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<br />11 <br />The general conclusion that the Cresson materials are net acid producers when total <br />sulfur levels are above about 0.2% and (estimated) sulfide sulfur levels are above <br />about 0.1% appears to be borne out by Table 1 data. <br />The trending of acid neutralization potential with depth in the Cresson materials seems, as <br />noted to support the general model ofpost-depositional weathering as set forth earlier in <br />the report. The overall reactions involved in this model (acid production by pyrite <br />oxidation and neutralization of acid waters by basic minerals in the deposit) are similar to <br />what we might expect in the disturbed overburden materials. This is not to say, however, <br />that the dynamics of water and air contacting the overburden piles will be such that we can <br />expect any discharge from them to be of exactly the same quality as waters which have <br />contacted in-place materials in the weathering deposit. <br />Paste pH Measurement <br />The paste pH measurements on 37 samples provide an interesting picture of the potential <br />acid generating and acid neutralizing potential of the materials when they are finely ground <br />(-60 mesh and probably about -150 mesh). I have replotted this data to compare net <br />neutralization potential and paste pH on common set of scales in Figure 1 in order to <br />review the data from a somewhat different perspective. <br />As noted in the report under review, although the materials tested have a NNP ranging <br />from about 24 to -50 tons of CaC03 per 1000 tons of material, the paste pH of these <br />samples, when finely ground, shows relatively little variation and is not below 4.29 for <br />even the highest sulfide material. Similarly, the highest pH observed for any of the <br />materials is 8.80. <br />This data suggests, that when both acid generating minerals and acid neutralizing <br />minerals are exposed by fine grinding, waters contacting the system will tend to <br />exhibit what amounts to a buffered pH in the range of about 4.3 to 8.8. This is <br />interestingly close to the pA range of waters in various parts of the natural <br />environment in the Cripple Creek district and may support the contention that the <br />area has a net buffering capacity to handle acid drainages so Iona as there is <br />sufficient contact between the acid waters and neutralizing minerals. <br />OMLR951 DEH <br />