New Paper on the Adsorption of Rare Earths in Lateritic Clay Deposits, published in Nature Communications
Subtropical weathering profiles developed on granites in Southern China are the worlds dominant source for heavy rare earth elements, used in many user electronics and green technologies. In these weathering profiles, feldspars and primary minerals containing REE are broken down to form secondary clay minerals. In the process of soil formation, the REE that are released from the minerals are inferred to loosely adsorb to the surfaces of supergene minerals, dominantly clays and Fe-Mn oxides.
Although these so-called ‘ion adsorption deposits’ are typically very low grade compared to primary magmatic deposits (carbonites/alkaline rocks), they can be exploited economically as the REE can simply be extracted via surface or heap leaching. The key requirement for this to work is that the REE are indeed adsorbed to the surface of clay minerals, rather than being hosted in insoluble secondary or relict mineral phases.
In our paper published in Nature Communications (Open Access: https://lnkd.in/dJf46UH) we compared the mineralogy and distribution of #REE in weathering profiles from the peralkaline #Ambohimirahavavy Complex in #Madagascar to weathering profiles from the #Zhaibei Granite in #China.
Specifically, we used X-ray Absorption Spectroscopy to find out exactly where the #REE were hiding in lateritic soil profiles from Madagascar and China.
Although primary mineralogy plays a key role in the development of easily-leachable REE deposits formed by weathering, we found that the adsorption mechanisms of REE to clay minerals, at the atomic level, are identical at both sites.
Our data demonstrated that Yttrium, representative of the heavy REE, is dominantly adsorbed as 8 to 9-fold hydrated outer sphere complexes, spatially associated with clay minerals, dominantly kaolinite and minor halloysite. We therefore prove that the REE are truly adsorbed to clay minerals, justifying the name ‘Ion Adsorption Deposits’.
Special Issue on Angola visit in the Applied Mineralogist
I was invited to write an item for the Applied Mineralogy Group Newsletter about our recent visit to Angola. Click here to read more about the history and economy of Angola, and highlights from our fieldtrip to the Nejoio Alkaline Complex. I presented this work at the Mineral Deposit Studies Group (MDSG2020) in London this January.
Article in The Conversation
Finch, Borst and Hutchison (2019) How volcanoes recycle the Earth’s crust to uncover rare metals that are vital to green technology.
This article highlights Will’s recent 2019 paper in Nature Communications, which presented sulfur isotope data of alkaline magmas providing insights in global recycling of the Earth’s crust into the mantle via subduction, and coming back to the surface via alkaline magmatism. This article in The Conversation explains to a more general audience how volcanoes can help us understand these global element cycles related to plate tectonics, and how metal resources for the future were concentrated in this cycle.
Alkaline Igneous Rocks of Angola, workshop and fieldtrip September 2019
In September, the St Andrews team took part in a workshop and fieldcourse in Angola, hosted by the Universidade Agostinho Neto (UAN) in Luanda. The purpose of our trip was to outreach our work on alkaline igneous rocks and to learn more about similar rocks found in Angola. Our visit was funded by the SFC Global Challenges Research Fund. Read more about our visit here…
Sulfur Isotopes Paper Published in Nature Communications
Our research led by Will Hutchison on sulfur isotopes of alkaline magmas is now published Open Access in Nature Communications. The work was led by the St Andrews team in collaboration with colleagues at Tübingen and Glasgow Universities. The group at St Andrews included four of our group (Will Hutchison, Adrian Finch, Nicky Horsburgh and Anouk Borst), our colleague Eva Stüeken (who works on chalcogen isotope fractionation) and Henrik Friis who is now Associate Professor at the University of Oslo.
Will compared the mantle signatures of Gardar magmas in Greenland with a compilation of data for alkaline igneous rocks across the globe. Variations in mantle sulfur signatures matched gross trends in the isotope values of the contemporary surface, which changed dramatically over Earth History. He concluded that the sulfur in the Gardar magmas contained a component that had been recycled from the Earth’s surface.
