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2008-10-03_REVISION - M1980244
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2008-10-03_REVISION - M1980244
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Last modified
6/15/2021 5:52:19 PM
Creation date
10/7/2008 7:42:26 AM
Metadata
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Template:
DRMS Permit Index
Permit No
M1980244
IBM Index Class Name
REVISION
Doc Date
10/3/2008
Doc Name
Additional Response to Adequacy Review
From
CC&V
To
DRMS
Type & Sequence
AM9
Email Name
BMK
Media Type
D
Archive
No
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DRMS appears to suggest it its comment that in order for the quality of the regional <br />ground water intersected by the Carlton Tunnel to be protected, the entire inventory of <br />carbonate minerals in the diatreme needs to be available to infiltrating leachate. This is <br />not so; CC&V has determined that a maximum of only 3/1000 (0.32%) of the entire <br />inventory needs to be available to the infiltrating leachate to neutralize the maximum <br />acidity that can be contained in that .leachate. Given the high rock porosity of the <br />rockmass, the long flow pathway for leachate from the ground surface to the regional <br />ground water table intersected by the Carlton Tunnel, the long residence time of the <br />leachate in the rockmass, and the plugging of preferential seepage pathways by the <br />products of acid neutralization, it is considered that there is a very high probability that <br />carbonates in the diatreme will be available and contacted by the entire leachate flow. <br />V1. O.: As nliningfiwes are C'xpose(l, periodic Sl)ot-cliecking of ABA is recommended as a QA1QC on <br />existing data. <br />CC&V Response: <br />The recommendation by DRMS to spot-check ABA for QA/QC is part of CC&V's past <br />and current mining practice. Immediately prior to mining each bench, CC&V performs <br />Level 1 inf ll exploratory drilling of the material to be mined, at approximately 100 foot <br />centers. Samples for this drilling are taken on a 5 foot basis, and tested for gold and <br />silver. Composited 20 foot samples are also tested for ABA parameters (sulfur, carbon) <br />by the LECO furnace method. The results from this testing are combined with the prior <br />Level 3 and Level 2 drilling data and the block model re-run and verify ore and ABA <br />conditions. <br />VI. R.: Whether this process is actually occurring or not is only bl7eculatlon, and the ansi-ver should he <br />apparent whenever the leachate ftoin waste rock eventually reports to the Carlton Tunnel. <br />CC&V Response: <br />The plugging of calcite veins by replacement gypsum formed by neutralization is <br />expected, based on the relative specific volumes of calcite (11.8 cubic feet per ton) and <br />the product of neutralization, calcium sulfate dihydrate (gypsum and selenite)(13.8 cubic <br />feet per ton). The 17% volume increase on reaction is slightly reduced by more calcium <br />sulfate than calcite remaining in the dissolved phase, but in general this reaction results <br />in complete or almost complete calcite replacement. Replacement is demonstrated in the <br />diatreme by the frequent observation of calcium sulfate dihydrate veins (appearing as <br />gypsum or selenite) in the diatremal rockmass. Most of this gypsum replacement appears <br />to be natural, occurring due to natural neutralization of acidic emplacement fluids, or by <br />neutralization of acid created by natural oxidation of sulfide in the diatremal rockmass. <br />Some of the replacement veining appears to be recent, likely the result of neutralization <br />of sulfide oxidation associated with underground mining. <br />CC&V agrees with DRMS that the answer should be apparent from the regional ground <br />water that is intersected by the Carlton Tunnel. It is already apparent. Since it was first <br />sampled, the Carlton Tunnel water has exhibited high concentrations of calcium, <br />bicarbonate, and sulfate, and has been continuously saturated in calcium sulfate and <br />calcium carbonate. These concentrations are a result of calcite neutralization of the <br />products of sulfide oxidation. This process was naturally occurring in the diatreme pre- <br />mining, and was accelerated by the underground mining and the progressive dewatering <br />of the diatreme by (primarily) the Moffat, Roosevelt, and Carlton 'Funnels. No break- <br />through of acidic water has occurred in the recorded history of the Carlton Tunnel, <br />despite more than 100 years of sulfide oxidation, acid generation, and neutralization in <br />the rockmass. This lack of creation of preferential pathways by dissolution of carbonate <br />is reasonably attributed to gypsum replacement plugging of acid seepage flow pathways <br />where the carbonate has been exhausted. The gypsum has and will continue to largely or <br />completely prevent bypass of acidic water to the regional ground water table intersected
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