European Geologist Journal 47

Exploration of flooded mines as support to the battery industry and the energy transition in Europe


By Giorgia Stasi*, Isabel Fernandez, Yves Vanbrabant

* RBINS – Geological Survey of Belgium, Rue Jenner 13, Brussels 1000, Belgium


The transition to renewable energy needs minerals to build wind, solar, and battery technology for energy production and storage. In order to help the development of this sector and to maintain and enhance the possibility of the EU to become more independent from the import of raw materials we need to improve the research activity for both known and undiscovered mineralization. For this purpose, the UNXEMIN project is developing autonomous submersible robots to explore, map and characterize abandoned flooded mines in Europe.  Along with robot development, the first inventory of flooded mines in Europe has been created, that now contains more than 8,000 entries from 24 countries. This database can be used in the European industrial framework as a resource for research in specific critical raw materials.

UNEXMIN as support to the battery industry in Europe

The UNEXMIN project is developing autonomous submersible robots to explore, map and characterize abandoned, underground flooded mines in Europe. These robots will be able to map and sample underground flooded mines at up to 500 m depth. But how can the UNEXMIN project help Europe in the energy transition?

The transition to renewable energy needs wind, solar and battery technology, which require a lot of minerals. Renewable energies like water, solar and wind power are often not continuously available, so efficient interim storage is necessary to ensure a steady supply of power. Battery storage systems are an advantageous option in this regard. The EU is highly dependent on imports of metallic minerals, as its domestic production is limited to about 3% of world production (COM (2008) 699). One of the main goals of Europe is to reduce the dependency on the import of raw materials and solve issues along the entire value chain. This project could steer the EU to the forefront in sustainable minerals surveying and exploration technologies; it can increase Europe’s capacity to re-evaluate its abandoned mines for their mineral potential, with reduced exploration cost and increased investment security for any future mining operations (Lopes et al., 2017).

Battery development and production is a strategic imperative for Europe in the context of the clean energy transition. There is a strong need to create competitive and sustainable battery manufacturing in Europe. Working towards this goal,  the European Commission is promoting a cross-border and integrated European approach covering the whole value chain of the battery ecosystem and focusing on sustainability, starting with the extraction and processing of raw materials, the design and manufacturing phase of battery cells and battery packs and their use, second use, recycling and disposal in a circular economy context. The Strategic Action Plan on batteries (COM (2018)293 Annex 2) combines targeted measures at EU level including the areas of raw materials (primary and secondary), research and innovation, financing/investment, standardisation/regulation and trade and skills development. The aim is to make Europe a global leader in sustainable battery production and use, in the context of the circular economy. More specifically it aims to facilitate access to European sources of raw materials and to secure access to raw materials from resource-rich countries outside the EU (COM (2008) 699). The policy is also based on sustainable domestic raw materials production and resource efficiency and supply of secondary raw materials.

Critical raw materials for batteries

At present, optimised LIB (Lithium Ion Batteries) cells represent the core technology for energy storage. The supply of critical raw materials for LIB is ensured by working along three routes: sourcing from third countries developing domestic sourcing; and promoting recycling of battery materials as well as reuse of batteries. The sourcing of the four essential raw materials (cobalt, lithium, nickel and graphite) is concentrated in only a few countries (Figure 1). The Democratic Republic of Congo is the source of 64% of the global supply of cobalt and Chile is the main supplier of lithium with 36%.

Figure 1: Countries supplying critical raw materials for batteries, amount (tonnes) and percentage of global supply (from EC SDW (2018)).

In the EU countries Finland is a major supplier of refined cobalt (it meets 66% of EU demands for ores and concentrates); however, the extent of domestic sourcing of EU demand is very limited for the other materials (nickel and lithium) (COM (2018)293 Annex 2).

In order to help the development of this sector and to maintain and enhance the possibility of EU to become more independent from the import of raw materials, an improvement in research activity for known and undiscovered mineralisation of the targeted materials (cobalt, lithium, nickel and graphite) is needed and expected.

