Finally, the average grades of Al₂O₃, Mn, CaO, MgO, and TiO₂ are 2.26%, 0.81%, 0.02%, 0.06%, and 0.17%, respectively. For processing using magnetic recovery technology, the particlesize distribution of the sediments is extremely important. The following size fractions were characterized: +0.250 mm, +0.150 mm, +0.106 mm, +0.075 mm, +0.045 mm, −0.045 mm, and −0.020 mm, with average values of 1.45%, 1.53%, 2.52%, 5.86%, 9.07%, 79.57%, and 56.62%, respectively. The contaminants SiO₂ and P determine the commercial quality of the product. For pellet feed, the product grade should contain 0.8 to 3% SiO₂ and 0.02 to 0.06% P, and for sinter feed the SiO₂ grade should be 2.5 to 5% SiO₂ and 0.07 to 1.12% P. At the Gelado dam, there is a high Fe grade with an average of 64%, with SiO₂ at 2% and P at 0.06%. The grades of Al₂O₃, Mn, CaO, MgO, and TiO₂ do not compromise product quality, showing that the deposited tailings are of high quality and fully marketable, and can contribute significantly to the circular economy. One challenge to address is the particle size of sediments finer than 0.01 mm, as there are technological limitations for recovery via magnetic separation. 3.5 Resource estimation For resource classification, the number of samples used in the estimation, the drilling grid, the number of search ellipsoid passes, and the kriging variance were evaluated. Cutoff points based on kriging variance were defined for resource classification (Table 2). Table 2 – Criteria for classifying geological resources Resources class Kriging variance of Fe% Occurrence (%) Measure resource 1 < 0.72 85,29% Indicates resources 2 0.72 - 0.90 4,68% Inferred resources 3 > 0.90 10,01% Potential resources: Blocks defined within an area containing drillholes identified in the database as waste rock were considered. In the research study carried out for the Gelado tailings dam, the measured resources amounted to 227.04 Mt, the indicated resources to 12.46 Mt, and the inferred resources to 26.66 Mt, totaling 266.17 Mt. The potential resource totals 21.25 Mt (Table 3). Table 3 – Inventory of resources estimated in this study Resource class Density (t/m3) Volume (Mm3) Ore mas (Mt) 1 2,5 90,82 227,04 2 2,5 4,98 12,46 3 2,5 10,67 26,66 1+2+3 266,17 Potential 2,5 8,37 21,25 Total 2 287,14 3.6 Methodology for tailings mining at the Gelado tailings dam
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