A presentation on the Mine Rock Geochemistry and Pit Lake Model associated with the Rosemont Copper Project developed by the Tetra Tech. This presentation was given to the Forest Service and their contractors during technical transfer meetings in November 2008.

1. Mine Rock Geochemistry and Pit Lake Model
For the Rosemont Copper Project
By Mark Williamson, PhD

2. Presentation Topics
§ Approach to characterization of mine rock (for
pit walls as well as waste disposal facilities)
and summary results
§ Tailings characterization
§ The conceptual pit lake hydrochemical model
§ Overview of components of pit lake model
§ The Dynamic Systems Model (DSM)

3. Mine Rock Characterization
Test Protocol Purpose
Acid-Base Accounting (ABA) Evaluate relative proportions of
potentially acid generation and acid-
consumption capacity.
Humidity Cell Testing (HCT) Accelerated weathering test for
samples showing potential or
unclear capacity to generate acidity.
Synthetic Precipitation Leaching Arizona-required laboratory leaching
Procedure (SPLP) test on powdered material using
weak acid solution.
Meteoric Water Mobility Procedure Laboratory leaching test on coarse/
(MWMP) run-of-mine rock using plain water

4. Summary of Mine Rock Tests
Anticipated Percent of Whole
Rock Type ABA SPLP MWMP
Tonnage Waste Rock
Arkose 620,630,000 49% 57 23 8 8
Limestone
119,448,000 9% 11 2 1 1
Conglomerate
Abrigo 102,460,000 8% 5 1 5 0
Overburden 91,620,000 7% 7 4 3 2
Horquilla 77,091,000 6% 19 3 8 3
Andesite 73,671,000 6% 35 12 4 5
Martin 39,084,000 3% 8 2 4 0
Bolsa 34,661,000 3% 13 1 6 0
Earp 27,680,000 2% 13 5 6 0
Epitaph 26,914,000 2% 14 1 5 0
Escabrosa 24,776,000 2% 9 3 4 0
Colina 22,200,000 2% 8 3 4 0
Qmp 14,555,000 1% 9 4 2 1
Totals 1,274,790,000 100% 208 64 60 20

5. Acid-Base Accounting
Rosemont Acid Base Accounting
200
Tailings
180 Qmp
NNP = -20 NP/AP = 1,
Overburden
NNP = 0
160 Martin
Acid Generating Potential (kg/T)
140 NNP = +20 Limestone
Leach Material
120 Horquilla
NP/AP = 3 Escabrosa
100 Earp
Colina
80
Bolsa
Arkose
60
Inert Material per ADEQ Andesite
40 policy Abrigo
Precambrian
20 Epitaph
0
0 100 200 300 400 500 600 700 800 900 1000
Neutralization Potential (kg/T)

6. Humidity Cell Testing (Andesite)
Andesite (AR2010-03)
1.67% Sulfide-S, NNP = -25.2 kg/t
100 9.0
Calcium
8.0 Sulfate
75
Acidity
Leaching Rate
(mg/kg/wk)
7.0 Alkalinity
pH
50 Iron
6.0 pH
25
5.0
0 4.0
0 10 20 30 40
Week

7. Mean Extractable Concentration (mg/kg)
Su
0.0001
0.001
0.01
0.1
1
10
lfa
te 100
S -
C
al
ci
um
Po
ta
ss
iu
m
C
hl
or
id
e
So
di
M um
SPLP vs MWMP
ag
ne
si
um
N Fl
O uo
2 rid
+ e
N
O
3
as
N
Se
le
ni
um
C
op
Constituent
pe
r
Ba
ri u
m
Al
um
Rosemont Geochemistry
in
Augusta Rosemont Geochemistry
um
Ar
se
M ni
c
an
ga
ne
se
Zi
nc
M
SPLP
er
c
MWMP
ur
y

8. Presentation Topics
§ Approach to characterization of mine rock and
summary results
§ Tailings characterization
§ The conceptual pit lake hydrochemical model
§ Overview of components of pit lake model
§ The Dynamic Systems Model (DSM)

