320 iron ore or used internally as aggregate and road base material. Macroscopic descriptions provided an initial assessment of the mineral paragenesis of the non-fragmented bench samples, allowing identification of primary minerals (igneous and sedimentary) and secondary minerals (metamorphic, hydrothermal, and weathering-related). Morphological and textural features were also documented, including foliation, banding, fracture filling, veinlets, breccias, and the degree of supergene alteration. Centimeter-scale areas were selected from each massive sample for cutting and preparation of thin sections and polished mounts to be analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). QEMSCAN® was also employed, generating detailed textural information as well as mineralogical composition and elemental distribution. Geochemical characterization was complemented by Xray fluorescence (XRF) analyses. Vale also collected 200 tonnes of fresh mafic rock directly from the N4E mine bench to evaluate the agronomic efficiency of rock powder through controlled soil experiments. The entire sampled mass was crushed and milled according to the physical specifications established by the Ministry of Agriculture, Livestock, and Supply (MAPA), ensuring that 100% of the material achieved a particle size of less than 2 mm. Laboratory incubation tests were conducted to estimate the acidity-neutralization potential of the fresh mafic rock in different soils, generating pH curves based on increasing application doses of the rock powder. This procedure simulates the dissolution of minerals— particularly carbonates and Ca- and Mg-rich silicates—present in the fine fractions. Two soils with contrasting textures, low pH values, and high levels of exchangeable Al were selected: a clay textured Red Oxisol (Latossolo Vermelho, LV) and a sandy Quartzarenic Neosol (NQ). The incubation doses of the rock powder were defined using increasing agronomic equivalence levels, with limestone doses included as reference treatments. The soils were homogenized, placed in 6-kg pots, and kept in a greenhouse for a 90-day incubation period. The pots received increasing doses of rock powder to assess mineral dissolution and rock reactivity in each soil type, with the zero dose (D0) serving as the control treatment. For the clay soil (LV), the applied doses were: 0 (control), 18, 45, 60, and 90 g pot⁻¹— equivalent to 0, 3, 7.5, 10, and 15 t ha⁻¹. For the sandy soil (NQ), doses were: 0 (control), 6, 18, 27, and 36 g pot⁻¹—equivalent to 0, 1, 3, 4.5, and 6 t ha⁻¹. After application, each pot was thoroughly homogenized. Following incubation, the pots were fertilized with macro- and micronutrients for soybean and corn cultivation. A 45-day plant-growth phase was then conducted (Figure 2). At the end of the experiment, the shoot and root biomass of both crops were collected and oven-dried at 65 °C for 72 hours to determine dry-matter production and nutrient uptake. Soil samples were also collected to assess changes in chemical attributes after cultivation.
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