You’re likely reading this text on a digital screen. Embedded in your screen and in the components that translate electricity to words and images on your screen are nearly two-thirds of the elements in the periodic table. And those are only the elements embedded in the computer. There are many other elements embedded in the upstream and downstream supply chain infrastructure that allow your computer to get to you. Our ability to extract all of these elements from nature, and purify and selectively combine them to manufacture a computer is among the infinite number of things that distinguishes humans from all other members of the animal kingdom. Your computer is but one of millions of “things” that makes life in modern society amazing. All of the things that enable modern medicine, education, transportation. Yes, there are problems and challenges. Without a doubt. But by almost every metric, our lives today are radically better than at any point in human history because of our ingenious use of natural resources and our continued ability to locate and extract those resources.
My research program is focused on the supply-side sustainability of the elements in your computer, and a growing and seemingly infinite number of products, seen and unseen, embedded in, and used by, our global society. Using resources is not new. Society has defined itself for millennia by searching for and using resources. The Torah, or Old Testament, describes the use of gold, copper, silver, tin, lead, and iron. Together with mercury, these metals are referred to as the seven metals of antiquity. Each of these metals played a critical role in the development of society. Archeological research indicates that humans were using gold by 6000 BCE, copper by 4200 BCE, silver by 4000 BCE, lead by 3500 BCE, tin by 1750 BCE, iron by 1500 BCE and mercury by 750 BCE. These metals literally put places on the map of the ancient world because resource availability defined the value of a place. Exploration for metal resources drove trade and communication. Successful use of natural resources was responsible for the rise of individual societies. For example, around 3000 BCE, metallurgists in Anatolia knew that copper melted at a high temperature and tin at a much lower temperature. They no doubt used inquiry-based learning to determine that adding about one part tin to four parts copper allowed them produce a tin-copper alloy that melted at an intermediate temperature below that of pure copper. That alloy is bronze, a metal alloy that is harder than and superior to pure copper, which was the predominant metal used by society at the time. This metallurgical discovery took society out of the Copper Age and into the Bronze Age. It is this discovery that led the ancient Greeks to explore for tin and find it in modern-day England, which the Greeks referred to as the Kaaaimpos, which means “tin islands” and is translated as Cassiterides for the naturally occurring tin oxide mineral cassiterite that was abundant in beach sands along the English coast. The next metallurgical revolution occurred about 1500 BCE when the Hittites learned to work iron metal, a finding that ushered in the Iron Age and continued progress for society.
Following the iron age, advancements in metallurgy progressed slowly. It wasn’t until the 13th and 14th centuries that the elements arsenic, antimony, zinc and bismuth were discovered. The 16th century saw the discovery of platinum. Then, during the 18th century, metallurgy took off. Twelve metals were discovered during the 18th century, forty-one during the 19th century, and eight during the 20th century. What drove the frenzied pace of discovery in the past few hundred years? A primary cause for rapid scientific advancement was the changing political climate that allowed creative destruction in England and the United States that incentivized private citizens, by way of patenting intellectual property, and academicians, by way of society publications, to discover not just how to purify all of these aforementioned metals from the natural minerals that contain them, but to ideate how to use them in products that improve society. Which brings me back to your computer. The metal copper, which the ancient Greeks mixed with tin to produce bronze, is embedded in, among other components, computer chips where it increases processing speed, and the power cord where it allows electrons to flow into your battery. Tin is also used in computers, where it is alloyed with indium to make a tin-indium alloy that is coated on glass. That alloy is responsible for the resistive touch screen capability of a computer, and your smart phone. Imagine the Ancient Greeks taking a time machine and witnessing how we use copper and tin today. They would surely be amazed and impressed at human ingenuity.
To sustain society’s insatiable appetite for all products that contain copper and tin, and all other elements woven into the fabric of modern society, requires exploration for, and discovery of, ore deposits where these valued resources can be extracted. Using copper as an example, modern society consumes about 40 billion pounds of newly mined, primary copper each year. Placed in historical context, if you sum all the copper that society consumed from the dawn of the copper age, roughly 3500 BCE, up to the year 1945, society consumed four times that entire quantity of copper during the 50-year period from 1945 to 1995. Based on projected global demand to 2050, slightly more than 2 trillion pounds of primary copper must be mined to satisfy demand.
The reality of this projected copper consumption raises many important questions, two of which are: Is increased consumption sustainable?; and, Where will society source all of their copper? The answer to the first question is, yes. Absolutely. We must. Not only to maintain and improve quality of life in developed countries, but to build medical, educational and housing infrastructure in developing countries. To allow diffusion of all that makes possible our first-world lives to the majority of global citizens who want the medical care, clean water, sanitation, housing, etc. that residents of developed countries often take for granted.
Geologists quantify resource availability by comparing the total quantity of a particular resource, for example, copper, that is known to exist “in the ground” and is extractable at a given price, a quantity defined as the geologic reserve, to the annual production (consumption) of copper. This reserves/production ratio can be crudely thought of as how many years of copper remain before we run out. Much is made of this ratio by the mainstream media, and resource availability is often framed as a crisis. However, for copper, this ratio has remained nearly constant, at about 40, since the early twentieth century. This is because geologists, by discovering new copper ore deposits, have increased the reserve of copper from 114 billion pounds in the year 1900 to about 4.6 trillion pounds in the year 2015. Thus, there is no crisis, or “peak” copper. There is fluctuation around a nearly constant reserves/production ratio.
