Metallogenic controls of mantle plumes on platinum-group elements and precious metals

Platinum-group elements (PGE) are important precious metals and critical raw materials, but are some of the rarest metals in the Earth’s crust. The PGE are chalcophile elements and their distribution is largely controlled by the behaviour of sulphur (as sulphide) in magmatic environments. Mineralisation of PGE is most likely to occur in mafic and ultramafic intrusive systems and these share an inherent link with intraplate basaltic lavas produced by partial melting of the mantle, particularly associated with mantle plume thermal anomalies. In this thesis, new whole-rock geochemical data from a range of basaltic lavas from geologically-recent intraplate (i.e., mantle plume-related) settings are presented with a particular emphasis on examining chalcophile elements such as Ni, Cu, Co, Au and particularly, the PGE. Much of these data represent the first complete suites of major and trace elements, including PGE and Au analyses for key regions, such as Paraná, Etendeka, and Tenerife. The relationship between the PGE compositions of intraplate magmas and the mantle plumes responsible for their generation is interrogated using the combined application of quantitative geochemical melt modelling and a novel machine learning workflow, created for this project and featuring the PCA, t-SNE and k-means clustering techniques. Variations in melting processes due to different geodynamic conditions for each mantle plume studied dominates the controls on PGE abundances in magmas and thus lavas, as revealed by a quantitative account of partial melting of sulphide and silicate minerals in the mantle. In settings with deep, low degree partial melts (e.g., Canary Islands and Hawaii) chalcophile behaviour inhibits substantial source liberation from residual mantle sulphides. In settings with shallower, higher degree partial melts (e.g., Iceland and Kerguelen), chalcophiles are easily liberated from mantle sulphides. The most strongly PGE-enriched intraplate lavas are located at the edges of continents (e.g., East Paraná and East Greenland), where the incorporation of metasomatised sub-continental lithospheric mantle boosts the PGE budgets of parental magmas, leading to variation in the metal basket of lavas (e.g., changing Pd and Pt ratio). The geochemical and machine learning approach developed in the thesis describes this scenario as the optimal target for ore body formation within the context of a global intraplate PGE Mineral Systems model

Distinct sulfur saturation histories within the Palaeogene Magilligan Sill, Northern Ireland: Implications for Ni-Cu-PGE mineralisation in the North Atlantic Igneous Province

This is the author accepted manuscript. The final version is available from NRC Research Press via the DOI in this record.The ~60 m thick Magilligan Sill is part of the British Palaeogene Igneous Province in the North Atlantic. The sill comprises layers of dolerite and olivine gabbro, and it intrudes a thick sequence of Mesozoic mudstones and marls, which are locally baked at the sill margins. Since 2014, the sill has been an exploration target for orthomagmatic Ni-Cu-PGE sulfide mineralisation analogous to the Noril’sk-Talnakh intrusion in Russia. We present new petrological, geochemical and S-isotope data to assess the prospectivity of the sill and the underlying magmatic plumbing system. Most sulfides in the dolerite portions of the sill are < 50 μm in size and comprise only pyrite with PGE abundances below detection limit. In the olivine gabbros, > 150 μm size pentlandite, chalcopyrite and pyrrhotite grains contain < 4 ppm total PGE, 1 460 ppm Co and 88 ppm Ag. Pyrite from the dolerites have δ34S ranging from -10.0 to +3.4 ‰ and olivine gabbro sulfides range from -2.5 to -1.1 ‰, suggesting widespread crustal contamination. The S/Se ratios of sulfides in the dolerites and olivine gabbros range from 3 500 to 19 500 and from 1 970 to 3 710, respectively, indicating that the latter may have come from upstream in the magma plumbing system. The Magilligan Sill records multiple injections of mafic magma into an inflating sill package, each with distinct mechanisms towards S-saturation. Whilst the sulfide minerals in the sill do not constitute significant mineralisation themselves, detailed in-situ studies highlight a divergence in Ssaturation histories, and suggest that a larger volume of olivine gabbro sulfides at depth may be prospective

From Continent to Ocean: Investigating the Multi-Element and Precious Metal Geochemistry of the Paraná-Etendeka Large Igneous Province Using Machine Learning Tools