The current status of mineral exploration activities for battery applications is shown in Figure 2 (EC SWD(2018)); activities remain concentrated in Portugal, Finland, Sweden and Central Europe. 

Figure 2: Status of mineral exploration activities for cobalt, graphite, lithium and nickel in 2017 (from EC SDW (2018)).

UNEXMIN inventory of flooded mines as a research tool

In the UNEXMIN project, along with the robot construction, project participants are carrying out a comprehensive inventory of underground flooded mines in Europe. The total number of flooded mines in Europe is still unknown. Depending on the definition (e.g. fully developed mine on an industrial scale versus artisanal medieval mining site or individual mine versus mining district), estimations range from ≈5,000 to >30,000 mines in Europe (ISRM 2008) but no comprehensive dataset has been available up to now.

In order to gather relevant data for the open-access database of UNEXMIN, information about flooded mines has been systematically collected by 15 national associations of the European Federation of Geologists (EFG) and by the Geological Survey of Belgium (RBINS-GSB). The data were retrieved through the review of existing datasets (ProMine, Minerals4EU), desk research and automated approaches (manual data extraction and automated data web-crawling). As the information related to the abandoned mines in Europe is mostly spread among different authorities, associations or publications, the quantity and the quality of the recovered information varies from country to country and from mine to mine.

UNEXMIN’s inventory currently covers ~8,100 mines from 24 countries (D5.4, 2018) (Figure 3) and contains information about the mine name(s), its location, its accessibility, the extracted commodities, the geological information related to the available maps and sections, the classification of the deposit, the ownership, the activity level, the potential legal restrictions and other useful information. This new open-access database could be used as a research tool to identify abandoned mines that could potentially be re-opened in the future.

Figure 3: Web interface of the UNEXMIN database.

Through the web interface of the UNEXMIN database it is possible to select all of the flooded mines with the targeted minerals as commodities (Figure 4a). At this current stage we count a total of 72 mines of Li, Co, and Ni as principal or secondary commodities in 10 countries (Figure 4b).

Figure 4: Selection of UNEXMIN mines for the EU battery industry: a) map distribution of the mines, b) graph distribution of the mines by mineral and country.

For each mine we have information about the deposit type, the geology of the area, the water level, the distance from the nearest road, the mine size and the year of the closure. The majority of the mines were closed at the end of the 19th century or in the middle of the 20th century, mostly due either to economic reasons or exhaustion of the principal commodity.

Czech Republic

One deposit of nickel as a secondary commodity has been found. This is a syn-deformational hydrothermal and replacement deposit. The mineral resource was considered exhausted in 1978 but now new exploration can be planned with the brand-new exploration technology.


As the primary commodity 5 nickel mines, 11 nickel and cobalt mines have been identified, plus 2 cobalt mines as secondary commodity. Except for one nickel-cobalt deposit of hydrothermal origin, all the other deposits are of magmatic origin. The two cobalt deposits are volcanogenic massive sulfide (VMS) deposits, one nickel deposit is associated with komatiite, and the others are VMS or synorogenic Ni-Cu deposits in (ultra)basic intrusions.


In Germany 24 underground flooded mines have been found, of which 8 contain lithium, 8 cobalt, 4 nickel and 4 nickel-cobalt. The lithium deposits are of magmatic, hydrothermal and metasomatic origin: these are porphyry-associated deposits, pegmatitic deposits and skarn deposits. The cobalt deposits are of hydrothermal origin, and the nickel deposits are VMS, a layered mafic-ultramafic intrusion deposit and a deposit with marine-sedimentary origin. The deposits with both nickel and cobalt as principal commodity are classified as porphyry-associated deposits and fractioned granitoid-associated deposits.


In Italy 7 nickel mines and 1 nickel-cobalt mine have been found. These deposits have magmatic origin.


