The Rock-to-Metal Ratio

USGS and large company publish new metric for tracking energy needed to mine metals.

Energy production over the past century has been focused on burning coal and light hydrocarbons extracted from Earth’s crust.  The burning of fuels enabled the birth and growth of nations throughout the world.  During the exploration of energy sources workers discovered precious rocks and various stones that further sparked interest and initiated the development of diversified mining industries.  

These rocks and stones contain small amounts of rare elements and metals that carry unique physical properties.  Over the years, researchers and engineers have figured out how to extract these elements so that they could be used to manufacture specialty materials and equipment.  The current battery and electrification revolution is underway, because more efficient extraction methods keep people optimistic on the future cost competitiveness of batteries and renewable energies.

Mining does not come without its challenges though.  Precious metals are more difficult to extract than hydrocarbons, and therefore take a lot more energy to harvest and incorporate back into society.  The US Geological Society and Apple created a foundational metric, the Rock to Metal Ratio, that incorporates the data and resources needed to produce metals.  The fantastic work displays an easy way to observe which metals take the most energy to harvest from hard rock sources.

The RMR (Rock to Metal) ratio for each metal was calculated with consideration of the quantity of ore mined (O), the amount of waste rock removed (W), quantity of mineral commodity produced at the mine (M), overall recovery rate in refining (R), and unit price of the commodity (P).  The full description can be found in the methodology portion of the paper page 2.

Note that the RMR calculation only considers the factors for mined rocks. Certain elements such as lithium and magnesium can also be harvested from brine (salt solutions). Extraction from brine is a different process, and therefore these supplies of lithium and magnesium were excluded from the RMR value.

This type of data can enable nations to focus on where resources should be spent to develop better extraction methods and/or determine future production sites for the global supply chain.  

The Numbers

The RMR for 25 different metals and elements was calculated.  In general as you make your way from left to right on the plot extracting pure metals becomes more efficient.

In fact, I pulled the most recent metals pricing from DailyMetalPrice and Google search to overlay the price/lb of each metal.  The RMR positively correlates to the price per pound of an element!  Titanium is the only outlier in this data set. 

Also take notice that some of the most important metals in today’s society have the lowest RMRs.  Elements such as iron and aluminum are two of the most critical elements in commercial construction and manufacturing.  Iron is a staple in the production of steel, while aluminum is a lightweight metal that is used in all types of mobility vehicles.  The low RMR is the result of over a century of scale and manufacturing efficiencies that have driven continued investment and optimization.

Supply Chain Snapshots

The authors do a great job of identifying the global supply for each of the 25 metals listed in the paper.  I specifically chose copper (Cu) shown in the geographic map below. Production is fairly diversified throughout the world even though volumes will have to continue to grow at above average paces to keep up with the electrification of the globe.  Have a look at the twenty four other maps in the supplementary information for interesting insights into the complex supply chains of metals and their ultimate end uses.

RMRs and Their Abundance

A simpler graphic shows the highest RMR ratios in red and lowest RMRs in blue.  On first glance one can see that lower atomic number elements tend to have lower RMRs, but that is not the best assumption for the whole periodic table. 

The authors graphed the RMR against the Earth’s element abundance (aka Clarkes number).  The visual gives clear objectives for which elements could be areas of focus going forward.  It would be practical to focus on elements with higher abundance and seeing if the RMR can be lowered over time.   

Conclusions:

This report is fitting for the revolutionary shift that is ongoing through the global supply chain.  The RMR metric is a clear metric and helps develop goals for improving efficiency of hard rock mining.  The electronics and batteries industries use more rare earth metals, which are in lesser abundance compared to more traditional elements. The RMR has multiple different factors, but in general, battery metals such as Li, Ni, Mn, Co and various rare earths should move downward on the chart over time.  The Rock-to-Metal ratio is a herculean effort that should help strategists think about the entire periodic table of elements and how they fit into the Earth’s dreams of a more sustainable ecosystem.

PS - the authors did hint at an area of further research. Brine reserves were excluded from a couple of metals. Could a BMR ratio be next?

Recommend reading the full report below.

References: 

1. Rock to Metal Ratio

2. Rock to Metal Research Paper