This article outlines the motivation behind and summarises results from our Nature Geoscience study Global distribution of sediment-hosted metals controlled by craton edge stability. You can download a free preprint here.
The societal importance of base metals
Copper, lead, and zinc form three of the four base metals (the other being nickel) and are heavily relied upon by modern society. Copper’s high electrical conductivity means that it is utilised in virtually all electronics and wiring. Lead is used in photovoltaic cells, high-voltage power cables, batteries, and super capacitors. Zinc is used in batteries and paints, but also in agricultural fertilisers and fungicides since it is a limiting micronutrient in many of the world’s crop soils (Alloway, 2009).
It comes as no surprise that global economic development and the transition to low-carbon energy sources are leading to ever-increasing demand for these metals. This demand extends to subsidiary critical minerals such as indium, cobalt, and molybdenum, which are produced as by-products of base metal mining. Policies such as the Paris Climate Agreement and the United Nations’ Sustainable Development Goals lay out ambitious guidelines detailing societal requirements to limit warming to less than 2°C above pre-industrial levels and eradicate global poverty. Critical to these endeavours is the development of high-tech solutions to decarbonise the global economy and provide sufficient food and water security to feed the world’s burgeoning population. For example, a recent study has suggested that between 2015 and 2050, the number of electric passenger vehicles needs to increase from 1.2 million to ~1 billion, battery capacity must rise from 0.5 to >12,000 gigawatt-hours, and solar photovoltaic capacity must increase from 223 GW to >7000 GW (IRENA, 2019). These technologies will require enormous quantities of metals including copper, lead, zinc, and cobalt. In a recent report, the World Bank projected that over 3 billion tonnes of minerals and metals will be needed to deploy the necessary wind, solar, and geothermal power, as well as energy storage, required for achieving a below 2°C future (World Bank, 2020). Metal demand over the coming decades is forecast to grow substantially beyond our current rates of supply, with shortfalls forecast for all four base metals.
The issue of base metal supply
The history of copper usage represents an informative case study for understanding the balance between supply and demand for base metals. Demand through time can be gauged by the amount of copper produced by the mining sector. Annual production at the turn of the 1900s was around half a million tonnes per year, and aside from minor spikes and dips associated with the World Wars and the Great Depression, it has steadily increased over the intervening 120 years to a value of ~20 million tonnes in 2019. The last two decades have seen an average annual increase in production of 2.1%. If we use this value to extrapolate future production, it takes only ~25 years for us to require as much copper again as has been produced in all of human history to date. Although improving the efficiency of copper recycling has a crucial role to play in meeting the needs of future supply, these numbers explain why recycling alone is insufficient, and primary copper must continue to be extracted (Ali et al., 2017).
Financial expenditure on mineral exploration has gone through several booms and busts over the last 50 years. Nevertheless, the most recent minerals boom from 2008–2013 saw inflation-adjusted expenditure of $135 million equivalent (in 2020 US dollars), which is more than three-and-a-half times greater than over any preceding six-year period (Ali et al., 2017). Despite this unprecedented level of spending, the number of new large deposits discovered has been underwhelming. Whilst there is always under-reporting of new finds that have yet to be fully appraised, it does not appear that there has been a single supergiant deposit (containing more than 50 million tonnes of copper) discovered in the last 25 years (Schodde 2019). A commonly held point of view is that the majority of regularly explored areas are now ‘mature’, in the sense that the easily discovered surficial deposits of any great size have already been found. For this reason, there is considerable effort being focused on opening up brand new areas for mineral exploration. A key frontier concerns deposits that are buried beneath the Earth’s surface, and has led to the development of new programs such as the UNCOVER Australia initiative. It is through the Australian government’s Exploring for the Future program that researchers from Harvard and Columbia Universities, Geoscience Australia, and the Australian National University came together to work on this intriguing problem.
So what have we done in this study?
Large quantities of copper, lead, and zinc have been deposited in sedimentary basins during the last 2 billion years. These deposits are quite desirable in comparison to magmatic counterparts, in part due to lower levels of environmental degradation during extraction. For example, ore grades are generally higher than in magmatic porphyry copper, resulting in lower volumes of rock that need to be processed. Meanwhile their total metal content is typically larger than found in volcanogenic massive sulphide deposits, resulting in fewer mines that need to be opened.
