Provenance of Coastal and Seabed Sediments Relative to Mining and Processing Wastes: The Case of Lavrion, Attiki Peninsula, Greece

Abstract

A detailed textural, mineralogical, and geochemical investigation of beach sands and seabed sediments from Thorikos and Oxygono bays of the eastern coast of Lavrion is performed, with the objective the provenance of the ore types exploited, the processing and beneficiation types employed, and the respective exploitation periods. The Oxygono Bay beach and seabed sands are highly heterogeneous, predominated by lithic clasts originating from surrounding lithologies. Examination of the fine-grained fraction from the seabed core revealed that only the upper 50 cm was affected by recent and ancient mining activity. Combining the mineralogy and geochemistry of Oxygono Bay sands with the radiochronological model of Pappa et al. (2018), four periods of recent exploitation (mid-19th—late 20th century) are distinguished: (1) The “1860–1875 A.D.”, involving exploitation of the ancient smelter slags, (2) the “1875–1900 A.D.”, with ongoing ancient smelter slag processing and the commencement of underground sulfide ore exploitation, (3) the “1900–1930 A.D.”, where heavy mining of the carbonate-hosted Pb–Zn–Ag ore occurs, (4) the “1930–1980”), where the implementation of flotation-type processing assisted in the exploitation of the poor skarn and porphyry-type ores. The latest “1980 A.D.—to date” period depicts the cessation of all mining and processing activities. The southern Thorikos Bay beach sands are homogeneous and fine-grained, are mainly composed of gangue and pyrite, and show elevated Fe, As, Pb, Zn, and Mn content. The southern Thorikos Bay beach sands clearly point to exploitation and processing by flotation of the carbonate-hosted Pb–Zn–Ag sulfide ore, and the tailings were disposed of from the nearby facilities to southern Thorikos Bay without any environmental concern during the “1930–1980 A.D.” period.

1. Introduction

The evolution and socio-economic development of human species go hand-in-hand with the exploitation of natural resources [1,2]. From the very early stages of human history, humanity has exploited all available resources, either in their primary state or after processing [3,4]. At the same time, various types of waste are produced, including both mining and processing wastes, with diverse effects on human health and the environment [2,5,6,7,8,9]. Although, the effect of sulfide ore exploitation on the environment has been described since the 16th century A.D. [10], the actual impact of exploitation and commodity production, and in particular metals, has not been known until the second half of the 20th century, especially with the identification of the acid mine/rock drainage phenomenon [11,12,13]. Therefore, even in recent years, most of the waste produced by mining and metal extraction has been disposed of in nearby areas [2].

Despite the exponential increase in exploitation of sulfide ores and extraction of metals during the past 200 years due to advances in processing techniques [2] (and references therein), very limited work has been done so far regarding the footprint and the historical perspective of relatively recent exploitations. Only a small number of studies have focused on the temporal evolution of areas with intense mining history, especially when different ore types are involved during ore extraction and various beneficiation techniques are employed during processing, as in the case of Lavrion (Attiki Peninsula, Greece) [14,15]. The vast majority of the published literature is focused on ore deposits mined during the early stages of human history by employing isotopic investigation, and in particular the Pb isotopic signature in prehistoric and historic alloys, in an attempt to distinguish the possible ore types exploited as well as the ancient commerce routes of metals [16,17,18,19].

The present study is focused on the examination of the coastal area at the eastern part of Lavrion (Attiki Peninsula, Greece), an area heavily affected by the disposal of mining and processing wastes after the exploitation of the Lavrion sulfide ores [14]. The study involves a detailed mineralogical and geochemical investigation of beach sands and seabed sediments. The results are combined with the radiochronological model of Pappa et al. [20], employed in the same area. In short, gamma-ray spectra of natural (²¹⁰Pb and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides were measured, and these values were used in the determination of the sedimentation rate (SR) [20,21] (for details on the methodology). The aim of the study is to decipher the exploitation and ore-processing history of the second period of mining activities between the mid-19th and late 20th century. The objective is to provide details on the provenance (origin) and temporal evolution of coastal and seabed sediments relative to exploitation and processing wastes of the various ore types found at Lavrion mining district and the way intense exploitation has affected the natural environment.

2. Regional Geology, Ore Deposit Types and Historical Flashback of Exploitation

Regional geology: The Lavrion mining district belongs to the Attic-Cycladic Massif (ACM), which comprises three different nappes: The lowermost Cycladic Basement and Basal Unit, the Cycladic Blueschist Unit, and the Upper Cycladic Unit [22,23,24,25] (Figure 1A). The ACM is characterized by diverse and complex geotectonic evolution related to the closure of the Tethys Ocean in the Paleocene-Eocene by subduction of the African plate below the Eurasian plate [26,27,28,29]. At Lavrion, the Basal unit (Kamariza Unit), the Lavrion Blueschist Unit (Lavrion Unit), and the Upper Cycladic Unit are exposed (Figure 1A). The Basal Unit Unit, with late Triassic-to-early Jurassic protoliths, comprises the Kessariani schists sandwiched between the Lower and Upper marbles [30]. The overlying Lavrion Blueschist Unit is separated from the lower Basal Unit by a major detachment fault and comprises late Jurassic-to-Cretaceous protoliths consisting of high-pressure, low-temperature metapelites, metasandstones, chlorite schists, and metabasic rocks. The Upper Cycladic Unit at Lavrion has limited exposure at Lavrion and consists of Upper Cretaceous limestones, cherts, and serpentinites [31].

Deposit geology: The geotectonic evolution of Lavrion during the Cenozoic and the related intrusion of the Plaka granodiorite between 8.3 and 9.4 Ma resulted in the development of various sulfide ore types [24,32,35]. In particular, five different mineralization types have been recognized in the Lavrion world-class ore deposit [34,35], with major ore types involving the magnetite-pyrrhotite Fe skarn-type [34,38,39], the sulfide-rich skarn-free type ores in close proximity to the Plaka granodiorite [33], and the carbonate replacement Pb–Zn–Ag ore, which was the main focus of exploitation. Other mineralization types, yet with limited spatial development, include a porphyry-style sulfide ore occurring as sheeted quartz veins and stockworks comprising molybdenite within the Plaka granodiorite [34] and the breccia-style sulfide ore [40]. The typical carbonate-replacement-type Pb–Zn–Ag ores occur at Kamariza (e.g., Hilarion, Clemence, Jean Baptiste, Serpieri, and Christiana mines) and Plaka (e.g., Adami and Villia mines) (Figure 1A). The carbonate-replacement orebodies are structurally controlled following the Lower and Upper marble contacts with the Kessariani schists, forming lenses, mantos, and chimneys with sizes up to tenths of meters in length [33]. The world-class Pb–As–Sb–Cu–Ag vein-type ores are mainly expressed by the «Filoni 80”» vein, which has not been heavily mined [41]. Since the Miocene, the Lavrion area has experienced uplifting, erosion, and extensional fracturing [42], and the primary sulfide ores suffered weathering due to the infiltration of oxidizing rainwater, resulting in the formation of the equally important supergene mineralization composed mainly of secondary carbonates (e.g., cerussite and smithsonite) [32,43]. According to Voudouris et al. [44], the thickness of the oxidation zone at Lavrion is one of the largest worldwide and locally is greater than 250 m.

