was only comparing it to aluminum. I realize that the absolute quantities required are still stupendous, and that the difference in energy cost partly reflects cheap coal (for iron reduction) vs. more expensive electricity (for aluminum). Increased recycling of steel is needed to reduce both energy and environmental costs.
You could start with the Energy required to just get the Taconite from Mesabi to one of the closer Mills in Chicago. Let alone imports to anywhere else. Sh*t, making the Firebrick for a Modern Blast Furnace alone is one huge energy suck.....
BZ
Look, any metal is an energy hog, in terms of production. I know it and you know it. I've been in plenty of smelters. I was merely saying that some are fatter hogs than others. Some people here assume that all metals are produced the same way, from the same types of ores and mines, using the same types of plants, and at the same relative energy costs, and that's simply not true.
Or it may get to the point that washing returnable bottles might be cost-effective again - which would be great news indeed for kids needing to earn a little money! I made more than a few dollars in my youth going around the neighborhood with a waggon and collecting bottles to return for the deposit. Of course, even if we still had returnable bottles these days, parents would be afraid to let their kids out of the house.
"The issue is the cost of mining will go up exponentially"
they haven't already? this is the same thing with agriculture. higher oil prices means higher prices for commodities. the price of oil and gold peaked about the same time in 1980.
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Where do you see the advances in reducing the energy requirement of mining being the greatest to date? Underground coal mining? Various kinds of ores? Very heavy oil?
There aren't that many major advances that I am aware of, though I am not really up to date in what is going on in many of the labs around the world. And again it is a matter of comparison, since as I have mentioned in the past, giving a knowledgeable coal miner a pick, and he can work the fractures in the coal to be much more efficient in energy use that a machine. And on the other hand the efficient use of explosives to break, and efficiently cast material is difficult to surpass in those operations where it can be really effective. But that does not include mining narrow veins where the blast fragments much more of the host rock on either side of the vein and incurs the cost of processing too much waste material. The use of geometrically modified blast-holes in those applications may well be a path into the future.
There is a balance in production vs downtime in increasing equipment size that may well now be being defined, particularly as larger becomes defined as much more expensive, in purchase and running cost. On-board monitoring in real time can extend life through better preventative maintenance which is more practiced today than it has been in the past. But there is a lot that can be done, and many opportunities - just a lack of manpower and will, at the present.
The history of mining is nearly as long as that of humans (going back to the first stone tools), and very many changes in technology have been made to lower costs, and to deal with lower grade ores. For example, as recently as 150 years ago, gold was commonly recovered by dissolving it in liquid mercury, and then distilling the mercury to get out the gold (so-called amalgamation; this is why many streams in California remain heavily mercury-contaminated, from the activities of the 49'ers). Direct smelting copper carbonate and oxide ores, generally carried by mule team to the smelter, were about exhausted when the so-called selective flotation milling process (that depended on the fact that sulfides, more than silicates, stick to organics) was developed shortly after 1900. This new technology eventually allowed the development of the great open pit copper mines of the Southwest, generally after about 1950. As diesel fuel got cheap, bucket-excavators and in-pit electric trains were replaced by conventional shovels and giant trucks; as oil got somewhat more expensive in the 1970's, in-pit crushers attached to conveyor belts lowered costs. Something similar occurred in underground mining as trackless mining by diesel trucks replaced tiny electric trains.
Also by the 1970's, air pollution laws required smelters to recover sulfuric acid; all this new acid (and rapidly declining metal prices afterwards) encouraged heap leaching (followed by copper cementation onto scrap iron, later replaced by more efficient SX-EW, or solvent extraction - electrowinning) of coarse-broken ore to replace the fine grind of the selective flotation mill (unfortunately, this cheaper technology recovered only copper, not by-product silver and molybdenum). Mining technology is constantly evolving, but it cannot change overnight, and changes are expensive to implement.
That said, and as you noted, perhaps the most efficient miner is still the one with a chisel, hammer, and pickaxe. He can mine a narrow vein far more efficiently than a machine, with far less waste. Similarly, hand sorting of mined ore by sharp-eyed individuals beside a long conveyor belt can be a far more efficient way to upgrade ore than the mechanical mill. These traditional techniques still ruled in Chinese mines until extremely recently, and may still be common today. (I don't know; it's been years since I went underground there.) The key, of course, is ridiculously cheap labor.
For the future, and speaking mainly of metal mining, I can speculate. Open pit metal mines get less and less attractive with time, owing to the increasing proportion of waste that must be mined on either side of the orebody. It is anticipated that many, with time, will be replaced by a more expensive underground mining technique called block caving, whereby the remaining deep orebody caves towards central drawpoints owing to its own weight and weakness, and the waste on either side remains in place. Energy price increases should accelerate this transition. Some open pit rock quarries near major cities are, I understand, already being replaced by more expensive underground mining operations, largely because hauling in the rock from distant quarries would be still more expensive in terms of energy.
For really deep underground mining, human miners may be largely replaced by machinery teleoperated by "miners" (more like video game players) sitting in an air conditioned office on the surface. The machines needn't be smart, or large, or diesel, just remotely operable with cameras. This could allow mining under deep temperature and humidity conditions that would kill a human operator in an hour, if a rock-burst (common in very deep mines) didn't kill him first. Ideally the machines would be somewhat expendable (no rescues needed). For obvious reasons, military and police applications will probably precede any use in mining.
As an analog to highly efficent human hand sorting, and as a partial alternative to fine grinding, many mining companies are already experimenting with or using a remote sensor of, e.g. radioactivity, or the gleam of metallic ore, coupled to a rod that will push the high-grade piece off of a conveyor belt into a concentrate bucket. High tech replaces high cost human hand-pickers or high energy grinding of raw ore.
As mentioned in another post, acid heap leaching of very low grade oxide and carbonate ores (formed by near surface weathering of sulfide ores) has long been practiced, as an energy-saving, relatively non-polluting alternative to milling and smelting. Recent advances, just being put into practice in copper mines, allow a similar process to be used with unweathered deep sulfide ores (albeit at high temperatures and pressures in an autoclave). The need for smelters should decrease as a result.
Of course, none of this will ever come to pass if energy scarcity causes the economy to cave, with associated price crashes for metals. It also won't happen if, as mentioned in the original post, the mines themselves can't get the energy they need, or obtain the huge sums of money needed to implement the new technology (mining is more capital intensive even than oil, as many oil companies that bought metal mines discovered to their chagrin following the 1970's).