Ugo Bardi’s The Universal Mining Machine

Below I’ve excerpted some of Ugo Bardi’s “The Universal Mining Machine” (24 January 2008 europe.theoildrum), but I’ve left a great deal out of this excellent article, I encourage you to read all of it if you have time.

Earth’s mineral resources

The Earth’s crust is said to contain 88 elements in concentrations that spread over at least seven orders of magnitude. Some elements are defined as “common,” with concentrations over 0.1% in weight. Of these, five are technologically important in metallic form: iron, aluminum, magnesium, silicon, and titanium.

All the other metals exist in lower concentrations, sometimes much lower.

Most metals of technological importance are defined as “rare” and exist mostly as low concentration substituents in ordinary rock, that is, dispersed at the atomic level in silicates and other oxides. The average crustal abundance of rare elements, such as copper, zinc, lead and others, is below 0.01% (100 ppm). Some, such as gold, platinum and rhodium, are very rare and exist in the crust as a few parts per billion or even less. However, most rare elements also form specific chemical compounds that can be found at relatively high concentrations in regions called “deposits”. Those deposits from which we actually extract minerals are called “ores”.

The total amount of mineral deposits in the crust is often described as inversely proportional to grade (“Lasky’s law”). That is, low grade deposits are much more common than high grade ones and contain a much larger amount of materials. As a consequence, when the progressive depletions of high grade ores forces the mining industry to move to low grade ores, you have the counterintuitive effect that the amount of resources available increases (“you don’t run out of resources, you run into them”, as Odell said in 1994). This apparent abundance is one of the reasons for the great optimism of some people about the availability of minerals.


Mining is a multi-stage process. The first is the extraction phase, in which ore materials are extracted from the ground. Then, there follows the beneficiation stage, where the useful minerals are separated from the waste (also called “gangue”). Further processing stages normally follow; for instance the production of metals requires a reduction stage and a refining one. All these stages require energy. To be exact, we should rather use the concept of “exergy” instead of energy, but in the context of mining the difference is marginal.

Let’s make a practical example. Today, we extract copper from ores – mainly chalcopyrite, CuFeS2 – that contain it in concentrations of around 1%-2%. The energy involved in the extraction, processing and refining of copper metal is in the range 30-65 megajoules (MJ) per kilogram (Norgate 2007) with an average value of 50 MJ reported by Ayres (2007). Using the value of 50 MJ, we need about 0,75 exajoules (EJ) for the world’s copper production (15 million tons per year). This is about 0.2% of the world total yearly production of primary energy (400-450 EJ) (Lightfoot 2007).

The world’s production of steel alone requires an amount of energy (24 EJ) equivalent to about 5% of the total of the world’s supply (ca. 450 EJ). Since making steel requires coal, this datum is in approximate agreement with the fact that 13% of the world’s coal production goes for steel and that coal accounts for about 25% of the world’s primary energy (source

In addition, cement uses 5% of the world’s coal energy.

Taken together, these data indicate that the total energy used by the mining and metal producing industry might be of the order of 10% of the total. This estimation seems to be consistent with that of Rabago et al (2001) who report a 4%-7% range and those of Goeller and Weisnet (1978) of 8.5% for the metal industry in the United States only.

Facing the mineralogical barrier

Over the history of mining, we have extracted minerals from high grade ores exploiting the energy provided for free by geochemical processes of the remote past (De Wit 2005). Ores embed a lot of energy, either generated by the heat of Earth’s core or by solar energy in combination with biological processes. The Earth is a geochemically live planet and the existence of ores and deposits is a consequence of that. But the processes that created ores are extremely rare and ores are a finite resource.

There is little hope of finding high grade sources of minerals other than those we know already. The planet’s crust has been thoroughly explored and digging deeper is not likely to help, since ores form mainly because of geochemical (especially hydrothermal) processes that operate near the surface.

The ocean bottom could be a source of minerals (Roma 2003) but so far not a single gram of anything has been extracted from there. The oceans themselves contain metal ions but in extremely minute concentrations. With the possible exception of uranium (Seko 2003), extracting minerals from seawater is out of question. For instance, all the copper dissolved in the oceans would last for just ten years of the present mine production (Sadiq 1992).

Finally, there is the old science fiction of dream of mining the Moon and the asteroids. But, if our problem is energy, then we can’t afford the energy cost of traveling there. Besides, the Moon and the asteroids are geochemically “dead” and contain no ores.

Therefore, as we keep mining, we have no choice but to move down progressively towards to low grade ores. In general, the energy required for extracting something from an ore is inversely proportional to the ore grade. That is, it takes ten times more energy to process an ore which contains the useful mineral in a ten times lower concentration (Skinner 1979). This relation holds for ores of the same composition which just change in grade.

We may also completely run out of a certain kind of ore and have to switch to ores of different chemical composition. That has already happened in the past, for instance for native metals. Iron, for instance, was once found in metallic form, ready to be forged, in the form of meteorites. That source has been completely exhausted as a mineral resource long ago. Switching ore normally involves an upward step in the amount of energy required.

