NI43-101Pre-Feasibility Study Report - page 482

Rare Element Resources
Bear Lodge Project
Canadian NI 43-101 Technical Report
October 9
, 2014
10135-200-46 - Rev. 0
Factors of safety (FOS) for cut and fill slopes and embankments and stacked
tailings slopes within TSF meet or exceed minimum allowable FOS as set by
the State Engineer’s office for like structures or as considered accepted
industry standards for TSF operations and not covered under the State
Engineer’s Office regulations. Criteria
Once the TSF is in operation, the site operations criteria will be regulated by
approved permit conditions and by health and safety regulations administered by the
U.S. Mine Safety and Health Administration (MSHA). Allowances were incorporated
in the TSF layout and design criteria for the TSF operations based on previous
experience with MSHA and anticipated environmental permit conditions. In particular,
the active tailings stacking area will be limited and the stability of the working area will
meet factor of safety allowances typical for end construction conditions in earthen
dams. It is assumed that placement of waste will be during day shift hours. Stockpile
facilities will be sized to accommodate 24-hour plant operations and will allow for
shut-down periods due to bad weather and for emergency equipment maintenance.
The actual storage volume will be determined in final design of the project facilities. A
temporary soil cover to limit runoff and moisture uptake control in the tailings during
periods of bad weather or prolonged exposure will be placed over the tailings as
needed. Hydromet Waste Streams
Two waste streams will be discharged from the Hydromet plant and mixed with lime
stone and quick lime for deposition into the TSF. They are identified as the acid leach
tailings from an initial processing step and the precipitate residue from the rare earth
element recovery process. Samples of these materials have been received from Rare
Element. No summaries of data for neutralization or geotechnical characterization of
the tailings are discussed at this time due to the incompleteness of the testing using
recent samples from the Hydromet Plant, and the fact that additional testing is
A) Mass Balance Estimates
Based on currently available production estimates, tailings from the Hydromet plant,
including neutralization amendments, will discharge at an initial rate of 294,354 tpy.
The rate of total tailings discharge from the Hydromet plant reporting to the TSF will
vary year to year with the minimum tonnage of 284,656 tons reporting in year 8 and
the maximum tonnage of 378,222 tons reporting in year 14. The average yearly
production of dry tailings, including neutralization amendments is 350,198 tpy over an
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