Metal concentrations in groundwater around Metal concentrations in groundwater around disturbed and undisturbed massive sulfide disturbed and undisturbed massive sulfide

depositsdeposits

Metal concentrations in groundwater around Metal concentrations in groundwater around disturbed and undisturbed massive sulfide disturbed and undisturbed massive sulfide

depositsdeposits

H. Pauwels, A. Lassin , J.C. Foucher,Y. H. Pauwels, A. Lassin , J.C. Foucher,Y. Deschamps, M. L. Tercier-Waeber, F. Deschamps, M. L. Tercier-Waeber, F.

Graziottin,Graziottin, R. Castroviejo, J. Samper, A. R. Castroviejo, J. Samper, A. LópezLópez

Objectives Objectives

To determine water-rock interactions around To determine water-rock interactions around VMS deposits with application to two VMS ore VMS deposits with application to two VMS ore deposits from Iberian Pyrite Belt:deposits from Iberian Pyrite Belt:– the effect of a deeply buried orebody on the composition of

groundwaters

– metal speciation and solubility controlling role of complexants

Applications in exploration and baseline studies Applications in exploration and baseline studies

La Zarza and Masa Valverde VMSLa Zarza and Masa Valverde VMSLa Zarza and Masa Valverde VMSLa Zarza and Masa Valverde VMS

La ZarzaLa Zarza Masa ValverdeMasa Valverde

Low to very low permeability Low to very low permeability of host-rockof host-rock Located in an area of Located in an area of hydrogeological rechargehydrogeological recharge

Low to very low permeability of Low to very low permeability of host-rockhost-rock

Located in a hydrogeological Located in a hydrogeological discharge zonedischarge zone

Buried at 400-600 m depthBuried at 400-600 m depth

Mined between 1853 and 1991Mined between 1853 and 1991

Remaining reserves: 110 MtRemaining reserves: 110 Mt

UnworkedUnworked

Reserves : 100 MtReserves : 100 Mt

Nearly outcropping to more Nearly outcropping to more than 500 m depththan 500 m depth

Hydrogeology and ChemistryHydrogeology and ChemistryHydrogeology and ChemistryHydrogeology and Chemistry

Cl SO4

CO2

0 25 50 75 100

Masa ValverdeMasa ValverdeLa ZarzaLa Zarza

R2 = 0.94

R2 = 0.80

0

100

200

300

400

0 50 100 150 200

Cl (mg/l)N

a (m

g/l

La Zarza

Masa Valverde .

Surroundings

Different chemical characteristics strengthened Different chemical characteristics strengthened by occurrence of two mixing trendsby occurrence of two mixing trends

Infiltrating waters

Deep groundwater flowDeep groundwater flow

Local groundwater flow

Eh:Eh: Masa Valverde : -285 to -230 mV Masa Valverde : -285 to -230 mV La Zarza : -30 to + 400 mVLa Zarza : -30 to + 400 mV

Metal determination: VIP and ICP-MS Metal determination: VIP and ICP-MS Metal determination: VIP and ICP-MS Metal determination: VIP and ICP-MS

• Analysis by ICP-MS for Cu, Pb, Zn, Cd, Analysis by ICP-MS for Cu, Pb, Zn, Cd, Fe, Mn, Co, Ni, Al, As Fe, Mn, Co, Ni, Al, As

Voltammetric In-situ Profiling System ( VIP):Voltammetric In-situ Profiling System ( VIP): Submersible voltammetric probe Submersible voltammetric probe + Calibration deck unit+ Calibration deck unit+ Surface deck unit + PC+ Surface deck unit + PC

Specificity:Specificity: measures only the concentration measures only the concentrationof the mobile fraction of trace metals ( free of the mobile fraction of trace metals ( free metal ions + small labile complexes <few metal ions + small labile complexes <few nm)nm)

• Analysis by VIP for Cu, Pb, Zn, Cd, MnAnalysis by VIP for Cu, Pb, Zn, Cd, Mn

IDRONAUT s.r.lIDRONAUT s.r.l

Metal contentsMetal contentsMetal contentsMetal contents

0

20

40

60

80

100

120

0 100 200 300 400

SO4 (mg l-1)

m

eta

ls (

µg

l-1) La Zarza

Masa Valverde( Zn+Cu+Pb+Cd+As+Ni+Co) ( Zn+Cu+Pb+Cd+As+Ni+Co) in a concentration range of in a concentration range of the same order at both sites, the same order at both sites, despite :despite :- very reducing conditions at - very reducing conditions at Masa ValverdeMasa Valverde-very low solubility of -very low solubility of sulphide mineralssulphide minerals

