Laserfiche WebLink
'~ <br />The reaction of aluminosilicates is, as noted, likely to be slower than the reaction of <br />carbonate minerals such as calcite or dolomite but, if the reactive surface area or <br />availability of these aluminosilicates is much greater than that of the cazbonate minerals, <br />their neutralization reaction contribution may be larger than simple comparisons of rate <br />data would suggest. <br />The release of trace metals, particularly zinc, from the Cresson overburden material is not <br />specifically addressed in terms of chemistry of solubilization reactions. Whether oxidation <br />or hydrolysis reactions are involved in mobilizing the trace metals is probably not of major <br />significance. The important expectation here is that we can expect increased mobilization <br />(or solubilization) of the trace metals as acidity increases whether this is due to release of <br />the trace metals from solubilized pyrite or from increased solubility of other trace metal <br />sulfides or other minerals as pH decreases. <br />The section of the report dealing with the background chemistry of minerals likely <br />or known to be present in the Cresson overburden material appears to be accurate <br />and sufficient in detail to use as a basis for analyzing the likely behavior of this <br />material in the environment of the minesite. <br />Cresson Deaosit Post-Depositional Weatherin¢ <br />Presented as a theoretical model to explain variations in mineral suites with depth in the <br />Cresson deposits, the explanation presented in the report appears to be based on <br />reasonable projections of the chemistry set forth in the preceding section. <br />The proposed weathering reactions would support the conceptual ability of the basic <br />minerals in Cresson materials to react with acidic contacting waters and thus to mitigate <br />development of net high acidic drainage from the area. This neutralization scenario, of <br />course, implies that the generation rate of acid is such that the available surface of basic <br />minerals is adequate to react with it in a prompt manner. That is, if for some reason an <br />elevated level of acid were released to contact the material containing the basic minerals, <br />there is no assurance that this "shock loading" migfit not exceed tfie neutralization capacity <br />of exposed basic minerals or their reaction rate and thus permit low pH solution to exit <br />from contact with this potentially neutralizing material. <br />The presented description of a likely post-depositional weathering scenario for the <br />Cresson deposit appears to be reasonable from the standpoint of the fundamental <br />chemistry involved. The preferential oxidation of pyrite in upper horizons and reaction of <br />acidic waters percolating from this zone to be neutralized by basic minerals in lower strata <br />could account for the areas termed "oxide" and "transitional". The lowest strata, with <br />highest remaining pyrite mineral populations, could then in fact be similar to the originally <br />deposited materials in the Cresson material. Heterogeneity and "islands" of one type of <br />material in horizons of another type of material would not be unexpected in this post- <br />depositional weathering picture. <br />OMLR951 DEH <br />