This is the final version. Available on open access from the Geological Society of London via the DOI in this recordData Availability Statement: The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author.Large Igneous Provinces, and by extension the mantle plumes that generate them, are frequently associated with platinum-group element (PGE) ore deposits, yet the processes controlling the metal budget in plume-derived magmas remains debated. In this paper, we present a new whole-rock geochemical data set from the 135 Ma Paraná-Etendeka Large Igneous Province (PELIP) in the South Atlantic, which includes major and trace elements, PGE, and Au concentrations for onshore and offshore lavas from different developmental stages in the province, which underwent significant syn-magmatic continental rifting from 134 Ma onwards. The PELIP presents an opportunity to observe magma geochemistry as the continent and sub-continental lithospheric mantle (SCLM) are progressively removed from a melting environment. Here, we use an unsupervised machine learning approach (featuring the PCA, t-SNE and k-means clustering algorithms) to investigate the geochemistry of a set of (primarily basaltic) onshore and offshore PELIP lavas. We test the hypothesis that plume-derived magmas can scavenge precious metals including PGE from the SCLM and explore how metal concentrations might change the metal content in intraplate magmas throughout rifting. Onshore lavas on the Etendeka side of the PELIP are classified as the products of deep partial melts of the mantle below the African craton but without significant PGE enrichment. Offshore lavas on both continents exhibit similarities through the multi-element space to their onshore equivalents, but they again lack PGE enrichment. Of the four onshore lava types on the Paraná side of the PELIP, the Type 1 (Southern) and Type 1 (Central-Northern) localities exhibit separate PGE-enriched assemblages (Ir-Ru-Rh and Pd-Au-Cu, respectively). It follows that there is a significant asymmetry to the metallogenic character of the PELIP, with enrichment focused specifically on lavas from the South American continent edge in Paraná. This asymmetry contrasts with the North Atlantic Igneous Province (NAIP), a similar geodynamic environment in which continent-edge lavas are also PGE-enriched, albeit on both sides of the plume-rift system. We conclude that, given the similarities in PGE studies of plume-rift environments, SCLM incorporation under progressively shallowing (i.e., rifting) asthenospheric conditions promotes the acquisition of metasomatic and residual PGE-bearing minerals, boosting the magma metal budget.University of Exete

A machine learning approach for regional geochemical data: Platinum-group element geochemistry vs geodynamic settings of the North Atlantic Igneous Province

This is the author accepted manuscript. The final version is available on open access from Elsevier via the DOI in this recordWhilst traditional approaches to geochemistry provide valuable insights into magmatic processes such as melting and element fractionation, by considering entire regional data sets on an objective basis using machine learning algorithms (MLA), we can highlight new facets within the broader data structure and significantly enhance previous geochemical interpretations. The platinum-group element (PGE) budget of lavas in the North Atlantic Igneous Province (NAIP) have been shown to vary systematically according to age, geographic location and geodynamic environment. Given the large multi-element geochemical data set available for the region, MLA was employed to explore the magmatic controls on these shifting concentrations. The key advantage of using machine learning in analysis is its ability to cluster samples across multi-dimensional (i.e., multi-element) space. The NAIP data set is manipulated using Principal Component Analysis (PCA) and t-Distributed Stochastic Neighbour Embedding (t-SNE) techniques to increase separability in the data alongside clustering using the k-means MLA. The new multi-element classification is compared to the original geographic classification to assess the performance of both approaches. The workflow provides a means for creating an objective high-dimensional investigation on a geochemical data set and particularly enhances the identification of metallogenic anomalies across the region. The techniques used highlight three distinct multi-element end-members which successfully capture the variability of the majority of elements included as input variables. These end-members are seen to fluctuate in prominence throughout the NAIP, which we propose reflects the changing geodynamic environment and melting source. Crucially, the variability of Pt and Pd are not reflected in MLA-based clustering trends, suggesting that they vary independently through controls not readily demonstrated by the NAIP major or trace element data structure (i.e., other proxies for magmatic differentiation). This data science approach thus highlights that PGE (here signalled by Pt/Pd ratio) may be used to identify otherwise localised or cryptic geochemical inputs from the subcontinental lithospheric mantle (SCLM) during the ascent of plume-derived magma, and thereby impact upon the resulting metallogenic basket.University of Exete

Leaf-applied sodium chloride promotes cadmium accumulation in durum wheat grain

Cadmium (Cd) accumulation in durum wheat grain is a growing concern. Among the factors affecting Cd accumulation in plants, soil chloride (Cl) concentration plays a critical role. The effect of leaf NaCl application on grain Cd was studied in greenhouse-grown durum wheat (Triticum turgidum L. durum, cv. Balcali-2000) by immersing (10 s) intact flag leaves into Cd and/or NaCl-containing solutions for 14 times during heading and dough stages. Immersing flag leaves in solutions containing increasing amount of Cd resulted in substantial increases in grain Cd concentration. Adding NaCl alone or in combination with the Cd-containing immersion solution promoted accumulation of Cd in the grains, by up to 41%. In contrast, Zn concentrations of grains were not affected or even decreased by the NaCl treatments. This is likely due to the effect of Cl complexing Cd and reducing positive charge on the metal ion, an effect that is much smaller for Zn. Charge reduction or removal (CdCl2 0 species) would increase the diffusivity/lipophilicity of Cd and enhance its capability to penetrate the leaf epidermis and across membranes. Of even more significance to human health was the ability of Cl alone to penetrate leaf tissue and mobilize and enhance shoot Cd transfer to grains, yet reducing or not affecting Zn transfer

Life cycle assessment and water use impacts of lithium production from salar deposits: Challenges and opportunities