The exciting conclusion is that the Earth’s sulfur cycle contains a significant component of surface sulfur being recycled back into the mantle. Will’s work draws attention to how useful alkaline igneous rocks are as windows on the composition of the sub-continental mantle through geological time.
Hutchison W, Babiel RJ, Finch AA, Marks MAW, Markl G, Boyce AJ, Stüeken EE, Friis H, Borst AM & Horsburgh NJ (2019) Sulphur isotopes of alkaline magmas unlock long-term records of crustal recycling on Earth. Nature Communications, 10, 4208.
The work has received significant national press coverage including of the following:
- The Herald – https://www.heraldscotland.com/news/17906666.scots-scientists-discover-secrets-earths-crust/
- The Courier – https://www.thecourier.co.uk/fp/news/local/fife/979895/st-andrews-scientists-unearth-secrets-of-earths-crust/
- Deadline – http://www.deadlinenews.co.uk/2019/09/16/ancient-volcanoes-reveal-earths-recycled-crust/
- Phys.org – https://phys.org/news/2019-09-ancient-volcanoes-reveal-earth-recycled.html
- Environmental News Network – https://www.enn.com/articles/59767-ancient-volcanoes-reveal-earth-s-recycled-crust
New paper out in special Rare Earth issue of Minerals
In this paper we quantify gains and losses of critical elements during late-magmatic hydrothermal alteration of eudialyte in the Ilimaussaq complex, Greenland. By microdrilling the alteration products of eudialyte – the primary host for REE, Zr and Nb – we found that certain metals (particularly those just mentioned) may be more mobile in the hydrothermal environment than we previously thought.
The alteration led to significant losses in Rare Earths and other High Field Strength Elements, and small gains in Large Ion Lithophile Elements (Rb, Th, U). We suspect that the elements that were removed from eudialyte by the fluids re-precipitated elsewhere in the rock. As such we infer that the alteration did not significantly influence the overall ore grade of the deposit. However, it does influence the ease by which we can extract the metals from the rock, as the metals are now hosted in a plethora of fine-grained intergrowths of secondary minerals. This has important implications for ore potential and mineral processing schemes of eudialyte-hosted ores, if we are to exploit these as a future source for green-technology metals.
van de Ven Mathijs, Borst Anouk M, Davies Gareth R, Hunt Emma J, Finch Adrian A (2019) Hydrothermal Alteration of Eudialyte-Hosted Critical Metal Deposits: Fluid Source and Implications for Deposit Grade. Minerals 2019, 9(7), 422; https://doi.org/10.3390/min9070422.
The paper is the result of an MSc project by Mathijs van de Ven, co-funded by the University of St Andrews, the VU University Amsterdam and SOSRARE. Mathijs graduated at the VU University Amsterdam with distinction in 2018, and now works as an exploration geologist at RSC Mining & Mineral Exploration in New Zealand.
New Ilímaussaq isotope paper in Lithos
Dating agpaitic rocks: A multi-system (U/Pb, Sm/Nd, Rb/Sr and 40Ar/39Ar) isotopic study of layered nepheline syenites from the Ilímaussaq complex, Greenland, Lithos. https://doi.org/10.1016/j.lithos.2018.10.037
Happy to announce that the last paper of my PhD is now published in Lithos. In this paper we investigate how late-magmatic fluid reactions affect initial isotopic ratios of different minerals and how this affects the accuracy of isochron age dating for peralkaline rocks.
Find a link to the paper here.
EGU Geochemistry, Mineralogy, Petrology & Volcanology Blog
Below is a link to a guest blog I wrote with Dr. Will Hutchison for the EGU Geochemistry, Mineralogy, Petrology & Volcanology website.
Will is a fellow postdoctoral researcher here at St Andrews. He studies active volcanoes and ancient magma chambers, and is currently working on the roof zones of alkaline magmatic systems in Greenland, as part of the Horizon2020 funded HiTech AlkCarb consortium.