Characterization and changes in the thermal behavior of the phosphorite sample from Toolse deposit (Estonia) along the drill-core

The changes in the thermal behavior of shelly phosphorite ore from Toolse deposit along the drill-core PH014B (depth 21.1–26.7 m) cut into sub-samples with a length of 0.1 m have been studied. The primary phosphorus-bearing mineral in Estonian phosphorite is fluorcarbonate apatite (francolite) originated from lingual brachiopod shells which during the following millions of years of deposition has partially transformed into fluorhydroxyl apatite. The experiments on a Setaram Labsys Evo 1600 thermoanalyzer coupled with Pfeiffer Omnistar Mass Spectrometer were carried out under non-isothermal conditions at the heating rate of 10 °C min.  up to 1200 °C in an oxidizing atmosphere containing 79% of Ar and 21% of O2. XRD, FTIR, and XRF methods were used to estimate the mineralogical and chemical composition of the sub-samples.
In all studied sub-samples, two minerals prevailed—apatite and quartz. The content of apatite in general decreased moving upwards and the content of quartz increased—both minerals with certain fluctuations depending on the changes in the geological scale of formation of these sediments. Pyrite was also present in all sub-samples, clay minerals (K-mica, illite, chamosite) almost in all, but K-feldspar (sanidine, orthoclase), mostly, in the upper layers. Carbonates (dolomite, calcite) were present in many sub-samples along the drill-core, at that, the content of dolomite was especially high in the deepest sub-samples—between 26.3 and 26.7 m. Organic carbon was concentrated in the upper layers (21.1–23.0 m) of the drill-core, which contained black shale interbeds. Analysis of the results showed a good correlation between the thermal behavior of sub-samples and the changes in their mineralogical and chemical composition along the drill-core.