This was a presentation given by AMEC to ADEQ at the kickoff of the APP permitting process. This provided the background for the Rosemont Project dry stack.

1. Dry Stack
Tailings Storage Facility

2. Advantages of Dry Stack TSF Over Conventional
Slurry Tailings
§ Tailings are placed under unsaturated conditions resulting in minimal
seepage
§ Dry Stack TSF not susceptible to breaching because there is no reclaim
pond
§ Significant water conservation minimizes water usage and consumption
requirements
§ Facilitates concurrent reclamation and revegetation during operation
§ Minimizes disturbance area
§ Minimizes visual impact from surrounding areas

3. Dry Stack TSF Design Criteria
n Production rate = 75,000 tpd (tons per day) or 27 MT per year
n Storage capacity estimated at 596 MT and mine life estimated at approximately
21 years
n Average tailings in-place dry density = 109 pcf (pounds per cubic foot)
n Compliance with all applicable regulations including the Arizona Best Available
Demonstrated Control Technology (BADCT) standards
n Rockfill Buttresses are placed around the perimeter of the facility in 50-foot high
lifts with 3H:1V side slopes and 25 foot benches
n 3.5H:1V overall side slope
n Dry Stack TSF will be constructed in two phases (Phases I and II)
n Implement dust control suppression measures throughout the production period
n Concurrent reclamation and revegetation during operations

4. Phase I Dry Stack TSF Characteristics
n Contains Approximately 12 years of production
n Maximum Buttress elevation = 5250 feet
n Maximum Tailings surface elevation = 5237.5 feet
n Total capacity = 343 million tons (MT)
n Total footprint of 706 Acres
n Footprint outside of McCleary Canyon

5. Phase I Dry Stack TSF Characteristics
n Evaporation ponds will be incorporated into tailings lifts to capture
stormwater runoff from the tailings surface
n Temporary perimeter ditches will be constructed where necessary to route
stormwater runoff to evaporation ponds
n A temporary diversion channel will be constructed at start-up to capture
stormwater runoff upstream of the phase I Dry Stack TSF through production
year 4
n A permanent Diversion Channel sized for the PMF and armored for the 200
year storm will be constructed at start-up and will divert stormwater
upgradient of the plant site into McLeary canyon north of Phase I

6. Phase I Dry Stack TSF

7. Phase I Dry Stack TSF Typical Sections

8. Phase I Dry Stack TSF Filling Curve

9. Phase II Dry Stack TSF Characteristics
n Contains approximately 8 years of production
n Maximum Buttress elevation = 5250 feet
n Maximum Tailings surface elevation = 5237.5 feet
n Total capacity = 253 million tons (MT)
n Total footprint 400 Acres

10. Phase II Dry Stack TSF Characteristics
n Evaporation ponds will be incorporated into tailings lifts to capture runoff
from the tailings surface
n Temporary perimeter ditches will be constructed where necessary to divert
stormwater to evaporation ponds
n An additional permanent diversion channel will be constructed in year 12 to
divert stormwater upstream of phase II as well as from the diversion channel
upgradient of the Plant site
n Dry Detention Basins will be constructed as part of Permanent Diversion
Channel system and will greatly reduce peak runoff produced by storm
events

11. Phase II Dry Stack TSF

12. Phase II Dry Stack TSF Typical Sections

13. Phase II Dry Stack TSF Filling Curve

14. Ultimate Dry Stack TSF

15. Dry Stack TSF
Production Progression

16. Production Year 0 to Year 1
Tailings capacity = 30 MT

17. Production Year 2 to Year 5
Tailings capacity = 153 MT

18. Production Year 6 to Year 10
Tailings capacity = 288 MT

19. Production Year 11 to Year 12
Tailings capacity = 333 MT

20. End of Phase I-Start of Phase II
Production Year 13
Tailings capacity = 357 MT

21. Production Year 14 to Year 15
Tailings capacity = 425 MT

22. Production Year 16 to Year 20
Ultimate Dry Stack TSF
Tailings capacity = 586 MT

23. Dry Stack TSF Site Conditions

24. Climate
n Tetra Tech conducted the meteorological analysis as part of their Feb 2009 design
process
Month Precipitation Pan Evaporation Projected Pan Evaporation
January 1.10 3.59 4.13
February 0.85 4.46 4.28
March 0.90 7.01 7.11
April 0.39 9.35 8.50
May 0.22 11.91 10.38
June 0.47 13.31 10.75
July 4.34 10.00 4.93
August 4.13 8.28 2.89
September 1.55 8.06 4.40
October 1.33 7.17 6.15
November 0.66 4.49 4.11
December 1.43 3.57 3.89
Total 17.37 91.20 71.52
Event 1-Hour 3-Hour 6-Hour 24-Hour
2-yr 1.42 1.60 1.83 2.21
5-yr 1.85 2.03 2.30 2.75
10-yr 2.16 2.38 2.68 3.18
25-yr 2.57 2.86 3.22 3.77
50-yr 2.87 3.24 3.66 4.23
100-yr 3.17 3.63 4.12 4.75
500-yr 3.84 4.59 5.24 6.00
1000-yr 4.14 5.03 5.76 6.57

