Review of the Exploration Potential of the Estonian …...Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit KINNITATUD Eesti Geoloogiateenistuse

Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite)

Deposit

RAKVERE 2018

Cover photo: The Uuga cliff at the Pakri cape is one of the best black shale exposures (a distinctive dark brown unit near the cliff wall base) in Estonia. Photo: H. Bauert.

Recommended citation style: Vind, J., 2018. Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit. Geological Survey of Estonia, Rakvere.

Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit

KINNITATUDEesti Geoloogiateenistuse

Teadusnõukogu otsusega nr 19-3

Töögrupi juht: Johannes VindEesti Geoloogiateenistuse direktor: Alvar Soesoo


Graptoliitargilliidi uurituse ülevaade maagiotsingute potentsiaali hindamise seisukohalt

Uurimistöö aruanne

RAKVERE 2018

Geological Survey of Estonia / Research Report EGF-8995

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Contents

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2. Introduction and Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1. Scope of Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2. Principal Sources of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3. Qualifications,ExperienceandIndependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3. Description and Location of Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4. Physiography, Accessibility, Infrastructure, Local Resources and Climate . . . . . . . . . . . . . . . . . . . . 12

4.1. Physiography and Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.2. Infrastructure and Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.3. Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5. Mining and Production History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6. Geological Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1. Overview of the Estonian Black Shale (graptolitic argillite) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.2. Organic Carbon and Metals Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

7. Deposit Type and Exploration Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8. Black Shale Exploration in Estonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

9. Mineralisation of the Black Shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

10. Results of Previous Drillings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

10.1. Data Integrity and Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

10.2. Uranium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

10.3. Vanadium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

10.4. Lead and Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

10.5. Molybdenum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

10.6. Precious and Rare Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

10.7. Condition and Availability of Drill Cores for Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

10.8. Target Area Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

11. Mineral Processing Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

12. Environmental Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

12.1. Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

12.2. Regional Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

13. Marketing Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

14. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

15. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

16. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52


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List of Tables

Table 1. Basic facts of the Estonian black shale deposit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table 2. Mineral and grain-size composition of the crystalline fraction of Dictyonema argillite (Petersell, 1997). . 17

Table 3. Comparison of the metal grades in different black shale (or schist) deposits. . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 4. “Order of magnitude” reserves of some metallic oxides in the black shale deposit. . . . . . . . . . . . . . . . . . . . . 24

Table 5. Concentrations of Cu, Pb, Zn, Mo and U in samples of black shale and associated sandstones from Kärdlaimpactstructurearea(K-prefixcores)andNWmainland(F-prefixcores).“Avg”denotestheaverage concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Table 6. Target area scenarios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Table 7. Recoveries of U, Mo, and V leaching in various media and conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

List of Figures

Figure1. GeologicalbedrockmapofEstoniaandageologicalcrosssection(modifiedafter:InstituteofGeology,Tallinn University of Technology, 2011). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 2. Probable distribution of black shales in Baltoscandia. E – Estonia, R – Russia, F – Fasta Åland, St – Stepeniokk, N – Nordaunevoll, O – Oslo, Ös – Östersund, Öl – Öland, Sk – Skåne, Bo – Bornholm (Hade, 2014). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 3. Thickness (colour scale) and depth (isobath contours) of the Estonian black shale deposit. The northern border of the occurrence area can be considered as a 0-isobath. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 4. Lithostratigraphy of the black shale (denoted as “Türisalu formation”, black colour). After (Heinsalu et al., 2003; Hints et al., 2014a). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure5. UraniumdepositsdefinedinEasternEstoniainthe1940-s(accordingtothedataoftheBalticexpedition).1—clays,siltstones,conglomerates(РR2);2—clays,siltstones,sandstones(Cm1);3—blackshale(O2-3), 4 — limestones, dolomites, marls (O2-3), 5 — sandstones, clays, dolomites (D2), 6 — uranium deposits. . . . 20

Figure6. Crosssectionofthedepositdefinedinthe1940-sinSillamäe(accordingtothedataoftheBalticexpedi-tion). 1 — Quaternary deposits — sand, sandy loam; 2–5 — Ordovician strata: 2 — limestones with inter-layers of sandy limestones, 3 — sandstones and clays with glauconite, 4 — black shale, 5 — shelly (Obolus) sandstones; 6 — exploratory wells; 7 — parameters of uranium mineralization: in the numerator — thick-ness of the ore layer (m), in the denominator — the uranium content (%). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 7. Position of the black shale occurrence area in Estonia with geochemical (sub)zones and geochemi-calprofilesshowninparagraph10.2.AbbreviationsintheLocationMapinupperleftare:SW—Swe-den, FI — FINLAND, RU — Russia and PL — Poland; green square indicates the location of Estonia (EE). GeochemicalprofilesaregiveninFigure13toFigure16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 8. Drill core and outcrop locations. “Modern” data are denoted with a star and the rest are categorised as “historical” data. DB stands for “database”, indicating the data that are currently digitally . . . . . . . . . . . . . 23

Figure 9. Distribution of V, U, Pb and Mo by geochemical zones, represented by box-and-whisker plots. Based on “Historical dataset”. Please refer to Glossary of Terms (Appendix 1) for the explanation of the plot types. 24

Figure 10. Comparison of quantitative wet chemical analysis and semiquantitative spectral analysis of V. Practically all the historical dataset is based on the semiquantitative spectral analysis. . . . . . . . . . . . . . . . 25

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Figure 11. Comparison of the semiquantitative analyses of U, Mo, Pb and Zn with quantitative control analyses. For U, Pb and Zn, the control method is wet chemical analysis and for Mo it is XRF. . . . . . . . . . . . . . . . . . . . 26

Figure 12. Borehole average concentration models depicting the distribution of V, U, Zn and Mo (Soesoo and Hade, 2014).NotethatthelateraldistributionofZnhassomesignificantartefactsduetothesmallnumbersofZn values available for modelling, especially in the westernmost and easternmost areas. . . . . . . . . . . . . . . 27

Figure13. West-easterlygeochemicalprofilesinWesternEstonia,1stgeochemicalzone.Theinterpolationmethod usedisKriging.LocationoftheprofilesisshowninFigure7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure14. North-southerlyprofilesinWesternEstonia,1stgeochemicalzone.TheinterpolationmethodusedisKriging.LocationoftheprofilesisshowninFigure7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure15. West-easterlygeochemicalprofilesinToolsearea,3rdgeochemicalzone.Theinterpolationmethodused isKriging.LocationoftheprofilesisshowninFigure7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure16. North-southerlygeochemicalprofilesinToolsearea,3rdgeochemicalzone.TheinterpolationmethodusedisKriging.LocationoftheprofilesisshowninFigure7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 17. The indicative “order of magnitude” reserves of U, Zn and Mo in the Estonian black shale deposit, values are given in tonnes per 400x400 m unit cell (Hade and Soesoo, 2014). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 18. Distribution of “historical” V values plotted on histogram, Tukey boxplot, as Empirical Cumula-tive Distribution Function and Cumulative Percentage Probability Plot. Please refer to Glossary of Terms (Appendix 1) for the explanation of the plot types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 19. Distribution of “modern” V values plotted on histogram, Tukey boxplot, as Empirical Cumulative Distribution Function and Cumulative Percentage Probability Plot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure20. GeochemicalprofileoftheblackshaleatSakaoutcropthatpossessesthehighestaverageV concentration — 1190 mg/kg V or 0,212 wt% V2O5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 21. The indicative “order of magnitude” reserves of V in the Estonian black shale deposit. Values are given in tonnes per 400x400 m unit cell. Calculated with the parameters and V average concentrations map (Figure 12) given in (Hade and Soesoo, 2014). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 22. Distribution of “historical” Pb values plotted on histogram, Tukey boxplot, as Empirical Cumulative Distribution Function and Cumulative Percentage Probability Plot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 23. Histograms of Au, Ag, Pt and Re distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 24. An example of an existing half-core-sampled black shale sequence from the borehole F330. . . . . . . . . . . 38

Figure 25. A target area scenario in the north-west Estonia where the thickness and potential reserves of the black shale are the highest. The two considered sub-scenarios are drawn with solid outline (3 Mt of black shale per year) and dashed outline (6 Mt per year). Discussed in and drawn after Kulli et al. 2016. . . . . . . . . . . . . 39

Figure26. DrillcoreaverageVconcentrations(“historic”data)intheeasternfieldofphosphoritedeposits (Toolse, Aseri and Rakvere). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 27. Geological cross-section of the Toolse phosphorite deposit area (Adamson et al., 1997). . . . . . . . . . . . . . . 40

Figure 28. Recoveries (%) of some of the metals in the bioleaching technology (Sipp Kulli et al., 2016). . . . . . . . . . . . . 44

Figure 29. An approximate value distribution of the main metallic components within the Estonian black shale deposit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

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1. SummaryThis report reviews the exploration potential of the Estonian black shale, known locally as “graptolitic argillite” or “dictyonema shale/argillite”. The assignment was initiated by Geological Survey of Estonia tofulfilthetasksoutlinedinthenationalstrategicdocument“General principles of Earth’s crust policy until 2050” (Ministry of the Environment, Republic of Estonia, 2017).