There are two answers to the second question. The simple answer is that we must get our resources from ore deposits, which are local volumes of Earth’s crust that contain anomalous enrichments of one or more elements, for example, copper. The complex answer to the question is that these ore deposits are becoming harder to find, requiring continued refinement of our understanding of how they form so that new deposits can be discovered. My research program is one part of this effort to figure out the geologic recipe for ore deposit formation and use that to help guide exploration strategies to ensure a sustainable supply of copper and other metals for society. I don’t pretend that my research in and of itself will find the next big copper deposit. However, I liaise with government and industry professionals in order to scaffold student-focused, inquiry-based research projects that help answer critical questions that benefit our search for resources. It is my goal that such synergy results in research products that appeal to academicians and also to industry professionals who are on the leading edge of supply-side sustainability.
I have focused my investigations on several different types of ore deposits that have special names, including porphyry deposits, Carlin-type gold deposits, iron oxide – apatite deposits, and iron oxide – copper – gold deposits. Porphyry deposits, which are found throughout the world, supply a little more than half of our total consumption of copper, and are also major sources of gold, silver and molybdenum. Carlin deposits are found only in the state of Nevada, U.S.A., and are Earth’s second largest accumulation of gold after the Witwatersrand Basin in South Africa. Iron oxide – apatite and iron oxide – copper – gold deposits are found globally and are major resources for their namesake metals as well as uranium, rare earth metals and silver. These ore deposits share some important commonalities. They form in the same type of geologic environment, namely along continental margins above a subduction zone where ocean crust is subducted into Earth’s mantle. Each of these deposit types is temporally and spatially associated with volcanic systems, and they form at shallow depths in the crust, usually a few hundred meters to a few kilometers. And for each deposit, high-temperature water-dominant fluid, referred to as hydrothermal fluid by geologists, was the agent responsible for the transportation and enrichment of metals. The formation of each of these deposits is a mass redistribution process where hydrothermal fluid(s) scavenges metals that are dispersed through a large volume of Earth’s crust and transports them to another, smaller area where they are concentrated to form an ore deposit. In reality, although far more complex, the process is analogous to pouring hot water, a geologist’s hydrothermal fluid, through ground coffee beans (or tea leaves). If you’ve ever made coffee, you know that as the water percolates through pore spaces surrounding the coffee grounds and chemically reacts with the coffee grounds, the water leaches, or dissolves, caffeine and other components from the coffee bean into the water. Once the caffeine and other components are dissolved in the hydrothermal fluid, the fluid exits the coffee grounds and is available for consumption. You probably have an intuitive sense that the temperature of the water and the duration of water-coffee interaction control the strength of the coffee, or the total quantity of material transferred from the coffee bean to the water. And that the type of coffee bean and the purity of the water also play a role in controlling the transfer of mass (caffeine, flavor) from the ground beans to the water. This analogy holds true for the aforementioned ore deposits as well.
Porphyry-type ore deposits form when a hydrothermal fluid is evolved within a body of molten rock, or magma, whereafter the fluid scavenges metals from the magma, ascends (percolates) through the magma and, owing to decompression, cooling and interaction with overlying rock, precipitates metals to form ore deposits. It is the same way that you make coffee, but turn that image upside down and allow the caffeine-infused steam to explosively escape the coffee grounds (magma) and percolate its way up, cooling and decompressing. This basic geologic framework has existed for nearly a century, and my research group works to refine our understanding of the genesis of porphyry deposits by performing laboratory experiments to selectively assess how the compositions of the hydrothermal fluid and the magma affect metal mobility (redistribution). We explore the effects of pressure and temperature, as well as the oxidation state, which you can crudely think of as the partial pressure of oxygen in the system. Currently, we are investigating the hypothesized role for mixing of different magma compositions as a necessary prerequisite for the formation of porphyry deposits, and the potential that the oxidation state of sulfur in the common mineral apatite can serve to record the initial oxidation state of the parent magmas for porphyry deposits. This research has broader implications for understanding the oxidation state of lunar magma systems and forecasting volcanic eruptions.
While there is general consensus for the genetic model for porphyry deposits, the opposite is true for Carlin-type gold deposits, and iron oxide – apatite deposits and iron oxide – copper – gold deposits. Carlin deposits were only discovered in the early 1960s and there are several working hypotheses for their genesis. A first step in improving these hypotheses is examination of ore deposits in the field. I worked with several graduate students who performed field-based thesis investigations of Carlin-type deposits. I contributed experimental data and expertise with respect to gold mobility in hydrothermal fluids to help develop a new genetic model for this deposit type. That work is among my most cited research publications and taught me the value of liaising with industry and government professionals to refine the research questions I ask such that they meaningfully impact exploration strategies.
