MineGuessr – Aggeria & Agia Irini, Milos (Greece): Bentonite Open Pits on a Volcanic Island

MineGuessr Advent Calendar 2025 – Door 14

Aggeria and Agia Irini are two overlapping bentonite open pits on the volcanic island of Milos in Greece – and one of the world’s best examples of large-scale industrial minerals mining. In our 2025 MineGuessr mining advent calendar, their distinctive white benches and deep stepped walls make for a striking mining satellite timelapse, challenging players to guess the mine from satellite imagery of mines alone.

On this page, we provide a concise, professional overview of Aggeria–Agia Irini – their location, geology, operational history and role in the raw materials value chain. The satellite timelapse helps illustrate how these pits have grown and been managed over time, supporting raw materials education for anyone interested in how industrial minerals such as bentonite are produced in Europe.

Aggeria & Agia Irini bentonite open pits, Milos – satellite view

Overview & location

From space, the Aggeria–Agia Irini complex appears as a series of bright, stepped amphitheatres cut into the north-eastern side of Milos. The benches are unusually light-coloured compared with typical metal mines – a visual clue that we are looking at a clay and industrial minerals operation rather than a metal sulphide open pit. The surrounding landscape alternates between untouched volcanic hills, access roads, processing areas and progressively rehabilitated slopes.

Together, Aggeria and Agia Irini form the core of Imerys’ bentonite hub on Milos, which is one of the most important bentonite districts in Europe and contributes a significant share of global supply. On some estimates, Milos alone accounts for around 10% of the world’s bentonite production.¹

Where in the world are Aggeria & Agia Irini?

The mines are located on the north-eastern coast of Milos, part of the South Aegean Volcanic Arc in Greece:

Aggeria–Agia Irini lies inland from the north coast, not far from the village of Zefyria and within easy reach of the island’s main port at Adamas.
The combined mining area stretches from the Agia Irini church towards Koufi, forming a single, elongated open-pit complex with multiple working phases and internal haul roads.²
Both pits are operated by Imerys Greece S.A., which mines bentonite at several deposits on Milos (Aggeria, Agia Irini, Koufi, Aspro Chorio, Zoulias) and processes it into a range of activated and speciality products.³

Recent CSR disclosures show annual bentonite production from Aggeria and Agia Irini in the hundreds of thousands of tonnes per year, underlining their status as major industrial minerals operations within Europe’s supply chain.^3,4

Geology & deposit type

Aggeria–Agia Irini is part of the cluster of Lower Pleistocene bentonite deposits on eastern Milos, formed by alteration of volcanic ash and tuffs within the South Aegean Volcanic Arc.^5,6 These deposits are dominated by smectite (montmorillonite) and have been extensively studied as reference materials for both industrial and repository applications.

Key geological features include:

Protolith: Mainly pyroclastic volcanic rocks (ash, tuffs) of andesitic to rhyolitic composition, altered in situ to bentonite through interaction with seawater and meteoric water under low-temperature hydrothermal conditions.^5,6
Mineralogy: Bentonite here is typically rich in montmorillonite (often >70% smectite), with variable amounts of quartz, feldspar and accessory minerals. Different deposits and horizons show distinct geochemical “fingerprints” connected to separate volcanic centres.^5,6,7
Industrial properties: Milos bentonite is regarded as a speciality bentonite rather than a commodity, because its swelling, rheological and binding characteristics allow use in a wide range of applications – from foundry sands and drilling muds to sealing, civil engineering and environmental barriers.⁸

For MineGuessr, Aggeria–Agia Irini represents the industrial minerals end of the advent calendar – contrasting with copper, gold or iron ore operations on other days, while still telling an important raw materials story.

What the mining satellite timelapse shows

The mining satellite timelapse for Aggeria–Agia Irini (1984–2022) compresses several decades of industrial minerals mining into a short video. In just a few seconds, you can see how bentonite excavation, internal haulage, waste placement and rehabilitation reshape a coastal volcanic landscape.

1980s–1990s – initial pit development

The earliest frames show a smaller, relatively shallow open pit cut into the hillside, with initial benches and a limited surface footprint.
Processing and load-out facilities begin to appear adjacent to the pit, with access roads connecting the mine to the island’s road network.

From space, this stage reads as a compact white scar, with benches just starting to stack up in a classic terraced pattern.

2. 1990s–2000s – expansion and overlapping pits

As production ramps up, the main Aggeria pit deepens and pushes laterally, while the neighbouring Agia Irini area is progressively opened up. Locally, people refer to “the Aggeria and Agia Irini Mines” as two overlapping pits rather than separate operations.^1,4
Internal haul roads become more pronounced, and external waste placement and stockpiles are more clearly defined.

In the timelapse, the original single pit evolves into a broader mining complex with multiple working faces and stepped walls.

3. 2000s–2010s – deep benches, steady production

By the mid-2000s and 2010s, Aggeria–Agia Irini is a mature operation with deep benches and a significant vertical dimension. Some descriptions highlight depths of over 150 m and a width of several hundred metres across the benches.²
Satellite frames show ongoing cutbacks and localised expansions, but the overall footprint stabilises as mining focuses on deepening within the established perimeter.
Additional internal roads, laydown areas and ancillary infrastructure (water management, stockyards) become clearer identifiers of a long-life open pit.

4. 2010s–2020s – optimisation, environmental management and rehabilitation

Recent CSR reporting from Imerys emphasises energy efficiency, dust and noise control, and ISO 14001–certified environmental management across its bentonite operations on Milos, including Aggeria and Agia Irini.^3,6
Mining remains active, with combined bentonite output from the two pits in the several hundred-thousand-tonne-per-year range, but more frames show reclaimed, terraced slopes and areas of progressive rehabilitation.^3,6
Elsewhere on Milos, Imerys has converted rehabilitated perlite quarries into vineyards, illustrating the longer-term land-use arc for industrial mineral sites on the island.³

For MineGuessr, this phase adds an ESG layer to the story: industrial minerals mines are not just holes in the ground – they are managed landscapes with explicit closure and rehabilitation plans.

Mining method & processing – how the ore moves

Aggeria–Agia Irini operates as a truck–shovel open pit mining system tailored to soft rock and industrial minerals:

Mining: Bentonite is extracted in stepped benches using excavators and front-end loaders, with care taken to segregate different quality horizons and avoid cross-contamination between ore and overburden.
Haulage: Trucks move run-of-mine bentonite to nearby processing facilities, where it is crushed, dried and, in many cases, activated with soda ash to obtain the rheological properties required for drilling fluids, sealing products and other applications.^3,6,8
Processing & products: The Milos hub produces a family of speciality bentonites that are shipped globally for use in foundry sands, iron ore pelletising, drilling muds, geosynthetic clay liners, civil engineering and environmental remediation.⁸

Role in the raw materials value chain and energy transition

Although bentonite is not a battery metal, the Aggeria–Agia Irini mines play a strategic role in the raw materials value chain and, indirectly, the energy transition:

Infrastructure & construction: Bentonite from Milos is used in slurry walls, tunnelling, diaphragm walls and geotechnical barriers, all critical to infrastructure projects that support renewable power, energy networks and transport.⁸
Environmental sealing: High-quality bentonite is a cornerstone of landfill liners, mine closure covers and engineered barriers in waste repositories, where it helps protect groundwater and ecosystems.^2,8
Foundry and steel: Bentonite-bonded moulding sands remain essential for steel and castings used in wind turbines, vehicles and industrial equipment.

From a MineGuessr perspective, Aggeria–Agia Irini reminds us that industrial minerals are just as critical to Europe’s resilience and infrastructure as the headline base and battery metals.

What to look for in the MineGuessr timelapse

As a MineGuessr player, we invite you to look for:

The very light-coloured benches of the bentonite pits, which stand out compared with darker volcanic rocks around them.
The way the two overlapping pits gradually coalesce into a single, elongated mining complex.
Progressive deepening and internal pushbacks, showing how industrial mineral operations can reach significant depths.
Signs of progressive rehabilitation on parts of the slopes and surrounding land, juxtaposed with active working faces.

MineGuessr perspective – why this mine was included

We selected Aggeria–Agia Irini for the MineGuessr mining advent calendar because it:

Showcases a world-class bentonite district on a small volcanic island – a reminder that industrial minerals can have global reach from very local geology.
Provides a clear life-of-mine visual story in the satellite timelapse, from initial pit development to deep, overlapping open pits and progressive rehabilitation.
Represents industrial minerals mining in Europe, complementing the base-metal, gold, iron ore and talc operations featured on other days.

In our GeoGuessr-style mine guessing game, Aggeria–Agia Irini helps spark conversations about bentonite, industrial minerals, and how “non-metallic” mines support infrastructure, environmental protection and the broader energy transition.

In December, keep opening a new door every day and explore all 24 mines featured this year on the main MineGuessr mining advent calendar page.