25. Site Geology Summary
n Project specific geology is discussed in the Tetra Tech report entitled “Geologic
Hazards Assessment” dated June 2007
n The geologic units underlying the Dry Stack TSF include
• Gila Conglomerate
• Mount Fagan Rhyolite
• Apache Canyon Formation
• Willow Creek Formation
• Alluvial materials

27. Seismic Hazard Analysis Summary
n The Maximum Credible Earthquake (MCE) based on a deterministic
analysis was used for the design of the TSF
n The deterministic analysis included:
• Identifying the largest potentially active fault close to the site
• Determining earthquake magnitude that the fault is capable of producing
• Determining the Peak Ground Acceleration (PGA) that will be produced at the site from this
event
n The Santa Rita fault zone determined to be the controlling of 27
contributing fault sources within a 200 kilometer radius of the project site
with a distance from site of 11.2 kilometers and a length of
approximately 52 kilometers.
n The Santa Rita fault zone capable of producing a PGA of 0.33g and a
magnitude 7.1 event

28. Geotechnical Investigation
n Geotechnical field investigation were carried out in two phases by Tetra
Tech, between November 2006 and March 2007 and between May and July
of 2008. The objective of the investigations included the following:
• To define general subsurface conditions for use in evaluation of the Dry Stack TSF stability
• To identify suspect zones that could affect the performance of the Dry Stack TSF
• To quantify engineering characteristics of the materials incorporated into the Dry Stack TSF
n A total of 10 test pits and 38 geotechnical borings in the vicinity of the Dry
Stack TSF allowed subsurface conditions to be defined
n A total of approximately 13,000 feet of seismic refraction survey was also
completed near the vicinity of the Dry Stack TSF footprint

29. Geotechnical Investigation

30. Geotechnical Investigation Summary
n Depth of Bedrock varied across the footprint from 0 to 100 feet
n Average depth to bedrock approximately 40 feet
n Soils included 1 to 3 feet of topsoil underlain by alluvial material
n Groundwater elevations vary across the footprint from elevations 4,650
to 4,850 feet

31. Geotechnical Investigation Summary
n The foundation consists primarily of relatively shallow, dense to very dense
granular soils.
n Foundation preparation will require stripping loose surficial soils providing a
uniformly dense founding surface for the tailings.
n A Laboratory testing program was completed on select disturbed samples and
bench scale tailing samples obtained from field investigations and pilot plant
studies.
n Two bench scale tailings samples, Colina and MSRD-1 were tested. Both samples
were determined to be low-plastic silt (ML) with a plasticity index of 1.
n Colina maximum dry density of 115.8 at 14.9%
n MSRD-1 maximum dry denstiy of 118.9 at 14.8%

32. Geologic Hazard Summary
n Landslides or rockfall hazard potential will be minimal within the Dry Stack
TSF project area.
n Collapsible soils are not considered to be an issue within the footprint.
n Historic mining activity will require further field reconnaissance to
determine the extent of workings for remediation purposes.
n Earthquake induced ground failure (liquefaction) is not anticipated to
occur within either the foundation or the Dry Stack TSF.

33. Tailings Testing Summary
n Other laboratory testing performed on the bench scale tailings samples included:
• One-Dimensional Consolidation
• Triaxial Shear
• Flexible Wall Permeability
• Rigid Wall Permeability
• Moisture Retention Testing
• Geochemical Tailings Characterization (Tetra Tech)
n Acid-Base Accounting
n Net Acid Generation
n pH Testing
n Humidity Cell Testing (Kinetic)
n Synthetic Precipitation Leaching
n Meteoric Water Mobility
• Solids Liquid Separation
n Flocculant Screening and Evaluation
n Static Thickening
n Dynamic High Rate Thickening
n Pulp Rheology
n Pressure Filtration Studies
n Vacuum Filtration Studies

34. Geochemical Test Results
n Tailings generally contain less than 0.01 percent sulfide-sulfur
n Tailings possess high capacity for acid neutralization
n Tailings produce very low metal concentrations in the resulting leachate
n Total-sulfur concentrations less than 0.3 percent and a neutralization potential ratio
greater than 3
n Testing indicate the tailings meet ADEQ criteria as inert

