PERMFILE59877

• Permit No: M1994117
• IBM Index Class Name: Permit File
• Doc Name: LIMITED IMPACT OPERATION 110 RECLAMATION PERMIT APPLICATION PACKAGE
• Media Type: D
• Archive: No

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additional borrow material and sands, and the cyple is repeated., Since the aub-
eequent layers of tailings are retained by the a~ee iv~e dikes, it was impo~ t__,
ant ror~e ~erw~~usos~e a ash Imtsally t7ue'~rQS~ved by_
• ~~ zoned eta er ch h`-^" ae an upetteam gradation from com-
pacted borrow material into a coarse sand zone around the interior of the dike.
the successive dikes were built over the underlying coame sand zones, rather
than oa top of the previously deposited, unconsolidated tailings. 'this variation
of the upstream method of tailings dam construction is preferred, because it
• keeps the slimes, and the free water surface, away from the upstream face of
the impoundment dam This prevents the tailings from piping through the
starter dike, allows the slimes to consolidate, promotes ideal stratification of
the tailings, and creates a relatively impervious seal in the bottom of the tail-
ings pond. Seepage can be controlled, because the phreatic line, or water sur-
face, is lowered on both the upstream and downstream faces of the tailings
• dam. A refinement of the upstream method of tailings dam construction
employe a hydrocyclone to separate the sand fivm the slimes. This classified
product is then used to achieve a broader sand zone, and to raise the success-
ive dikes. Since cyclones recover more dam building material fom very finely
ground tailings, this permitted faster dam construction. y adhe '
• deli features during the construction and o ration o e s pond, a
orizon ve en o to 1 was maintained on e -
ace o e unpoun en auperna or oating, water is
emov se m a pon , followed by decantation. 'This type of
tailings dam construction is well suited for milling operations which have
relatively low tonnage rates, utilize a coarse grinding circuit, and allow the
• tailings to become well compacted before slowly raising the level of the im-
poundmentdam.
Construction of the tailings dam commenced with the erection of the starter
dike, or tce dam. The starter dike was built from locally available borrow
• material, in a zoned embankment that has an upstream gradation into sand.
To increase the shear strength of the starter dike, compaction of the borrow
material was obtained by dynamically dropping it, and by making repeated
passes over it with the excavation equipment. The initial dimensions of the
starter dike were between 4 and 6 feet in height, and 11 and 17 feet in width;
depending upon the quantity of borrow material found to be suitable for dam
• construction. The starter dike was constructed between the 8,550 foot and
8,565 foot elevation contours. It extends at least 50 feet upstream along the
lateral edges of the tailings pond. This provided apace around the downstream
perimeter of the starter dike for it to be widened and raised with additional bor-
row material before the initial level of the tailings pond was increased.
• The tailings are pumped fiom the mill to the discharge line, which is placed
around the periphery of the starter dike. The discharge line releases the tail-
ings into the tailings pond from spigots located every 10 to 20 feet along the
upstream crest of the starter dike. By selectively controlling the location of
the spigots, the tailings are discharged in a manner that promotes the favora-
~ ble separation of the tailings. While the slimes and water pool are maintained
in a central position, away from the embankment; the sand beach that forme
ff~'