Mining history: The Lavrion district is known for its mining activity, which lasted from ancient times until the late 20th century. The first traces of exploitation date back to 3000–3500 B.C., whereas the peak of exploitation took place during the Classical period (6th to 4th century B.C.) [14,15,45]. The underground works resulted in over 2000 mine shafts and more than 300 km of galleries [46]. During that period, the metallurgical processes of “cupellation” and reductive roasting and smelting were employed to extract Ag and Pb from primary (galena) and secondary (cerussite, anglesite) Pb ores for commercial purposes [14,47]. According to Conophagos [14], the Ag grade of the carbonate-replacement ores exploited by the ancient Greeks ranged from 1 to 4 kg per ton of Pb (average of 2 kg per ton), and the total production for that period reached 3.5 kt of Ag and 1.4 Mt of Pb.

The Lavrion mines were abandoned during 1st century B.C. and were re-activated in 1864 A.D. by the Italian-French company “Roux-Serpieri-Fressynet C.E” (also known as “Hilarion Roux et Cie”) with the objective of exploiting the abandoned ancient smelter slags and wastes (“ekvolades”) [14]. In 1865, the first processing facility was built at “Ergastiriakia” (near the contemporary Lavrion port, Figure 1B), and exploitation began. The total quantity of the ancient smelter slags was calculated at ~1.5 Mt with a 10% Pb average, whereas the ancient wastes (ekvolades) were estimated to be more than 10 Mt. In 1873, due to legal disputes, the French Company was bought by Greek investors (A. Syggros) and the bank of Constantinople, and the “Hellenic Metallurgical Company” (Societè des Usines du Laurium) was founded with a focus on the ancient smelter slags and wastes. By 1910, the ancient slags were exhausted, and the company ceased operations in 1917. During the period of operation (1873–1917), the total production of the Hellenic company reached 310 kt of Ag-bearing Pb (i.e., 290 Kt between 1873 and 1910 and 20 kt between 1910 and 1917) [14]. Meanwhile, in 1876, the “Compagnie Franҫaise des Mines du Laurium” was founded, and new facilities were built at “Cyprianos” site (Figure 1B) to host the ore-beneficiation plants of reductive roasting and smelting [48]. The company constructed a new type of furnace (“Water Jacket”) and was planning on exploiting the widely spread underground carbonate-replacement sulfide ores for Ag, Pb, Zn, and Cu [44,49,50]. Due to the gradual depletion of the carbonate-replacement ores, the company faced financial problems and was sold in 1930 to the international consortium “Penarroya”, which built the first “flotation plant” [14]. During a century of operations of the French company (1876–1977), nearly 490 kt of Pb were produced. According to Conophagos [14], the total production of Lavrion mines since 3000 B.C. and until the late 20th century A.D. was approximately 2.3 Mt of Pb and 7.8 kt of Ag. Termination of all mining activities comes during the industrial crisis of the 1970s and more specifically in 1977 due to the global drop in Zn and Pb prices, whereas ore-processing and metallurgy continued until 1989.

The result of the extensive exploitation and processing during the nearly 5000-year period of exploitation was the disposal of large quantities of mine and processing wastes in the broader Lavrion area without any environmental concern [37]. According to Kontopoulos et al. [36], the main waste types in the eastern part of the Lavrion area, where the processing facilities were built, include:

• Smelter slags disposed of close to the former smelting plants, with their total quantity estimated at 7 Mt (Figure 1B). It is worth mentioning that the largest part of the slag has been removed due to the construction of the new Lavrion port in the early 2000s,

• carbonatic tailings (light) after hydromechanical processing of carbonate ore, estimated at 5 Mt (Figure 1B), and

• sulfidic flotation tailings with a total estimated quantity of ~0.8 Mt (Figure 1B). The quantities disposed of in the southern part of Thorikos Bay reach approximately 120 kt, building a pile of waste with an average height of 3.5 m.

Consequently, the disposed wastes were susceptible to atmospheric conditions leading to their weathering and dispersal of heavy and toxic metals into the environment, thus affecting the human population, fauna, flora, and the ecosystem in general [36,37,50,51,52,53,54].

3. Methodology, Sampling, and Analytical Techniques

The flow chart of the methodology employed in this study is depicted in Figure 2. A total of 13 beach sand samples were collected from Oxygono Bay (samples OB1 to OB8; Figure 3A) and the southern part of Thorikos Bay (samples TB1 to TB5; Figure 4A) in two sampling periods (February and September 2019). The specific sites were selected because they are located very close to former processing facilities and were also used as waste disposal sites. Specifically, 2–3 kg of sample was collected from a depth of 20 cm from the surface with the use of a small shovel (Figure 3C and Figure 4C). At the lab, pebbles of lithic clasts as well as plant parts were removed by hand, and the samples were placed on aluminum plates and dried at room temperature. The dried samples were examined under the stereoscope, and the −1000 μm fraction was the most promising and was selected as the grain size threshold for mineralogical and geochemical analyses. Following, the beach sands were dry sieved at the lab of the Section of Geological Sciences, School of Mining and Metallurgical Engineering, National Technical University of Athens, and were separated into the following sieve fractions: +1000 μm, −1000 + 250 μm, and −250 μm. The fraction −250 μm was further ground with agate mortar for XRD and geochemical analyses, whereas the −1000 + 250 μm fraction was used for thin section and polished block preparation for mineralogical and mineral-chemistry analyses (Figure 2).