The depletion of high grade ores is a problem that, eventually, will lead us to face Skinner’s mineralogical barrier. The amount of minerals on the “other side” of the barrier is huge. If we could manage to extract from this region of concentrations, we wouldn’t have problems of depletion forever or at least for the “7 billion years” that Julian Simon mentioned. However, that would require an amount of energy well beyond our present capabilities.

Let’s make an approximate calculation for evaluating this energy. Consider copper, again, as an example. Copper is present at concentrations of about 25 ppm in the upper crust (Wikipedia 2007). To extract copper from the undifferentiated crust, we would need to break down rock at the atomic level providing an amount of energy comparable to the energy of formation of the rock. On the average, we can take it as something of the order of 10 MJ/kg. From these data, we can estimate about 400 GJ/kg for the energy of extraction. Now, if we wanted to keep producing 15 million tons of copper per year, as we do nowadays, by extracting it from common rock, this calculation says that we would have to spend 20 times the current worldwide production of primary energy. Prices can’t make common rock a source of rare metals any more than ghost shirts could make Indians invulnerable to bullets.

Of course, this is just a rough order of magnitude estimation. We may not need to really pulverize the rock at the atomic level and we may find areas of the crust which contain more copper than average. For instance, Skinner (1979) proposed that we could extract copper from a kind of clay named biotite and that would need a specific energy of extraction approximately ten times larger than the present requirements. If the problem were copper alone, that would be doable. But if we have to raise the energy requirement of a factor of ten for all the rare metals, clearly we rapidly run into levels that we cannot afford, at least at present.

The future of mining

In the short run, we don’t seem to face critical problems in terms of ore supply, at least as long as we can keep our energy supply stable.

Let’s consider copper again as an example. The U.S. Geological Survey (USGS) estimates the world copper reserve base at 950 million tons (2007) (although Grassmann and Meyer (2003) report a lower value). If we could keep a steady extraction rate, we would have around 60 years of copper supply. Of course, the extraction rate has never been constant over the extractive history of copper. A more realistic model (Bardi and Pagani 2007) takes into account the growth and decline of the supply and sees the copper production peak in about 30 years from now.

However, there are cases where depletion looks like a more pressing problem, such as for indium, a metal important for the electronics industry and that may be in short supply soon. Also, some metals may be facing serious depletion problems because of an increase in the demand. For instance, if we were to use fuel cells on a large scale for road transportation, the known reserves of platinum would be most likely insufficient for the catalytic electrodes. (Department of Transport 2007)

These are serious problems, but are marginal in comparison to the real problem we have, which is also much more immediate. Ores, as we said, are defined in terms of the energy necessary for exploitation. To keep mining from the present ore supply, we need at least a constant supply of energy. But, in the near future, our energy supply may go down instead of up. Dwindling energy supply affects all the stages of production of mineral commodities, not just the extraction and beneficiation. That can have immediate and adverse effects on the production of mineral commodities.

Today, the energy used in extracting and processing minerals comes mainly from fossil fuels and, in some cases, it is directly dependent on liquid fuels produced from crude oil. For instance, it is reported (DOE 2007) that 34% of the energy involved in the US mining industry is in the form of diesel fuel. Fossil fuels are a mineral resource that has been heavily exploited in the past and they are undergoing rapid depletion and are expected to peak within a few decades at most. Peaking in the production of a mineral resource is a general phenomenon which is related to the increasing costs of extraction and processing as the resource becomes rare and more expensive. [Global peak oil production occurred in 2005] and is expected to start an irreversible productive decline in the coming years (see e.g. The other two main fossil fuels, natural gas and coal, are expected to peak at a later time, but in the coming decades.

We don’t need to wait for the actual production peak to see a resource becoming more expensive both in terms of energy and in monetary terms. If it takes more energy to extract and refine oil, this extra investment in energy will directly affect the extraction processes that make use of oil as an energy source. So, if the present trend of decline in the production of fossil fuels continues, we won’t be able to exploit all the mineral resources that exist on the “good” side of the mineralogical barrier. If nothing changes, in a not far future we are going to see a decline in the production of all mineral commodities: “peak minerals” (See Bardi and Pagani 2007). Peaking of minerals production poses a serious and immediate problem in terms of maintaining a supply of mineral commodities to the world’s economy.

Our civilization has deeply changed the chemical composition of the upper crust of the Earth. Elemental deposits that were formed in hundred of thousands of years of geochemical processing (Shen 1997) have been removed, transformed, and in large part dispersed.

We inherit from past generations a planet that is very different from what it was before the industrial revolution. The cheap and abundant minerals that our ancestors have used to build the industrial society are no more.

In the worst case hypothesis, considering also the likely damage deriving from climate change, the crisis could be so bad that it may push us back to an agrarian society. With the scraps left by our civilization, it would be a metal rich kind of agrarian society, but still a low technology one. Could it ever restart with a new industrial revolution? It is difficult to say. The industrial revolution that we know was strictly linked with the availability of cheap coal and that is gone forever after we burned it. It is hard to run Satanic mills with wood charcoal only; forests tend to run out too fast. Perhaps there will be only one industrial revolution in the history of mankind.


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