There are also several viable working hypotheses that explain the genesis of iron oxide – apatite deposits and iron oxide – copper – gold deposits. Some suggest a geologic continuity between the deposit types, whereas others do not. I have worked with several graduate students, and with external graduate students and collaborators, to develop a new genetic model that geologically links these two deposit types as a geologic continuum. Such a model has important implications for exploration strategies. Our model was developed based on research at one particular deposit in the Chilean Iron Belt, and we are now investigating other deposits with the goal to use the data from other deposits to refine our genetic model. This work is really exciting and our papers are being cited at a fast clip. I am being invited to give talks at conferences that attract industry professionals as well as academicians. Our research to date has focused on ore deposits in Chile, where the majority of these deposits are located. My effort to develop a new genetic model for these ore deposit types has involved collaboration with Chilean geologists.
Okay, my narrative to this point would suggest that my research program is completely focused on ore deposits. Looking at my CV, some colleagues have suggested that my record is a bit eclectic. I worked with two graduate students and synchrotron beamline scientists to develop the use of a diamond anvil cell technique to quantify mineral solubilities in hydrothermal fluids at conditions appropriate for element cycling in subduction zone environments. I worked with two other PhD students to investigate compositional evolution of magmas erupted from a volcano in Russia and the origin of elevated carbon dioxide concentrations in magmas erupted in Uganda. Each of these projects was essentially a mass redistribution problem where my expertise gained from studying the evolution of ore deposits could be applied to other scientific questions. And each of these projects was really enjoyable. As a connoisseur of both coffee and tea, I’m driven by trying to figure out how Mother Nature moves elements around.
At home, I have a wooden box of recipes from my paternal grandmother. She and I share the same birthday. She was an amazing cook, having grown up at a time when nothing was prepared by an employee behind a deli counter. Everything came from the so-called perimeter of the grocery store. Inside the wooden box are recipes that come from her mother and grandmother. Many of them are annotated with subtle tweaks. Some compare the tweaks among sisters. These tweaks are so subtle that at first glance, one cannot fathom how such a small change in the recipe might affect the final product. But they do. Nature does the same. As soon as we think we’ve got it figured out, she throws a curveball. She reminds us that scientific questions are never answered completely. The beauty of ore deposits is that every system is unique. There are commonalities and general recipes, but finding the next big copper deposit to supply the wiring for your next computer and home renovation requires searching for all the ways that nature annotates her recipes. That excites me and drives my research program. Humans had it easy for the past few thousand years. We literally tripped over the ore deposits that put places on the map and made society better in every way imaginable. Today, however, there are no more deposits to trip over. We have to find the deposits buried a little deeper. But we’re really good at it. Economic geologists pride themselves at keeping that reserve to production ratio constant. We have to.
If one accepts it as a moral imperative to lift global society out of poverty, reduce infant mortality, cure disease, provide access to clean water and sanitation, to education, then we have to embrace all research aimed toward those goals. If society wants the developing world to skip the need for a fossil-fuel-based energy infrastructure and build a so-called renewable energy infrastructure, then we have to embrace the need for more exploration, discovery and extraction of copper, among the many, many other metals embedded in solar panels and wind turbines, each of which has a finite lifetime and requires replacement. Modern society does not and cannot work in a resource vacuum.
I have enjoyed continuous support from the National Science Foundation as well as direct and in-kind support from mining companies who grant access to their properties and proprietary data. I also leverage collaboration with mining companies to allow my graduate students to gain experience that is critical for guiding their career decisions. My research group consistently has at least three graduate students and I have mentored one post-doctoral research fellow and co-mentored a visiting scientist. All but one of my graduate students work in industry and I am dedicated to using my research program to help students achieve their academic and post-academic goals. I travel with my graduate students to academic and industry conferences to disseminate our research to both audiences. I also involve undergraduate students in research, having had twenty students do research with me and my graduate students since joining the faculty of the University of Michigan in 2012.
My future research plans are focused on refining our understanding of ore deposit formation by a combination of field, laboratory and experimental methods. Since 2012, I have developed several collaborations with faculty at the University of Chile and the University of Hannover (Germany). Each collaborator contributes expertise that I lack, and also allows me to expose my graduate students to international collaboration. I have three graduate students investigating the origin of ore deposits in the Chilean Iron Belt by combining stable iron and oxygen isotopes with high-resolution chemical mapping of oxide minerals. I have two students performing experiments in internally heated pressure vessels (IHPV) in Hannover. Their IHPV apparatuses are each equipped with a decompression valve and Shaw membrane, which allow us to decrease pressure very slowly and to control hydrogen fugacity very precisely. One student is quantifying the relationship between oxygen fugacity and the oxidation state of sulfur in apatite, which we are using to develop a sulfur-in-apatite oxybarometer. A second student is performing experiments to explore chemical exchange across the interface of juxtaposed mafic and felsic magmas to test the hypothesis that mafic underplating supplies sulfur and metals to overlying porphyry ore deposits. All of these projects will improve our understanding of mass redistribution in subduction zone volcanic systems that host the ore deposits needed to sustain the developed world and, perhaps more importantly, to enrich the lives of citizens in developing countries who want and deserve what we have.