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FORT KNOX MINE
Final permits and public process documents were issued on July 3,
2007 by the State of Alaska for the Fort Knox Mine Heap Leach Project
near Fairbanks, Alaska as follows:
PROJECT DESCRIPTION
The Fort Knox Mine is an open-pit gold mine, located approximately
26 miles northeast of Fairbanks, Alaska. The operator proposes
to add a heap leach gold recovery facility in the Walter Creek drainage. The
mine was originally permitted in 1994, and currently produces about
330,000 ounces of gold annually. The mine site is located primarily
on lands owned by the State of Alaska and the Mental Health Trust. FGMI
employs 400-425 people at the mine and mill, which operate on two shifts,
24 hours per day, 365 days per year.
The valley fill heap leach will be located in the upper end of the
Walter Creek drainage immediately upstream from the existing tailings
storage facility (TSF). Excluding the haul road and access roads, the
heap leach pad with an in-heap storage embankment and base platform
will cover approximately 310 acres and will have a total capacity for
leaching 165 million tons of ore. The haul road to the pad will cover
approximately 40 additional acres. The pad is to be constructed in
five stages, which are illustrated on Figure 1.2 of the Heap Leach
Facility Project Description. Table 1.0 provides the area and tonnage
planned for each stage of development. The clearing of brush and trees,
initial earthwork in preparation of liner construction, the site access
road, the portion of the in-heap embankment outside the pad limit,
and establishment of drainage control will occur over the entire 310
acres at the beginning of the project. Within that area, 130 acres
of lined pad will be constructed for the first two stages and loaded
with ore. Each of the three additional stages will be constructed as
needed for loading ore.
Table 1.0: Area and Tons for Each Stage of Development
|
Lifts |
Pad Area
[Square Feet] |
Pad
Area
[Acres] |
Cumulative
Leach Pad
Area [Acres] |
Capacity
By Stage
[Thousand Tons] |
Cumulative
Capacity
[Thousand Tons] |
Stage 1 |
1-4 |
3,034,731 |
70 |
70 |
13,716 |
13,716 |
Stage 2 |
5-7 |
2,362,850 |
54 |
124 |
21,659 |
35,375 |
Stage 3 |
8-10 |
2,422,613 |
56 |
180 |
31,567 |
66,942 |
Stage 4 |
11-13 |
2,392,773 |
55 |
234 |
36,049 |
102,991 |
Stage 5 |
14-19 |
2,030,238 |
47 |
281 |
58,202 |
161,193 |
Ore for the heap leach pad will consist of run-of-mine rock from the
Fort Knox Pit as well as lower grade ore that was previously placed
in various stockpiles. The Barnes Creek and Fish Creek stockpiles currently
contain 29 million tons of lower grade ore that will be loaded on the
heap leach pad. The ore is characterized by relatively high permeability
that will promote efficient flow in the heap for rapid solution recovery
and drainage and for rapid rinsing at closure.
In-heap storage of process solution and storm water will be accomplished
uphill of an embankment at the downstream toe of the heap. The rock
that will be used to construct the embankment for the in-heap storage
pond is sound, durable, and of high strength similar to the quality
of the rock that has been used to construct the downstream random fill
for the Fort Knox Mine Tailing Storage Facility (TSF).
The valley fill heap leach pad will be constructed with a 12-inch
prepared subbase with a coefficient of permeability of less than 1×10-5
cm/sec overlain by a geomembrane liner of 80-mil thick LLDPE or similar
material. Above the geomembrane liner, there will be an overliner consisting
of 3 feet of crushed rock containing a network of pipes to promote
rapid drainage. The overliner will protect the geomembrane liner during
ore loading and will help promote leachate collection and maintain
a low head on the geomembrane liner.
The facility will utilize in-heap storage to collect pregnant (gold-bearing)
solution. In addition to providing the necessary operating capacity
for pregnant solution, the in-heap storage pond will be sized to contain:
(1) solution from a 24-hour drain down, plus (2) the runoff from the
100-year/24-hour storm event.
Beneath the in-heap storage pond, a Leachate Collection and Recovery
System (LCRS) will be constructed between an overlying primary geomembrane
liner and an underlying secondary geomembrane liner underlain by a
12-inch-thick layered prepared subbase. The LCRS will consist of a
drainage layer that will report to a pump back system to return any
solution passing through the primary liner back to the in-heap storage
pond. The LCRS constructed in conjunction with the double liner
in the area of the in-heap storage reservoir will provide leak monitoring
and collection. A Process Component Monitoring System (PCMS) will be
constructed under the main header lines for the solution collection
system, outside of the LCRS, providing additional leak detection. An
underdrain system consisting of a network of drainage channels containing
drain rock will route water from baseflow in Walter Creek, and other
seeps and springs under the subbase to the tailing impoundment providing
a third level of leak detection.
Barren (non-gold-bearing) solution will be applied on the heap leach
using drip emitters, or possibly sprinklers during the warm months.
The solution will flow through the run-of-mine ore. Pregnant solution
will flow to the in-heap storage reservoir, which will have an operating
capacity of about 68 million gallons, or 9.1 million cubic feet. The
pregnant (gold-bearing) solution that collects in the wells in the
in-heap storage reservoir will be pumped to the Carbon-In-Columns (CIC)
plant using vertical pumps located in the solution collection wells.
Barren solution and pregnant solution will be pumped in pipes between
the pad and the CIC plant. Loaded carbon will be processed in the existing
Fort Knox mill facilities.
The heap leach pad will be located immediately upstream of the tailing
impoundment. The tailing dam is a zoned, earth-filled structure designed
to hold tailing and process water from the mill as well as surface
runoff water. The dam is designed and will be maintained to contain
the 100-year/24-hour storm event and the average 30-day spring breakup
plus provide 3 feet of freeboard. During the time of operation of the
heap leach pad, the tailings dam will remain operational and the minimum
allowable freeboard will be increased to include the full volume of
the in-heap storage pond, for the extremely unlikely event of a catastrophic
failure of the heap leach pad embankment dam. The tailing impoundment
is a zero discharge facility. The mill recycles water from the tailing
impoundment for reuse in the beneficiation process. The water in the
tailing impoundment will also be utilized for the heap leach process.
KEY PROJECT DOCUMENTS (submitted by FGMI)
FGMI has issued six documents detailing the reclamation and closure of the Fort Knox Mine as well as the construction, operation, reclamation, and closure of the proposed heap leach facility.
Archive of June 2006 Applications, Draft Project Authorizations, and Public Process
Annual Meetings and Annual Reports
2009 Annual Agency Meeting
March 18, 2009 1PM to 3PM at the Princess Hotel in Fairbanks
2008 Annual Agency Meeting
March 12, 2008 9AM to 11AM at the Princess Hotel in Fairbanks
2007 Annual Agency Meeting
March 28, 2007 9:30AM to noon at DNR in Fairbanks
If you would like to find out more about the state’s permitting process for the Fort Knox Mine, please contact:
State of Alaska Large Mine Permitting Team
Jack DiMarchi, Project Manager
ADNR / Office of Project Management & Permitting
3700 Airport Way, Fairbanks, AK 99709
Telephone: (907) 374-3708
Fax: (907) 451-2703
Email: john.dimarchi@alaska.gov
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