One nickel mine has been identified in a lateritic-nickel-cobalt deposit.


In Portugal there are 3 lithium mines: 2 of magmatic origin, a syn-deformational hydrothermal and replacement deposit and a pegmatitic deposit; and 1 fractionated granitoid-associated deposit.


In Serbia a skarn deposit with cobalt as a secondary commodity has been found.


In Slovakia there is a layered mafic-ultramafic intrusion deposit with nickel and cobalt as primary commodities.


In Sweden there are 4 nickel-cobalt mines and 1 mine of nickel. One nickel-cobalt mine is located in a VMS deposit while the others are associated with komatiite, as is the nickel mine.


A total of 4 cobalt mines, 5 nickel mines and 1 nickel-cobalt mine have been found in the UK. All these mines are in vein type deposits of hydrothermal origin.


Figure 5 graphically represents the UNEXMIN data and the exploration activities in 2017 (EC SWD(2018) 245/2)[1]. Comparing this graph  and the maps (Figures 2 and 4) it is possible to notice that, while in most of the countries the number of exploration activities in 2017 reflect approximately the closed or abandoned mines listed in the UNEXMIN inventory, in Germany there could be the possibility to expand the exploitation of cobalt, lithium and nickel. As the UNEXIM database is currently being updated it is not possible to compare figures for France or Spain, but preliminary results suggest that a similar situation will emerge for France.

Figure 5:  Distribution of mines among European countries, comparison of selected UNEXMIN database (UX) results and the status of mineral exploration activities in 2017 (EC SDW (2018)). The selected UNEXMIN mines are closed or abandoned but can be reconsidered for future exploitation after further study.

Many of these mines may still contain profitable quantities of raw materials. The main reason for the closure or the abandonment of the mines was economic: the technology and the methods used for mineral extraction were too expensive and it was more convenient to import the necessary raw material from other countries (e.g. Chile, Congo, China, etc.). With the geological information, the deposit classification and the last owner’s data, the UNEXMIN database is a potentially important research tool for the initial estimation and identification of potential sites for future exploitation for the battery industry.

Nowadays, with the development of new mining and refining technologies, mines that were considered no longer exploitable for economic and technical reasons at the time of closure can be re-contemplated and re-evaluated in order to reduce the dependency of Europe on the import of raw materials.

The UNEXMIN submersible robot can be used in the study of potential sites. It is able to explore and map underground flooded mines and to provide useful data for the mining industry with its scientific instrumentation. The scientific equipment includes a water sampler, a conductivity and pH measuring unit, a sub-bottom profiler, a magnetic field measuring unit, UV fluorescence imaging and multispectral imaging units (Lopes et al., 2017).  It is hoped that the UNEXMIN database and robot will both contribute to expansion of the battery industry in Europe.


EC SWD(2018) 245/2 final. Report on raw materials for battery applications.

COM(2018) 293 final. Annex 2. Strategic action plan on batteries.

COM(2008) 699. The raw materials initiative.

Lopes, L., Zajzon, N., Henley, S., Vörös, C., Martins, A., Almeida, J.M. 2017. UNEXMIN: a new concept to sustainably obtain geological information from flooded mines. European Geologist, 44. 54–57.

ISRM. 2008. Mine closure and post mining management: International state of the art. Technical report. International commission on Mine Closure, International Society of Rock Mechanics.

Public deliverable UNEXMIN project. 2018. D5.4 Inventory of flooded mines in Europe. Available at:

Science for Environment Policy. 2018. Towards the battery of the future. Future Brief 20. Brief produced for the European Commission DG Environment by the Science Communication Unit, UWE, Bristol. Available at:

[1] Austria did not participate in the UNEXMIN project. Spanish data are under update and at the time of writing there is no mine that fit the research criteria for the battery industry.

This article has been published in European Geologist Journal 47 – Geology and the energy transition.