The demand for metals and raw materials, such as Ni and Cu, has been projected to expand in the coming decades, driven by the global energy transition, the need for green technologies and expanding infrastructure. Consequently, the increasing extraction and production of mining waste can have adverse impacts on surrounding environments and human health. The aim of this thematic collection is to fill critical knowledge gaps in the present-day cycles of metal(loid)s from source to larger sinks, and the effect of environmental management, anthropogenic development and climate change. Altogether, the studies have been conducted in different natural settings around the world and comprise investigations in laterites, a soil–medicinal plant system, watersheds and banded iron formations, among others. The geochemical applications in tracing mineralization, its secondary products and/or potential impact on the immediate environment are highly diverse with applied tools ranging from isotope tracers to major and trace element systematics. In particular, the use of rare earth elements, their patterns and anomalies, are methods employed by several studies in this collection. We summarize the findings to offer a potential future direction for the use of geochemical tracing techniques in resource exploration in the context of climate change and environmental challenges.

metal(loid)s, pollution, geochemical tracers, isotope chemistry

Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

Mining activity will continue to grow as the demand for minerals and raw metals increases due to the transition to environmentally friendly and sustainable energy production systems (OECD 2019). The technological applications for green energy require raw materials, in particular major and trace metals (Al, Li, Ni, Cu and Co, including rare earth elements (REEs)) and graphite. In the light of the growing need for geological raw materials and improving extraction technologies to exploit low-grade ores, the amount of mining wastes will subsequently increase. If these wastes are not appropriately managed and mitigated, adverse impacts of mining and related industries are expected to increase. Much research has been conducted to understand the geochemistry associated with these deposits, as well as changes to the mine wastes’ chemistry, after their extraction and exploitation (OECD 2019). Natural weathering of metal ore deposits has the potential to negatively affect adjacent environments (Parviainen et al. 2014; Feige Gault et al. 2015). Additionally, physical and chemical processing of ore materials – including extraction, crushing, milling, separating/concentrating the target and residual components, leaching and eventual disposal – means that mining products and residues are exposed to weathering conditions, potentially leading to accelerated release of metal(loid)s or alteration of their interaction pathways with ecological media (such as soil, water and biota), with detrimental effects on the surrounding soils and water bodies (Nordstrom 2011; Nieto et al. 2013; Nordstrom et al. 2015). Climate change may alter the rate or intensity of weathering of both outcropping natural ore deposits and mining residues by modifying chemical conditions (e.g. pH, temperature, redox potential). Consequently, both natural (i.e. weathering, oxidation, hydrothermal activity, volcanic activity) and anthropogenic processes (i.e. mining, excavation) may induce mobilization of metal(loid)s in environmental systems. Increased release and discharge of metal(loid) to soils, surface water and/or groundwater, and potential uptake by biota, can pose a threat to living organisms, including humans, when levels reach toxicity thresholds (FAO and UNEP 2021). Therefore, understanding the geochemical enrichment and distribution processes of potentially toxic elements (PTEs), both in natural geological processes as well as promoted by anthropogenic activities such as mining, is crucial for sustainable development and the green energy transition (e.g. Andrade et al. 2010; Miller et al. 2019, 2020; Palmer et al. 2021; Galloway et al. 2024).

Environmental systems are under the effects of natural and anthropogenically enhanced geochemical cycling of PTEs, including resource development and climate change, which may occur at different spatial (local and over-regional) and temporal scales (Streets et al. 2019; McConnell et al. 2024). Differentiating between their cumulative effects or interactions may be challenging but it is essential for future ecological protection and guiding sustainable resource development. This thematic collection aims to identify and address the current knowledge gaps related to the compounding influence of environmental management, anthropogenic development and climate change on the reactivity, mobility, fate, transport and toxicity of metal(loid)s from mineralized sites. The overarching aim is to trace and quantify changes to the present-day cycles of metal(loid)s from source to larger sinks. In this thematic collection, different elemental isotopes proved to be important tracers at different stages of mining activities, including mineral exploration, to understand the origin of metals (Knaack et al. 2023) and post-mining environmental studies to trace pollutants and impacts of mining in the surrounding water bodies and soils (Beisner et al. 2023; Chen et al. 2023). Normalized REE data were also used for interpreting geochemical processes, both for understanding ore formation and the impacts of mining activity (Chen et al. 2023; Hakim et al. 2023; Fakhri-Doodoui and Alipour-Asll 2024). Furthermore, human health risks associated with enrichment processes in the Earth's surface environment were also addressed. Chen et al. (2023) and Wang et al. (2023) explored the health risks which may arise from potential contact with soils and also through translocation of PTEs in plants via ingestion of, for instance, medicinal plants.