For Thorikos Bay, an additional sample of approximately 50 kg (from various sites of 50 cm depth) was also collected for grain size distribution and pre-enrichment analyses to define the heterogeneity of the material. The sample was processed in the Lab of Mineral Processing, Metallurgy and Material Processing, School of Mining and Metallurgy, National Technical University of Athens, using a Jones sampler to obtain representative sub-samples of approximately 363 g each. Following, the material was dry-sieved into the +600 μm, −600 + 300 μm, −300 + 150 μm, −150 + 75 μm, and −75 μm sieve fractions, which were further used for mineralogical and geochemical analyses. Besides the beach sand samples collected in 2019, material (with −2000 μm particle size) from seabed sediments (samples N1 to N5; Figure 3A) and the seabed core (Core 1; Figure 3A) near Oxygono coast were also used for geochemical and mineralogical analyses (Figure 2).

The grain percentage calculations were performed by point counting under the scanning electron microscope on the prepared thin sections and blocks. The selected grid (frame) was based on the average grain size and was set to 1000 μm × 1000 μm, and point counting was performed every third frame in both horizontal and vertical directions (ESM 1).

The mineralogy of the beach sands, the seabed, and the seabed core from Oxygono and Thorikos bays was examined by transmitted and reflected light optical microscopy, X-ray diffraction, and scanning electron microscopy at the Lab of the School of Mining and Metallurgy, National Technical University of Athens. X-ray diffraction involved the use of a BRUKER D8 FOCUS X-ray diffractometer with Cu(kα) radiation at 40 kV/40 mA operating conditions. Scanning electron microscopy was performed using a JEOL JSM 6380 LV scanning electron microscope combined with energy dispersive X-ray spectrometry (OXFORD ISIS Link electron microprobe) and equipped with a JEOL Analytical back-scattered electron detector. Operating conditions for the SEM were 20 kV accelerating voltage, 20 mm working distance, and 1.0 nA beam current. Counting time for each analysis was 50 s, with 15 s dead time.

The beach sands and seabed samples were commercially analyzed at ALS Laboratories, Ireland, by X-ray fluorescence following the lithium borate fusion method with the addition of strong oxidizing agents for As, Bi, Co, Cu, Mo, Pb, S, Sb, Sn, and W (ALS Code ME-XRF15c) and loss on ignition—LOI (ALS Code OA-GRA05x). The “AMIS0366”, “MP-1b”, and “SRM277” standards were employed by ALS for XRF analyses. The standard deviation (S.D.) was calculated from duplicates, and the values range between <0.1% (for Bi, Co, Cu, Mo, Sb, and W) and 0.1% (for Pb), 0.3% (for As), and 1.2% (for LOI). Moreover, the fractions deriving from Thorikos Bay (+600 μm, −600 + 300 μm, −300 + 150 μm, −150 + 75 μm, and −75 μm) were also analyzed by XRF at the labs of the School of Mining and Metallurgical Engineering, National Technical University of Athens.

4. Results

4.1. Oxygono Bay

4.1.1. Beach Sands

Field observations reveal very poor sorting of Oxygono Bay beach material, consisting predominantly of boulders—pebbles and silt-sand-sized material (Figure 3B,C). The fine-grained fraction (silt-sand) is subangular to sub-rounded, indicative of limited transportation and circulation (Figure 5, Figure 6 and Figure 7). Lithic clasts (including both carbonate and silicate clasts) predominate in Oxygono beach, followed by lower amounts of smelter slag clasts. Quartz calcite and Fe-oxides are the major phases identified (ESM 2; Figure S1), whereas other silicates and gangue (e.g., plagioclase, micas, K-feldspar, prehnite, pumpelleyite, diopside, ankerite, dolomite, and barite) are either minor or traces (Figure 8A). Pyrite is a minor phase in Oxygono Bay beach sands, and arsenopyrite, galena, sphalerite, rutile, Ti-magnetite, magnetite, and ilmenite are found as traces (Figure 9A). Besides Fe-oxides/hydroxides other secondary facies identified as traces include mimetite [Pb₅(AsO₄)₃Cl], conichalcite [CaCu(AsO₄)(OH)], beudantite [PbFe(AsO₄)(SO₄)(OH)₆], smithsonite, and cerussite (Figure 10A, Table 1) (ESM 3; Tables S1–S3, Figures S1 and S2). Noteworthy is the presence of litharge (PbO) after Pb-ore processing to produce Ag (Figure 7D and Figure 10A). The Oxygono Bay beach sands show elevated As and Pb content (approximately 1.0% and 0.5% on average, respectively); Mo reaches 1000 ppm on average, whereas Bi, Co, Cu, Sb, Zn, Sn, and W are found in contents lower than 200 ppm (Table 2).

4.1.2. Seabed Sediments–Seabed Cores

Relative to the onshore beach sands, the Oxygono Bay seabed sediments and the seabed core consist of angular to subangular material (Figure 6). As in the case of the beach sands, lithic clasts originating from the lithologies of the Lavrion broader area (marbles and schists) predominate, while smelter slag clasts (Figure 7A) are minor (Figure 8B,C). Angular quartz fragments predominate, followed by calcite and ankerite, and traces of other silicates and gangue (Figure 8B,C). Regarding primary ore phases, pyrite (occasionally with galena inclusions; Figure 7C) and arsenopyrite are minor, followed by traces of galena, sphalerite, chalcopyrite, rutile, magnetite, Ti-magnetite, and ilmenite (ESM 3; Tables S1–S3, Figures S1 and S2). Only pyrite shows signs of post-disposal weathering (Figure 7B). Traces of tungstenates [scheelite—CaWO₄, ferberite—FeWO₄ and hubnerite—MnWO₄] are detected at the 14–16 cm and 30–32 cm intervals of the seabed core (Figure 9B,C, Table 1) (ESM 4). The secondary phases identified involve goethite and hematite (ranging from major to minor), and mimetite, conichalcite, ankerite, smithsonite, and cerussite as traces (Figure 10B,C, Table 1). The lowest part of the seabed core (48–50 cm depth) is predominated by angular calcite bioclasts (percentage higher than 95% of the total material) with traces of quartz fragments and framboidal (biogenic) pyrite (Figure 8B,C and Figure 9B,C). The fine-grained fraction of Oxygono Bay seabed sediments shows relatively increased Mn, As, Pb, and Zn contents (0.53%, 075%, 0.31% and 0.75% on average, respectively), whereas they are characterized by lower Bi, Co, Cu, Mo, Sb, Sn, and W loads (Table 2).

