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Cresson Project Hvdroaeochemistry AdrianBrown <br />1. All sulfur in the rockmass is present as pyrite, and oxidizes completely. <br />2. All carbon in the rockmass is present as carbonate, and is available to react completely. <br />3. Neutralizing potential of lime added to ore for agglomeration and pH control (11 -12 lb /ton) is <br />ignored for the purposes of ABA accounting. <br />4. Ore will ultimately oxidize, and the products of oxidation will leave the ore -pad. <br />The potential effect of the mining process is to make the sulfide in the rockmass available for oxidation, <br />thereby moving forward in time the oxidation of the sulfides in this material. If the material were to <br />remain un- mined, the sulfide would over time oxidize naturally, and the products would require the <br />same mass of natural carbonate for neutralization. In this respect, the mining process has no net potential <br />chemical impact. <br />Each of the overburden storage sites and mine backfilling sites has been designed to allow storage of <br />any overburden of any geochemistry that is found in the District, thus eliminating quality control issues <br />at storage locations. <br />Closure of the VLFs comprises cyanide neutralization, followed by breaching of the liner systems of the <br />internal ponds, and reclamation of the surface of the facilities. After closure, water and air will infiltrate <br />through the surface cover, allowing the sulfide in the ore material to oxidize. The products of oxidation <br />will pass through the ore material and enter the subsurface materials. This exfiltrating water is expected <br />to reach the Diatreme, either through direct flow to the diatremal rockmass, or by collection by the <br />drawdown cone in the granitic rockmass around the Diatreme caused by flow of regional ground water <br />from the Carlton Tunnel <br />3.2.5 Exposed Mine Walls <br />At the completion of mining, the Altman, East Cresson Mine Extension ( "ECME "), Wildhorse, and <br />Wildhorse Extension ( "WHEX ") portion of the East Cresson Mine area, and the Schist Island and Globe <br />Hill (western) portions of the North Cresson Mine area will be substantially backfilled with overburden <br />materials. The South Cresson portion of the Main Cresson Mine area and a portion of the Globe Hill <br />(eastern) portion of the North Cresson Mine areas will be un- backfilled, and the Main Cresson portion <br />of the Main Cresson Mine area will be partially backfilled. <br />Accordingly, there will remain some areas of mine wall which will remain exposed to the atmosphere, <br />and will be subject to sulfide oxidation. The sulfide oxidation products from these walls have been <br />evaluated by the following process: <br />1. The areas of the mine walls that will be exposed at the end of mining and mine reclamation were <br />determined by measurement from the mine closure plan (Plate 2). <br />2. The depth within the walls that can be subject to oxidation due to mining was assumed to be <br />equal to the depth of a single bench excavation (35 feet), as this is the maximum wall penetration <br />that could be affected by blasting, unloading, and mining activities. The oxidation of pyrite in <br />materials deeper in the wall is assumed to be unchanged by surface mining from its pre- mining <br />rate. <br />1385L.20120125 16 <br />