Geochemical Characterization and Source Loading Predictions

Bruce MattsonLorax 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

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14

Total S (%)

Pyr

itic

S (

%)

Chemical Sediments

Felsic Volcanics

Intermediate Volcanics

Mafic Volcanics

SULPHUR CONTENT• Sulphur content of hanging wall

waste rock < 1%S

• Acid potential calculated by difference of S total and HCl sulphate

• Provides a conservative estimate of acid potential

• Over estimates for sediments

West Zone

AB Zone

D Zone

ARD POTENTIAL AB ZONE

0.0001

0.001

0.01

0.1

1

10

100

1000

0.01 0.1 1 10 100

Total S (%)

CaN

P/S

AP

DiabaseGranodioriteSubvolcanic MaficsChemical SedimentsClastic SedimentsFelsic VolcanicsIntermediate VolcanicsMafic Volcanics

• 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)

ARD POTENTIAL D ZONE

0.001

0.01

0.1

1

10

100

1000

0.01 0.1 1 10

Total S (%)

CaN

PR

Diabase

Skarn

Granodiorite

Diorite/Tonalite

Subvolcanic Mafics

Clastic Sediments

Felsic Volcanics

Intermediate Volcanics

• 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

NEUTRALIZATION POTENTIAL (NP)• Carbonate NP consistently lower than

MEND NP indicates non-carbonate minerals contribute to measured NP

• NP difference most pronounced in granodiorite samples

• Kinetic test program indicates a portion of the non-carbonate NP source is available in granodiorite

• Use of CaNP is considered conservative, does not include non-carbonate NP sources

0

20

40

60

80

100

120

140

160

180

0 50 100 150

Mend NP (kg CaCO3/t)

CaN

P (

kg C

aC

O3 /

t)

DiabaseGranodioriteSubvolcanic MaficsChemical SedimentsClastic SedimentsFelsic VolcanicsIntermediate VolcanicsMafic Volcanics

0

20

40

60

80

100

120

140

160

180

200

0 50 100 150 200Mend NP (kg CaCO3/t)

CaN

P (

kg

CaC

O3 /

t)DiabaseSkarnGranodioriteDiorite/TonaliteSubvolcanic MaficsClastic SedimentsFelsic VolcanicsIntermediate Volcanics

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140Mend NP (kg CaCO3/t)

CaN

P (

kg C

aC

O3 /

t)

Chemical SedimentsFelsic VolcanicsIntermediate VolcanicsMafic Volcanics

West Zone

AB Zone

D Zone

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

0.00001

0.0001

0.001

0.01

0.1

1

As Cd Cu Pb Mo Ni Se Zn

Lo

adin

g (

mg

/kg

)

HC5 Mafic Subvolc HC5 Final

HC6 Felsic Volc HC6 Final

HC7 Mafic Volc HC7 Final

HC8 Sediment HC8 Final

HC9 Diabase HC9 Final

0.00001

0.0001

0.001

0.01

As Cd Cu Pb Mo Ni Se Zn

Lo

ad

ing

Ra

te (

mg

/kg

)

HC1 High S HC1 Final

HC3 Low S HC3 Final

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

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35 40 45

Cycle

pH

HC 5 Mafic Subvolcanic

HC 6 Felsic Volcanic

HC 7 Mafic Volcanic

HC 8 Clastic Sediment

HC 9 Diabase

HC 1 High S Granodiorite

HC 3 Low S Granodiorite

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45

Cycle

Su

lph

ate

(mg

/L)

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

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

0 5 10 15 20 25 30 35 40 45

Cycle

Alk

alin

ity

(mg

CaC

O3/

L/w

k )

HC 5 Mafic Subvolcanic

HC 6 Felsic Volcanic

HC 7 Mafic Volcanic

HC 8 Clastic Sediment

HC 9 Diabase

HC 10 Leached Diabase

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

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

Bin4 MV 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

Sediment n=17 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

• 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)

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