heavy metals in groundwater around massive sulphide deposits : exploration and environmental aspects
DESCRIPTION
Heavy Metals in groundwater around massive sulphide deposits : exploration and environmental aspects. H. Pauwels, M. L. Tercier-Waeber, M. Arenas, R. Castroviejo, Y. Deschamps, F. Graziottin, A. Lassin , A. Molina. Objectives . - PowerPoint PPT PresentationTRANSCRIPT
Heavy Metals in groundwater around massive Heavy Metals in groundwater around massive sulphide deposits : exploration and sulphide deposits : exploration and
environmental aspectsenvironmental aspects
H. Pauwels, M. L. Tercier-Waeber, M. H. Pauwels, M. L. Tercier-Waeber, M. Arenas, R. Castroviejo, Y. Deschamps, F. Arenas, R. Castroviejo, Y. Deschamps, F.
Graziottin,Graziottin, A. Lassin , A. MolinaA. Lassin , A. Molina
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 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 Chemistry
Cl SO4
CO2
0 25 50 75 100
Masa ValverdeMasa ValverdeLa ZarzaLa Zarza
R2 = 0.94
R2 = 0.800
100
200
300
400
0 50 100 150 200
Cl (mg l-1)Na
(mg
l-1) 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 flow
Local groundwater flow
EhEh 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
• 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
Specifity:Specifity: measures only the concentration measures only the concentration of 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 contents
0
20
40
60
80
100
120
0 100 200 300 400
SO4 (mg l-1)
m
etal
s (µ
g 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-MS
Cu (ppb)
0
50
100
150
0 1000 2000 3000
Zn (ppb)
0
0.5
1
1.5
0 50 100
Cd (ppb)
020406080
100
0 500 1000 1500
Pb (ppb)
0
100
200
300
400
0 500 1000 1500
ICP-MSICP-MS
Volta
mm
e try
Volta
mm
e try
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 Modelling
1.E-111.E-091.E-071.E-051.E-031.E-011.E+011.E+03
1.E-02 1.E-01 1.E+00 1.E+01 1.E+02
Measured conc. (ng.l-1)
Cal
cula
ted
conc
. (ng
.l-
1 )
Cu
Pb
Zn
Using EQ3NR: Using EQ3NR: - Estimation of undectable - Estimation of undectable H2S from equilibrium with H2S 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 complexes Zn presents as free ions + small labile complexes
Conclusions 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 : :
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:
Conclusions and Perspectives : Conclusions and Perspectives : Environmmental assessmentEnvironmmental 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: