Transcript 071202-06MN082-Zinifex Geochemical Presentation-176-IMAE.ppt

Geochemical
Characterization
and Source Loading
Predictions
Bruce Mattson
Lorax Environmental
GEOCHEMICAL
CHARACTERIZATION
• Geochemical Studies
conducted to minimize impact
to the aquatic environment
through characterization and
Management
• Evaluated Geochemical
Characteristics of
– Mine Rock, Tailings, and
Road
• Characterized Leaching
behaviour of mine rock
• Predicted source
concentrations from exposed
mine rock
STUDY OBJECTIVES
• Rationale is to obtain necessary geochemical
information to develop mitigation and
management plans
– Identify materials with a high ML/ARD potential that
require special management and identify the elemental
constituents that may be leached and affect water
quality
– Detailed characterization of materials that are used for
construction and mitigation purposes to ensure that
these materials, that will be exposed in the weathering
profile, do not contribute unacceptable elemental loads
to mine drainage
• Characterization designed to drive management
– Iterative process
– Management drives characterization
WASTE ROCK SAMPLING
RATIONALE
•
Static test samples selected to evaluate ARD characteristics of
different lithologies, spatially through the AB and D Zone
•
Sample frequency was selected to delineate sufficient material with
low ML/ARD potential to implement the proposed management
plan
– AB Zone – Hanging wall n=52, Footwall n=54, Ore Zone n=5
– D Zone – Hanging wall n = 35, Footwall n = 15
– 50 Additional samples in D Zone and AB Zone hanging wall
•
A lower sampling frequency was used to characterize materials in
the West Zone underground as management plans were
developed to handle this quantity of material
–
Placement in core of AB Dump (AB PAG)
– Temporary storage and rehandling underground (D Zone – West Zone)
•
It is acknowledged that non-PAG material will comprise a portion of
the material defined as PAG in the management plan
STATIC TEST METHODS
• ARD analytical methods provided Geochemical
Characterization and Source Loading Study - Appendix E.
• Total S, HCl sulphate S, HNO3 sulphide S, Inorganic C, NP,
paste pH, and leachable metals (Aqua regia leach)
• Aqua regia leach method is widely applied method in
environmental studies (noted in BC ARD Guidelines) to
examine extractable rather than total element
concentrations, to evaluate the mobility of heavy toxic
metals and their bioavailability.
– Provides the appropriate precision for inter-sample
comparison.
– Residual element fractions that are not released by aqua
regia digestion would not weather.
• “MEND NP” refers to modified Sobek NP method with
addition of hydrogen peroxide following filtration of HCl
leachate
SULPHUR CONTENT
45
40
4.5
35
Sulphide S (%)
•
5
Sulphur content of hanging wall
waste rock < 1%S
4
3.5
Acid potential calculated by
difference of S total and HCl
sulphate
30
AB Zone
25
20
15
10
Pyritic S (%)
•
Diabase
Granodiorite
Subvolcanic Mafics
Clastic Sediments
Felsic Volcanics
Intermediate Volcanics
Mafic Volcanics
Chemical Sediments
5
3
0
0
5
10
15
20
25
30
35
40
45
Total S (%)
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
Over estimates for sediments
2.5
3
3.5
4
1
14
5
D Zone
10
West Zone
0.9
8
Sulphide S (%)
Chemical Sediments
12
4.5
Total S (%)
0.8
Felsic Volcanics
Intermediate Volcanics
0.7
6
4
2
Mafic Volcanics
10
0
Pyritic S (%)
•
Provides a conservative
estimate of acid potential
Pyritic S (%)
•
8
0.6
0
2
4
6
Total S (%)
8
10
0.5
Diabase
Skarn
0.4
Granodiorite
6
Diorite/tonalite
0.3
Subvolcanic Mafics
0.2
4
Clastic Sediments
Felsic Volcanics
0.1
Intermediate Volcanics
2
0
0
0.1
0.2
0.3
0.4
0.5
Total S (%)
0
0
2
4
6
8
Total S (%)
10
12
14
0.6
0.7
0.8
0.9
1
1000
•
•
Non Acid Generating
Granodiorite with low
leaching potential in
hanging wall of AB Zone
Material in 10 – 30 m
interval above AB zone
included as PAG for
waste management
calculations (includes
mafic subvolcanic)
100
10
CaNP/SAP
ARD POTENTIAL
AB ZONE
Diabase
Granodiorite
Subvolcanic Mafics
Chemical Sediments
Clastic Sediments
Felsic Volcanics
Intermediate Volcanics
Mafic Volcanics
1
0.1
0.01
0.001
0.0001
0.01
0.1
1
Total S (%)
10
100
ARD POTENTIAL
D ZONE
1000
100
• Non-acid generating mafic
subvolcanic and granodiorite
in the
D Zone hanging wall
• Predominance of potentially
acid generating lithologies in
footwall (east)
• Clearly defined zones of
waste rock in pit for effective
operational segregation
• Sampling maps of drill collars
do not illustrate true sample
location
– Inclined boreholes
– Review sample sections
CaNPR
10
1
Diabase
0.1
Skarn
Granodiorite
Diorite/Tonalite
0.01
Subvolcanic Mafics
Clastic Sediments
Felsic Volcanics
Intermediate Volcanics
0.001
0.01
0.1
1
Total S (%)
10
NEUTRALIZATION POTENTIAL (NP)
•
Carbonate NP consistently lower than
MEND NP indicates non-carbonate
minerals contribute to measured NP
180
Diabase
Granodiorite
Subvolcanic Mafics
Chemical Sediments
Clastic Sediments
Felsic Volcanics
Intermediate Volcanics
Mafic Volcanics
160
140
•
•
CaNP (kg CaCO3/t)
NP difference most pronounced in
granodiorite samples
Kinetic test program indicates a portion
of the non-carbonate NP source is
available in granodiorite
•
120
AB Zone
100
80
60
40
20
Use of CaNP is considered
conservative, does not include noncarbonate NP sources
0
0
50
100
150
Mend NP (kg CaCO 3/t)
200
140
100
160
80
60
D Zone
Diabase
Skarn
Granodiorite
Diorite/Tonalite
Subvolcanic Mafics
Clastic Sediments
Felsic Volcanics
Intermediate Volcanics
180
CaNP (kg CaCO3/t)
120
CaNP (kg CaCO3/t)
West Zone
Chemical Sediments
Felsic Volcanics
Intermediate Volcanics
Mafic Volcanics
140
120
100
80
60
40
40
20
20
0
0
0
20
40
60
80
100
Mend NP (kg CaCO 3/t)
120
140
0
50
100
Mend NP (kg CaCO 3/t)
150
200
MINERALOGY
• Mineral identification and quantification
conducted using XRD with Rietveld
refinement on major waste rock
lithologies.
• Optical examination on granodiorite,
sediments and diabase samples
• Calcite was the predominant carbonate mineral in all
lithologies although dolomite identified in diabase
• Pyrite is the predominant sulphide mineral
– Chalcopyrite and pyrrhotite identified in granodiorite
– Sphalerite and chalcopyrite observed in sediments
• Additional optical mineralogy on carbonate and
sulphides
MINE WASTE MANAGEMENT
•
Lithology and ABA results were used to demarcate PAG from
non-PAG rock in the hanging wall of AB and D Zones
•
Demarcation line typically lies 10 to 30 m above the
mineralized zones – Easy Segregation
•
Non acid generating waste rock from hanging wall of AB Pit
and D Pit account for ~ 40% of total waste rock
•
Waste rock mined from underground accounts for 4% of total
waste rock and will be managed as potentially acid generating
Mine Pit/Zone
Pre-feasibility mining estimates (M tonnes)
Total Waste Rock
PAG Waste Rock
NAG Waste Rock
AB Open Pit
14.4
8.6
5.8
D Open Pit
9.8
5.9
3.9
West Zone Underground
0.92
0.92
-
AB Underground
0.12
0.12
-
D Underground
0.09
0.09
-
Totals
25.3
15.6
9.7
MINE WASTE MANAGEMENT
• Non acid generating waste rock from hanging wall of AB Pit
and D Pit - foundations, roads, dams and shell of AB Dump
• Potentially acid generating waste rock will be stored:
– In a frozen condition in the core of the AB Dump
– Temporary storage on surface and final placement as backfill in
underground mine workings
•
Collection and treatment of ore and temporary waste rock drainage
•
Cover reactive pit walls – tailings, waste rock and water
•
Large WMF (High Lake) for flow and loading attenuation
HUMIDITY CELL TESTING
•
Eleven humidity cell tests were conducted to evaluate
metal loading rates
•
Sample selection near or above 50 percentile for solid
phase sulphur and metal concentrations
•
Metal loading predictions updated with leaching rates
following at least 40 test cycles
•
Updated metal leaching rates consistent with original
rates, Zn and Cu show increase
1
HC5 Final
HC6 Felsic Volc
HC6 Final
HC7 Mafic Volc
HC7 Final
HC8 Sediment
HC8 Final
HC1 High S
HC1 Final
HC9 Final
HC3 Low S
HC3 Final
HC9 Diabase
0.01
0.01
Loading Rate (mg/kg)
Loading (mg/kg)
0.1
HC5 Mafic Subvolc
0.001
0.001
0.0001
0.0001
0.00001
0.00001
As
Cd
Cu
Pb
Mo
Ni
Se
Zn
As
Cd
Cu
Pb
Mo
Ni
Se
Zn
HUMIDITY CELL TESTING
• pH is variable during final weeks
(consistent signature for cells)
• Sulphate and Alkalinity do not have
a corresponding increase
• Granodiorite, mafic subvolcanic,
mafic volcanic and diabase have
low sulphate release
• Felsic volcanic and sediment
samples are the most reactive
10
9
pH
8
7
HC 5 Mafic Subvolcanic
6
HC 6 Felsic Volcanic
HC 7 Mafic Volcanic
HC 8 Clastic Sediment
5
HC 9 Diabase
HC 1 High S Granodiorite
HC 3 Low S Granodiorite
4
0
5
10
15
20
25
30
40
45
Cycle
40
35.0
HC 5 Mafic Subvolcanic
HC 1 High S Granodiorite
HC 3 Low S Granodiorite
HC 5 Mafic Subvolcanic
HC 6 Felsic Volcanic
HC 7 Mafic Volcanic
HC 8 Clastic Sediment
HC 9 Diabase
HC 6 Felsic Volcanic
35
HC 7 Mafic Volcanic
30.0
HC 8 Clastic Sediment
HC 9 Diabase
HC 10 Leached Diabase
30
25.0
Sulphate (mg/L)
Alkalinity (mg CaCO3/L/wk )
35
20.0
15.0
25
20
15
10.0
10
5.0
5
0.0
0
5
10
15
20
25
Cycle
30
35
40
45
0
0
5
10
15
20
25
Cycle
30
35
40
45
FIELD BIN TESTING
• Five field bins constructed September 2005
Bin
Zone
Rock Description
1
D
Mafic Subvolcanics (Hanging Wall)
2
AB
Granodiorite
3
AB
Felsic Volcanics (Footwall)
4
West
Mafic Volcanics (Footwall)
5
AB
Sediments (Footwall)
• Leachate sample September 2007 following two
years of leaching
• Leachate concentrations used to increase
predicted source concentrations of Co, Cu, Mo
and Ni
FIELD BIN SAMPLE COMPOSITION
• Granodiorite and felsic volcanic field bin samples enriched
in As, Cu, Ni and Se
• Sediment field bin sample enriched in As and Ni
• These anomalies are noted when evaluating leachate
concentrations (As and Se not increased)
Ag
Al
As
Ca
Cd
Co
Cr
Cu
Fe
Hg
K
Mg
Mn
Mo
Ni
Pb
Sb
Se
Zn
ppm
%
ppm
%
ppm
ppm
ppm
ppm
%
ppm
%
%
ppm
ppm
ppm
ppm
ppm
ppm
ppm
Bin1 MSV
0.1
2.15
0.8
1.4
<.1
19.9
89.5
57.5
2.4
0.07
0.23
1.91
291
0.8
101.5
4.2
<.1
<.5
32
Mafic
Subvolc n=30
0.1
2.4
0.9
0.9
0.1
19.7
63.1
46.4
2.5
0.01
0.09
1.9
271
1.1
75.7
3.3
0.1
0.5
40
Bin2 GD
0.3
1.96
1252
1.3
0.1
41.7
141
548
5.1
0.06
0.24
1.84
434
3.5
1054
10.4
27.6
4.2
83
Granodiorite
n=46
0.1
1.5
0.6
1.1
0.1
15.6
75.5
47.4
2.9
0.01
0.13
1.3
298
1.6
22.6
4.4
0.1
0.5
51
Bin3 FV
1.3
2.7
21.3
0.1
0.2
20.9
156
2094
4.6
0.06
0.21
2.4
303
3.9
16.3
27.4
0.8
12.3
133
Felsic Volc
n=47
0.6
2.5
2.8
0.2
0.1
8.7
90.8
237
3.7
0.01
0.13
2.3
264
3.3
4.9
14.5
0.3
0.7
123
0.7
3.4
2.3
1.1
0.1
16.8
85.5
97.0
4.0
0.04
0.92
3.6
991
1.4
21.5
69.1
0.5
0.8
132
Mafic Volc
n=9
0.1
4.1
1.0
0.6
0.1
17.0
64.1
22.4
4.1
0.01
1.23
4.7
590
1.5
11.5
17.5
0.1
0.5
92
Bin5 CS
0.9
2.8
48.4
0.2
0.3
23.9
140
1152
4.7
0.04
0.24
2.5
323
4.3
43.8
9.6
1.3
2.2
171
1.4
3.1
1.9
0.1
0.3
16.7
71.9
913
5.4
0.01
0.07
2.5
287
2.8
3.1
9.1
0.2
3.4
215
Bin4 MV
Sediment
n=17
SOURCE TERM
CONCENTRATION PREDICTION
• Source terms revised with loading data reported
in Humidity Cell Test Results report (Lorax, 2007)
• Source term base case – Waste Rock
– loading derived from 5 m active freeze/thaw zone rather
than 3 m reported in the DEIS
• Incremental waste rock source terms were
calculated for active layers of 10, 15 and 20 m
• Predicted source term scrutinized with respect to
36 parameters field bin leachate concentrations
pH
HCO3
Cl
SO4
Al
Sb
As
Ba
Be
B
Cd
Ca
Cr
Co
Cu
Fe
Pb
Li
Hg
Mg
Mn
Mo
Ni
P
K
Se
Si
Ag
Na
Sr
Tl
Sn
U
V
Zn
Zr
WASTE ROCK SOURCE TERM
•
•
•
•
•
•
•
Source loads weighted using waste rock
tonnage from each major lithologic unit
Apply loading rates (mg/kg/wk) from humidity
cells for the major stratigraphic units
Adjust for the particle size and the effect of
incomplete flushing in dump (next slide)
Calculate porewater concentrations from
monthly net infiltration into the dumps applied
to the total available loads
Equilibrium with atmospheric CO2(g) and O2(g);
If solutions are supersaturated, allow
precipitation of: Al4(OH)10SO4, barite, calcite,
ferrihydrite, gypsum and rhodochrosite; and
adsorption of trace metals in solution onto
freshly precipitated ferrihydrite
Adjust predictions based on field bin data
WASTE DUMP FLUSHING
• Coarse and fine, horizontal and inclined layers
• Unsaturated flow preferentially occurs in finest
grained layers (< % of dump)
• Under extreme precipitation conditions, preferential
flow channelling in coarse conduits (<<<% of dump)
• Complete rinsing of waste rock does not occur in
arid environments
PIT WALL SOURCE TERM
• Loading calculated for:
scenario 1 – total pit
scenario 2- pit above
discharge elevation
• AB Pit rapid fill with tailings
• D Pit natural fill with
contingency for tailings fill
• Calculate rinse-water
concentrations from monthly
net infiltration
• Pit wall source terms assume
80% of load rinses from wall
• Secondary mineral controls
on the calculated water
chemistry
ROAD SAMPLING
• Initial sampling of potential rock quarries for road
construction completed for EIS
• It is recognized that additional characterization
and risk assessment will be required along road
alignment
• Quarry site selection will include geochemical
considerations and be sited accordingly to avoid
ML/ARD issues
• Due to the ability to move quarry locations
detailed sample characterization associated with
road would be appropriate as a Water and/or
Land Use Licence requirement
OPERATIONAL MONITORING
• Objective
– gather additional data to guide management of mine
waste during mining and post-closure
– confirm the original characterization work completed at
the site.
• ML/ARD operational monitoring of the EB Pit
waste rock will include sampling on dumps during
deposition.
• ML/ARD sampling of ultimate pit walls as the final
pit walls are exposed.
• A subset of samples for QA/QC
• Field leach bins will continue to operate at site
– Leachate collected and reported on an annual basis
• Seepage surveys from the toe of waste rock
dumps and pit waters
SUMMARY
• Used conservative methods for
determining both acid generating
potential (NP/AP)
• Used conservative methods for
predicting drainage chemistry
(sample selection and methods)
• Established that there are sufficient
quantities with low metal leaching
potential to implement appropriate
management and mitigation