Johannes Vind
Geological Survey of Estonia
The Geological Survey of Estonia (EGT) aims at conducting drilling operations in Lääne- and Ida-Virumaa this summer. The objective of these activities is to control on the basis of new drill cores the dataset of phosphorite research accomplished more than 40 years ago. The plan is to make 16 drill holes. In addition, an application is being compiled for an exploration permit of drilling at another 14 locations. The planned investigation has three main objectives: firstly — controlling the existing research data, secondly —preliminary work for presenting the Soviet era dataset and information from studies of new drill cores according to internationally recognized research standards, and thirdly — collecting information about the occurrence of potentially exploitable rare and trace metals in phosphorite and its overburden.
Extensive research of phosphorite was conducted in north Estonia from the 1950s to the 1980s, which led to the identification of the Rakvere, Toolse and Aseri phosphorite deposits. More than 2000 boreholes were drilled during that period for exploring phosphorite. Written records of such investigations covering all those boreholes have been preserved at the Geological Archive. However, the information is mostly restricted to determining the thickness of the phosphorite strata in the drill cores and presenting results of geochemical analysis regarding the concentrations of phosphorus, iron and magnesium, i.e. the chemical elements of interest for fertilizer production in those times.
In order to anticipate the question, why old drill cores are not being utilized for controlling earlier studies, one has to note again the fact that drill core sections containing phosphorite have simply not been preserved. An important aspect of using rocks held in storage is also that the properties of these materials change in the course of time — certain minerals crumble and recrystallize, and they cannot be used for research. It is essential to note in regard with earlier phosphorite studies that in parallel with geological research, large-scale technological experiments of producing phosphoric acid were also carried out. The whole available drill core of the phosphorite strata was used up for experimenting. Drill cores containing black shale (locally known as graptolite argillite) do exists in storage, but they have mainly been bored in north-western Estonia. Where possible, EGT has been using the old drill cores for research. We do consider them as essential base material for investigations, however, primarily for studying different kinds of mineral occurrences.
The Soviet era dataset relies on numerous drill holes. In the long run, it would be the basis for creating spatial models of the distribution of phosphorite and its geochemical characterization that fulfil modern research standards. However, the reliability of Soviet era geological and geochemical datasets should first be controlled by drilling a number of new, so-called duplicate boreholes, which would be located in the immediate vicinity of the old boreholes. The studies of new drill cores and the achieved geological-geochemical data will be reported following the international PERC standard of mineral exploration (http://www.percstandard.eu/) that is in use in Europe. This will provide a guarantee of completeness and truthfulness of accomplished investigations, both to the state and to private enterprises carrying out geological exploration. However, several steps will precede the compilation of reports matching the standards. Further on, supplementary drilling operations will be needed.
The principal objective of phosphorite investigations has so far been to find out such properties of raw material that serve the production of phosphate fertilizer. However, the demand on rare-earth elements (REE) has quickly increased globally during the last twenty years, in connection with the development of green energy. Rare-earth elements have been included from 2011 on in the list of critical raw materials because of supply risk and great demand. It is known on the basis of geochemical analyses of phosphorite samples from a few natural outcrops that together with other REE, a significant amount of neodymium is found in Estonian phosphorite raw material. Neodymium is an essential component of permanent magnets used in wind turbines and electric cars. Elevated concentrations of vanadium are known to occur in black shale overlying the phosphorite strata in north Estonia. Vanadium has mainly been used as an additive in the production of cemented steel. However, research during recent years indicates the possibility of using vanadium in the production of large-capacity power banks, which would primarily store green energy produced with wind turbines and solar panels. Glauconite sandstone overlies black shale immediately above it. Complementary technological studies should provide an answer to the question — is it possible, and for what kind of purpose, to use glauconite sandstone with an elevated concentration of potassium?
In summary, the new drilling operations for phosphorite exploration about to be started soon and the subsequent investigations should make it possible to carry out controlling of existing geological dataset from the Soviet era. They should also make it possible to assess the usability of corresponding historical dataset in compilation of new models of mineral resources following the PERC exploration standard and to find out possibilities for the use of phosphorite, graptolite argillite and glauconite sandstone as a complex resource.