Day 1 - Aitik (Sweden, copper-gold open pit)
A large, low-grade copper operation south of Gällivare
👉 Open Door 1 - Aitik
Day 2 - Björkdal (Sweden, gold)
Gold mine near Skellefteå, combining open-pit and underground mining.
👉 Open Door 2 - Björkdal
Day 3 - Kemi (Finland, chrome)
Chrome mine in northern Finland, Europe’s only chromite operation.
👉 Open Door 3 - Kemi
Day 4 - Ørtfjell (Norway, iron ore)
Iron ore mine in Norway’s Dunderland Valley, evolving from large open pits to underground mining.
👉 Open Door 4 - Ørtfjell
Day 5 - Trimouns (France, talc)
World’s largest working talc quarry high in the French Pyrenees above Luzenac.
👉 Open Door 5 - Trimouns
Day 6 - Skouries (Greece, copper-gold porphyry)
High-grade copper–gold porphyry project in the forests of Halkidiki, still under construction.
👉 Open Door 6 - Skouries
Day 7 - Las Cruces (Spain, copper)
High-grade hydromet copper mine in the Iberian Pyrite Belt north-west of Seville.
👉 Open Door 7 - Las Cruces
Day 8 - Assarel–Medet (Bulgaria, copper)
Twin porphyry copper open pits in the Panagyurishte district, from Europe’s former largest open-pit copper mine at Medet to today’s modern Assarel operation.
👉 Open Door 8 - Assarel–Medet
Day 9 - Glomel (France, andalusite)
World-class andalusite open-pit quarry in Brittany’s Montagnes Noires, supplying refractory minerals for Europe’s steel, foundry, cement and glass industries.
👉 Open Door 9 - Glomel
Day 10 - Parnassos–Ghiona (Greece, bauxite)
Karst-type bauxite mines in the Parnassos–Ghiona mountains, a historic alumina feedstock district supplying Greece’s aluminium industry.
👉 Open Door 10 - Parnassos–Ghiona
Day 11 - Kittilä (Finland, gold)
Europe’s largest primary gold mine at the Suurikuusikko orogenic gold deposit north of the Arctic Circle.
👉 Open Door 11 - Kittilä
Day 12 - Oltenia Energy Complex (Romania, lignite)
Cluster of large open-pit lignite mines and mine-mouth power plants in Gorj County, now at the centre of Romania’s coal phase-out and just transition plans.
👉 Open Door 12 - Oltenia Energy Complex
Day 13 - Cornwall china clay (UK)
Historic Imerys china clay pits near St Austell, where bright white kaolin benches and tips reshape “Clay Country” over decades of mining and restoration.
👉 Open Door 13 - Cornwall china clay
Day 15 - Skouriotissa (Cyprus, copper & hydromet)
Ancient copper mining district in the Troodos ophiolite, now a hydrometallurgical hub processing copper, gold and battery-metal feed.
👉 Open Door 15 - Skouriotissa
Day 16 - Tunstead (UK, limestone & cement)
The UK’s largest limestone quarry near Buxton, feeding an integrated lime and cement works with long-term restoration and biodiversity plans.
👉 Open Door 16 - Tunstead
Day 17 - Narva (Estonia, oil shale)
Large open-pit oil shale mine in Ida-Viru County, supplying the Narva power plants and reshaping the landscape with strip mining and reclamation.
👉 Open Door 17 - Narva
Day 18 - Sydvaranger (Norway, iron ore)
Arctic banded iron formation at Bjørnevatn near Kirkenes, evolving toward DR-grade magnetite for Europe’s green steel transition.
👉 Open Door 18 - Sydvaranger
Day 19 - Kevitsa (Finland, nickel–copper–PGE)
Multimetal open-pit mine in Finnish Lapland, combining Ni–Cu–PGE production with trolley-assisted haulage for lower-emission mining.
👉 Open Door 19 - Kevitsa
Day 20 - Styrian Erzberg (Austria, iron ore)
Terraced “pyramid” open-pit iron ore mine at Eisenerz, turning 12 Mt of rock into ~3 Mt of ore each year for Austria’s steel industry.
👉 Open Door 20 - Styrian Erzberg
Day 21 - Minas de Alquife (Spain, iron ore)
Europe’s largest open-pit iron ore mine in Granada, restarting in 2020 after two decades of closure to supply high-grade ore to European steelmakers.
👉 Open Door 21 - Minas de Alquife
Day 22 - Siilinjärvi (Finland, phosphate)
EU’s only operating phosphate mine in central Finland, mining an Archean carbonatite for fertiliser-grade apatite and creating distinctive pale tailings and phosphogypsum stacks.
👉 Open Door 22 - Siilinjärvi
Day 23 - Tellnes (Norway, ilmenite/titanium)
World-class ilmenite open pit in the Rogaland Anorthosite Province, supplying TiO₂ pigment feedstock from one of Europe’s largest titanium deposits.
👉 Open Door 23 - Tellnes
Day 24 - Elatsite (Bulgaria, copper–gold porphyry)
High-altitude porphyry copper–gold open pit in Bulgaria’s Srednogorie zone, with ore conveyed under the Balkan Mountains to a separate flotation–tailings complex.
👉 Open Door 24 - Elatsite

About Gosselin Mining

At Gosselin Mining, we work with the same kinds of long-life operations showcased in the MineGuessr advent calendar – from large open pits and underground metal mines to industrial minerals sites producing kaolin, talc, bentonite and perlite. If you’d like to stress-test a life-of-mine plan, benchmark your project against Nordic and European peers, or explore ESG, decarbonisation and rehabilitation options for your own asset, you’re very welcome to book a meeting with us.