4.2. Southern Thorikos Bay Beach Sands

The onshore beach sands of the southern part of Thorikos Bay consist of fine-grained material ranging between coarse sand and fine silt, whereas coarser material (e.g., granules, pebbles, or boulders) is absent. The grain size distribution of the Thorikos Bay beach sands reveals that the −300 + 150 μm fraction predominates over the other fractions (Table 3). At the shore, natural separation between lighter (Fe-oxides/hydroxides) and heavier (pyrite, arsenopyrite) material is observed at the surface (Figure 4B), while at the same time, pyrite banding is present at depths between 30 and 80 cm from the surface. The pyrite bands show a maximum thickness of 2 to 5 cm, separated by reddish bands composed mainly of Fe oxides and hydroxides (Figure 4C).

The Thorikos Bay beach sands are predominated by angular to subangular quartz and calcite fragments and pyrite clasts, constituting in total more than 60% of the beach sand material (Figure 5C,D, Figure 8D and Figure 9D) (ESM 2; Figure S2). Arsenopyrite (ESM 4), goethite, and hematite are minor phases, whereas other silicates (e.g., muscovite, albite, K-feldspar, and chlorite), primary ore phases (galena, sphalerite, chalcopyrite, magnetite, Ti-magnetite, and ilmenite), and secondary facies (conichalcite, ankerite, and smithsonite) are found as traces (Figure 8D, Figure 9D and Figure 10D) (ESM 3; Tables S1–S3, Figures S3 and S4).

The beach sands from Thorikos Bay are characterized by elevated heavy metal loads and relatively high LOI values (17.9% average; Table 2). The metal content of the Thorikos Bay beach sands is higher with decreasing grain size (Table 3), ranging from 2.1% for the −75 μm fraction, to almost 1.1% for the +600 μm fraction. All fractions present similar trends regarding their metal load (Figure 11).

5. Discussion

5.1. Correlation between Coastal Detritus and Ore Type

The beach sands from the southern part of Thorikos Bay are geochemically consistent and homogeneous, with poor sorting as nearly 90% of the material ranges in size between 150 and 300 μm (Table 3). The beach sands are characterized by higher As (up to 2.3 wt%), Pb, Bi, and Cu content relative to the fine-grained fraction of Oxygono Bay beach sands and seabed sediments (Table 2). The textural and mineralogical characteristics (Figure 8D, Figure 9 and Figure 10D) support the hypothesis of exploitation of a single mineralization-type, in particular the carbonate-hosted replacement type sulfide ore, with pyrite, galena, sphalerite (former P.B.G.), chalcopyrite, and arsenopyrite as major ore phases [41]. This is the most significant mineralization type in Lavrion, and its exploitation in the 19th century started only after the foundation of the “Compagnie Franҫaise des Mines du Laurium”. Additionally, the grain size, texture, and consistency in the geochemistry and mineralogy between the various fractions of Thorikos Bay beach sands (Figure 5) clearly point to ore dressing by a single processing method, and in particular flotation, with subsequent production of galena, sphalerite, and chalcopyrite concentrates (only found as traces in the beach sands). On the other hand, pyrite and arsenopyrite were not recovered and were disposed of along with gangue (carbonates, silicates, and oxides) as tailings at Thorikos shore [36]; therefore, their content in the beach sands is increased (Table 1). Based on our findings, the southern Thorikos Bay beach sands are nearly 100% composed of tailings material, and the processing activities were rather effective, as only traces of galena, sphalerite, and chalcopyrite are present. Interestingly, there is one sample (TB4) where relatively increased Mo content is detected, accompanied by slightly increased As and W (Table 2). Yet, no molybdanates or tungstenates were identified during mineralogical analyses. The observed banding of Thorikos beach sands at shore, with pyrite and Fe-oxide bands, is attributed to gravity separation of the material due to sea waving activity at very shallow depth.

The Oxygono Bay beach sands and seabed sediments are highly heterogeneous and show distinctive textural differences when compared to sands from Thorikos Bay. The material comprising Oxygono Bay may be separated into two fractions; the first one predominates (ranging between 80 and 90% of the bulk material) involving rounded to sub-rounded pebbles and boulders, whereas the second is fine-grained and comprises lithic clasts, mining, ore processing, and smelting wastes. Interestingly, despite the difference in the bulk heavy metal load (higher for Thorikos Bay), the beach sands from both locations are characterized by elevated contents of the same heavy metals (Table 2). This observation clearly points to similar ore processing and mining wastes contributing to their formation. The Oxygono Bay material is affected by various sources and anthropogenic activities, including:

• Large size material (pebbles and boulders) originating from nearby lithologies and related to natural weathering/erosion and transportation of lithic clasts to lower stratigraphic levels (rounded-subrounded material).

• Circulation and transportation of ancient and recent smelter slag material, since Oxygono Bay is very close to areas where smelter slags were disposed (e.g., Mavri paralia is largely composed of smelter slags; Figure 1B).

• Mining and ore processing wastes characterising the various ore types and processing technologies.

Based on the mineralogy and geochemistry of the Oxygono Bay beach sands and seabed sediments, processing wastes related to the carbonate-hosted sulfide (primary) and carbonate (supergene) ore are present, e.g., pyrite and arsenopyrite from the primary ore, and cerussite, smithsonite, and ankerite from the supergene ore (Figure 5A,B). Smelting wastes are also identified, including traces of litharge and smelter slag clasts (Figure 7F–H), although it is unclear whether the smelting wastes are related to ancient or recent (1860–1980) activities.

Another distinctive feature of Oxygono Bay seabed sediments is the presence of angular fragments of primary tungstenates (scheelite, ferberite, and hubnerite) at 14–16 cm and 30–32 cm intervals of the seabed core. The presence of tungstenates points to two distinctive mineralization types developed in the Lavrion area; (1) the porphyry-style Mo ± W mineralization hosted in the Plaka granodiorite with pyrite, molybdenite, chalcopyrite, pyrrhotite, and scheelite, accessory monazite-(Ce), xenotime-(Y), zircon, and rutile, and gangue quartz and sericite [34]; and (2) The Fe skarn-type mineralization in close proximity to the Plaka granodiorite with magnetite-pyrrhotite ± (pyrite-chalcopyrite) and a gangue assemblage predominated by quartz, calcite, and chlorite, where tungstenates and in particular wolframite form fine-grained crystals between magnetite and pyrrhotite grains within the massive ore. It is worth mentioning that company records also reveal processing of W-bearing ore imported from other parts of Greece (e.g., Chalkidiki) during the 1930s (personal communication). The mineralogy of Oxygono Bay seabed sediments cannot provide conclusive results on which of the ore types was exploited during the latest part of the 1900–1930 period (30–32 cm interval) and during the 1930–1980 period (14–16 cm interval) (see paragraph 5.2. for details on the periods of exploitation), as no characteristic detrital phases for each type and in particular the porphyry-style ore (e.g., molybdenite, monazite) are identified. Yet, the natural radionuclide content of the Oxygono Bay seabed, which is the highest during that period (Figure 12), clearly points to the exploitation and processing of material genetically associated with Plaka granodiorite, as granites and granodiorites are characterized by higher radioactivity relative to other rock types [56] (and references therein). Additional information regarding the plausible origin of the tungstenates in the Oxygono Bay seabed is provided by the records of the “Compagnie Francaise des Mines du Laurium”. According to these records, during the 1930s (latest part of Period III and early part of Period IV; Figure 12), the German State was focused on producing metal iron from every possible Fe source, including the low-quality Fe ores from Lavrion. In particular, the pyrrhotite-magnetite skarn mineralization of Plaka and the associated supergene Fe ore were processed, and the finer-grained phases, including tungstenates, could have been disposed of as waste.