Impossible distinction between La Zarza and Masa Impossible distinction between La Zarza and Masa Valverde G.W. using any particular metalValverde G.W. using any particular metal

Metal Speciation: Comparison VIP / ICP-MSMetal Speciation: Comparison VIP / ICP-MSMetal Speciation: Comparison VIP / ICP-MSMetal Speciation: Comparison VIP / ICP-MS

Cu (ppb)

0

50

100

150

0 1000 2000 3000

Zn (ppb)

0

0.5

1

1.5

0 50 100

Cd (ppb)

020

4060

80100

0 500 1000 1500

Pb (ppb)

0

100

200

300

400

0 500 1000 1500

ICP-MSICP-MS

Vo

ltam

met

ryV

olt

amm

etry

La Zarza G.W. :La Zarza G.W. :

% of concentration % of concentration measured by VIP with measured by VIP with respect to ICP-MS :respect to ICP-MS :

Cu : less than 6%Cu : less than 6%

Zn : 0.5 to 21 %Zn : 0.5 to 21 %

Cd : less than 27 %Cd : less than 27 %

Pb: 8 to 100%Pb: 8 to 100%

Cu, Zn and Cd present as macromolecules and/or adsorbed on Cu, Zn and Cd present as macromolecules and/or adsorbed on colloids/small particles colloids/small particles

Pb presents as free ions + small labile complexes Pb presents as free ions + small labile complexes

Metal Speciation: Geochemical ModellingMetal Speciation: Geochemical ModellingMetal Speciation: Geochemical ModellingMetal Speciation: Geochemical Modelling

1.E-11

1.E-09

1.E-07

1.E-05

1.E-03

1.E-01

1.E+01

1.E+03

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02

Measured conc. (ng.l-1)C

alcu

late

d c

on

c. (

ng

.l-1

)

Cu

Pb

Zn

Using EQ3NR: Using EQ3NR:

- - Estimation of undetectable Estimation of undetectable HH22S from equilibrium with S from equilibrium with respect to pyriterespect to pyrite

- Estimation of Cu, Pb, Zn - Estimation of Cu, Pb, Zn concentrations expected concentrations expected from equilibrium with from equilibrium with respect to chalcopyrite, respect to chalcopyrite, galena and sphaleritegalena and sphalerite

Masa Valverde G.W.Masa Valverde G.W.

Cu and Pb present as macromolecules and/or adsorbed on Cu and Pb present as macromolecules and/or adsorbed on colloids/small particles colloids/small particles

Zn presents as free ions + small labile complexesZn presents as free ions + small labile complexes

Conclusions and PerspectivesConclusions and PerspectivesConclusions and PerspectivesConclusions and Perspectives

• Similar total metal concentrations at Similar total metal concentrations at both disturbed and deep buried both disturbed and deep buried unworked depositsunworked deposits

• Enhancement of total metal Enhancement of total metal concentrations in GW by the formation concentrations in GW by the formation of complexes or by metal adsorption on of complexes or by metal adsorption on colloids or small particlescolloids or small particles

Two major observationsTwo major observations : : Two major observationsTwo major observations : :

Conclusions and Perspectives : Conclusions and Perspectives : Mineral explorationMineral exploration

Conclusions and Perspectives : Conclusions and Perspectives : Mineral explorationMineral exploration

• Enlarge the field of potential applications for Enlarge the field of potential applications for deep orebody exploration using deep orebody exploration using hydrogeochemical methods at local scalehydrogeochemical methods at local scale not only restricted in case of acid mine drainage despite low solubility of sulphide minerals

• Contribute to support the possible role of G.W.-Contribute to support the possible role of G.W.-rock interactions in the formation of surface rock interactions in the formation of surface geochemical anomalies identified by enzyme geochemical anomalies identified by enzyme leach, MMI selective digestions and others... leach, MMI selective digestions and others...

These results:These results:These results:These results:

Conclusions and Perspectives : Conclusions and Perspectives : Environmental AssessmentEnvironmental Assessment

Conclusions and Perspectives : Conclusions and Perspectives : Environmental AssessmentEnvironmental Assessment

• Confirm the importance of a natural Confirm the importance of a natural baseline study in order to determine realistic baseline study in order to determine realistic achievable targets for remediation. achievable targets for remediation.

• Pose the problem of suitable methods for Pose the problem of suitable methods for estimating natural background total metal estimating natural background total metal concentration at abandoned mine sites:concentration at abandoned mine sites: Predictive modeling constitutes an upper limit in the

case of acid mine drainage and a lower limit in the absence of significant oxidation.

These results:These results:These results:These results: