INSPEC32881

• Permit No: M1983141
• IBM Index Class Name: Inspection
• Doc Date: 3/24/1992
• Doc Name: LIST OF EXHIBITS FOR CORRECTIONS TO SYNOPSIS OF EVENTS
• Media Type: D
• Archive: No

1
I process. A 2.8 to 1 horizontal to vertical slope gradient
will be maintained during the construction of the tailings
dam, which will be raised in successive stages to a maximum
height of 30 feet. When the tailings impoundment dam has
' reached its storage capacity, it will occupy a rectangular
area that will have the dimensions 400 feet by 260 feet at its
longest and widest points.
This milling complex has been designed to maintain a stable
water balance throughout the ore processing and tailings
impoundment system. The milling operation will require 4 tons
of water for every ton of ore processed in the gravity and
' flotation concentration circuits. Fresh water will be intro-
} duced into the milling process in the grinding circuit (see
Figure 1). Most of the water that will be used in grinding and
classification, and in the gravity concentration circuit, will
' be recycled from the thickener tank overflow launder back to
the ball mill. Fresh water will also be added to the thick-
ened pulp as it passes from the thickener tank unde rf low to
the flotation concentration circuit. A closed circuit has
been planned to recycle the water that will accompany the
' tailings pumped from the mill to the tailings retention
structure. The excess water that accumulates in the tailings
pond will be decanted from the water pool and stored under-
ground in the Hazel A. adit. A steel pipe with water decant
' holes will be used to remove the excess water that collects in
the tailings pond. This decantation line will be 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 embank-
ment. Additional sections of steel pipe will be connected to
' the decantation line to regulate the elevation of the water
~
pond as the tailings dam's height is increased. Several seep
rings will be attached to the steel pipe to prevent the
' tailings from piping along the decantation line. The decan-
~~ '` ration line will be connected with the Hazel A. adit through
one of the test holes that were drilled by the U.S. Bureau of
Mines. This underground storage area will be used to clarify
~~~ the decanted water by allowing it to settle prior to recycling
' ~ ~ the water through the mill. It will also provide additional
reservoir capacity for the excess water removed from the
S ' tailings pond.
' ` "1 The amount of water that will be decanted and stored under-
rimarily determined by
adit will be
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j the water balance maintained throughout the processing and
~ 1 impoundment system. The water consumed in the milling process
' ~` and lost in evaporation from the tailings pond is not expected
' ~. ~ to exceed 20 percent of the water used in the mill. The water
consumed in the ore milling process will mainly result from
i water entrapped in the gravity and flotation concentrates and
i ; in the unconsolidated tailings. Because of the altitude and
' limited size of the tailings pond, only a relatively small
'~ amount of water is expected to be lost due to evaporation.
Recycling the mill water will reduce the amount of fresh water
-' ~ needed in the milling process, and decrease the quantity of
water pumped from Left Hand Creek.
Because of the hillside location selected for the tailings
impoundment structure, water runoff inflow will not be sub-
stantial. A drainage diversion ditch will be excavated above
' the tailings pond to intercept surface water runoff and convey
it away from the tailings impoundment area.
' k A seepage collection ditch will also be excavated around the
downstream perimeter of the tailings embankment dam. The
water that collects in this ditch will be conveyed by a
~~ pipeline to the Hazel A. adit for underground storage and will
' be recycled through the milling facility.
' Fxh, b:f J
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