5.2. Oxygono Bay—Periods of Exploitation

The mineralogical investigation of the 48–50 cm interval shows the absence of detritus related to mining, ore processing, and/or smelting. It is predominated by calcitic bioclasts, traces of quartz and calcite fragments, and fine-grained, authigenic framboidal pyrite indicative of microbial activity [57,58]. This observation clearly indicates that Pb–Ag production since antiquity as well as recent mining and ore processing (1860–1980) have only affected the upper 50 cm of the Oxygono Bay seabed sediments.

Following the work of Pappa et al. [20] and combining the textural, mineralogical, and geochemical results of Oxygono Bay beach sands, seabed sediment, and the seabed core, four periods of exploitation, processing, and smelting are distinguished, with a later period depicting the cessation of all exploratory and processing works (Figure 12):

Period I—1860–1875 (46–52 cm depth): This is the first period of recent exploitations focused on re-processing and smelting of ancient smelter slags and wastes (ekvolades) by “Roux-Serpieri-Fressynet C.E”; hence, the Oxygono Bay seabed is characterized by the lowest metal content when compared to the following periods. The Cu, As, and Pb contents are low, whereas only Zn and Mn show a gradual increase, possibly depicting the disposal of low-grade ore rich in Zn and Mn (secondary, carbonate Zn ores, known as “calamine”) [14]. At the same time, the natural radionuclide load is both low (4–8 Bq/kg for total ²²⁶Ra and 0–1.5 Bq y⁻¹ cm⁻² for excess ²²⁶Ra) and relatively constant on average.

Period II—1875–1900 (37.5–46 cm depth): This is the second period of recent exploitations. Relative to the first period, an increase in the heavy metal load of the seabed sediments is observed. For Zn and Mn, the increasing rate is higher relative to Period I (1860–1875), whereas for As, Cu and Pb the observed increasing rate is lower. The natural radionuclide content shows a similar trend to geochemistry and increases at a steady rate (4–10 Bq/kg for total ²²⁶Ra and 0–4 Bq y⁻¹ cm⁻² for excess ²²⁶Ra). The observed increase in the metal and radionuclide load of the Oxygono Bay seabed sediments is related to both the continuing processing and smelting of the ancient smelter slags and wastes (ekvolades) by the “Hellenic Metallurgical Company”, and the commencing of exploitation (mining, ore beneficiation, and smelting) of the underground primary sulfide and supergene carbonaceous ore by the “Compagnie Francaise des Mines du Laurium”.

Period III—1900–1930 (28–37.5 cm depth): The Zn, Cu, As, and Mn content of the seabed increases even further and at even higher rates. Only Pb shows different behavior: An increasing rate during the first decade of the 20th century (1900–1910) and a slight decrease during the next 20 years (1910–1930). Moreover, a steep increase in the natural radionuclide content is also observed (7–14 Bq/kg for total ²²⁶Ra and 1.2–4.5 Bq y⁻¹ cm⁻² for excess ²²⁶Ra) for the same period, depicting both increased Pb–Ag production and increasing quantities of mining and smelting wastes. During this period, the newly developed “Water Jacket”-type furnace was employed by the “Compagnie Franҫaise des Mines du Laurium”, thus exploitation and processing of the underground carbonate-hosted primary sulfide and supergene carbonaceous ore were taking place. Most probably, at the early stage (1900–1910), the “Water Jacket”-type furnace was still under development; therefore, the metal content of the wastes was characterized by fluctuations, and a significant part of the metal load was disposed of as waste. On the other hand, during the period between 1910 and 1930, ore beneficiation and processing were significantly improved, resulting in less Pb being disposed.

Period IV—1930–1980 (11.5–28 cm depth): The takeover of the “Compagnie Franҫaise des Mines du Laurium” by the Penarroya Consortium led to the construction of the flotation plant on the hill right above Thorikos Bay (Figure 1B). The flotation method was employed for both sulfidic (primary) and carbonaceous (secondary) ore [36], providing a rather stable and constant metal load in the seabed sediments throughout this period. The radionuclide content during this period is the highest among the 4 periods distinguished (Figure 12), with very small fluctuations (12–16 Bq/kg for total ²²⁶Ra and 3–4.7 Bq y⁻¹ cm⁻² for excess ²²⁶Ra). The high total ²²⁶Ra and excess ²²⁶Ra combined with the presence of detrital tungstenates in the 14–16 cm interval of the seabed core indicates exploitation of either the skarn-type or porphyry-type mineralization, or even both. Therefore, it is reasonable to assume that after exhausting the carbonate-hosted sulfide ore, mining continued to other, poorsulfide ores, including the Fe skarn type and possibly the porphyry-style mineralization hosted in the granodiorite intrusion. However, it is worth mentioning that in the 1950s the world-class Filoni 80 at Plaka started being mined.

Period V—1980 A.D.—to date (11.5–0 cm): The seabed metal content is stable or shows limited fluctuations (e.g., As and Zn), indicating the cessation of mining and processing activities. The radionuclide content is variable, depicting both natural and anthropogenic effects, while the bay is mostly fed by detritus from the surrounding lithologies (mainly calcitic marbles and schists).

5.3. Effect of Mining and Processing Wastes in the Lavrion Coastal Environment

The geochemical and mineralogical characteristics of the beach sands from Oxygono and Thorikos bays depict, to varying degrees, the genetic relation between the beach sands and mining and ore processing of sulfide ores. For Oxygono Bay, although the beach sands are largely composed of silicate and/or carbonate clasts (between 80 and 90% of the total material), the heavy metal load of the fine-grained fraction (Table 2) is rather elevated, and at the same time, sulfide fragments (namely pyrite and arsenopyrite) are still present. This indicates that the potential for sulfide weathering and the consequent liberation of heavy metals from the environment is possible. Moreover, the mineralogical investigation revealed that the degree of supergene alteration is rather limited, with pyrite showing a relatively low degree of alteration (Figure 8B), whereas arsenopyrite clasts tend to develop secondary arsenate rims, depicting the effect of supergene weathering. Other secondary phases identified include Fe-oxy(hydroxides) and arsenates (e.g., mimetite, conichalcite) and the texture of these clasts/fragments in the beach sands indicates that they originated from the exploited locations and were not formed in the coastal environment. The geochemistry of the fine-grained fraction of Oxygono Bay seabed sediment and beach sands shows elevated concentrations of As and Pb (up to 1.02 wt% and 0.49 wt%, respectively; Table 2), depicting the potential for As and Pb liberation with hazardous consequences to the environment. Yet, the mineralogical investigation of the seabed core revealed no significant differences in the degree of alteration with depth, indicating stable physicochemical conditions in the Oxygono Bay seabed environment.

The beach sands from the southern part of Thorikos Bay are nearly 100% composed of processing wastes, in particular flotation tailings after processing of the carbonate replacement Pb–Zn–Ag sulfide ore (Figure 6C,D). Relative to Oxygono Bay, fine-grained sulfide fragments comprise nearly 35% of the material (ESM 1), and at the same time, the beach sands are characterized by elevated As and Pb loads (up to 2.3 wt% and 0.49 wt%, respectively; Table 2). Based on the aforementioned characteristics, Thorikos Bay beach sands are considered environmentally even more hazardous relative to Oxygono Bay beach sands. Towards this direction, several studies have been performed on both the environmental characterization of these materials and the implementation of case-specific methodologies for remediation [37,51].

Our study shows the adverse effects of ancient and recent mining and ore processing activities on the subsequent assimilation of heavy metals and their carriers in the coastal environment of eastern Lavrion, with increased AMD generation potential. This is evident from recent epidemiological and clinical studies that revealed the severe effect on the health of the population as well as both flora and fauna [50,59].

6. Conclusions

Despite the proximity of Thorikos and Oxygono bays, there are significant differences in texture, mineralogy, and geochemistry of the beach sands between the two sites, depicting both different and varying evolutions in recent Lavrion mining activity.

The Oxygono Bay beach sands, seabed sediments, and seabed core are highly heterogeneous and predominated by lithic clasts of surrounding lithologies, characterized by lower heavy metal content relative to southern Thorikos Bay beach sands. The fine-grained fraction is also highly variable in both mineralogy and geochemistry. Examination of the seabed core revealed that only the upper 50 cm of the sea floor is affected by recent and ancient mining activity, as this interval is predominated by calcitic bioclasts, quartz fragments, and traces of authigenic framboidal pyrite. The mineralogy and geochemistry of Oxygono Bay sands combined with the radiochronological model of Pappa et al. [20] revealed four distinctive periods of exploitation during recent exploitation history (mid-19th—late 20th century):

• 1860–1875 A.D. (46–52 cm depth), with primary focus on the ancient smelter slags scattered in the broader Lavrion area.

• 1875–1900 A.D. (37.5–46 cm depth), where exploitation of the ancient smelter slags continues and, at the same time, the exploitation of underground sulfide ore commences (gradual increase in radionuclide content).

• 1900–1930 A.D. (28–37.5 cm depth), where the replacement type sulfide ore was heavily mined, and production reached its peak due to the implementation of a “Water-jacket” type furnace (steep increase in radionuclide content).

• 1930–1980 A.D. (11.5–28 cm depth), where the replacement type carbonate hosted ore is nearly depleted, and the implementation of flotation-type processing assisted in the exploitation of other poor sulfide ore types, such as the skarn and porphyry type ores. The presence of tungstenates (hubnerite, scheelite, and ferberite) in the seabed material and the highest radionuclide content among all periods support this hypothesis.

Thorikos Bay beach sands are homogeneous and fine-grained, predominated by calcitic and quartz detritus and angular pyrite fragments. The mineralogy and texture of the material clearly dictate that the southern Thorikos beach sands are up to 100% tailings material originating after processing by flotation of the carbonate-hosted, replacement-type Pb–Zn–Ag sulfide ore. These flotation tailings were disposed of from the nearby flotation facilities to Thorikos Bay without any environmental concern during the 1930–1980 A.D. period.

Author Contributions

Conceptualization, S.S.T.; methodology, S.S.T., G.A. and F.K.P.; software, A.P., C.S. and N.K.; validation, S.S.T., G.A. and S.F.T.; formal analysis, S.S.T.; investigation, C.S. and N.K.; resources, F.K.P., M.F. and V.S.; data curation, S.S.T., G.A., F.K.P. and S.F.T.; writing—original draft preparation, S.S.T.; writing—review and editing, S.S.T., G.A., F.K.P., S.F.T. and M.F.; visualization, S.S.T.; supervision, S.S.T.; project administration, S.S.T. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

Data are contained within the article and supplementary materials.

Acknowledgments

The authors would like to thank anonymous reviewers for their valuable contributions during the submission process of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Footnotes

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Figures and Tables

Figure 1. (A) Simplified geological map of Lavrion area (with modifications after) [32,33,34,35]. (B) The locations and types of the mining and processing wastes dumped in the broader area of Lavrion city during the past 160 years (with modifications after) [14,36,37].

Figure 2. Flow chart of the methodology employed in the study.

Figure 3. (A) Google Earth image of Oxygono Bay with the corresponding beach sand sampling points (OB1 to OB7), seabed sediments (N1 to N5), and the seabed core (Core 1). Samples N1 to N5 and Core 1 are from Pappa et al. [20]. (B,C) Field photos of Oxygono Bay where the poor sorting is evident.

Figure 4. (A) Google Earth image of Thorikos Bay and the corresponding beach sand sampling points (TB1 to TB5). (B) Close-up photo of the beach sands at Thorikos Bay where natural, temporal enrichment is evident on the surface. (C) Banding of heavier (e.g., pyrite, brown-gold color) relative to lighter (mainly Fe-oxides/hydroxides, orange-red color) material is also present with depth.

Figure 5. Backscattered electron images of the beach sands from Oxygono and Thorikos bays (−1000 μm + 250 μm fraction). The angular-subangular shape of the clasts is evident. (A,B) Beach sands from Oxygono Bay with Fe-oxides/hydroxides (Fe-ox) and lithic fragments, including carbonate (crb-clast) and silicate (Si-clast) clasts, predominating. (C,D) Beach sands from southern Thorikos Bay, where the abundance of angular pyrite crystal fragments is pronounced. Abbreviations after [55]: Ab: albite, Ank: ankerite, Cal: calcite, Cer: cerussite, Dol: dolomite, Gn: galena, Kfs: K-feldspar, Mgs: magnesite, Qz: quartz, Prh: prehnite, Py: pyrite, Rt: rutile, Smt: smithsonite, Sp: sphalerite, Cnh: conichalcite, Ti-mag: Ti-magnetite, Fe-ox: Fe oxides/hydroxides, Mg-As: Mg-arsenate, Crb clast: carbonate clast, Si clast: silicate clast, Fe-ox clast: Fe oxides/hydroxides clast.

Figure 6. Backscattered electron images of Oxygono Bay heavy mineral phases from the seabed core collected a few tens of meters from the shore (images A–E) and the beach sands (images F–H). (A) Arsenopyrite (Apy) and pyrite (Py) angular fragments (0–2 cm depth from seabed surface). (B) Mimetite (Mim) subangular fragment (14–16 cm depth from seabed surface). (C) Barite (Brt) and scheelite (Sch) angular-subangular fragments (14–16 cm depth from seabed surface). (D) Wolframite (Wlf) subangular fragment (14–16 cm depth from seabed surface). (E) Scheelite (Sch) subangular fragment (30–32 cm depth from seabed surface). (F) Subangular litharge (Ltr) fragment, Ti-magnetite (Ti-mag) and Fe-oxide/hydroxides (Fe-ox) from Oxygono Bay beach sand (sample OB6). (G) Angular-subangular barite (Brt), subangular secondary phases clast with Fe-oxides/hydroxides (Fe-ox), conichalcite (Cnh) and beudantite (Beu) from Oxygono Bay beach sand (sample OB6). (H) Mimetite (Mim) subangular clast, Ti-magnetite (Ti-mag) and slag fragment from Oxygono Bay beach sand (sample OB6). Abbreviations after [55]: Ank: ankerite, Apy: arsenopyrite, Beu: beudantite, Brt: barite, Cal: calcite, Cnh: conichalcite, Ltr: litharge, Mim: mimetite, Qz: quartz, Pmp: pumpelleyite, Py: pyrite, Ti-mag: Ti-magnetite, Fe-ox: Fe oxides/hydroxides, Sch: scheelite, Wlf: wolframite, Carb clast: carbonate clast, Si clast: silicate clast, Fe-ox clast: Fe oxides/hydroxides clast.

Figure 7. Backscattered electron images of processing and smelting wastes from Oxygono Bay seabed and beach sands. (A) Slag fragment from the surface of the seabed sediment (Core 1, 0–2 cm interval). (B) Pyrite (Py) angular fragments showing signs of post-disposal weathering, whereas arsenopyrite (Apy) fragment remains fresh. The pyrite fragments are weathered to an unidentified secondary Fe–Ca–Pb–As phase (Core 1, 14–16 cm interval). (C) Galena (Gn) inclusions in pyrite (Py) fragment, indication of poor ore processing (Core 1, 30–32 cm interval). (D) Litharge (Ltr) fragment weathered to cerussite (cer) after disposal (sample OB6). Abbreviations after [55]: Apy: arsenopyrite, Cal: calcite, Brt: barite, Gn: galena, Ltr: litharge, Qz: quartz.

Figure 8. Histograms with standard error bars of gangue phases, lithic, smelter clasts and bioclasts of Oxygono bay beach sands (a), Oxygono bay seabed sediment (b), Oxygono bay seabed core (c) and Thorikos bay beach sands (d). The percentage of the corresponding fraction relative to total fine-grained material examined is also given. Results after scanning electron microscopy point counting.

Figure 9. Histograms with standard error bars of ore and metal-bearing phases of Oxygono bay beach sands (a), Oxygono bay seabed sediment (b), Oxygono bay seabed core (c) and Thorikos bay beach sands (d). The percentage of the corresponding fraction relative to total fine-grained material examined is also given. Results after scanning electron microscopy point counting.

Figure 10. Histograms with standard error bars of secondary (detrital) and post-secondary (in situ) phases of Oxygono bay beach sands (a), Oxygono bay seabed sediment (b), Oxygono bay seabed core (c), and Thorikos bay beach sands (d). The percentage of the corresponding fraction relative to total fine-grained material examined is also given. Results after scanning electron microscopy point counting.

Figure 11. Metal load trend (in ppm) of the various pre-enrichment fractions of southern Thorikos Bay beach sands.

Figure 12. Correlation of the temporal model of Pappa et al. [20] relative to the ore type exploited and the processing technology involved for Oxygono Bay. The226Ra concentration of the seabed sediments is also depicted (black line: total 226Ra concentration, red dashed line: excess 226Ra concentration). Period 1860–1875 (blue color, depth 46–52 cm): Exploitation of ancient, abandoned smelter slags after production of Ag and Pb. Period 1875–1900 (purple color, 37.5–46 cm): First attempts of primary sulfide ore exploitation (carbonate hosted massive sulfides). Period 1900–1930 (red color, depth 28–37.5 cm): The heavy metal content of the seabed core gradually increases (particularly Zn and Mn). Period 1930–1980 (green color, depth 11.5–28 cm): Stable metal content of the seabed during this period 1980–2014 (yellow color, depth 0–11.5 cm): The metal content is rather stable, whereas only As and Zn show a relative decreasing trend. With modifications after [20].

Table 1

Representative SEM-EDS analyses of heavy mineral phases identified in Oxygono Bay (results in wt%).

