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PERMFILE54436
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PERMFILE54436
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Last modified
8/24/2016 10:57:32 PM
Creation date
11/20/2007 4:09:48 PM
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Template:
DRMS Permit Index
Permit No
M1994117
IBM Index Class Name
Permit File
Doc Name
APPLICATION FOR A MILLING AND RECLAMATION PERMIT GOLD HILL MILL LIMITED IMPACT PERMIT
Media Type
D
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No
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<br />type of discharge. The coarsest sand particles drop out closest to the point of <br />discharge, and the finest particles (the slimes) flow into the center of the tail- <br />ings dam, where the excess water forme a localized pond. Because of the <br />relatively large size differential between the coarse and fine fractions of the <br />tailings, the coarse sand particles form a beach in front of the spigots. 'The <br />sand beach that is formed around the upstream perimeter of the starter dike ie <br />used for raising the height of the impoundment dam This is accomplished in <br />stages. When the initial pond is nearly filled, the starter dike is raised with <br />additional borrow material and sands, and the cycle is repeated. Since the aub- <br />eequent layers of tailings are retained by the successive dikes, it was import- <br />ant for these dikes to be built on a stable base. Initially, this was achieved by <br />building a zoned starter dike, which has an upstream gradation from com- <br />pacted borrow material into a coarse sand zone around the interior of the dike. <br />The successive dikes were built over the underlying coarse sand zones, rather <br />than on top of the previously deposited, umm~aolidated tailings. 'This variation <br />of the upstream method of tailings dam construction is preferred, because it <br />keeps the slimes, and the free water surface, away from the upstream face of <br />the impoundment dam 'This prevents the tailings from piping through the <br />starter dike, allows the slimes to consolidate, promotes ideal stratification of <br />the tailings, and creates a relatively impervious seal in the bottom of the tail- <br />ings pond. Seepage can be controlled, because the phreatic line, or water sur- <br />face, is lowered on both the upstream and downstream faces of the tailings <br />dam. A refinement of the upstream. method of tailings dam rnnatruction <br />employe a hydrocyclone to separate the Band from the slimes. 17ris classified <br />product ie then used to achieve a broader sand zone, and to raise the success- <br />ive dikes. Since cyclones recover more dam building material fiom very finely <br />ground tailings, thin permitted faster dam construction. By adhering to these <br />design features during the construction sad operation of the tailings pond, a <br />horizontal to vertical elope gradient of 1.5 to 1 was maintained on the down- <br />stream face of the impoundment dam 'The supernatant, or floating, water is <br />removed by settling in the tailings pond, followed by decantation. 'This type of <br />tailings dam construction is well suited for milling operations which have <br />relatively low tonnage rates, utilize a coarse grinding circuit, and allow the <br />tailings to become well compacted before slowly raising the level of the im- <br />poundmentdam. <br />Construction of the tailings dam commenced with the erection of the starter <br />dike, or tce dam. The starter dike was built from locally available borrow <br />material, in a zoned embankment that has an upstream gradation into sand. <br />To increase the shear strength of the starter dike, compaction of the borrow <br />material was obtained by dynamically dropping it, and by making repeated <br />passes over it with the excavation equipment. 'T$e initial dimensions of the <br />starter dike were between 4 and 6 feet in height, and 11 and 1? feet in width; <br />depending upon the quantity of borrow material found to be suitable for dam <br />construction. 'Ihe starter dike was constructed between the 8,550 foot and <br />8,565 foot elevation contours. It extends at least 50 feet upstream along the <br />lateral edges of the tailings pond. This provided space around the downstream <br />perimeter of the starter dike for it to be widened and raised with additional bor- <br />row material beforo the initial level of the tailings pond was increased. <br />
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