Investigations from natural and mined ore deposits, and their effects on the surrounding environment and biota, throughout the world are contained in this thematic collection, including studies from Canada, China, Indonesia, Iran and the United States of America (Fig. 1). Mineralized deposit types include: sediment-hosted massive sulfide; banded iron; coal, bauxite; and sedimentary breccia pipes hosting uranium and copper ores. Fertilizer is often derived from mined mineralized deposits and one study investigates medicinal plant uptake of trace elements. The following is a summary of the highlights of the investigations included in this thematic collection. The data are also summarized in Table 1.

Knaack et al. (2023) utilizes Tl isotopes from a sediment-hosted massive sulfide deposit in Canada as an indicator of Tl sources, and alteration which can be used to fingerprint samples from mineralized and unmineralized zones. The Tl isotopic ratios in this study correlate with some economically important metals and redox indicator U/Th.

Fakhri-Doodoui and Alipour-Asll (2024) analyse REEs and fluid inclusions to better characterize a banded iron formation in Iran from an understudied geologic time period, suggesting control from syn-basinal volcanism in an active continental rift margin anoxic submarine environment. Better understanding of geochemical signatures of source deposits help to inform depositional history, which may be relevant to other deposits as well as tracers for mine waste after mining.

Beisner et al. (2023) utilizes multiple geochemical tracers to differentiate groundwater influenced by interaction with the nearby Orphan Mine, a mineralized breccia pipe U/Cu deposit in the United States of America. Open mine workings of the Orphan Mine allow modern precipitation to interact with mine waste and mobilize metals that can move through artificial pathways created by mining. These can then mix with native groundwater, resulting in the highest U concentrations in groundwater of the Grand Canyon region. Groundwater in the watershed of Horn Creek, close to the Orphan Mine, is vulnerable to changes in precipitation related to climate change, and chemical tracers suggest a component of modern water relative to nearby springs that are composed of older water.

Hakim et al. (2023) focuses on understanding weathering processes related to REE exploration in tropical areas. As detailed in Hakim et al. (2023), bauxite residue from the Western Indonesia Bauxite Province contains Sc. REEs are higher in lower parts of the bauxite layer, suggesting leaching by recharged meteoric water. Light REEs (Sc, La, Ce and Nd) are more strongly enriched in red mud associated with the bauxite deposit.

Chen et al. (2023) explores the relationship of trace element enrichment and silica to understand potential implications between mineralogy and geochemistry of coal at a deposit in China, and the high incidence of lung cancer near the mine. Trace elements in normal tissue of Xuanwei lung cancer patients are higher than those of healthy human lungs, mainly for Mn, V, Cr, Co, Ni, Cu and Cd. Multivariate statistics suggest that exposure to elevated concentrations of both quartz (silica) and trace elements could have an influence on lung cancer.

Wang et al. (2023) investigates accumulation and health risk of major and trace elements in a soil–medicinal plant system in China. Elevated trace elements in soil correspond to an enrichment in medicinal peony plants, especially for Cr. These authors suggest human-related sources, such as fertilizer (which may come from mined deposits), urban atmospheric deposition on soil or legacy mining activities as a potential cause of the trace element enrichments in soils. Metal uptake by plants has been more thoroughly studied in crops and some native plants, but there is limited information on metal uptake in medicinal plants. Assessment of the health risk posed by ingestion of the peony samples is conducted in this study and suggests low probability for adverse health effects from plants grown in this study area. There is an opportunity to expand this approach to other areas or to assess available medicinal herbs for trace element enrichment and associated health risks.

Building on what was learned from these studies, there is an opportunity for additional research to understand changes in PTE mobility related to changing climate (i.e. precipitation intensity, duration and timing, as well as air temperature changes) for material removed during mining as well as the natural mineralized deposits.

Future research directions

Geochemical approaches as vectors for resources localization and environmental impacts from mining

The mineral exploration and mining industry is confronted with new challenges and developments of novel exploration vectors. One relatively low-cost, effective and environmentally friendly approach is the application of biogeochemical vectors for mapping underlying resources. This technique investigates the presence of potentially anomalous metal concentrations in soils, plants, fungi, etc., to localize a possible underlying mineralization (Dunn 2007). The geochemical fingerprinting of plants and trees can prove useful, especially for regions dominated by the lack of bedrock outcrop, where these are extremely weathered or overlain by variably thick layers of younger deposits (overburden). An additional feature is that the roots of plants and trees can reach greater depths and transport a more pronounced mineralization signal than surficial soil sediments in some cases. Studies where metal-tolerant plant species were successfully used as mineralization fingerprinting include in Australia (Au, Cu; Reid and Hill 2010; Lintern et al. 2013; Wolff et al. 2018), Finland (Au, REEs; Närhi et al. 2014) and Canada (U; Dunn 2007). It is also worth exploring further the potential of heavy metal isotopes such as, for example, Fe, Zn, Cu and Cd, as well as S, as tools to localize mineralization plumes and direction of mineralization. Some examples are the studies of Ke et al. (2024) for Zn, Jiang et al. (2024) and Mahan et al. (2023) for Cu, and Faisal et al. (2022) for S. A challenge in using these tools is that they can be sometimes accompanied by variable isotope fractionation mechanisms (e.g. fluid migration, mineral precipitation) that require adequate quantification.

Increased resource demand also means re-opening formerly abandoned mines, reprocessing of mine wastes and/or opening those that were once considered sub-economical. Consequently, more research is needed to understand, model and predict changes in the release of metals from natural deposits and from the weathering of spoil heaps to the aerial, terrestrial and aquatic environment. As highlighted by the diverse and multidisciplinary research in this thematic collection, isotopic signatures and REEs are necessary tools, in addition to conventional geochemical methods, to fingerprint sources of elevated metal concentrations and aid in differentiating modern human impact (Beisner et al. 2023) from enrichment due to long-term natural processes (Hakim et al. 2023; Fakhri-Doodoui and Alipour-Asll 2024). Application of these geochemical tools has the potential to provide a more holistic understanding of element cycling and mobility in both pristine and impacted environmental systems, the interplay between mineral extraction and environmental health, and provide a critical step towards supporting sustainable resource development. Geochemical tools in soils, vegetation and water should also be developed and exploited as a method of tracking problem areas (waste handling), and the efficacy of companies’ environmental protection programmes (removal of PTEs from waste waters etc.) developed. Novel, low-cost tools, like the investigation of bioindicators around mining sites, such as lichen (e.g. Bačkor and Loppi 2009; Yang et al. 2023; Parviainen et al. 2024) and tree bark (e.g. Viso et al. 2021), are well-established tools to evaluate the environmental effects and potential human exposure of aerial metal pollution in the vicinity of mines.

Diminishing exploration and mineral resources close to the Earth's surface means that mining extends to ever deeper levels. This brings new technical and environmental challenges to ore extraction, and also to modelling of mineralized ore bodies in the subsurface. With the advancements of analytical techniques, several geochemical tools (Huston and Gutzmer 2023), encompassing radiogenic, and light and heavy stable isotope analyses, are successfully applied to obtain information about the age and shape of mineralization.

Finally, recent and future increasing demand for elements required for new technologies, including electric vehicles (e.g. Ni, Co, Cu, Li), may lead to increased mining of the deep seabed in the Atlantic, Indian and Pacific oceans. The potential mining of Mn nodules rich in these elements of interest, as well as polymetallic sulfides (associated with high amounts of Cu, Zn, Fe, Pb, Ag, Au and Co), is a topic of current global relevance and debate (e.g. Rasper 2024). A major concern is the relatively unknown environmental impact of such mining activity on the local, over-regional or global scale. Scientists, and environmental protection organizations and agencies, emphasize the potential dramatic consequences, such as biodiversity loss, disturbance of nutrient cycles, and effects on fisheries and the food industry. Long-term underwater monitoring and in situ analyses would likely be necessary to understand the impacts, such as chemical release, sediment swirling and higher temperatures, on deep marine ecosystems.

Climate change and future environmental challenges

As a response to climate change threats, we are now transitioning towards green energies and finding new ways to minimize CO2 release. Along with the world's population growth and energy transition, the demand for metal resources will increase (Santosh et al. 2024). Subsequently, the amount of mineral waste accumulation will also increase as technologies are rapidly upgraded and developed, especially as extraction technologies improve to exploit low-grade ores.