In spite of these points, magmatic deposits are more often the focus of exploration than sediment-hosted mineral systems due to our enhanced ability to predict their locations. We generally understand where magmatic deposits form within the framework of plate tectonics, and can quickly zoom in on geological regions that are likely to be fertile. Sedimentary basins, on the other hand, cover ~75% of the continental surface, yet only contain metal deposits in very specific locations. The ingredients required to form these deposits are common in most of these basins, making it difficult to narrow down prospective regions for exploration.
In this study, we have discovered a relationship between the locations of large sediment-hosted mineral systems and the thickness of tectonic plates. Using the velocity of seismic waves that are generated by earthquakes and travel through the Earth to seismometers, we can estimate the depth to the base of the lithosphere, which represents the rigid upper portion of the tectonic plates. Older regions of the continents are generally on thicker lithosphere and are known as cratons. It is sedimentary basins located on the edges of these cratons that contain all of the giant sediment-hosted base metal deposits.
This discovery is important for three reasons:
- It suggests that there is a link between shallow geological processes operating in sedimentary basins and Earth’s mantle hundreds of kilometers beneath our feet. This result improves our knowledge of sediment-hosted mineral systems, increasing predictive power.
- Since these deposits are up to 2 billion years old (which is nearly half the age of the Earth), the relationship suggests that the transition between thick and thin continental lithosphere can generally persist for billions of years without being appreciably modified or destroyed through the plate tectonic cycle.
- Our estimates of plate thickness from seismology, in combination with other geological observations, allow identification of new prospective regions for mineral exploration. These ‘treasure maps’ will also work for deposits that are hidden beneath Earth’s surface.
Together with improving both the efficiency of recycling and the extraction of deposits in a socially and environmentally conscious manner, we believe that increasing exploration success is crucial to combating climate change and supporting sustainable development. These ongoing efforts will require collaboration between policymakers, academics, and industry, and necessitate studies that cross traditional discipline boundaries. Please feel free to get in touch if you would like any more information.
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Thanks Mark.
He is exactly right about these deposits. There is one right off of the central Virginia Carolina borders that had enough rare earths and others to meet the quota needed by 2050 and that craton is atop the earth on the smallest fault zone on the fault map. I have done the geology and the research is true!!!
Where can we find maps of specific geographic regions with this information? I would like to see a detailed high res image of MT. Thanks!
There are detailed maps of each continent starting on page 25 of the supplementary information (https://eartharxiv.org/2kjvc). And you can download digital copies of the data to plot up yourself on this link: https://osf.io/twksd
7 2 20 Hello Mark Hoggard, I read the news today; OH boy! Thank you for a fascinating post. When does the mining start? Geology (fossils/rocks) has been a hobby of mine since childhood and I enjoy information about the topic. Stay safe, keep calm, and be well. v
Thanks Virginia. I’m glad you enjoyed it.
I find this new use of seismic geophysics information an interesting evolution and outcome of the developments of the idea of continental drift that were argued over in the early 1960s in the Phillips 66 office in Brisbane. The Geology PhD argued vociferously against. The lesser degrees (such as my father) had open minds and worked hard at digesting and trying to use this new paradigm to view their understanding of the geologic processes. This now brings an enormous change to hard rock thinking.
Hi Mark,
Brilliant work that you and colleagues have done on the global perspective of crustal thickness, sedimentary basins and ore deposit formation. One area you’ve identified continues to surprise us.
In the 1980’s I presented a way to target deposit formation on a global scale using deep crustal penetrating structures to Noranda Exploration and Mining. Our new company has spent the last nine years consolidating the mineral rights in one of these target areas that is an area your work has identified. Last year, we discovered a new massive sulphide zone with anomalous copper, zinc, and lead. The region has been explored for over 100 years. We used gravity and magnetotelluric geophysics to identify the target area. Our second hole in the magnetotelluric target intersected the zone at 800 metres depth. This is 300 metres below historical drilling in the 1970’s and 1980’s. Although the grade of mineralization is low, the geophysics suggests that we are on the edge of something potentially much larger. See Vine Property in presentation https://pjxresources.com/gold-discovery-potential.pdf . We may have also serendipitously stumbled on something that no-one in this area has identified before, the potential for nickel and cobalt. The area also has significant gold deposit potential based on the focused, yet extensive, distribution of placer gold in the creeks for over 60 kilometres.