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early in the history of coal diagenesis by bacterial reduction of sulfate and ferrous iron <br /> in order to metabolize the organic compounds presents. (ln this discussion, the name <br /> "pyrite" will be used to indicate both pyrite and marcasite). It is apparently in this <br /> setting t hat framboidal pyrite forms (Caruccio and others, 1977). Framboidal pyrite, is <br /> comprised of submicron-sized crystals of pyrite. Studies by Caruccio (Caruccio and <br /> Parizek, 1967; Caruccio, 1968; Caruccio, 1970; Caruccio and Ceidel, 7982) have shown that <br />framboidal pyrite is responsible for the production of acid, while other forms (massive, <br />plant replacement, primary euhedral and secondary cleat filling) do not react rapidly <br />enough to produce substantial acid. According to Caruccio and others (1977), the <br />occurrence of framboidal pyrite is related to depositional environment. It is found more <br />commonly in near marine (back bay and lower delta plain) than in upper delta plain <br />environments. The second important factor in the production of acid is the presence or <br />absence of carbonate minerals in rocks associated with the pyrite. <br />Different laboratory techniques have been used for predicting the potential for acid <br />generation, and result in a value termed the "Acid Base Potential" or ABP. In order to <br />measure or calculate the potential acidity either (1) the pyrite (plus organic sulfur, in <br />some techniques) content is measured, and potential acidity is calculated, or (2) a sample <br />is oxidized with hydrogen peroxide (after treating with acid to remove carbonates and <br />gypsum, and rinsing) and the amount of acid produced is measured by titration. The <br />neutralization potential is measured by titration, and is indicative of the content of <br />alkaline carbonates, exchangeable bases, and readily weatherable silicates. These two <br />measurements are expressed in terms of equivalent CaC03. The ABP is calculated by <br />subtracting the potential acidity from the neutralization potential. If the ABP is <br />positive, reactions of the overburden with water are likely to yield pH's greater than 7. <br />A negative A8P indicates that acidic conditions may develop. <br />An important assumption in this approach is that all the pyrite present is reactive. When <br />the acid potential is determined by oxidation with hydrogen peroxide, the use of elevated <br />temperatures encourages oxidation of the non-framboidal pyrite. Smith. and others (1974, <br />p, 48) discuss the excellent agreement between potential acidity determined by oxidation <br />and that calculated from total pyrite content, which indicates that pyrite oxidation <br />during the laboratory procedure is complete, or nearly so. Hence, the potential acidity <br />parameter overestimates the amount of acid that might be produced because non-framboidal <br />• forms of pyrite are oxidized fn addition to the other forms. <br />17-39 Revised 04/11/88 <br />