Factual Report on XRF Analysis Conducted on Bulk Sedimentary Rock Samples from the Mesohellenic Trough – Project: PilotStratergy

Analysis date: 30.04.2024

Report date: 02.05.2024, Revision date: -

Written by: Christos L. Stergiou, Geologist, PhD

Reviewed by: Pavlos Tyrologou, Geologist, PhD

Advice also: Previous factual report files “Report_SEM_Round1_Bulk samples.docx” and “Report_XRD_PilotStrategy03.04.2024.docx” for additional information on the mineralogy of the samples included in this report.

1. Materials and Methods

Three (3) sedimentary rock samples originating from the Tsotyli (sample Tsot-1; marly SANDSTONE), Eptachori (sample Ept-2; fine GREYWACKE) and Pentalofos (sample Pent-3; greywacke) Formations of the Mesohellenic Trough were powdered and analyzed by X-ray fluorescence (XRF) to determine their mineralogical composition. The samples were field collected by hummer and obtained as rock chips. Pulps produced from the rock chip samples were formed into pressed pellets by mixing 2.4 g of the binder CEREOX® with 9.6 g of rock pulp (i.e. sample-to-wax binder ratio of 4:1). The mixed material was homogenized in a mechanical mixer working at 24 rpm for 15 minutes and then pressed at 5 kbr (Fig. 2). The XRF analysis was performed using Bruker S4-PIONEER with a wavelength-dispersive X-ray fluorescence (WDXRF) analytical system at the Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki. The spectrometer uses an Rh lamp and a system of 5 crystals: LIF200, LIF220, LIF420, XS-55, and PET. It also has two detectors: a gas proportional counter and a scintillation counter. The X-ray beam was used at its maximum energy of 50-60 kV. The element lines that were measured were the Ka and La lines, depending on the element. The method includes corrections for overlaps and matrix effects. Analytical results are presented in Table 1, while major conclusions after XRF analysis are presented below by taking into consideration conclusions previously made after XRD and SEM-EDS analysis. Previous published investigations on these samples include geomechanical and petrophysical methods for the evaluation of the parent sedimentary formations to capture and store CO₂ (Tyrologou et al. 2023).

Table 1. Bulk geochemical analyses of major and minor elements for the analyzed samples Tsot-1, Ept-2 and Pent-3 from the Mesohellenic Trough.

*LOI = Loss of ignition, bdl = below detection limit.

5. Conclusions

The XRF analysis confirms suggestions and conclusions made on previously acquired SEM-EDS and XRD analytical results focusing on bulk samples obtained by hammering from marly SANDSTONE (Tsot-1) and greywacke (Ept-2, Pent-3) originating from the Tsotyli, Eptachori and Pentalofos Formations of the Mesohellenic Trough (Fig. 1).

Bulk geochemical analysis reveals that calcium and silica are the most enriched elements (Table 1). Sample Tsot-1 (24.85 wt.% SiO₂) is slightly siliceous in composition, sample Epth-2 (36.25 wt.% SiO₂) is dominantly siliceous, while sample Pent-3 is dominantly calcareous in composition (42.42 wt.% CaO, Table 1). These results are complementary to the semi-quantitative estimates obtained by XRD analysis (cf. Report_XRD_PilotStrategy03.04.2024.docx). In sample Tsot-1, calcite content is 30 wt.%, while quartz (29 wt.%) and albite (19 wt.%) percentages sum to 50 wt.%, supporting the siliceous profile acquired by XRF. In sample Ept-2, quartz (37 wt.%) is the dominant mineral phase followed by calcite (29 wt.%), while in sample Pent-3, calcite (41 wt.%) is the more enriched mineral phase, supporting the obtained geochemical results where SiO₂ is 36.25 wt.% in sample Ept-2 and CaO is 45.42 wt.% for sample Pent-3. In addition, the geochemical results support the suggested level of maturity of the analyzed samples with Etp-2 showing the highest and Pent-3 the lowest maturity.

Finally, sample Ept-2 shows the highest enrichment in minor elements, including 1,680 ppm of Cr and 990 ppm of V (Table 1). Relative enrichments in these trace elements, as well as in Co, Cu, Ni and Zn could be related to the highest incorporation of detrital material related to the ophiolitic basement rocks of the Mesohellenic Trough. Variations in trace elements may be associated with minor mineral phases not detected by the XRD analysis and the SEM-EDS examination of bulk samples. The study of thin-polished sections under a plane polarized and an electron scanning microscope shall clarify the mineral composition of the samples and conclude the mineralogical and geochemical investigation.

6. References

Tyrologou, Pavlos, et al. (2023). Progress for carbon dioxide geological storage in West Macedonia: A field and laboratory-based survey." Open Research Europe 3. https://doi.org/10.12688/openreseurope.15847.2