Climate change is expected to exacerbate extreme weather conditions, including higher temperatures over prolonged periods, extreme drought, heavy rains and storms accompanied by flooding and so on (Bolan et al. 2024). The effects of increasing temperature and variation in precipitation may alter pH, water residence time and chemical loadings, directly impacting the weathering intensity of natural deposits as well as under anthropogenic conditions. Recent research suggests extreme meteorological events have the potential to alter geochemical processes, particularly redox reactions, and, in turn, the stability of metals and metal complexation in both groundwater systems (Dao et al. 2024) and mining-impacted lakes (Galloway et al. 2018; Miller et al. 2020). Melting of glaciers exposes new deposits to weathering, while the meltdown of ice also raises water levels, leading to flooding of areas of seashore where flooding hasn't previously occurred (Bolan et al. 2024). The changes in wind strength and direction, and temperature and precipitation, due to climate change may affect air quality (Bolan et al. 2024), and may also affect the reach of airborne particulate matter originating from mining activities, including fly ash and smelting processes. Additionally, other climate change-related events, such as increased frequency and severity of forest fires, have also been demonstrated to influence the loading and cycling of metals and inorganic compounds in groundwater systems (Mansilha et al. 2020). Increased focus on the relationship between metal(loid)s and organic matter in lakes, soils and groundwater suggest that climate-induced changes may also alter the complexation and stability of metal(loid)s in these environments (see review by Dao et al. 2024).

All these climate events have the potential to alter current geochemical cycles and processes affecting air, water and soil quality (Fayinminnu et al. 2024). It is important to note that research on this relationship is currently limited, as are the implications for mineral exploration, mine waste management and rehabilitation of degraded environments. Addressing this deficit in our understanding is becoming more urgent as demand for critical minerals grows to support the green energy transition. The effects of current and future climate change on ore deposits and mine wastes should be further explored to understand how changing weathering intensities, related to the phenomena mentioned earlier, may change the unique geochemical weathering patterns. Climate change will influence these compounding factors uniquely in each mineralized or mined environment, and therefore each site must be investigated as a unique deposit. Similarities in mineralized deposits that exist at sites located far from each other in the present continental configuration at different climatic conditions may offer information and help to predict potential future processes. It is crucial to understand these multifaceted factors to facilitate environmental rehabilitation and ensure the protection of human health.

In the context of climate change, carbon dioxide removal (CDR) may also be considered as a major line of research for the future. There is a growing body of research of CDR techniques, and the role of mining waste is of major interest. CDR researchers are exploring the potential of fine-powdered mine wastes from metal and diamond mines, particularly ultramafic rocks and Cu deposits, as stock for enhanced weathering and drawdown of atmospheric CO2 (Bullock et al. 2021). However, the potential for metal release and accumulation in soils during the spreading of fine-grained mine wastes on agricultural land (e.g. Beerling et al. 2020) needs to be understood before these techniques are taken to widespread trials. The danger of metal accumulation in plants, especially those employed for medicinal use (Wang et al. 2023) and crops, has been demonstrated in this collection, and they may potentially pose a threat to human health.

Concluding remarks

We are living in a rapidly changing global environment where understanding of geochemical processes related to mined, milled or natural metal deposits is ever more important. Global demand for metals is expected to increase continuously over the twenty-first century to provide society with the goods and services required for meeting basic human needs of a growing global population as well as supporting the transition to cleaner energy sources (Santosh et al. 2024). The research articles in this thematic collection highlight the latest advances in geochemical tools fundamental to supporting sustainable resource development and the green energy transition. A commonly highlighted topic within this thematic collection is the critical implications of climate in REE mobility and isotopic fractionation in both palaeo- and modern-day metal-enriched environments (Hakim et al. 2023; Knaack et al. 2023; Fakhri-Doodoui and Alipour-Asll 2024). Fakhri-Doodoui and Alipour-Asll (2024) and Knaack et al. (2023) demonstrate the influence of climate-related factors, such as atmospheric oxygen, sea-level variations and redox conditions on REE distribution in depositional environments. Similarly, Knaack et al. (2023) concludes that isotopic compositions, in particular Tl, may provide crucial insights to metal(loid) distribution and palaeoclimate conditions. In modern-day environments, weathering and leaching processes were demonstrated to influence the mobility and fate of REEs (Hakim et al. 2023). These articles contribute to the challenge of untangling the compounding natural and human-driven mechanisms which result in element enrichment across a wide array of geological and environmental contexts – and further draw attention to the emerging concerns and knowledge gaps which should be addressed in future studies. Sustainable production of critical metals provides a number of confounding and unresolved challenges.

We wish to acknowledge all the contributing authors of this thematic collection, and we are also grateful for the peer reviewers for their time and effort in contributing their valuable feedback on the manuscripts.

AP: visualization (lead), writing – original draft (lead), writing – review & editing (lead); KB: writing – original draft (lead), writing – review & editing (equal); JB: writing – original draft (equal), writing – review & editing (equal); EMO: writing – original draft (equal), writing – review & editing (equal); CM: writing – original draft (equal), writing – review & editing (equal); CR: conceptualization (equal), visualization (equal), writing – original draft (equal), writing – review & editing (equal).

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

No data were generated or analysed for this summarizing article. Please refer to individual data availability statements in the respective articles of the thematic collection.