PERMFILE54436

• 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
• Archive: No

The tailings are pumped from 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 forma
in front of the npigote is used to raise the tailings dam in 1 or 2 foot increments.
If the desired gradation, permeability, and compaction characteristics of the
tailings cannot be obtained by using spigots, a cyclone is employed to control
the nand separation protean. A 2.8 to 1 horizontal to vertical elope gradient
was maintained during the mnatruction of the tailings dam, which wan raised
in successive stages to a maximum height of 30 feet. When the tailings im-
poundment dam reacher its storage capacity, it will occupy a rectangular area
that has the dimensions 400 feet by 260 feet at its longest and widest points.
This milling complex wan designed to maintain a ratable water balance
throughout the ore processing and tailings impoundment system. The milling
operation requires 4 tone of water for every ton of ore processed in the gravity
and flotation concentration circuits. Fresh water is introduced into the milling
process in the grinding circuit (see Figure 1). Moat of the water that is used in
grinding and claeaification, and in the gravity concentration circuit, is recycled
from the thickener tank overflow launder back to the ball mill. Fresh water is
also added to the thickened pulp as it passes from the thickener tank underfloor
to the flotation concentration circuit. A closed circuit was planned to recycle
the water that accompanies the tailings pumped from the mill to the tailings
retention structure. The excess water that accumulates in the tailings pond is
decanted from the water pool and stored underground in the Hazel A. edit. A
steel pipe with water decant holes is used to remove the excess water that
collects in the tailings pond. This decantation line is used to control the water
level in the tailings pond, and to keep the water pool as far as possible from the
crest of the embankment. Additional nections of steel pipe were connected to
the decantation line to regulate the elevation of the water pond an the tailings
dam's height increased. Several seep rings were attached to the steel pipe to
prevent the tailings from piping along the decantation line. The decantation
line was connected with the Hazel A. edit through one of the test holes that
were drilled by the U.S. Bureau of Mines. This underground storage area is
used to clarify the decanted water by allowing it to nettle prior to recycling the
water through the mill. It also provides additional reaerwir capacity for the
excess water removed from the tailings pond.
The amount of water that is decanted and stored underground in the Hazel A.
Adit is primarily determined by the water balance maintained throughout the
processing and impoundment system The water consumed in the milling pro-
ceeaand loot in evaporation from the tailings pond does not exceed 20 percent
of the water used in the mill. The water consumed in the ore m'11~r,g process
mainly results from water entrapped in the gravity and flotation concentrates
and in the umm~iaolidated tailings. Because of the altitude and limited size of