The existing exploration data points out that the Estonian black shale deposit represents an impor-tant future resource for several commodity metals (vanadium — V, uranium — U, molybdenum — Mo, lead — Pb, zinc — Zn) with additional value from the organic component. From a geological and explo-ration perspective, the follow-up investigations should be relatively easy to perform. The black shale deposit has a simple geometry and it is buried under a shallow cover. Based on a review of existing information, the established metal occurrence patterns make it easy to target prospective areas for further exploration.

Standard-compliant resource estimates are not feasible to be calculated based on existing data. How-ever,thereservesbasedonpreliminarycalculationsaresignificant,forexample19,2megatonnesforMoO3, 6,7 megatonnes for U3O8 and 88,0 megatonnes for V2O5.

Further research is required to develop methods of extracting valuable compounds with maximum recoveryfactorwhilecausingminimalenvironmentalimpact.Currently,thereisnodefinedup-to-dateextraction technology available and the adaptation of existing methods has either not been trialled or been tested only in lab scale.

Due to the fact that the black shale directly overlies the Kallavere formation, which contains phosphorite deposits (Obolus sandstone), the minerals contained in the shale have potential as a valuable by-prod-uct for phosphorus producers.

Tags: geochemical research, graptolite argillite, Dictyonema Shale, black shale

1. KokkuvõteKäesolev aruanne on kokkuvõtlik graptoliitargilliidi (ingl harilikult black shale) uurituse ülevaade, mis pöörab tähelepanu eelkõige maagiotsingute potentsiaali hindamisele. Ülesandepüstitus lähtub Riigikogu otsusest Maapõuepoliitika põhialused aastani 2050 (Keskkonnaministeerium, Eesti Vabariik, 2017).

Olemasolev andmestik viitab, et graptoliitargilliit kujutab endast mitmete metallide (nt vanaadium, uraan, molübdeen, tsink) kõrgenenud sisalduste tõttu olulist väärtust potentsiaalse maavarana. Täien-dav väärtus seisneb kivimi orgaanikasisalduses.

Rahvusvahelistele standarditele vastavat varude hinnangut pole olemasoleva andmestiku põhjal võima-lik koostada, kuid varude ligikaudsed mahud on märkimisväärsed: 19,2 miljonit tonni MoO3-e, 6,7 mil-jonit tonni U3O8 ja 88,0 miljonit tonni V2O5. Üks olulisemaid piiranguid ressursi kasutuselevõtul on hetkel töötlemistehnoloogia puudumine. Asjaolu, et paljudes piirkondades lasub graptoliitargilliit fosforiidi-lasundi peal, võib aga luua võimalusi nende materjalide ühtseks kasutamiseks.

Märksõnad: geokeemilised uuringud, graptoliitargilliit, diktüoneemakilt

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2. Introduction and Purpose

2.1. Scope of Work

The purpose of this report is to review the mineral occurrence properties throughout the whole Estonian black shale deposit for the purposes of mineral exploration. Possible exploration target areas are analysed using different scenarios or strategies.

The compilation of this report was initiated by Geological Survey of Estonia (GSE) and its purpose is to: 1) provide concentrated information about the deposit for internal use, 2) provide information on the exploration (and exploitation) potential of the resource to the Government of Estonia as well as to interested third parties. By compiling the report, GSE follows the path envisioned in “General princi-ples of Earth’s crust policy until 2050” (Ministry of the Environment, Republic of Estonia, 2017).

2.2. Principal Sources of InformationThe primary sources of information are the reports compiled by the Geological Survey of Esto-nia and its predecessor institutions (see: https://www.egt.ee/et/ajaloost) throughout the his-tory of black shale studies in Estonia. The reports are stored in the Geological Report Archive (https://www.egt.ee/et/struktuur-kontakt/geoloogiafond) located in Tallinn, Estonia. Most of the reports are in Russian and are stored as hard copies and to this date a small portion of the reports have been scanned. The reports cover a period between the years 1950 and 1991 when continu-ous research was taking place. Reports drafted prior to 1950 were not archived since that was a periodwhentheinformationregardingthemineralisationofuraniumwashighlyclassified.

A mineral occurrence map for the black shale deposit was published in 2008. The map was based onadigitaliseddataset,whichcontainedaverageconcentrationsoffivemetalsfrom468bore-holes (Niin et al., 2008). Other academic studies conducted in recent years have relied on the same dataset (Hade, 2014; Hade et al., 2017; Hade and Soesoo, 2014; Soesoo and Hade, 2014). There are at least 99 reports in the Geological Report Archive that concern various aspects of black shale deposit or its processing (geochemistry/exploration, environmental impact, process-ing). Some of these reports are referred to by their codes, which consist of the letters “EGF” fol-lowed by four digits. The list of reports also includes topics that are not directly relevant to black shale (e.g. geological mapping, groundwater, other mineral resources such as phosphorite or oil shale) but still contain geological and geochemical data of the black shale deposit. In fact, much of the black shale’s geochemical data has been sourced along with the exploration of phos-phorite (Obolus sandstone), which underlies the black shale in Estonia.

The literature review also included more recent academic papers and reports concerning geo-chemistry and, to a lesser extent, the environmental concerns around Estonian black shale (Hade and Soesoo, 2014; Hints et al., 2014b, 2014a; Jüriado et al., 2012; Kiipli et al., 2000; Lippmaa et al., 2011; Lippmaa and Maremae, 2000; Loog et al., 2001; Loog and Petersell, 1995, 1994; Soesoo and Hade, 2014; Tarros, 2013; Voolma et al., 2013). While the more recent studies use data from a very limited number of samples and sampling sites, the collected geochemical variables are much more diverse compared to the historical ones. Samples were collected from outcrops, new drill

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cores (two on Suur-Pakri island — SP2 & SP3), as well as from a few re-sampled old drill cores. The data from the samples was obtained by techniques recognized in modern day exploration (ICP-MS/OES, WD-XRF, AAS). The collected data from a total of 503 samples was compiled into a dataset which is referred to in this report as “modern dataset”.

Much of the previously collected exploration data (from a total of 3576 samples) was digitalised in order to complete this report. That process included scanning data tables from reports to a pdf format, after which they were digitized by Optical Character Recognition (ABBYY Fine Reader 14), andthensubsequentlyverified.Thisdatasetisreferredtoas“historicaldataset”inthisreport.Due to the different methods and technologies used to gather data for these datasets, they are reviewed separately. In the context of this report, “historical data” was collected prior to the year 1990 and “modern data” after that.

Drill cores were inspected at the core storage centre (Arbavere, Lääne-Virumaa) of Geological Survey of Estonia. The digital drill core database (https://geoportaal.maaamet.ee/est/And-med-ja-kaardid/Geoloogilised-andmed/Puursudamikud/Puursudamike-andmebaas-p382.html)wascomparedtotheactualavailabilityandconditionofthecores.Nofurtherfieldworkorsite visits were performed.

2.3. Qualifications,ExperienceandIndependenceGeological Survey of Estonia is the government institution responsible for “conducting geologi-cal research and exploration, preserving geological information in an accessible form, advising governmental agencies and informing the public on geological matters” (https://www.egt.ee/en/news/geological-survey-estonia-started-work).

Johannes Vind, leading author of present contribution, is a geologist experienced in sedimentary and igneous environments in Europe.

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3. Description and Location of Study AreaBlack shale is found under the sedimentary cover throughout northern Estonia, the western islands Hiiumaa and Vormsi and a few smaller islands. The total area covered by black shale is approximately 12210 km².

There is one active exploration licence issued for drilling three drill holes (Sõtke II puuraukude uuringuruum, no 331667) in north-eastern Estonia. The licence is held by the Geological Survey of Estonia. It is valid from 07.09.2018 until 06.09.2020. The purpose of the drilling is to collect drill cores, which provide information from the metal-rich eastern part of the deposit and to provide material for bioleaching experiments.

12


4. Physiography,Accessibility,Infrastructure,LocalResources and Climate

4.1. Physiography and AccessibilityMost of the landscape in northern Estonia is flat and low with elevation ranging between 5 to 60 meters. The landscape was shaped by continental glaciers that started retreating about 11 000 years ago, eroding much of the underlying rock. Most of the black shale occurrence area is well accessible, the exception being some of the wetlands located in the western part of the country.

4.2. Infrastructure and Land UseThe north-eastern part of the country is where most oil shale mines are located, which means it has a well-developed infrastructure for the mining industry. The landscape in north-eastern is heavily affected by mining activities. Some of the old mines have been rehabilitated, but most of the landscape affected by the mining remains in a post-mining condition.