Location	Mineral	Na2O	CaO	CuO	PbO	CdO	MnO	FeO	As2O5	P2O5	SO3	WO3	Total
Core 1 14–16 cm depth	Scheelite	n.d.	19.4	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	80.31	99.65
Core 1 14–16 cm depth	Hubnerite	n.d.	n.d.	n.d.	n.d.	n.d.	21.39	0.77	n.d.	n.d.	n.d.	77.01	99.17
Core 1 30–32 cm depth	Scheelite	n.d.	17.67	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	81.47	99.14
Core 1 14–16 cm depth	Scheelite	n.d.	18.67	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	81.87	100.54
Core 1 14–16 cm depth	Ferberite	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	22.29	n.d.	n.d.	n.d.	78.60	100.89
Core 1 30–32 cm depth	Ferberite	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	22.29	n.d.	n.d.	n.d.	77.08	99.37
Core 1 14–16 cm depth	Scheelite	n.d.	18.90	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	82.35	101.25
OB 6	Beudantite	n.d.	n.d.	n.d.	34.81	n.d.	n.d.	35.18	15.44	n.d.	8.51	n.d.	93.94
OB 6	Beudantite	1.62	6.21	n.d.	34.96	2.61	n.d.	36.57	13.39	1.97	n.d.	n.d.	97.33
OB 6	Conichalcite	n.d.	23.48	30.02	n.d.	n.d.	n.d.	n.d.	43.40	n.d.	n.d.	n.d.	96.90
OB 6	Conichalcite	n.d.	21.64	34.88	n.d.	n.d.	n.d.	n.d.	.	1.09	n.d.	n.d.	97.10
Core 1 14–16 cm depth	Mimetite	n.d.	3.88	n.d.	69.22	n.d.	n.d.	n.d.	23.54	n.d.	n.d.	n.d.	96.64
Core 1 30–32 cm depth	Mimetite	n.d.	n.d.	n.d.	72.56	n.d.	n.d.	n.d.	23.22	n.d.	n.d.	n.d.	95.78
Core 1 30–32 cm depth	Mimetite	n.d.	n.d.	n.d.	72.36	n.d.	n.d.	n.d.	24.08	n.d.	n.d.	n.d.	96.44

n.d.: not detected.

Table 2

Representative XRF analyses of the fine-grained fraction of beach sands and seabed sediments from Oxygono Bay and bulk material from Thorikos Bay beach sands (results in wt%).

Sample	Fe *	As	Mn *	Bi	Co	Cu	Mo	Pb	Sb	Zn *	Sn	WO3	LOI
Oxygono Bay, N1	1.27	0.55	0.93	b.d.l.	b.d.l.	0.02	0.03	0.26	b.d.l.	0.72	0.02	b.d.l.	11.30
Oxygono Bay, N2	1.24	0.58	0.75	b.d.l.	b.d.l.	0.01	0.03	0.32	b.d.l.	0.74	0.02	b.d.l.	14.77
Oxygono Bay, N3	0.78	0.26	0.42	b.d.l.	b.d.l.	0.01	b.d.l	0.32	b.d.l.	0.57	0.01	b.d.l.	23.36
Oxygono Bay, N4	0.8	0.26	0.5	b.d.l.	b.d.l.	0.01	b.d.l	0.23	b.d.l.	0.49	0.01	b.d.l.	15.12
Oxygono Bay, N5	2.06	1.00	1.13	b.d.l.	0.01	0.02	0.07	0.41	b.d.l.	1.25	0.02	0.01	11.12
Oxygono Bay, OB4	n.a.	1.02	n.a.	0.01	0.01	0.02	0.09	0.49	b.d.l.	n.a.	0.02	0.01	12.75
Thorikos Bay, TB4	n.a.	2.30	n.a.	0.02	0.01	0.04	0.16	0.49	0.01	n.a.	0.01	0.02	23.36
Thorikos Bay, TB5	n.a.	0.60	n.a.	b.d.l.	b.d.l.	0.05	0.05	0.49	b.d.l.	n.a.	0.02	0.01	12.43
Standard deviation (S.D.):	-	0.3%	-	<0.1%	<0.1%	<0.1%	<0.1%	0.1%	<0.1%	-	<0.1%	<0.1%	1.2%

* Data from [20] Pappa et al., 2018. Detection limits: Bi < 0.01 wt%; Co < 0.01 wt%; Mo < 0.01 wt%; Sb < 0.01 wt%; WO₃ < 0.01 wt%. LOI: loss on ignition.

Table 3

Geochemistry and grain size distribution (538.1 g total mass) of the pre-enrichment fractions from Thorikos Bay beach sands (major elements in wt%, all other elements in ppm).

			Fraction
	−75 μm	+150 − 75 μm	−300 + 150 μm	−600 + 300 μm	+600 μm
Major elements
Si	3.59	8.5	7.26	6.08	3.38
Al	1.29	2.66	2.51	2.24	1.65
Mg	0.74	1.6	1.58	1.37	1.81
K	0.48	0.52	0.57	0.56	0.31
Ca	12.3	11.59	16.78	16.11	17.26
Fe	31.03	22.62	10.6	8.33	10.18
S	9.8	8.83	4.32	4.25	11.46
Trace elements
As	>0.5	>0.5	>0.5	>0.5	>0.5
Ti	392	1143	1251	986	536
V	90	b.d.l.	54	44	19.1
Cr	32.8	104.2	106	237	118
Co	723	452	267	170	195
Ni	b.d.l.	12.1	22.6	23.7	34.8
Cu	552	288.1	245.4	212.9	151.2
Zn	11,490	10,390	11,520	9126	7884
Br	88	17.2	8	10.4	14.7
Rb	b.d.l.	18.3	28.5	28.8	17.7
Sr	76.3	47.9	76.3	83.1	145.1
Y	b.d.l.	24.4	b.d.l.	b.d.l.	15.2
Ag	9.6	5.1	6.9	5.2	b.d.l.
Cd	13.5	32.8	42.5	29.6	24.7
Sb	273	95.2	74.9	66.7	70.9
Ba	233	296	160	178	238
Hg	b.d.l.	14	10.1	3.1	16.5
Pb	7978	3910	2737	2568	2607
Mass (g)	1.7	1.5	324.9	27.9	2.1
% total mass	0.47	0.42	90.73	7.79	0.59

b.d.l.: below detection limit. Ga, Ge, Se, Mo, Sn, Te, W, Tl, Bi, Th, U below detection limit. Detection limits: Ga: 12 ppm; Ge: 8.1 ppm; Se: 6.2 ppm; Mo: 46 ppm; Sn: 6.7 ppm; Te: 12 ppm; W: 56 ppm; Tl: 53 ppm; Bi: 47 ppm; Th: 14 ppm; U: 4.2 ppm; V: 18 ppm; Ni: 12 ppm; Rb: 2.1 ppm; Y: 5.8 ppm; Ag: 3.6 ppm; Hg: 1.4 ppm.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min14010033/s1, Supplementary S1 (ESM 1): SEM point counting data for samples analyzed; Supplementary S2 (ESM 2): SEM mapping of Thorikos and Oxygono bays beach sands; Supplementary S3 (ESM 3): Semiquantitative mineralogical analyses and representative XRD patterns from Thorikos and Oxygono bay beach sands; Supplementary S4 (ESM 4): Representative SEM-EDS analyses of detrital phases from Oxygono Bay seabed core and Thorikos beach sands.

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