This is the final version. Available from Elsevier via the DOI in this record. Lithium is a critical raw material for the energy transition and the salar brine deposits of South America host ∼70% of global resources. However, there are concerns regarding water use, and the associated impacts, of lithium production from these deposits. Life Cycle Assessment (LCA) is becoming increasingly prevalent in the analysis of raw materials sustainability, but current methods are regarded as unsatisfactory for assessing water use impacts related to lithium production from salar deposits. This work explores the challenges and opportunities for improvement in this context. We outline how the classification and assessment of water types could be improved and identify Water Availability Assessments, groundwater specific CFs, salar-specific methodologies and multiple mid-point indicators as areas for further investigation. This will aid the development of LCA methodology and enable an improved assessment of the sustainability of lithium production from salar deposits in South America and by extension help decouple decarbonisation efforts from negative impacts.Natural Environment Research Counci

Ethnic differences in Glycaemic control in people with type 2 diabetes mellitus living in Scotland

Background and Aims: Previous studies have investigated the association between ethnicity and processes of care and intermediate outcomes of diabetes, but there are limited population-based studies available. The aim of this study was to use population-based data to investigate the relationships between ethnicity and glycaemic control in men and women with diabetes mellitus living in Scotland.&lt;p&gt;&lt;/p&gt; Methods: We used a 2008 extract from the population-based national electronic diabetes database of Scotland. The association between ethnicity with mean glycaemic control in type 2 diabetes mellitus was examined in a retrospective cohort study, including adjustment for a number of variables including age, sex, socioeconomic status, body mass index (BMI), prescribed treatment and duration of diabetes.&lt;p&gt;&lt;/p&gt; Results: Complete data for analyses were available for 56,333 White Scottish adults, 2,535 Pakistanis, 857 Indians, 427 Chinese and 223 African-Caribbeans. All other ethnic groups had significantly (p&#60;0.05) greater proportions of people with suboptimal glycaemic control (HbA1c &#62;58 mmol/mol, 7.5%) compared to the White Scottish group, despite generally younger mean age and lower BMI. Fully adjusted odds ratios for suboptimal glycaemic control were significantly higher among Pakistanis and Indians (1.85, 95% CI: 1.68–2.04, and 1.62,95% CI: 1.38–1.89) respectively.&lt;p&gt;&lt;/p&gt; Conclusions: Pakistanis and Indians with type 2 diabetes mellitus were more likely to have suboptimal glycaemic control than the white Scottish population. Further research on health services and self-management are needed to understand the association between ethnicity and glycaemic control to address ethnic disparities in glycaemic control.&lt;p&gt;&lt;/p&gt

Baseline albumin-bilirubin (ALBI) in Western patients with hepatocellular carcinoma treated with stereotactic body radiotherapy (SBRT)

Purpose: To assess the baseline albumin-bilirubin (ALBI) score as a predictor of toxicity and survival in a prospective cohort of Western patients with hepatocellular carcinoma (HCC) treated with stereotactic body radiation therapy (SBRT) in 2 prospective trials. Methods and Materials: The study included 102 patients with Child-Pugh class A liver disease who received 6-fraction SBRT for HCC. Univariate and multivariable logistic regression investigated factors associated with toxicity, defined as an increase in Child-Pugh score ≥ 2 within 3 months of SBRT. Univariate and multivariable Cox regression analyses investigated factors predictive of overall survival (OS). The ALBI score was analyzed as a continuous and binary variable in separate analyses. Results: On multivariable analysis of toxicity, including the ALBI score as a continuous variable, the ALBI score (odds ratio [OR] per 0.1-unit increase, 1.51; 95% confidence interval [CI] 1.23-1.85; P = .00074), mean liver dose (OR, 1.31; 95% CI 1.02-1.68; P = .036), and dose received by 800 cm3 of normal liver (OR, 1.10; 95% CI 1.01-1.20; P = .028) were significant. When the ALBI score was included as a dichotomous variable, the ALBI grade remained a significant predictor of toxicity (OR, 7.44; 95% CI 2.34-23.70; P = .00069). On multivariable analysis of OS, including the ALBI score as a continuous variable, the ALBI score (hazard ratio [HR] per 0.1-unit increase, 1.09; 95% CI 1.03-1.17; P = .004), tumor thrombus (HR, 1.94; 95% CI 1.23-3.07; P = .004), and treatment in trial 1 versus trial 2 (HR, 1.92; 95% CI 1.23-3.03; P = .004) were significant. Similarly, when the ALBI score was included as a binary variable, the ALBI grade, tumor thrombus, and trial were significant predictors of OS. When the ALBI score was considered, the Child-Pugh score (A6 vs A5) was not significant in multivariable models analyzing toxicity or survival. Concordance statistics indicated models containing the ALBI score were superior to those containing the Child-Pugh score. Conclusions: The baseline ALBI score was more discriminating than the Child-Pugh score in predicting OS and toxicity in patients with Child-Pugh class A liver disease. The ALBI score should be used as a factor for stratification in future HCC SBRT trials