Geological Survey of Estonia compiled a review of the Estonian black shale (graptolite argillite) deposit. Its emphasis was on the question, which is the metal exploration potential of the GA occurring in the Estonian territory? In other words, which is the potential that the GA deposit hosts ore-grade mineralisation occurrences?
For a brief explanation, it should be mentioned that the metalliferous black shale occurring in Estonia has been locally termed as graptolite argillite due to the occurrence of specific fossils within it and the fine-grained nature of the rock.
The review was initiated from the fact that the world metal markets are constantly at a change and therefore there was need to put the Estonian black shale on the background of current trends. For many years, black shales have been primarily considered as low-grade uranium ores or as a source of shale gas, with some examples also presenting the successful exploitation of copper. What we are witnessing at present is a growing demand towards the so-called “battery and electric car” metals. In that perspective, black shales are being considered and explored primarily for the contents of vanadium (V) but also for cobalt, nickel, rare earth elements and more
To fulfil the current task, the existing research reports and academic articles were reviewed. However, majority of the information currently exists only on hard copies produced during the soviet era. A selection the most significant information was scanned and digitalised by optical character recognition. The work resulted in a database containing geochemical and geological data of about 4000 samples. The number of variables, however, is not large and usually the concentrations of V, U, Mo and Pb as well as calorific value are available. With this effort, data has been made available that allows to apply modern statistical methods as well as geospatial analyses on the information (example in Figure 1).
The new report indicates that V might comprise more than 80% of the value of the metals contained within the black shale. Although the historical data has some serious quality problems, it can be referred that V should be the most valuable component of the Estonian black shale. This statement obviously assumes a high recovery of V from the resource. The latter brings into light a shortcoming in the perspective of black shale exploitation — there is currently no process available to valorise the shale. Nevertheless, the exploration potential of the Estonian black shale can be significant, especially when considering its large occurrence territory (12210 km², partly exposed) and the immense “order of magnitude“ reserve of about 88 megatons of vanadium pentoxide.
In the light of recent exploration targets in the rest of the world, the Estonian black shale might remain as a low-grade ore after all. The highest average concentrations of vanadium pentoxide per drill core exceed 0,2%, while there are reports of nearly 5% vanadium pentoxide concentrations in some projects being developed. The successful exploitation would require the development of a technology that would recover a high amount of the shale constituents.
- Review of the Exploration Potential of the Estonian Black Shale (Graptolitic Argillite) Deposit (8.37 MB, PDF)
- Johannes Vind