Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit
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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 KINNITATUD Eesti Geoloogiateenistuse Teadusnõukogu otsusega nr 19-3 Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit Graptoliitargilliidi uurituse ülevaade maagiotsingute potentsiaali hindamise seisukohalt Uurimistöö aruanne Töögrupi juht: Johannes Vind Eesti Geoloogiateenistuse direktor: Alvar Soesoo RAKVERE 2018 Geological Survey of Estonia / Research Report EGF-8995 Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit 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, Experience and Independence . 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 5 Geological Survey of Estonia / Research Report EGF-8995 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 Kärdla impact structure area (K- prefix cores) and NW mainland (F- prefix cores). “Avg” denotes the average 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 Figure 1. Geological bedrock map of Estonia and a geological cross section (modified after: Institute of Geology, 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 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.. 20 Figure 6. Cross section of the deposit defined in the 1940-s in Sillamäe (according to the data of the Baltic expedi- 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- cal profiles shown in paragraph 10.2. Abbreviations in the Location Map in upper left are: SW — Swe- den, 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.. 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 6 Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit 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). 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.. 27 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. 28 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.. 29 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.. 30 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.. 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 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. 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 Figure 26. Drill core average V concentrations (“historic” data) in the eastern field of phosphorite deposits (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 7 Geological Survey of Estonia / Research Report EGF-8995 1. Summary This 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 to fulfil the tasks outlined in the national strategic document “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.