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Section 2 <br />Investigation Approach and Activities <br />2.2.1 Development Rock <br />-Forming Potential Analyses <br />potential DMO status is the potential for <br />ing. Acid base accounting (ABA) analyses are <br />tential for a sample to generate acid at some time in <br />a well-established and widely used method to <br />evaluate the potential for a rock generate acid. The propensity for a rock to <br />generate acid drainage is dependent on both the acid generating and acid neutralizing <br />potential of a rock. Acid generation results from oxidation of sulfide minerals, such as <br />pyrite (FeS2). Acid neutralization results from minerals that will neutralize acid, such <br />as calcite (CaC03) and dolomite aMg(C03)2). <br />A primary concern with regard <br />development rock to be acid for <br />commonly used to estimate the <br />the future. The ABA procedure <br />Acid potential is estimated based) on a series of sulfur analyses. Sulfur is analyzed in <br />fractions of the sample that are soluble in water, hydrochloric acid (HCI), and/or <br />nitric acid (HN03). A total sulfur analysis is also performed. Sulfur measured in the <br />various digestions is interpreted to represent different types of sulfur-containing <br />minerals. The ABA method assumes that pyrite is the only sulfide mineral present <br />and that the pyrite is oxidized by oxygen producing four moles of protons (H+) per <br />mole of pyrite as shown below. <br />FeS2 +3.7502 +1 5Ir20 _+ MOM 3(,) +2504'- +4fI" <br /> <br />Neutralization potential is estim a ted by adding a known quantity of hydrochloric <br />acid to the sample followed by ti ration of the solution back to a pH of 8.3. The <br />quantity of remaining acid is estimated based on the amount of sodium hydroxide <br />necessary to raise the pH back to a value of 8.3. The quantity of acid consumed by the <br />sample is the neutralization pote tial, which is estimated by difference and expressed <br />in units of tons per kiloton calcium carbonate equivalent (t/kt CaC03 eq). <br />In interpretation of ABA analyst: <br />to be neutralized by 2 moles of c <br />factor of 31.25 t/ kt CaC03 eq. p( <br />potential and neutralization pot( <br />CaC03 eq. However, the acid ge <br />interpretation are not unique. Tl <br />based on empirically derived tha <br />between the acid potential and r <br />neutralization potential (NNP), <br />and the acid potential (NP:AP). + <br />ABA data include the following: <br />NNP values relative to the <br />¦ <0 t/kt CaC03 eq. indicates a <br />¦ 0 to 20 t/kt CaC03 eq <br />acidity produced by one mole of pyrite is assumed <br />:ite, which results in a stoichiometric conversion <br />percent pyritic sulfur. This allows both the acid <br />tial of a rock to be expressed in equal units of t/kt <br />,ration and neutralization reactions used in the ABA <br />,efore, interpretation of ABA analyses is commonly <br />;holds. These thresholds are based on the difference <br />.itralization potential, referred to as net <br />d/or the ratio between the neutralization potential <br />,mmonly applied thresholds for interpretation of <br />tial to generate acid in the future: <br />potential. <br />an uncertain potential. <br />¦ >20 t/kt CaC03 eq. indicates an unlikely potential. <br />2-4 <br />• <br /> <br /> <br />T:\64986-Denison Mines\Ta