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r <br /> �° ITASCA <br /> Denver, Inc. <br /> The relationship between AGP calculated based on total sulfur and AGP calculated based on <br /> sulfide sulfur is shown in Figure 3-2. Sulfide sulfur is the most prevalent type of sulfur measured <br /> in the samples, on average accounting for 77%of the total sulfur. As discussed in Section 3.1.2, <br /> some sulfate minerals do generate acidity (i.e., alunite,jarosite, and acid-sulfate salts) and some <br /> do not (i.e., gypsum, anhydrite, and barite), and thus total AGP provides a conservative measure <br /> of the potential for acid generation relative to sulfide AGP. <br /> The NNP values ranged from-213.3 to 12.2 kg CaCO3/t,with an average value of-80.8 kg CaCO3/t. <br /> Twenty-seven of the 29 Phase I samples were net acid-generating.These samples had NNP values <br /> that were less than zero. Two samples had NNP values that were greater than zero but less than <br /> 20.0 kg CaCO3/t, indicating that they are net neutralizing but within the range that is generally <br /> considered to be uncertain. Seven of the samples had negative NNP values that were <br /> between -20.0 and 0 kg CaCO3/t, indicating that their potential to generate acidity is uncertain. <br /> The net acid-generating samples, as measured by ABA analysis, do not correspond to a specific <br /> rock type. Four of the five rock types represented by the Phase I samples had one or more <br /> samples with NNP values that were less than -100 kg CaCO3/t. Lamprophyre was the only rock <br /> type for which none of the Phase I samples had NNP values that were less than -100 kg CaCO3/t, <br /> although the lamprophyre rock type is represented by only one Phase I sample. The NNP for this <br /> sample was -62.4 kg CaCO3 A. <br /> These results indicate that the acid-generating minerals controlling the NNP of the samples do <br /> not preferentially occur within one rock type.These results are consistent with the evaluation of <br /> the overall NNP value distributions for Project rock types, as illustrated in Figure 2-3. <br /> 3.2 NET ACID-GENERATION TESTING <br /> Some of the limitations associated with ABA methods can be overcome using another type of <br /> static test that is also designed to evaluate the overall potential for samples to generate acidic <br /> leachate, the NAG test. The NAG test addresses issues relating to the simplifying assumption of <br /> 17 <br />