Global demand for copper is growing rapidly with some of the better studies estimating the world’s demand for copper could exceed supply in as little as six years.  For those looking for electrification of transport and distributed generation this is a major warning sign of what could be ahead.

Copper supplies are an issue that has to be taken more seriously. With rare earth elements also racing to the last marginal gram for sale, adding copper to the list of semiprecious metals could be a major industrial drag.  No matter how efficient or fuel saving or energy extending, if the materials aren’t there for mass production the prices of goods will not get to positive mass economic impact.

Copper is hard to find.  The earth has been pretty well scoured for economically viable copper.  The big economically useful deposits are already being mined.  More needs to be found.

A new Rice University study published this week in the journal Science found nature conspires at both the large scale of tectonic plates down to small-scale molecular bonds to keep most of Earth’s copper buried dozens of miles below ground.

Geochemist Cin-Ty Lee, the lead author of the study explains the situation, “Everything throughout history shows us that Earth does not want to give up its copper to the continental crust. Both the building blocks for continents and the continental crust itself, dating back as much as 3 billion years, are highly depleted in copper.”

Garnet Pyroxenite Xenolith. Click image for the largest view.

The Rice team didn’t start the research looking for copper – they were looking at how continents formed and the role oxygen played.  For the research the Lee led the team to examine the Earth’s arc magmas, the molten building blocks for continents.

Arc magmas get their start deep in the planet in areas called subduction zones, where one of Earth’s tectonic plates slides beneath another. When plates subduct, two things happen, they bring oxidized crust and sediments from Earth’s surface into the mantle and the subducting plate drives a return flow of hot mantle upwards from Earth’s deep interior. During this return flow, the hot mantle not only melts itself but may also cause melting of the recycled sediments. Arc magmas are thought to form under these conditions, so if oxygen were required for continental crust formation, it would mostly likely come from these recycled segments.

Lee explains the expected clue with, “If oxidized materials are necessary for generating such melts, we should see evidence of it all the way from where the arc magmas form to the point where the new continent-building material is released from arc volcanoes.”

The team examined xenoliths, rocks that formed deep inside Earth and were carried up to the surface in volcanic eruptions. Specifically, they studied garnet pyroxenite xenoliths thought to represent the first crystallized products of arc magmas from the deep roots of an arc some 50 kilometers (31 miles or 163,680 feet) below Earth’s surface.

Rather than finding evidence of oxidation, they found sulfides – minerals that contain reduced forms of sulfur bonded to metals like copper, nickel and iron. If conditions were highly oxidizing, Lee said, these sulfide minerals would be destabilized and allow these elements, particularly copper, to bond with oxygen.

Here’s the bad news – because sulfides are also heavy and dense, they tend to sink and get left behind in the deep parts of arc systems.  Lee likens the effect to a blob of dense material that stays at the bottom of a lava lamp while less dense material rises to the top.

Lee’s theory, “This explains why copper deposits, in general, are so rare. The Earth wants to hold it deep and not give it up.”

Lee and the research team are pointing out that where to look for undiscovered copper deposits requires an understanding of the conditions needed to overcome the forces that conspire to keep it deep inside the planet.

Lee explains, “As a continental arc matures, the copper-rich sulfides are trapped deep and accumulate. But if the continental arc grows thicker over time, the accumulated copper-bearing sulfides are driven to deeper depths where the higher temperatures can re-melt these copper-rich dregs, releasing them to rejoin arc magmas.”

This can be seen in the Andes Mountains and in western North America. He said other potential sources of undiscovered copper include Siberia, northern China, Mongolia and parts of Australia.  They are not likely at the surface like Chile or Montana, but the chances for discoveries look much better now.

Encouraging but not reassuring.  The confidence needed for copper supplies to stay abundant hasn’t changed.  Copper might be the next commodity for a massive price increase.

Lee wouldn’t have gotten this far without some serendipity.  Daphne Jin, a high school intern played a role in the research paper that’s now a freshman at the University of Chicago found the continents are depleted in copper.

Lee personalizes the story with, “The paper really wouldn’t have been as broad without Daphne’s contribution. I originally struggled with an assignment for her because I didn’t and still don’t have large projects where a student can just fit in. I try to make sure every student has a chance to do something new, but often I just run out of ideas.”

Eventually Lee asked Jin to compile information from published studies about the average concentration of all the first-row of transition elements in the periodic table in various samples of continental crust and mantle collected the world over.

“She came back and showed me the results, and we could see that the average continental crust itself, which has been built over 3 billion years of Earth’s history in Africa, Siberia, North America, South America, etc., was all depleted in copper,” Lee said. “Up to that point we’d been looking at the building blocks of continents, but this showed us that the continents themselves followed the same pattern. It was all internally consistent.”

Over the coming years, barring another large find or two, copper will likely rise in price.  At the moment, China is building a copper stockpile to the puzzled consternation of curious analysts.  For an industrial nation the plan is: A, use the copper for producing goods, or plan B, be hold it as a store of wealth.

Maybe the question is becoming, “Where are copper bars for sale?”


1 Comment so far

  1. Sander van Rossen on April 7, 2012 9:21 AM

    Well at least one potential benefit from a copper shortage could be that it might actually (eventually) make economic sense to dig up all the old copper internet/tv cables and replace them with fiber optics … I for one wouldn’t complain about that!

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