There is a rare earth elements and rare metals (Ta, Nb) processing plant in Eastern Estonia, Silla-mäe. The plant is currently owned by Neo Performance Materials (https://www.neomaterials.com/about-neo/our-locations/). The processing facility is the successor to the Sillamäe uranium processing plant that started operating in the late 1940-s.

Due to the proximity of the sea, there are at least 4 ports that can support economic activities in Northern Estonia (Sillamäe, Tallinn, Muuga, Paldiski).

The area around the capital city of Tallinn has high population density and is focused mainly on the servicing sector.

Compared to the capital region, the north-western part of the country has a low population den-sity and rather poorly developed infrastructure.

4.3. ClimateThe climate in Estonia is moderate. The annual average precipitation is 672 mm. The winters are cold (average temperature in February is -4.5°C), but still relatively warm given its latitude (~57° – 59° N) due to the warming effect of the Gulf Stream. July is the warmest month with an average temperature of 17,4 °C (https://www.ilmateenistus.ee/kliima/kliimanormid/sade-med/?lang=en).

13


5. Mining and Production HistoryThe radioactivity of black shales (referred to as “dictyonema shale” at that time) deposited along the southerncoastoftheGulfofFinlandwasfirstreportedinearly20thcentury.Thedepositswerefirstuti-lised for industrial development in 1948. During late 1940s and early 1950s, approximately 22,5 tonnes of elemental uranium was produced for industrial use (Veski and Palu, 2003).

Due to the discovery of more uranium-rich ores in other nearby regions, the extraction of uranium from shale was discontinued in 1952.

Over the past half-century, uranium extraction from the Baltic basin has been deemed non-viable due to low metalconcentrations,lackofefficientextractiontechnologiesandrisksconcerningenvironmentalimpacts.

Between 1964 and 1991, approximately 73 million tonnes of black shale was extracted overlying unit of the phosphorite thatwas targeted for phosphate production atMaardu refinery. The black shalewas considered a waste product and it was disposed of using irresponsible methods, such as being dumped in heaps mixed with overburden or buried between limestone residues (Puura et al., 1999; Puura and Neretnieks, 2000). The irresponsible disposal practice resulted in one of Estonia’s most severe environmental damage due to the leaching of heavy metals. Dumping in heaps also resulted in the self-combustion of the black shale mainly due to the oxidation of pyrite (Jüriado et al., 2012).

14


BBedrockmap of Estonia

Tartu

Narva

Pärnu

Paide

Viljandi

RUSSIA

Tallinn

Kallaste

Võru

Valga

Lihula

Jõhvi

Kärdla

Kuressaare

LATVIA

A

SILURIAN

ORDOVICIAN

SILURIAN

EDIACARAN

CAMBRIAN

path

of t

he g

eolo

gica

l cro

ss-s

ectio

nA-

BDEVONIAN

DEVON

PROTEROZOIC

South A)

0 m100

200100

400

800

0 m100

200100

400

800

DEVONIAN SILURIANORDOVICIAN

B)

Geological cross-section

North

CRYSTALLINE BASEMENT (PROTEROZOIC)

The Tremadocian black shale (locally termed as graptolitic argillite or dictyonema shale/argil-lite) inEstoniaisanorganic-richfine-grainedsedimentaryrockwithanabundanceofcarbon,sulphur and trace metals (particularly U, V, Pb, Zn and Mo). It is a continuation of the black shale (alum shale) occurring in Southern Sweden (Figure 2), while the Cambrian to Ordovician black shales extend from Oslo region in Norway all the way to north-western Russia. The black shale in Estonia is unmetamorphosed and thermally immature (Kosakowski et al., 2017).

Figure 1. Geological bedrock map of Estonia and a geological cross section (modified after: Institute of Geology, Tallinn University of Technology, 2011).

6. Geological Setting

6.1. OverviewoftheEstonianBlackShale(graptoliticargillite)Estonian bedrock geology is relatively simple. The region is situated on the Southern bank of the Baltic Shield. The crystalline basement (Proterozoic) is overlain with unmetamorphosed Paleo-zoic sedimentary rocks that dip southward at a rate of about 2–4 m per kilometre (Figure 1).

15


Figure 2. Probable distribution of black shales in Baltoscandia.

E – Estonia, R – Russia, F – Fasta Åland, St – Stepeniokk, N – Nordaunevoll, O – Oslo, Ös – Östersund, Öl – Öland, Sk – Skåne, Bo – Bornholm (Hade, 2014).

The basic information on the deposit is outlined in Table 1. The data relies mainly on recently conducted GIS-based reviews (Hade, 2014; Hade and Soesoo, 2014).

The deposit has a simple monolithic sub-horizontal bedding. The deposit is thickest in West-ern mainland Estonia (up to 7 m) and it thins considerably towards the east (1–2 m), as seen in Figure 3. The strata pinches out in the southern and eastern margins of the occurrence area. The western part is stratigraphically older compared to the eastern part (Figure 4). The deposit dips southward at a rate of about 3 m per kilometre. Black shale is mainly overlain by Paleozoic sedimentary carbonate rocks. The carbonates are covered with glacial tills with variable thick-ness.

Area 12210 km²Rock volume 31,92 billion m³Mass,consideringaspecificgravityof2100kg/m³ 67 billion t

Table 1. Basic facts of the Estonian black shale deposit.

16


-50-100

-150

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-50

-100

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-250

-100

400000 450000 500000 550000 600000 650000 700000 750000

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Latvia

EstoniaRussia

Sweden

Finland

Deposit thickness(m)

0,05 - 1

1,1 - 2

2,1 - 3

3,1 - 4

4,1 - 5

5,1 - 6

6,1 - 7

7,1 - 8

Isobath of the deposit's upper surface (m)

Coordinate system: L-EST97

N

E

Figure 3. Thickness (colour scale) and depth (isobath contours) of the Estonian black shale deposit. The northern bor-der of the occurrence area can be considered as a 0-isobath.

Figure 4. Lithostratigraphy of the black shale (denoted as “Türisalu formation”, black colour). After (Heinsalu et al., 2003; Hints et al., 2014a).

SAKAPAKRI

Tremadocian

Tallinn Kunda Narva

Varangu Formation

Türisalu Formation

Kallavere Formation

Tabasalu MemberToolse Member

Suurjõgi MemberKatela Member

Orasoja Member

Rannu MemberMaardu Member

Pakerort

Varangu

Furongian

Conodont zone

Paltodus deltiferpristinus

Cordylodusangulatus

Cordylodusproavus

Litostratigraphy North EstoniaSystem Stage Regional

stage

Ordovician

Cambrian

Cordyloduslindstromi

W E

The rock exhibits mainly fine laminate bedding with minor occurrences of cross-beds. Finemm-scale quartzose silt interlayers are frequent and more abundant in the eastern part of the deposit. The layering is mainly described as a result of variations in C content. Thin cm-scale pyrite or pyritized sandstone/siltstone layers are also present, although they occur rather heter-ogeneously throughout the deposit.

Most of the rock is composed of minerals (65–75%), while the organic matter is estimated in the range of 15–20% and amorphous content is about 15%. The organic C content as well as major oxide composition is rather homogeneous throughout the deposit. Clay minerals, micas, and feldspars are the principal mineral phases found in the shale (Table 2). The occurrence of pyrite is heterogeneous, generally ranging from 2–6 wt%.

Based on previous work, the distribution of trace elements and commodity metals is extremely uneven throughout the deposit (Loog and Petersell, 1994; Pukkonen and Rammo, 1992; Voolma et al., 2013).

17


Fraction Grain-size (µm)

Content (%)

Mineral composition, %Montmoril- lonite-illite

Swelling illite, illite

Micas Chlorites Quartz Feldspars

Pelite

< 0,2 15,54 1000,2 – 0,35 0,83 93,57 1,43 2,14 2,860,35 – 0,5 1,09 92,14 5,00 2,860,5 – 0,75 1,59 93,57 2,14 4,290,75 – 1,0 2,29 84,29 7,14 8,57

1,0 – 2,0 6,0 76,43 8,00 14,142,0 – 5,0 35,95 40,71 1,43 24,29 34,295,0 – 10 16,38 19,29 0,71 35,43 43,71

Silt 10 – 100 20,33 10,29 0,57 37,86 50,14<0,2 – 100 100 15,54 24,56 5,42 0,51 22,96 30,54

Table 2. Mineral and grain-size composition of the crystalline fraction of Dictyonema argillite (Petersell, 1997).

6.2. Organic Carbon and Metals PotentialBlack shales are often thought of as a “two-fold” (future) energy source. One energy-provid-ing component is the organic content and the other is uranium. There is clear potential for multi-component extraction since the rock contains considerable concentrations of U, V, Mo, Pb, Zn, Co, Ni as well as traces of precious metals like Au and PGE.

