771 2.5 Occurrence of Fe in the dam sediments The study shows that Fe occurs at concentrations equal to or greater than 65% in the discharge areas of Arms 1 and 4 over nearly 500 m, in the eastward and northward directions, respectively, and then decreases slightly to 64–65% over approximately 1,500 m. From the discharge points of Arms 2 and 3, Fe occurrence is 63–64%, progressing in the direction N70°E for approximately 6,000 m. Toward the end of this trend, Fe grade drops to 62–63%, and locally—at the dam’s northeastern extremes—falls below 62% (Figure 5). Figure 5 – Horizontal distribution of iron within the Gelado tailings dam At depth, along the east–west section, it is possible to observe that iron occurrence is very similar to the horizontal distribution (Figure 6). Figure 6 – Vertical distribution of iron within the Gelado tailings dam 2.6 Occurrence of silica (SiO₂) and phosphorus (P) At the Gelado dam, the SiO₂ component occurs at an average grade of 1.97%, inversely to Fe—that is, the higher the Fe grade, the lower the SiO₂ grade. Using the SiO₂/Fe ratio, it can be seen that in the highFe areas this ratio ranges from 1/64 to 1/66, increasing to 1/22 and finally 1/15. This behavior is related to the density and particle size of Fe, which have average values of 2.6 g/cm³ and 0.075 mm, respectively, and of SiO₂, with 2.0 g/cm³ and 10 to 100 nm, respectively (Figure 7).
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