770 Compositing (regularization) was performed for 801 samples for Fe, SiO₂, P, Al₂O₃, and Mn, and for 529 samples for CaO, MgO, TiO₂, and particle-size fractions from +0.250 mm to −0.020 mm. A high mean Fe grade of 64.09% was observed, along with 1.97% SiO₂ and 0.12% P (Table 1). Table 1 – Iron, associated elements, and particle-size distribution of sediments in the Gelado tailings dam Variable Samples number Minimum (%) Maximum (%) Average (%) Variance (%²) Standard deviation (%) Fe 801 56,56 66,77 64,09 2,23 1,49 SiO2 801 0,58 10,4 1,97 1,21 1,1 P 801 0,03 0,12 0,06 0 0,01 Al2O3 801 0,75 4,56 2,26 0,45 0,67 Mn 801 0,32 2,06 0,81 0,06 0,25 CaO 529 0,01 0,3 0,02 0 0,01 MgO 529 0,02 0,72 0,06 0 0,02 TiO2 529 0,04 0,3 0,17 0 0,04 +0.250 mm 529 0 27,4 1,45 9,4 3,07 +0,150 mm 529 0 15,2 1,53 4,53 2,13 +0,106 mm 529 0 18,8 2,52 8,89 2,98 +0,075 mm 529 0 25,8 5,86 34,99 5,91 +0,045 mm 529 0 36,2 9,07 72,01 8,49 -0,045 mm 529 26 100 79,57 327,66 18,1 -0,020 mm 272 0 96,59 56,62 248,39 15,76 Through variogram modeling, it is possible to define the spatial continuity of iron and other associated elements in three directions. The variogram shown in Figure 4 corresponds to Fe. The sill is close to 1.0, and the nugget effect is about 12% of the total variance, which is not high; therefore, Fe shows reasonable continuity. On the other hand, the range of 70–80 m indicates that up to these distances there is relevant spatial correlation along the drillholes; beyond that, the correlation is practically null. Figure 4 – Modeled variograms for the Fe variable: (a) direction 1, (b) direction 2, (c) direction 3
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