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 3.3 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).
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