321 Figure 2 – Soybean and corn plants after 45 days of growth in the greenhouse trials. 4. RESULTS AND DISCUSSION 4.1 Geochemical Characterization The geochemical results confirm the suitability of these rocks for use as soil remineralizers. The average sum of bases (CaO, MgO, and K₂O) reached 12.64%, while the mean K₂O content was 3.4%, both exceeding the minimum requirements established by Brazilian regulations. Concentrations of potentially toxic elements (As, Cd, Hg, and Pb) were generally low, with mean values of 1.12 ppm, 0.45 ppm, < 0.01 ppm, and 48.69 ppm, respectively. An outlier Pb concentration of 1184.6 ppm (sample SN4-FD00096-AE022) was identified, likely related to the presence of sulfide minerals confined to that specific sampled interval (Table 1). The combination of chemical analyses and macroscopic core descriptions enabled the identification of two distinct lithological groups: mafic basaltic rocks, associated with the Parauapebas Formation; and plutonic gabbro–diorite rocks (Table 2), which occur more abundantly in the N5 mine and display higher potassium contents, averaging between 3% and 7%. These findings highlight the agronomic potential of mafic lithologies in the region, particularly due to their mineralogical composition and low concentrations of contaminant elements. The three samples collected from the N4E mine bench also fully met the chemical criteria required for use as soil remineralizers (Table 3). Table 1 – Chemical results for the sum of CaO + MgO + K₂O and the concentrations of K₂O, As, Cd, Hg, and Pb in samples collected from drill cores in the Serra Norte and Serra Sul mines (MS – fresh mafic rock; GBC – fresh gabbro)
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