35. Engineering Properties of Tailings
n Laboratory gradations of the tailings indicate an average of approximately 72.6
percent by weight passing the No. 200 sieve
n Atterberg limit testing indicates the tailings have:
• PI of 1
• PL of 20
• LL of 21
n The tailings classify as a low-plastic silt (ML), as defined by the USCS
n Average effective shear strength approximately 36.5 degrees

36. Engineering Properties of Alluvium/Foundation
n Average of approximately 26.8 percent by weight passing the No. 200 sieve
n Atterberg limits ranging between non-plastic and 26
n Average effective shear strengths ranging between 33 and 41 degrees with
cohesions ranging between 1,600 and 2,500 psf

37. Dry Stack TSF
Design

38. Dry Stack TSF Design
n The Dry Stack TSF consists of two separate areas referred to as Phase I
and Phase II
n Phase I is located between the McCleary Canyon wash and the Waste
Rock Storage Area (12 years, 343 MT)
n Phase II is an extension of the phase I facility and will be constructed
north of Phase I within McCleary Canyon (years 12-21, 253 MT)
n Tailings properties were determined through testing of bench scale
tailings samples.
n The specified moisture range of placed tailings is 15% (by weight) plus or
minus 3%.

39. Dry Stack TSF Design
n Foundation preparation will include clearing and grubbing, tree removal,
access road construction and topsoil salvaging and stockpiling.
n In the TSF footprint, most of the existing natural drainages will be filled
with inert rock and function as flow-through drains.
n An initial starter buttress will be constructed in the lower Barrel Canyon
drainage to accommodate three months of tailings storage.
n Rockfill Buttresses will advance ahead of tailings in 50-foot high lifts using
upstream construction methods.
n Buttresses will have 150-foot top widths to accommodate two-way haul
traffic and outer slopes of 3H:1V.

40. Dry Stack TSF Design
n Dry tailings will be delivered from the filter plant by conveyor and placed
in 25-foot lifts using a radial stacker upgradient of the Rock Buttress.
n Tailings will be spread with a dozer and compacted with a vibratory
smooth drum roller to provide compaction for trafficability of the
conveyor and to minimize dust.
n The outer perimeter of the tailings beneath the Rock Buttress will be
placed in 5-foot lifts and compacted 90% of standard proctor density.
n A bypass conveyor will be provided to allow temporary disposal of tailings
during primary conveyor movement, maintenance or upset conditions.

41. Dry Stack TSF Design
n Flow-through drains will be constructed of 12-inch minus rockfill and
separated from the tailings above by a layer of 10 oz/yd2 geotextile.
n Seepage is anticipated to peak at year 18 at a rate of 8.4 gpm.
n Natural seepage and springs will be captured with collection drains
consisting of shallow trenches filled with rockfill wrapped in 10 oz/yd2
non-woven geotextile.
n Existing water wells within the Dry Stack TSF footprint will be abandoned
according to ADWR regulations.

42. Dry Stack TSF
Surface Water Management

43. Dry Stack TSF Surface Water Management
n Water management will be addressed in the Water Management Plan to
be submitted in July 2009. General water management concepts specific
to the Dry Stack TSF are listed below:
n Perimeter ditches and evaporation ponds will collect stormwater runoff
from the tailings surface
n Flow-through drains will allow stormwater that does not come into
contact with tailings to be routed beneath the Dry Stack TSF
n Diversion channels will be constructed in two phases concurrent with the
Dry Stack TSF phases. They will be sized to pass the PMF and armored
to protect against the 200 year/24 hour storm.
n A Temporary diversion channel will be constructed upstream of the initial
lifts of phase I and will function through year 4

44. Dry Stack TSF
Seepage Analysis

45. Dry Stack TSF Seepage Analysis
n Seepage analysis conducted using the finite element method based
computer program SVFlux Version 2.0.13
n Tailings modeled at average moisture content of 18% (or less) by weight
n One-dimensional tailings column models were incrementally evaluated
using 50 foot lifts to the full height of 550 feet
n Developed isopach maps representing average depths of tailings for each
lift and phase
n Each successive model incorporated the pore water distributions from the
previous model

46. Dry Stack TSF Seepage Analysis
n Included climatic flux comprised of environmental factors including
precipitation, pan evaporation, relative humidity and temperature.
n The greatest average annual precipitation of 22.2 inches was used, and
the lowest average annual pan evaporation of 71.5 inches was used.
n The dry stack tailings are considered to be relatively homogeneous in
nature.
n Laboratory testing was performed to determine hydraulic conductivity at
various depths.
n Hydraulic conductivity ranges between 4 x 10-3 cm/sec near the top of
the Dry Stack TSF and 6 x 10-7 cm/sec at depths of 50 feet or greater.