The Estonian black shale calorific value ranges from 4.2–6.7MJ/kg (Pukkonen and Rammo,1992) and the Fischer Assay oil yield is 3–5 %.

The following is a comparison of metal concentrations in some of the most important black shale deposits that are being exploited or explored (Table 3). The summary is adapted and extended based on Sipp Kulli et al., (2016). The grades of the Estonian black shale are based on calculations of average concentrations from the “modern” dataset (504 samples), except for the organic C and Au concentrations that are reported as average values from the “historical” data.

18


Major component %

Estonia Graptolite

argillite

Alum Shale(Central Sweden,

Kyrk Tåsjö) (Bhatti, 2015)

Alum Shale(Central Sweden, Häggan) (Revee,

2018, 2017)

Kupferschiefer(Poland) (Gouin et al., 2015;Włodarczyket

al., 2015)

Talvivaara, Findland

Black schist(Loukola-Ruskeeniemi,

1992; Loukola-Rus-keeniemi and Lahtinen,

2013)

Organic C 11,83 10,77 7,98Total S 2,77 5,25 1,9–3,9 8,4Ore metal (mg/kg)U 117 160 161* 17V 1055 920 2400* 943–1084,3 570Mo 177 470 207** 168,9 45Zn 336 790 431** 26–117,6 5300Ni 154 210 316** 292,6–333,5 870–2600Cu 117 140 34 958–77 300 910–1400Pb 126 50 121,1 47As 61 160 1598 86Co 24 20 334,5–1287 93Cd 2,5 10 10Au 0,07 0,0095Re 0,159

* at 2200 mg/kg V cut-off (Revee, 2018)** at 85 mg/kg U cut-off (Revee, 2017)

Table 3. Comparison of the metal grades in different black shale (or schist) deposits.

19


7. DepositTypeandExplorationModelBlack shales are considered as low-grade metal ores rather than a hydrocarbon source. However, along with other approaches, considerable effort has been put into investigations of shale gas and oil potential of the black shales.

Important exploitable or historically exploited black shales are located in Germany/Poland (Kupfer-schiefer)(Vaughanetal.,1989;Włodarczyketal.,2015),andSweden(AlumShale)(Andersson,1985;Schovsbo, 2002). Metamorphosed black shales or black schists are exploited in Finland, Talvivaara (Sotkamo mine). The latter is a unique example, where the complex processing of Ni, Co, Cu, Zn, (Mn) and (U) is performed via the bio-heap leaching method (Pattinson et al., 2013; Riekkola-Vanhanen, 2013).

Fluctuations in metal market prices are currently restructuring the black shale exploration models. The development and demand for vanadium batteries, mainly required for storing energy in renewable source power plants, has seen a rapid increase in vanadium prices (Desjardins, 2017). In the Häggan deposit in Sweden, exploration focus has almost completely shifted from U to V in recent years, resulting in the project to now be known as the “Battery metals project”. In the Häggan deposit, a high-grade vanadium zone,startingattheupperstratum,hasbeendefinedwitha0,4wt%V2O5 cut-off scenario at 0,42 wt% average V2O5 (2352 mg/kg V). The estimated resource is 90 million tonnes of shale at this cut-off value. Different scenarios are outlined by cut-off values with the minimum being 0,1 % V2O5 (Revee, 2018).

20


8. BlackShaleExplorationinEstoniaAs mentioned in chapter 2, the original information about the early exploration in the 1940s and 50s of the Estonian black shale is missing from the Geological Report Archive of EGS. During this period, informationaboutU-containingmineralresourceswasclassifiedandthereportswerenotarchivedinEstonia.Onlysomeunofficialextracts fromthoseearly reportsareavailable thatprovideschematiccross-sections and general deposit maps (e.g. Figure 5, Figure 6).

Figure 5. Uranium deposits defined in Eastern Estonia in the 1940-s (according to the data of the Baltic expedition). 1 — clays, siltstones, conglomerates (РR2); 2 — clays, siltstones, sandstones (Cm1); 3 — black shale (O2-3), 4 — limestones, dolomites, marls (O2-3), 5 — sandstones, clays, dolomites (D2), 6 — uranium deposits.

21


In 1944, the information concerning radioactivity was checked and confirmed by geologists of theUSSR’s North-Western Geological Administration. The largest concentrations were recorded in the mid-dle part of the deposit within the northeast of Estonia and the western part of St. Petersburg (Leningrad at the time) region. Uranium concentrations varied from thousandths to a few hundredths of a percent (0,008 wt%–0,075 wt%). In addition to uranium in the shale, elevated molybdenum and vanadium con-tents were also recorded.

Since1945,theBalticexpeditionidentified14depositsoflow-gradeuraniumore—Sillamae,Toila,Aseri,Saka and others in the present-day Russian territory. The deposits were explored by boreholes along forming networks of 250x250 m and 125x125 m. Alongside uranium exploration, a black shale enrich-ment technology was developed to produce uranium concentrates from the rock.

Much of the information on the black shale deposit after the 1950s was gathered along with the explo-ration of oil shale (kukersite), phosphorite (Obolus sandstone) and during geological mapping projects. Since the exploration results were physically stored in Estonia after the 1950s, they have since been then passed over to the currently operating Geological Survey and are thus fully accessible (currently mainly as hard copies, digitalisation process is ongoing).

The exploration for phosphorite was especially intensive in the 1980s. One of the strategies for the ex-ploitation of phosphorite was for it to be mined a nd used together with the black shale, which resulted in a detailed surveying of primarily U, Mo, Pb and V distribution in the black shale. The drill cores of one of theprincipalexplorationcampaignhaveprefixes“D”andtheidentifierofthereportisEGF4359(Rammoet al., 1989). Much of the data collected for the “historical” dataset is based on this report.

Figure 6. Cross section of the deposit defined in the 1940-s in Sillamäe (according to the data of the Baltic expedition). 1 — Quaternary deposits — sand, sandy loam; 2–5 — Ordovician strata: 2 — limestones with interlayers of sandy limestones, 3 — sandstones and clays with glauconite, 4 — black shale, 5 — shelly (Obolus) sandstones; 6 — exploratory wells; 7 — parame-ters of uranium mineralization: in the numerator — thickness of the ore layer (m), in the denominator — the uranium content (%).

22


9. MineralisationoftheBlackShaleThe mineralisation of the economically important metals (U, Mo, V, Pb) is thought to be mainly syn-geneic or early diagenetic. The distribution of these metals is thought to be heterogeneous both ver-tically and laterally, although certain regularities are also evident (e.g. higher concentrations of some metals at the base of the strata).

The general understanding is that Pb, Zn, Cu, As and Ni are associated with sulphide phases (mostly pyrite) in the deposit. At times, Ni reaches very high concentrations (4000 mg/kg) in pyrite mixed with thin (< 2mm) pelitic layers (Pukkonen and Rammo, 1992). In the occurrence of high Zn concentrations (0,5–1 wt%), sphalerite presence is documented. In certain 2–3 cm silty interlayers, sphalerite presence has been estimated to reach 8–10 % of the rock mass (Petersell et al., 1991).

The concentrations of V, Mo and U are thought to be mainly associated with the organic matter. This is not a clear trend as the distribution of the metals between the carriers can be bimodal. In other words, in the case of higher concentrations, there is a tendency to prefer sulphide (or phosphate) mineralisa-tion and vice versa (except for V that does not accumulate to pyrite). The duality of the association with organic matter is referred from the statistical analysis that implies a clearer covariance with the organic materialinthecaseoflowerV,MoandUconcentrations.Thecovariancebecomeslesssignificantinthecase of higher V, Mo and U, while it remains the strongest in the case of V.

Lippmaa, 2011 states that V occurs as V porphyrine in the deposit, however the source of this informa-tion is unclear. On the other hand, in the case of Häggån “Battery metals project” that is geologically analogous, V “is present mainly in the form of V(III) hosted with the mica mineral roscoelite” (Revee, 2018). A study of the V occurrence forms at the The Mecca Quarry Shale Member from Velpen, Indiana, names authigenic illite and orgnic matter as the main carriers of V (Peacor et al., 2000). Even free oxide is reported to be an occurrence form of V in one Chinese black shale unit (Min-ting LI 2010). The “Grap-tomet 1 and 2” technology (see section 11) authors claim the decomposition of most of the organic compounds. At the same time there isn’t any indication of V release to the leachate (Figure 28) (Menert et al., 2017; Sipp Kulli et al., 2016). The latter example also emphasises the uncertainty in the knowledge of V speciation. This paper questions whether the assumption of V existing mainly in metalloporphy-rines is supported by evidence in the case of Estonian black shale?

Generally, many metals occur as metalloporphyrines in black shales (Szubert et al., 2006). In Southern Sweden, the thermally immature black shales were shown to host U in biogenic matter as well as within phosphate nodules (Lecomte et al., 2017). The association of U with P has also been implied in the case of Estonian deposit, but not as a primary one (Petersell et al., 1991; Pukkonen and Rammo, 1992). It is noted that a small fraction of U could be also associated with silicate minerals as well as a discrete uraninite phase. Currently, there is no literature on detailed mineral occurrence speciation by modern methods with regards to any commodity metal contained in black shale.

23


10. Results of Previous DrillingsThe black shale deposit can be divided into four geochemical zones, numbered 1 to 4 from west to east (Figure 7). Zones 3 and 4 are sometimes grouped together as a single zone, which would result in the definitionofWestern,MiddleandEasternzones.However,since therearedistinctdifferences in thelateral distribution of U and Mo, but also V (see Figure 12), the 4-part zonation model is considered to be more appropriate for a general description of the deposit (Figure 7). Subzone 1a refers to a region where the middle part of the strata contains elevated amount of sandy/silty intervals with concurrent elevated U and Mo concentrations, compared to the homogeneous black shale in the surrounding stra-ta.Subzone1bdenotestheregion,wheretheprofilesareenrichedinUandMothroughoutthedepositin contrast to the typical trend of downwards-enrichment. This is discussed further in sections 10.2 and 10.5 (Figure 14).

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LegendGeochemical profiles with boreholelocations

Geochemical zones (1-4)

Black shale occurrence area

Geochemical subzones


(2)(1)(3) (4)

(1a)

(1b)

E

N

RUFI

PL

SW EE

Figure 7. Position of the black shale occurrence area in Estonia with geochemical (sub)zones and geochemical profiles shown in paragraph 10.2. Abbreviations in the Location Map in upper left are: SW — Sweden, FI — FINLAND, RU — Russia and PL — Poland; green square indicates the location of Estonia (EE). Geochemical profiles are given in Figure 13 to Figure 16.

Figure 8. Drill core and outcrop locations. “Modern” data are denoted with a star and the rest are categorised as “historical” data. DB stands for “database”, indicating the data that are currently digitally

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400000 450000 500000 550000 600000 650000 700000 750000

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Latvia

EstoniaRussia

Sweden

Finland

Legend

_ Locations of cores and outcrops with "modern data"

" Drill cores with average composition collected to DB

( Drill cores with data by intervals colleted to DB


24


25

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ZoneU

(mg/

kg)

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Figure 9. Distribution of V, U, Pb and Mo by geochemical zones, represented by box-and-whisker plots. Based on “Historical dataset”. Please refer to Glossary of Terms (Appendix 1) for the explanation of the plot types.

Table 4. “Order of magnitude” reserves of some metallic oxides in the black shale deposit.

Regardless of the lateral metal grade distribution, the western part of the deposit contains the most reserves due to the greatest thickness of the deposit (5–7 m). While preliminary calculations of resourc-es can be performed, proper standard-compliant resource estimates cannot be done with the current level of available information and knowledge. To have an overview of the possible magnitude of the ton-nages, the “order of magnitude” reserves for the black shale deposit are given in Table 4:

Resource “Order of magnitude” reserve (Mt) ReferenceMoO3 19,2 (Hade and Soesoo, 2014)U3O8 6,7 (Hade and Soesoo, 2014)ZnO 20,6 (Hade and Soesoo, 2014)V2O5 88,0 Current

25


10.1. Data Integrity and QualitySampling methods have varied throughout different exploration campaigns. It is possible to identify spot sampling (thin slices extracted from the core), chip sampling or full core sampling. At the time of the conditionally termed “historical” exploration, split core sampling was not prac-ticed. Some of the samples were acquired by trenching in the frame of phosphorite exploration.

Samples for “modern” dataset have been either collected as split core samples from old drill cores and two new drill cores (Suur-Pakri 2 and 3), or from outcrops. In some instances (Loog et al., 2001), only certain sections of the core have been sampled instead of the full core.

Thus, samples in both the “historical” and “modern” dataset have a different magnitude of representativeness.

Comparison of the V analysis by two methods indicates an underestimation of the semiquanti-tative spectral V by an average of 42 % (EGF 4085). The underestimation is systematic, as seen on the plotted values in Figure 10. The likeliness of V underestimation in the “historical” dataset isalsosupportedbythe“modern”dataset.Whilethe“modern”datasethasasignificantlysmallersamplesizeaswellasgeographicalcoverage,italsohasasignificantlyhigheraverageconcen-tration value (1055 mg/kg V) than the historical dataset obtained by semiquantitative spectral analysis (average 649 mg/kg V).

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Atom absorption analysis (V mg/kg)

Figure 10. Comparison of quantitative wet chemical analysis and semiquantitative spectral analysis of V. Practically all the historical dataset is based on the semiquantitative spectral analysis.

26


Similarly, the semiquantitative analyses of U (EGF 3200) Mo and Zn (EGF 4085) that comprise majority of the “historical dataset” are systematically underestimated (Figure 11). On average, U is underestimated by 19 %, Pb by 46 %, and Zn by 75 %. The pattern is slightly different for Mo, for which the differences typically range from -24 % to +11 %, with a few samples, where the con-centration is underestimate by more than 200 %.

Since U has historically been the main focus in the exploration of black shale, its analyses have been conducted with a greater attention to detail, which is supported by the smallest differences (19 %) in the comparison. In most of the exploration reports, quality assessment of U measure-ments is included.

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Figure 11. Comparison of the semiquantitative analyses of U, Mo, Pb and Zn with quantitative control analyses. For U, Pb and Zn, the control method is wet chemical analysis and for Mo it is XRF.

The results above lead to the following conclusions:

(1) The “historical dataset” is too unreliable for making resource estimates other than “order of magnitude” type;

(2) The effect of systematic underestimation shows where true anomalies lie, i.e. the geo-chemical data can be used as relative information of mineralised rock sequences.

27


Figure 12. Borehole average concentration models depicting the distribution of V, U, Zn and Mo (Soesoo and Hade, 2014). Note that the lateral distribution of Zn has some significant artefacts due to the small numbers of Zn values available for modelling, especially in the westernmost and easternmost areas.

For gridding used method:

Kriging OrdinaryGaussian semivariogram modelSearch radius: VariableUsed number of nearest inputsample points 12.

Zn concentration (ppm)0 25 5012,5

Kilometers

Russia

U concentration (ppm)0 25 5012,5

Kilometers

Mo concentration (ppm)

Russia

0 25 5012,5Kilometers

Russia

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Russia

Estonia

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U, ppmHigh : 329

Low : 38

Zn, ppmHigh : 593

Low : 39

V, ppmHigh : 1083

Low : 482

Mo, ppmHigh : 751

Low : 71

Tallinn

10.2. UraniumThe highest average uranium concentrations are found in the eastern part of the deposit, in the 4th geochemical zone. This is also the area where black shale has historically been exploited. It is well established throughout the deposit that U is concentrated vertically towards the lower parts oftheprofiles(Figure13,Figure14).

28


Figure 13. West-easterly geochemical profiles in Western Estonia, 1st geochemical zone. The interpolation method used is Kriging. Location of the profiles is shown in Figure 7.

29


Figure 14. North-southerly profiles in Western Estonia, 1st geochemical zone. The interpolation method used is Kriging. Location of the profiles is shown in Figure 7.

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30


Geochemicaldistributionprofilesoftheavailableanalytesintheeasternpartofthedepositareshown in Figure 15 and Figure 16.

Figure 15. West-easterly geochemical profiles in Toolse area, 3rd geochemical zone. The interpolation method used is Kriging. Location of the profiles is shown in Figure 7.

020040060080010001200140016001800

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31


Figure 16. North-southerly geochemical profiles in Toolse area,3rd geochemical zone. The interpolation method used is Kriging. Location of the profiles is shown in Figure 7.

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The reserves of uranium and accompanying elements - nickel, molybdenum, vanadium, sulphur - have been calculated for the deposits explored in the 1940-s. A total of 72,0 thousand tonnes of uranium have been explored in the Baltic area in poor ores.

IntheSillamäefield,theReservesCommissionapproveduraniumreservesforcategory“B”intheamount of 5464 tonnes with an average grade of 0,026 % uranium in the ore. In addition to ura-nium, the ore contained other elements in following concentrations: Ni — 0,026%, Mo — 0,045%, V — 0,084%, S — 5,25%. In the Toila deposit, 7,0 thousand tonnes of uranium with an average content of 0,025% U in the ore was explored.

The indicative distribution of reserves of U over the extent of the total deposit is given in Figure 17 (Hade and Soesoo, 2014). The distribution of potentially available reserves per area is mainly controlled by the thickness (Figure 3) rather that the commodity metal grade of the rock (Figure 12) in the case of all presented metals.

32


Figure 17. The indicative “order of magnitude” reserves of U, Zn and Mo in the Estonian black shale deposit, values are given in tonnes per 400x400 m unit cell (Hade and Soesoo, 2014).

10.3. VanadiumLaterally, the distribution of V is perhaps the most complex, yet the concentrations are somewhat less spread than those of the U, Mo and Zn. The highest V concentration zone is in the Toolse and Sillamäe area, coinciding partly with the Toolse and Aseri phosphorite deposits.

V concentrations are populated above 1000 mg/kg in the modern dataset compared to the “his-torical” dataset, for which the main population is under 1000 mg/kg. This once again emphasizes the underestimation of V and the possibility of actual V concentrations being much higher than described in the past.

33


Figure 18. Distribution of “historical” V values plotted on histogram, Tukey boxplot, as Empirical Cumulative Distribution Function and Cumulative Percentage Probability Plot. Please refer to Glossary of Terms (Appendix 1) for the explana-tion of the plot types.

Figure 19. Distribution of “modern” V values plotted on histogram, Tukey boxplot, as Empirical Cumulative Distribution Function and Cumulative Percentage Probability Plot.

5 10 20 50 100 200 500 1000 2000

0200400600800

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Histogram

V (mg/kg)

N = 2829

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N = 2829

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34


The distribution patterns in vertical sections are uneven, sometimes indicating an increase towards lower part of the section, but there appears to be no clear trend. TheW-E profile inFigure 13 depicts the cross-over from the higher V in the western 1st geochemical zone to the middle low-enrichment level of the 2nd zone. The vertical distribution is therefore different to the onedocumentedinSweden’sHäggandeposit,wherethehighestVcontentsareidentifiedintheupper part of the stratum (Revee, 2018).

The highest “modern” V core/outcrop weighted average concentrations are recorded in Saka outcrop (0,212 wt% V2O5, Figure 20), Toolse core 811 (0,206 wt% V2O5), WE mainland cores F348 and F346 (both 0,201 wt% V2O5). The highest V2O5 values reach 0,375 wt% in “historic” and 0,378 wt% in the “modern” dataset.

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Saka outcrop

V

U

Mo

Pb Figure 20. Geochemical profile of the black shale at Saka outcrop that possesses the highest average V concentration — 1190 mg/kg V or 0,212 wt% V2O5.

The “order of magnitude” V reserves distribution over the extent of black shale occurrence area is given in Figure 21.

%

%

%%%NARVAMAARDU

KÄRDLA

TALLINN SILLAMÄE

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V mass in tonnes1850

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N

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SW EE

Figure 21. The indicative “order of magnitude” reserves of V in the Estonian black shale deposit. Values are given in tonnes per 400x400 m unit cell. Calculated with the parameters and V average concentrations map (Figure 12) given in (Hade and Soesoo, 2014).

35


10.4. Lead and ZincPb occurs in uniformly elevated concentrations (average 127 mg/kg Pb in the “historical” data) throughout the deposit and anomalous concentrations are relatively rare, yet some samples exhibit concentrations of > 500 mg/kg. The distribution of Pb in vertical sections is indifferent when comparing upper and lower parts. The Zn levels in Estonian black shale are relatively low compared to the average values seen in black shales elsewhere in the world. The lateral distri-butionofZndepictedinFigure12hassomesignificantartefactsduetothesmallnumbersofZnvalues available for modelling.

The most intense Pb-Zn mineralization is located on the NE of the external slope of the Kärdla impact structure in Hiiumaa island. In boreholes K-11, K-14 and K-15, intensive pyrite-galena- sphalerite mineralization is observed in the upper stratum of black shale (Table 5). The interbed of sapropelite-containing sandstone lying in the lower strata of the bed is cemented by pyrite, galena and sphalerite. In the lower stratum of black shale within the Obolus sandstones, mineral-ization is represented only by pyrite and sphalerite, and with lower intensity compared to the one seen in upper layers (Petersell et al., 1991).

Below the black shale near Dirhami in north-western Estonia, intensively pyritized sandstones are present with an abnormally high Pb content (up to 0.14 wt% in F334), Mo (up to 0.16 wt% in the wellFЗЗ1),andAg(upto2.3mg/kginF334)(Peterselletal.,1991).

Figure 22. Distribution of “historical” Pb values plotted on histogram, Tukey boxplot, as Empirical Cumulative Distribu-tion Function and Cumulative Percentage Probability Plot.

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36


Table 5. Concentrations of Cu, Pb, Zn, Mo and U in samples of black shale and associated sandstones from Kärdla impact structure area (K- prefix cores) and NW mainland (F- prefix cores). “Avg” denotes the average concentration.

Core

Sampling interval (m)Black shale and sandstone*

Thickness (m)

Cu (mg/kg) Pb (mg/kg) Zn (mg/kg)min avg max min avg max min avg max

K-14 96.3-97.2 0.9 52 92 104 420 2150 26500 1230 3480 12860102.3-103.1 0.8 21 71 73 57 163 230 363 1120 3800

K-15 97.6-98.8 0.8 83 94 104 180 6166 15360 1410 5234 10120103.3-103.8 0.5 52 54 65 113 132 150 300 2442 15400

F330 90.4-90.5* 0.1 110 300 40F331 52.0-53.0* 1.0 50 65 80 50 140 200 30 50F334 46.8-47.0* 0.2 300 1300 120F335 69.7-70.1 0.4 50 90 11 50F337 90.2-90.4 0.2 75 140 250

Core

Sampling interval (m)Black shale and sandstone*

Thickness (m)

Mo (mg/kg) U (mg/kg) Ni Asmin avg max min avg max

K-14 96.3-97.2 0.9 24 208 294 20 61 67102.3-103.1 0.8 2 11 12 5 9 13

K-15 97.6-98.8 0.8 80 150 239 39 51 65103.3-103.8 0.5 4 11 15 11 13 16

F330 90.4-90.5* 0.1 22 420F331 52.0-53.0* 1.0 490 870 1600 150F334 46.8-47.0* 0.2 100 1100 1100F335 69.7-70.1 0.4 250 380F337 90.2-90.4 0.2 230 150

10.5. MolybdenumMolybdenum’s lateral distribution is similar to V as the highest concentration levels are present in the 3rd geochemical zone (392 mg/kg Mo on average). Further towards the east, concentra-tions drop. Mo is vertically very distinctly partitioned. The top of the unit has Mo values around 50–100 mg/kg while the lowest part immediately close to footwall (lowest ~0,5 m) is has concen-trations of 500 mg/kg and above.

10.6. Precious and Rare MetalsIn the end of the 1980’s, a study on the content of Au and Pt in black shales was conducted by the atomic absorption method. Anomalously high contents of these elements were found in the shale samples (Au up to 0,94 mg/kg, Pt up to 1,80 mg/kg). Although the number of reliable analyses is still low (Au n = 59, Pt n = 57; earlier reports name higher number), the results indicate a high percentage of anomalous concentrations. The “modern dataset” does not include dedicated Au measurements, but along with other trace element analyses, there are 14 measurements of Au and none of them exceed 0,1 mg/kg. Preliminary correlation analysis of the elements considered

37


Figure 23. Histograms of Au, Ag, Pt and Re distribution.

withtheotheranalysedtraceelementsandorganiccontentdoesnotindicatespecificregular-ities. Studied core samples were extracted from the bottom half of the cut cores of black shale, and 4 samples were taken from Maardu quarry. A simple statistical analysis of the estimates indicates that the distribution of the contents of Au and Pt in black shales does not obey even a lognormal distribution law. It is worth to note that technological studies of black shale from MaarduquarryindicateaneasyphysicalbeneficiationofAu(Peterselletal.,1991).

During the black shale exploration, considerable attention was also given to the rare element rhenium (Re). The bulk crustal average concentration of Re in the rock is estimated at 0,19 µg/kg (Rudnick & Gao, 2003 while the maximum recorded values in existing data reach 1,33 mg/kg, indicatingsignificantconcentrationsofthisrareelement.

38


Figure 24. An example of an existing half-core-sampled black shale sequence from the borehole F330.

10.7. Condition and Availability of Drill Cores for SamplingA review from the Estonian Land Board database (https://geoportaal.maaamet.ee/est/And-med-ja-kaardid/Geoloogilised-andmed/Puursudamikud/Puursudamike-andmebaas-p382.html) and other resources revealed the possibility of 110 existing cores so there is a lack of drill cores for sampling. The ones that are stored, are mainly associated with the crystalline basement mappingandbeartheprefix“F”(Figure24).Visualinspectionrevealedthattheconditionofthecores is variable. However, there are several cores that show minimum signs of weathering/deg-radation/oxidation and therefore have potential for sampling.

The currently available cores have been drilled mainly in north-western Estonia. For the purposes of a following study, 11 cores were chosen for geochemical sampling.

Defining the actual state and availability of the drill cores must wait until the thoroughre-organising process of the drill core facilities is complete (estimated around mid-2019).

39


10.8. Target Area ScenariosThe possible scenarios can be divided mainly into two categories or approaches:

(1) choosing whether to envisage the exploitation as “independent”, i.e. only black shale would be extracted, or as complex exploitation together with phosphorite or any other potential mineral resource (e.g. limestone, glauconite sandstone);

(2) choosing an area following the highest concentration/reserve potential of a valuable compo-nent (e.g. vanadium).

An example of independent exploitation scenario is discussed in Kulli et al. 2016 in the north-west-ern part of the country, where the black shale deposit is at its thickest (Figure 25). The discussion in the report mainly addresses mining engineering related issues.

Figure 25. A target area scenario in the north-west Estonia where the thickness and potential reserves of the black shale are the highest. The two considered sub-scenarios are drawn with solid outline (3 Mt of black shale per year) and dashed outline (6 Mt per year). Discussed in and drawn after Kulli et al. 2016.

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KEILA

Turba

Rummu

Suursoo

PALDISKI

Riisipere

Pakri poolsaar

4

5

L9

L8L6L5

L4L3 L2

f4

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11

L13

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L11L10

AD1

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133

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D-57

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D-33

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D-24

D-23

D-22

D-21

D-14

D-13

D-12

D-11

D-10

F342

F341

F340

F339

F338

F337

F336

F335F334

F333

F332F331

F330

F328

F327

F326

F325

F324

F323F323

F322

F321

F320F320

F319

F318

F317

F316

F315

F314

F313

F312

F310

F306

D-192D-160

D-146

D-145

D-144

D-143

D-141

D-140

D-139

D-138

D-121D-120

D-119D-118D-117D-116D-115D-114D-113D-111D-110

D-109D-108D-107

D-106D-105D-104

F331B

D-179-I

7 Padise

480000 490000 500000 510000 520000

6550000

6560000

6570000

6580000

A target area scenario in the North-West Estonia3 Mt/y

6 Mt/y


! Drill cores with average composition collected to DB

_ Locations of cores and outcrops with "modern data"

Coordinate system: L-EST97Background topographic map: Estonian Land Board 2019

E

N

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EERU

Since in many areas the black shale directly overlies the phosphorite deposits in Estonia, co-extraction of the two resources has been widely discussed, albeit never put to practice. The most prospective phosphorite deposits coincide with the relatively high concentrations of some metals (particularly V and Mo, Figure 26), making this a strategy worth considering.

40


%

%

%JÕHVI

KUNDA

RAKVERE

AseriToolse

Rakvere Rakvere

620000 630000 640000 650000 660000 670000 680000 690000

6570000

6580000

6590000

6600000

6610000

Drill core average concentrationV (mg/kg)

190 - 480

481 - 648

649 - 821

822 - 1064

1065 - 1600

Phosphorite deposits


Estonian shoreline


E

N

EE

LV

RU

Figure 26. Drill core average V concentrations (“historic” data) in the eastern field of phosphorite deposits (Toolse, Aseri and Rakvere).

The geological cross section of the Toolse phosphorite deposit area is shown in Figure 27 (Adamson et al., 1997). The cover of phosphate rock also includes glauconite sandstone as a po-tential resource. The limestone in the area is part of the resource (Aru-Lõuna deposit) exploited by Kunda cement factory.

One potential exploration scenario is in the Sillamäe region of north-eastern Estonia, where there’s experience in industrial ex-ploitation of black shale along with high con-centrations of mineralised rocks (mainly U).

The overview of different scenarios and relat-ed properties is provided in Table 6.

Figure 27. Geological cross-section of the Toolse phosphorite deposit area (Adamson et al., 1997).

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Table 6. Target area scenarios.

Strategy/approach Area Strengths WeaknessesIndependent exploitation

NW Estonia Thick deposit (5-7m) Lower concentrations of metals

Large reserves per land area

Less developed infra-structureDense network of pro-tected areasLow altitude area with large wetlands

NE Estonia (3rd or 4th geochemical zone), e.g. Sillamäe

High concentrations of targeted metals

Thin deposit (1-2 m)

Available infrastructure and historical experi-ence

Smaller reserves per land area

Complex exploitation together with phosphorite

Toolse Available infrastructure Smaller reserves per land area

High V (+ U, Mo) zoneHigher sustainability — black shale should be excavated anyway (in case of open-pit mining)

Technologically more complex

Aseri High V (+ U, Mo) zone Thinner deposit than Toolse

Higher sustainability – black shale should be excavated anyway (in case of open-pit mining)

Rakvere Not applicable Black shale pinches out

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11. Mineral Processing ResearchBased and modified after a manuscript text by V. Petersell

Theoriginsofblackshaleprocessingweresolely related to theextractionofU.Thefirst trialsweremade hurriedly in 1944-45 concurrently with early prospecting of U resources. Several types of selec-tive leaching and extraction methods were trialled with raw as well as roasted shale. Early research was conducted only on Estonian ore, later the studies moved to other ores as well. Many institutes across the Soviet Union were participating in the development of extraction technologies. While the U extraction was generally acknowledged to be feasible, the recoveries rarely exceeded 50% and improvements were found to be arduous. Eventually this led to a conclusion of the process being uneconomic, much like in the case of Sweden’s alum shale.

In the second half of the 20th century, the processing of black shale was investigated at the Institute of Chemistry of the Academy of Sciences and at the Geological Survey of Estonia in the 1970s.

The Institute of Chemistry had started black shale’s complex processing studies already in the 60’s. As a result of various chemical experiments, researchers concluded that the elements U, V, Mo and others could be dissolved out from a slurry of ash in a concentrated sulfuric acid environment (Maremäe, 1989). Itwasassumedthatthefiringofshaleforenergeticpurposesisrealisticunderthefluidizedbedcondi-tions (~800 °C), which would also reduce the associated atmosphere contamination. The applicability of burning in the fluidized bed was already established in 1965 (Leene and Ülesoo, 1966). The results of the technological studies at the Institute of Chemistry are described in various publications (Maremäe, 1989, 1988; Maremäe and Kirret, 1989, 1990). The published works do not address the environmental problems associated with converting the material into ash in the fluidised bed. Studies conducted in the chosen direction for nearly 30 years did not yield the expected positive results. The principal investiga-tor, E. Maremäe, notes (Maremäe et al., 1991) that the main drawbacks of the technological scheme are the high concentrations of H2SO4 (400 kg per tonne of ash) and high amounts (81-84% of ash mass) of acidic, radioactive and other types of heavy metals containing waste.

Itturnedoutthattherearenoprospectsformechanicalbeneficiationmethods.Acomparisonoftheelements of ash and shale, obtained from the fluidized bed conditions for the purposes of clarifying the possibilities of black shale combustion, showed that the majority of Hg, approximately 10% of U and various amounts of other metals are volatile in the fluidized bed (Pihlak et al., 1977). Since at that time, there was no technology available for the entrapping of trace elements from combustion gases and very fineflyashdust,theapproachwasdiscontinuedduetotheassumedsignificantenvironmentalimpactand the fact that it would likely be uneconomical. Based on the information gathered, the Tallinn Depart-ment of Geological Survey investigated the possibilities of separating metals by chemical methods. The work was done from scratch to clarify the properties of metal leaching and organic matter behaviour in acidic and alkaline environments (Table 7). Coke recoveries in the same experiment series ranged from 83 – 87,5 %, while the oil recovery is highest at 7,5 % in 10 % NaOH solution (T = 370 °C; P = 250 - 300 atm; t = 4 h). Under the same conditions, U, Mo and V leaching into solution is stopped.

43


Table 7. Recoveries of U, Mo, and V leaching in various media and conditions.

Sample Media U Mo V

mg/kgRecovery

%

mg/kgRecovery

%

mg/kgRecovery

%Residue Dry residue Residue Dry

residue Residue Dry residue

Concentration in ini-tial material (mg/kg) 135 253 970

To = 20°C, P – ambient; time 4 h

D-1.1 H2O 126** 7 200 3 21 900 20 7

D-1.2 NaOH 5% 101 25 43 2140 83 831 1070 14

D-1.3 H2SO4 5% 89 34 268 90 ? 834 730 14

D-1.4 HCl 5% 94 33 210 60 17 1110 200 -

D-1.5 HNO3 5% 106 22 240 6 5 929 200 4

To = 100°C, P – ambient; time 4 h

D-1.1 H2O 111 29 18 200 15 21 1000 6 ?

D-1.2 NaOH 5% 116 29 14 23 2340 91 741 1200 24

D-1.3 H2SO4 5% 83 39 290 15 ? 834 460 14

D-1.4 HCl 5% 99 27 234 15 8 834 460 14

D-1.5 HNO3 5% 96 34 29 253 10 ? 834 400 14

T = 370°C; P = 250 - 300 atm; time = 4 h

D-1.1 H2O 131 8 3 232 0,6 7 1088 <3 ?