9. Tailings Characterization
Current Testing Whole
Sample Date ABA NAG SPLP MWMT Kinetic
Status Rock
May 2006 Completed X X X X
February 2007 Completed X X X X
June 2007 Completed X X X X X
July 2008 In Progress X X X X X

10. Tailings Characterization
§ Net acid consuming material
§ High pH/generally low TDS humidity cell effluent
• Recent sample relatively high TDS
§ Low trace metals in SPLP, MWMT and HCT

11. Presentation Topics
§ Approach to characterization of mine rock and
summary results
§ The conceptual pit lake hydrochemical model
§ Overview of components of pit lake model
§ The Dynamic Systems Model (DSM)

12. Conceptual Pit Lake Hydrochemical Model
Direct Precipitation
Q = 22”/yr x Area
C = Weighted means (NADP)
Wall Runoff
Q = 22”/yr x Area
C = weighted means (SPLP)
Evaporation
Q = 75”/yr x Area
Rosemont Pit Lake Groundwater Inflow
Q = groundwater flow model (gpm)
C = mean from bedrock wells

13. Conceptual Pit Lake Model
§ Sum of flows and
concentration
n
§ Monthly time steps
∑Q C
i =1
i i § Geochemical
equilibration
§ Probabilistic simulation

14. Presentation Topics
§ Approach to characterization of mine rock and
summary results
§ The conceptual pit lake hydrochemical model
§ Overview of components of pit lake model
§ The Dynamic Systems Model (DSM)

15. Hydrologic Components
§ Groundwater Inflow
§ Direct Precipitation
§ Wall Runoff
§ Evaporation

16. Groundwater Inflow
§ Principal hydrologic component
§ Important considerations:
• Terminal vs. flow-through
• Rates of infilling
§ Groundwater model currently under
development

17. Direct Precipitation
Comparison of Rosemont and Santa Rita Monthly Precipitation
6
Santa Rita (1950-2006)
Rosemont (2007-2008)
5
Precipitation (inches)
4
3
2
1
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month

18. Pit Wall Runoff

19. Evaporation
18
Measured Pan Evaporation:
Total = 107 inches.
16
Calculated Lake Evaporation:
Total = 75.1 inches.
14
Evaporation (inches)
12
10
8
6
4
2
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month

20. Geochemical Components
§ Groundwater Flow
§ Direct Precipitation
§ Pit Wall Runoff

21. Groundwater Inflow Chemistry
§ Typically the largest potential contributor of
chemical mass
§ Requires characterization of local groundwater

22. Precipitation Chemistry
National Atmospheric Deposition Program
(NADP)

23. Pit Wall Runoff
§ Derived from mine rock characterization
• Representative Sampling
• Chemical loading parameters
• Outcrop areas

24. Representative Sampling
§ How many is enough?
§ Sample until no improvement
60
50
40
NNP
30
20
10 NNP - Mean
NNP - Std. Dev.
0
0 5 10 15 20 25 30 35 40
Number of Samples

25. Chemical Loading Parameters
§ SPLP data used as source concentration for pit wall
outcrops
§ SPLP, long-term HCT water composition and MWMP
produce consistent results
§ Due to general lack of sulfide mineralization, water
composition more closely tied to equilibrium than
kinetic concerns

26. Areas of Exposed Rock Types

27. Dynamic Systems Model (DSM)
§ GoldSim
§ Graphical User Interface
§ One time data and formula entry
§ Probabilistic ability
• Range of possibilities as a result of parameter uncertainty
• Probability of occurrence

28. Rosemont Pit Lake DSM

29. Hydrology Module

30. Summary and Status
§ Mine rock is, on total mass basis, acid-consuming
§ Representative samples of principal lithologies
outcropping pit complete
§ Geochemical characterization of pit wall lithologies
complete
§ DSM largely complete, dependant upon completion
of hydrologic evaluation
§ No useful DSM runs to date

31. Questions
Mark Williamson, PhD
mark.williamson@tetratech.com
970.223.9600