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38 <br />• ore body. In the Georgetown-Silver Plume District, the ore <br /> primarily occurs in veins stringing along the fractures in <br /> the granite host rock and the contact of the water with veins <br /> minerals is much less efficient. <br /> The second parameter to be considered is the height <br /> of the water table in relation to the ore occurrence. The <br /> location of the ground water table in relation to the ore <br /> body is important because the dissolution of pyrite is an <br /> oxidation reaction. <br /> 2FeS2 + 702 + 2H20 } 2Fe2+ + 4SO4 + 4H+ <br /> Oxygen is a necessary reactant, even when the reaction <br /> is catalyzed by bacteria. If the ore occurs below the water <br /> table, contact with air is cut off and oxidation occurs at <br /> a much lower rate. If the ore occurs above the water table, <br /> dissolution of the vein minerals is promoted. The secondary <br /> alteration of ore bodies which at some time have risen above <br /> the water table is caused by the same chemical situation. <br /> The Argo Tunnel was built to drain the Central City <br /> District and it has been quite efficient. No natural springs <br /> occur in the district and the water table is about at the <br /> level of the Argo Tunnel with much of the disseminated ore <br /> occurring above the water table. In other mining districts <br /> in the Front Range, drainage tunnels are not as extensive <br /> and springs can typically be found nearby. This implies <br /> that the water table is higher in relation to the ore and <br /> oxidation of the vein minerals is less extensive. <br /> d <br /> Certainly many mines are operated above the groun