47. Saturated Hydraulic Conductivity With Depth

48. Dry Stack TSF Seepage Analysis
n A series of moisture retention laboratory tests were completed on the
tailings samples .
n These tests were used to develop a soil water characteristic curve
(SWCC) for the tailings materials.
n The SWCC defines the soil’s ability to store and release moisture.

49. Soil Water Characteristic Curve
INSERT SWCC Curves

50. Relative Hydraulic Conductivity Function

51. Dry Stack TSF Seepage Analysis Results
n As the Dry Stack TSF expands over time, the estimated seepage rate
increases to a peak value of approximately 8.4 gpm, at production year 18.
n The upper 8 feet of the tailings performs as a storage-release unit, where
moisture lost to evaporation is replenished by precipitation.
n Based on the model, the seepage is due solely to drainage of pore water.
n Meteoric influences will have a small recharging effect on the top several
feet of tailings, but due to the large evaporation rate there will be an overall
negative flux at the surface.
n A two-dimensional model of the ultimate Dry Stack TSF was also developed
to verify the results.

52. Seepage Over Life of Mine

53. Seepage After Life of Mine

54. Moisture Content with Depth Over Time
Note:
The data
represents a typical
100-foot column.
The initial moisture
content was
modeled at 18% by
weight

55. Dry Stack TSF Seepage Analysis Results
n The estimated maximum seepage from the Dry Stack TSF is expected to
be 0.007 gpm/acre. For comparison, the following tailings disposal
methods and associated expected seepage rates are as follows:
n Slurry Tailings (no liner) 6.4 gpm/acre
n Slurry Tailings (with liner) 0.06 gpm/acre
n Paste and Thickened tailings 0.4 gpm/acre

56. Dry Stack TSF
Stability Analysis

57. Dry Stack TSF Stability Analysis
n Establishment of stability design criteria for static and seismic loading
conditions based upon laboratory testing, field investigation, and seismic
hazard analysis
n Development of representative cross sections.
n Completion of static and seismic stability analyses utilizing limit
equilibrium methods.
n Slope stability was evaluated using Spencer’s method.

58. Dry Stack TSF Stability Analysis Methodology
n The minimum factors of safety used in accordance with the BADCT
Guidance Manual guidelines are 1.3 and 1.0 for static and seismic
analyses, respectively with appropriate laboratory and field testing.
n The stability of the Dry Stack TSF under earthquake loading was
evaluated using the pseudostatic approach.
n The cross sections were developed at the maximum sections of the
facility
n For conservatism, the tailings 1,100 feet from the crest of the buttress
were modeled as having no strength.

59. Dry Stack TSF Stability Analysis Material
Properties
Effective Stress Analysis Total Stress Analysis
Strength Parameters Strength Parameters
Moist Cohesion
Friction Angle Cohesion Friction Angle (lbs/ft2)
Unit Weight (degrees) (lbs/ft2) (degrees)
Material Type (lbs/ft³)
Alluvium / -
130 36 0 -
Colluvium
Tailings 110 28 0 18 1,300
Compacted -
116 32 0 -
Tailings
No Strength -
110 0 0 -
Tailings
Rockfill 125 38 0 - -

60. Dry Stack TSF Stability Analysis Results
n For tailing impoundment facilities the minimum factors of safety, as required by the
BADCT Guidance Manual, are 1.3 and 1.0 for static and seismic analyses.
Static Pseudostatic
Cross Section Analysis Modeled Factor of Safety Factor of Safety
Effective 2.3 1.2
Phase I
Total 1.9 1.0
Effective 2.3 1.2
Phase II
Total 1.9 1.0

61. Dry Stack TSF Stability Analysis - Liquefaction
n Liquefaction can be generally defined as the loss of shear strength in loose,
saturated, and cohesionless soils due to the generation of excess pore pressures as
a result of large shear strains induced by undrained cyclic loading.
n The dry stack tailings will be unsaturated and will be under large confining pressures
producing a uniformly dense fill, hence the propensity for liquefaction will be very
low and is not anticipated to occur
n The majority of native foundation soils were very dense or hard for granular and fine
grained material and are not susceptible to liquefaction.

62. Phase I Stability Analysis

63. Phase II Stability Analysis

64. Dry Stack TSF
Closure Concept

65. Dry Stack TSF Closure Concept
n The primary goal of closure/post-closure plan is to eliminate any
reasonable probability of further discharge from the Dry Stack TSF.
n Concurrent with operations, portions of the Dry Stack TSF will be
reclaimed to reduce erosion due to wind and water.
n The top of the Dry Stack TSF will be graded inward to create an
evapotranspiration pond capable of containing the PMP.
n The top of the Dry Stack TSF will be revegetated with native seed mixes
designed to maximize evapotranspiration.