Abstract The critical metals are vital to modern life due to their use in a variety of domestic, green, and military high technology applications but have supplies that are inherently insecure. This study provides an overview of the concept of criticality as applied to the critical metals and outlines key issues around the resources and future supply of these metals. The methods used to quantify the criticality of critical metals have advanced over time, demonstrating that some metals are more strategically important than others, depending on the viewpoint of the organization considering criticality. However, global resources and reserves of a number of critical metals as well as their production statistics remain unclear. Methods exist to quantify the resources of critical metals with reasonable accuracy but these methods rely on information provided by the mining industry, indicating that better reporting practices would improve our knowledge of the global resources and cycling of these key commodities. Criticality can also be addressed in numerous ways, including the analysis of known mine supply chains to enable the economic extraction of critical metal by-products, the determination of the critical metal prospectivity of mining/mineral processing wastes (given a significant amount of critical metals currently deport to waste), increased amounts of recycling intermediates or end-use products containing critical metals, and the discovery of new and economic deposits of the critical metals. However, all of these approaches and the associated policy around them require more information in terms of mineral resource accounting, mineral economics, material flow analysis, mineral processing, as well as increased economic geology knowledge that would enable the making of future discoveries and increase the likelihood of critical metals being extracted as either primary or by-products. Without this information, significant parts of our knowledge base on the supply (and the security of this supply) of the critical metals will remain opaque.

Abstract Asbestos mineral-fibre exposure is a well established cause of pulmonary fibrosis (asbestosis) and malignancies (bronchogenic carcinoma and mesothelioma). In this chapter, we review the work of numerous groups employing asbestos fibres to investigate the early molecular events promoting alveolar epithelial cell (AEC) injury, a key event for inciting and advancing pulmonary fibrosis. First, we summarize the accumulating evidence implicating the crucial role of the AEC in the pathobiology of pulmonary fibrosis, including asbestosis. We summarize briefly the mechanisms by which AEC toxicity from asbestos exposure results from the generation of reactive oxygen species (ROS) from at least three sources: (1) by redox reactions occurring on the fibre surface; (2) by surrounding inflammatory cells, especially macrophages; and (3) by AECs, especially from the mitochondria. Second, we review the emerging evidence showing that asbestos fibre-derived ROS induce AEC mtDNA damage important for promoting mitochondrial dysfunction and mitochondria (intrinsic)- and p53-regulated apoptosis, events important in facilitating lung fibrosis and malignant transformation. We focus on a novel role for AEC mtDNA damage repair by 8-oxoguanine DNA glycosylase (OGG1), a base excision repair enzyme, and mitochondrial aconitase (ACO-2) in preserving mtDNA integrity important in preventing asbestos-induced AEC apoptosis and lung fibrosis. Third, we examine studies implicating autophagy (lysosomal degradation of cytosolic materials), autophagy of mitochondria (mitophagy), and kinase signalling pathways in modulating lung epithelial cell toxicity following asbestos exposure and in patients with idiopathic pulmonary fibrosis (IPF). Finally, we review the evidence implying that an “exaggerated” aging lung is important in the pathogenesis of IPF and asbestosis. We focus on the role of the sirtuins (SIRT), especially SIRT3, in maintaining mitochondrial integrity important for preventing mtDNA damage and fibrosis. Collectively, the asbestos paradigm is informing our understanding of the cellular and molecular mechanisms underlying AEC mitochondrial dysfunction, autophagy/mitophagy and apoptosis that can promote lung fibrosis. Importantly, these studies are providing the scientific basis for novel therapeutic targets that may prove useful for the management of asbestos pulmonary toxicity with broader implications for other age-related diseases, including IPF and lung cancer, for which more effective treatments are urgently required. Acronyms : Alveolar epithelial cell (AEC); alveolar epithelial type I cell (AT1); alveolar epithelial type II cell (AT2); Alveolar macrophage (AM); autophagy protein 5 (ATG5); base excision repair (BER); bronchoalveolar duct (BAD); cigarette smoke (CS); c-Jun N-terminal kinase (JNK); endoplasmic reticulum (ER); epidermal growth factor receptor (EGFR); extracellular matrix (ECM); extracellular superoxide dismutase (EC-SOD); electron transport chain (ETC); extracellular signal-related kinase (ERK); genome-wide association studies (GWAS); idiopathic pulmonary fibrosis (IPF); inositol requiring kinase 1 alpha (IRE1α); mammalian target of rapamycin (mTOR); mitochondria-associated ER membrane (MAM); mitochondrial aconitase (ACO-2); mitochondrial DNA (mtDNA); mitochondrial membrane potential (∆ψ m ); mitogen-activated protein kinase (MAPK); multi-walled carbon nanotubes (MWCN); nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (Nox-4); non-small cell lung cancer (NSCLC); 8-oxoguanine-DNA glycosylase 1 (OGG1); particulate matter (PM); protein kinase-like ER kinase (PERK); PTEN-induced putative kinase 1 (PINK1); reactive nitrogen species (RNS); reactive oxygen species (ROS); sirtuin (SIRT); sirtuin 3 (SIRT3); surfactant protein C (SPC); transforming growth factor beta (TGF-β); thioredoxin interacting protein (TXNIP); tricarboxylic acid (TCA) cycle; unfolded protein response (UPR).