D-1.2 NaOH 5% 137 ? 241 3 4 750 6 23

D-1-3 H2SO4 5% 133 ? 238 0,6 5 1062 <3

Most of the elements listed in the table are determined by the semi-quantitative spectral analysis. It is notable that Mo went almost completely to solution with 5% NaOH leaching at a temperature of 100 °C (Petersell et al., 1979) and that V recovery factors remain very low under all tested conditions.

An unconventional bioleaching method is currently being developed that attempts to create both meth-ane gas as well as leach metals from the shale by disintegrating the metal porphyrins. The process takes place by utilising a selected bacterial community from the black shale itself (Menert et al., 2017; Sipp Kulli et al., 2016, 2014). The technological flowsheet is divided in two principal steps:

(1) Biogenic methane production in anaerobic atmosphere with simultaneous release of certain organic-bound metals (called the Graptomet 1);

(2) Aerobic bioleaching of sulphide-bound metals (called the Graptomet 2).

The process takes place at a temperature of 37 °C and at atmospheric pressure conditions.

44


Figure 28. Recoveries (%) of some of the metals in the bioleaching technology (Sipp Kulli et al., 2016).

Therewasapatent (WO2017140324A1)filed for this technology in2016 (Menertetal.,2017).To theauthors’ knowledge, no technological upscaling tests have been completed but the work is ongoing.

Theefficiencyoftheproductionofmethanecanberegardedbeinghigh,withamaximumproductionof14,5 l of methane per 1 kg of shale. The bioleaching of metals is still in development, progress so far has yielded relatively low recoveries (Figure 28).

45


12.EnvironmentalConsiderationsBlack shale is a natural source of radiation and an emitter of radon (Rn) since it contains uranium and potassium. In areas near black shale outcrops and shallow occurrences, Rn emission is being moni-tored from a public health point of view (Petersell et al., 2017; Petersell and Åkerblom, 2005). Because of naturally occurring processes, heavy and other potentially harmful elements can be released to soil, ground water etc. (Hade et al., 2017).

Black shale, due to its sulphide content (mainly pyrite) is susceptible to oxidation in aerated conditions. Oxidation of the shale can release heavy elements to the environment as potential pollutants. The pos-sible environmental impact is caused due to the complex effects of the presence of oxygen, sulphide minerals, water and microbial communities.

12.1. GroundwaterBlack shale (graptolite argillite, Türisalu formation) belongs to the Ordovician-Cambrian aquifer system,whichrepresentsanimportantwatersupply.Asafine-grainedargillaceousrock,blackshale behaves as a local aquitard and therefore protects the underlying aquifer system.

Due to the reasons of groundwater protection, the in situ processing of the Estonian black shale is considered unfavourable (Sipp Kulli et al., 2016, 2014).

12.2. Regional AspectsFor various reasons, the eastern part of the country is likely to be more flexible with regards to environmental restrictions compared to western Estonia. The eastern part (especially north-east) of the country has the most technogenic landscape in Estonia as a result of over 100 years of oil shale mining (http://www.ene.ttu.ee/maeinstituut/mgis/mapofhistory.htm). In compari-son, the north-western part of the country is quite densely populated with various protected areas, although a report by (Sipp Kulli et al., 2016) discusses a possible mining area near Paldiski (see section 10.8 and Figure 25).

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13. Marketing ConsiderationsAtthisstageofexploration,itwouldbeveryhypotheticaltospeakaboutthevalueandprofitabilityofthedeposit. Mainly because 1) we are reviewing the complete deposit in Estonia and in case of exploitation, only a minor fraction would be used, and most importantly 2) the processing technology is not devel-oped. The latter is also one of the main conclusions of the coherent BiotaTec (formerly BiotaP) prelimi-nary economic assessment (recommended literature on this topic, albeit in Estonian) for understanding the marketing considerations in depth (Sipp Kulli et al., 2016).

However, in the recent years the proportions of different black shale valuable components have changed significantly, and the main mineral of interest from all the metallic compounds is likelyvanadium (Figure 29).

8%7%

1%

84%

Value distribution

MolybdenumUraniumZincVanadium

Figure 29. An approximate value distribution of the main metallic components within the Estonian black shale deposit.

The preliminary economic assessment of the black shale exploitation by the means of bioleaching con-sidered the vanadium pentoxide price at 19 640 USD/t (31.08.2016), while the current pentoxide price is at 61 619 USD/t (21.11.2018), thus showing a three-fold increase in the given period.

47


14. ConclusionsThe existing exploration data points out that the Estonian black shale deposit represents an important resource for several commodity metals (V, U, Mo, Pb, and potentially others) with additional value in the organicmatter.Choosingaspecificexplorationtargetorasetoftargetsrequiresoutlyingrequirementsfrom the developer and combining them with existing data. From a geological and exploration perspec-tive, the follow-up investigations should be relatively easy to perform. The black shale deposit has a simple geometry and it is buried under a shallow cover. Based on a review of existing information, the established metal occurrence patterns make it easy to target prospective areas for further exploration. The existing information can be used to isolate parts of the deposit with high metal concentrations, de-fineanomaliesandincreasethedrillinggridinareasofinterest.

Standard-compliant resource estimates are not feasible to be calculated based on existing data. How-ever,thereservesbasedonpreliminarycalculationsaresignificant,forexample19,2megatonnesforMoO3, 6,7 megatonnes for U3O8 and 88,0 megatonnes for V2O5.

Further research is required to develop methods of extracting valuable compounds with maximum recoveryfactorwhilecausingminimalenvironmentalimpact.Currently,thereisnodefinedup-to-dateextraction technology available and the adaptation of existing methods (e.g. the Ranstdad technology, the Talvivaara type bio-heapleaching, etc) has either not been trialled or been tested only in lab scale.

Due to the fact that the black shale directly overlies the Kallavere formation, which contains phosphorite deposits (Obolus sandstone), the minerals contained in the shale have potential as a valuable by-prod-uct for phosphorus producers.

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15. RecommendationsA few important steps that should be prioritised for the purposes of successful exploration of the Estonian black shale deposit:

(1) Even if retrieved with outdated technical capabilities, all possible black shale exploration datashouldbecollectedintoadigitaldatabasetofacilitateaflexibleandefficientsearchforexploration targets;

(2) Drilling campaigns, if initiated, should attempt to verify the existing information with up-to-date techniques;

(3) It is necessary to speciate the occurrence forms of the economically important metals (V, U, Mo, …) prior to metallurgical tests.

(4) Metallurgical tests are unavoidable to better understand the exploitability of the deposit; this does not necessarily require drilling as representative material can be collected from out-crops.

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APPENDIX 1

Glossary of TermsAAS chemical analyses technique sensitive to trace amounts of chemical elements — Atomic

Absorption Spectroscopy

black shale a fine-grained shale type of sedimentary rock that is rich in organic content as well assulphides e.g. pyrite

box and whisker plot a statistical distribution diagram, where the middle horizontal line denotes median of the sample population, edges of the boxes denote the 25th and the 75th quartile and tips of the whiskers mark 5th and 95th quartiles; in the diagrams shown in current report the crosses mark minimum and maximum values

calorific value the energy contained in a material

continental glacier large ice glacier that covered vast regions in the Northern Hemisphere during the ice ages

dictyonema shale out-dated local term for the Estonian black shale that refers to the mistakenly identified“dictyonema” fossils

glacial till glacial sediment that contains unsorted sediment particles in all sizes

glauconite sandstone sandstone rich in the mineral glauconite that gives the rock a greenish colour; a potential K-rich mineral resource

graptolite argillite a local (Estonian) term denoting black shale; refers to the relative (although debatable) abun-dance of “graptolite” fossils and the fine-grained aluminosilicate-abundant (argillaceous)nature of the rock

ICP-MS/OES chemical analyses techniques sensitive to (ultra)trace amounts of chemical elements — Inductively Coupled Plasma Mass Spectrometry / Optical Emission Spectroscopy

Obolus sandstone sandstone rich in the fossil brachiopod “Obolus” shells that in terms of mineral resources is a phosphate resource

oil shale organic-rich sedimentary rock that is exploited for energetic purposes

Optical Character Recognition electronic conversion technique that converts scanned text/numbers into a digital format for further processing

Tukey boxplot a similar statistical distribution map like box and whisker plot, but the upper and lower whiskers are calculated as 1,5 times the interquartile range (difference between 25th and 75th percentile) and minus 1,5 times the interquartile range; the remaining plotted values are the near outliers (crosses) and far outliers (circles)

WD-XRF chemical analyses technique — Wavelength Dispersive X-Ray Fluorescence Spectroscopy

Review of the Exploration Potential of the Estonian …...Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit KINNITATUD Eesti Geoloogiateenistuse

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