technical report on the nechalacho deposit, thor lake project ...

• To allow the observational approach to be utilized in the ongoing design, construction,
and operation of the facility. The observational approach is a powerful technique that
can deliver substantial cost savings and high level of safety. It also enhances
knowledge and understanding of the site-specific conditions. For this method to be
applicable, the character of the project must be such that it can be altered during
construction (Peck, 1969).
The construction will be scheduled to ensure that there is always sufficient storage capacity
available in the facility to avoid overtopping. The embankment raising schedule provides
sufficient freeboard to safely accommodate the supernatant pond and Environmental Design
Storm event, combined with wave run-up. A spillway is included to pass the Inflow Design
Flood event.
Options Assessment
A review of potential storage location options was completed as part of 2009 studies. The
review considered slurry tailings disposal in seven different topographic basins within the Thor
Lake project area as well as submarine tailings disposal in Thor, Long and Elbow Lakes. The
Ring and Buck Lake basin was selected as the preferred option based on an assessment of
<strong>technical</strong>, environmental, economic and socio-economic factors.
Design Basis
The pre-feasibility level design of the Thor Lake TMF has been based on an approximate mine
life of 15 years with a total ore reserve of approximately nine million tonnes. The average
mining rate for the Nechalacho Deposit will begin at approximately 1,000 dry tpd and increase to
2,000 dry tpd in year four of operations.
Tailings and Water Management
The tailings and water management strategy for the Thor Lake pre-feasibility design consists of
a closed loop system to minimize impact to the natural hydrologic flows within the Thor Lake
watershed area. All tailings solids and fluids as well as impacted water from the Process Plant
will <strong>report</strong> to the Tailings Basin. The TMF design currently proposed includes a Polishing Pond,
and excess water from the Tailings Basin will be treated (if necessary) and discharged from the
Polishing Pond to Drizzle Lake. Ultimately, all water from the TMF will return to Thor Lake via
Drizzle and Murky Lakes. Fresh water for operations will be drawn from Thor Lake and reclaim
water will be drawn from the Tailings Basin. The pre-feasibility water balance has assumed that
the process water feed to the Process Plant will consist of 50% fresh water and 50% recycled
water from the Tailings Basin
Technical Report 43-101 – March 13, 2011 Page 18-43
Prepared by Avalon Rare Metals Inc.