Abstract The capacity of hydrothermal fluids to transport metals in concentrations sufficient to form ore deposits is due in large part to the polar nature of the water molecule and the ability of metals to form strong aqueous complexes with a number of ligands commonly found in nature. In this paper, we review the properties of hydrothermal liquids and vapors, show how the hard/soft acid/base (HSAB) principle can be used to predict why certain metals form strong complexes with particular ligands, and review the experimental data on the aqueous speciation of a selection of base, precious, and critical metals in high- and low-density hydrothermal fluids. Based on these data, we identify the important complexes for each metal and determine the physicochemical conditions under which they may predominate and thereby control hydrothermal metal transport. This information is used to quantitatively determine the solubility of the main ore minerals in hydrothermal liquids and vapors, and evaluate the mechanisms of metallic mineral deposition (cooling, fluid mixing, boiling, and fluid-rock interaction) in selected ore-forming systems.

Abstract Lake Tanganyika, in the East African Rift System, provides an important modern analog for source-rock deposition in tropical lacustrine environments. In order to test models for source-rock deposition and to improve our understanding of critical processes, we have applied a computer model to simulate deposition of organic carbon in Lake Tanganyika that combines a water-body circulation model with an ecosystem model. Lake Tanganyika is deep, highly elongated, and subjected to strong southerly winds along the axis of the lake during the dry season, May through August. Our simulations show that deep-water upwelling in the southern lake results from northward wind-driven surface flow during May through August, which causes nutrient enrichment in surface waters and results in strong phytoplankton blooming. During the wet season, weak upwelling, nutrient enrichment, and phytoplankton blooming in the northern lake result from oscillation of the lake. Our simulations suggest that although surface phytoplankton productivity is higher in the southern lake, flux of particulate organic carbon (POC) to the lake bottom is lower than in northern lake. Because the mixing depth is deeper in the southern lake, more oxygen is supplied to the deep part of the lake, which promotes the decomposition of organic matter. In addition, advection of organic matter to the deeper part of the lake was identified as an important process. Organic-matter flux is relatively insensitive to variation in seasonal wind direction. It is highly sensitive to variation in wind velocity, which affects the strength of lake water circulation, with weaker winds resulting in decreased POC flux to the lake bottom and stronger winds resulting in increased POC flux.

Abstract Porphyry Cu and porphyry Mo deposits are large to giant deposits ranging up to >20 and 1.6 Gt of ore, respectively, that supply about 60 and 95% of the world’s copper and molybdenum, as well as significant amounts of gold and silver. These deposits form from hydrothermal systems that affect 10s to >100 km 3 of the upper crust and result in enormous mass redistribution and potential concentration of many elements. Several critical elements, including Re, Se, and Te, which lack primary ores, are concentrated locally in some porphyry Cu deposits, and despite their low average concentrations in Cu-Mo-Au ores (100s of ppb to a few ppm), about 80% of the Re and nearly all of the Se and Te produced by mining is from porphyry Cu deposits. Rhenium is concentrated in molybdenite, whose Re content varies from about 100 to 3,000 ppm in porphyry Cu deposits, ≤150 ppm in arc-related porphyry Mo deposits, and ≤35 ppm in alkali-feldspar rhyolite-granite (Climax-type) porphyry Mo deposits. Because of the relatively small size of porphyry Mo deposits compared to porphyry Cu deposits and the generally low Re contents of molybdenites in them, rhenium is not recovered from porphyry Mo deposits. The potential causes of the variation in Re content of molybdenites in porphyry deposits are numerous and complex, and this variation is likely the result of a combination of processes that may change between and within deposits. These processes range from variations in source and composition of parental magmas to physiochemical changes in the shallow hydrothermal environment. Because of the immense size of known and potential porphyry Cu resources, especially continental margin arc deposits, these deposits likely will provide most of the global supply of Re, Te, and Se for the foreseeable future. Although Pd and lesser Pt are recovered from some deposits, platinum group metals are not strongly enriched in porphyry Cu deposits and PGM resources contained in known porphyry deposits are small. Because there are much larger known PGM resources in deposits in which PGMs are the primary commodities, it is unlikely that porphyry deposits will become a major source of PGMs. Other critical commodities, such as In and Nb, may eventually be recovered from porphyry Cu and Mo deposits, but available data do not clearly define significant resources of these commodities in porphyry deposits. Although alkali-feldspar rhyolite-granite porphyry Mo deposits and their cogenetic intrusions are locally enriched in many rare metals (such as Li, Nb, Rb, Sn, Ta, and REEs) and minor amounts of REEs and Sn have been recovered from the Climax mine, these elements are generally found in uneconomic concentrations. As global demand increases for critical elements that are essential for the modern world, porphyry deposits will play an increasingly important role as suppliers of some of these metals. The affinity of these metals and the larger size and greater number of porphyry Cu deposits suggest that they will remain more significant than porphyry Mo deposits in supplying many of these critical metals.