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Cresson Pro'ect H dro • eochemist AdrianBrown <br />3.3.2 Neutralization of products of sulfide oxidation from mine extension overburden <br />The amount of calcium carbonate required to neutralize the acid produced by complete oxidation of the <br />reactive pyrite in the mined rock from the start of surface mining to the end of MLE2 has been <br />computed using the following neutralization equation: <br />CaCO + 2H+ = Ca + H + CO <br />Based on these results presented in Table 5, if all of the reactive pyrite in all of the 1.6 million tons of <br />rock that will be affected by mining were to oxidize, then: <br />Calcium carbonate required to neutralize oxidation products < 38 million tons. <br />This computation takes credit for the neutralizing capacity in the rock produced. The computation does <br />not take credit for any neutralization by lime added to the ore. <br />3.3.3 Carbonate Abundance in the Diatreme <br />The protection of regional ground water quality by neutralization in the diatremal rocks requires an <br />adequate mass of calcite to react with the sulfide inventory in the mined overburden. <br />The calcite inventory of the Diatreme has been evaluated from testing of drill samples obtained from the <br />drilling of the diatremal materials. Three deep holes have been drilled and sampled to provide <br />neutralization data from depths down to and below the Carlton Tunnel elevation: <br />• CC -2272 - Located in the south center of the Diatreme (5030 ft deep) <br />• GHC -474 - Located in the west of the Diatreme (2915 ft deep) <br />• GC -07 -704 - Located in the north of the Diatreme (3465 ft deep) <br />These data have been combined with data for neutralization capacity from a total of 520 other shallower <br />holes that sampled diatremal material. The average carbonate concentration in all holes has been <br />determined by sample elevation, and is presented in Table 7, and presented graphically in Plate 16. <br />The total mass of available carbonate that is present in the diatremal rocks is computed from the <br />carbonate abundance and the diatremal rock mass, in 500 foot thick elevation slices (Table 8). <br />Ground water infiltrates vertically downward through the unsaturated Diatreme to the regional ground <br />water system, at an elevation between 7,000 ft msl (at the Carlton Tunnel) and 7,200 ft msl (remote from <br />the Carlton Tunnel). The regional ground water then flows essentially horizontally in the saturated <br />diatremal materials; the thickness of the rock that hosts this flow is estimated based on modeling to be at <br />least a further 1,000 feet depth, down to elevation 6,000 ft msl (see Plate 13). Accordingly, infiltrating <br />ground water contacts calcium carbonate in the entire diatremal rockmass down to at least an elevation <br />of 6,500 ft msl. From Table 8: <br />Mass of carbonate available for neutralization of infiltrating ground water = 2055 million tons <br />3.3.4 Adequacy of Neutralization Capacity <br />The adequacy of the identified calcite in the diatremal rock to neutralize the maximum amount of acidic <br />seepage that can be generated by oxidation of sulfide contained in the entire inventory of mined rock <br />1385L.20120125 18 <br />