3D Integration of seismic, petrophysical and ...€¦ · 3D Integration of seismic, petrophysical and lithogeochemical data to elucidate the effects of hydrothermal alteration on

3D Integration of seismic, petrophysical and lithogeochemicaldata to elucidate the effects of hydrothermal alteration on the

seismic response of the Lalor VMS footwall sequence

Ernst Schetselaar, Gilles Bellefleur, Nadjib El Goumi

Direct and indirect seismic targets associated to a VMS deposit

hydrothermal vent

regional conformable alteration zone

massive sulphide orefelsic host rocks

mafic cover rocks sulphide stringer ore

Seismic Reflection:

The Lalor VMS deposit: the ideal ‘laboratory’

Large hydrothermal alteration zone in proximal footwall of mineralization

Digital drill hole database, including >8000 whole-rock lithogeochemical analyses

Multi-method geophysical surveys

Physical rock properties

TGI4 3D seismic & gravity borehole surveys

Lalor seismic & 3D modelling cubes

Bailes and Galley, 1999

Hydrothermal alteration Lalor deposit

K-Fe-Mg assocation

K association

Less intense alteration

Balloch basalt

Lalor HW mafic rocks

Threehouse basalt S Ballochrhyodacite

N Ballochrhyodacite

FW basalt

100 m

10 Lens

20 lens

Gold zone

Massive sulphides

Mg-Ca association

Mg-Fe association

sericite-pyrite-biotitekyanite

anthophyllite-cordierite-garnet-biotite-staurolite

quartz-biotite-kyanite

carbonate-chlorite withCa-Mg amphiboles

Caté et al. 2013

ρ1

ρ2ρ3?

W E

Seismic detection of sulphide ore

time slice at 283 ms (approx. 835 m)

Crossline

Inline

1000

1150

1000

1350

1075

Inline

1000

1150

1075

1175

Crossline

1000

1350

1175

1 km

1 km

F1

FW HW

H7

H6

H3

H5H5?

10, 11, 20F2

?

21

Seismic synthetics

Synthetic traceOre zone

NESW

T/DDUB245

(2 Points)

0.10

0.20

0.30

500

1000

T-D Chart

5800 6000

LogVelocity(m/s) (g/cm)3

5000 7000

Density

2.62.9 3.2

AI

20000

RC

-0.1 0.1

WaveletExtracted

Ref. log Synthetic Synthetic(Density) (+) (-)

TraceLalor_3D_DMOMIG

Inline:1088, Crossline:1196

Borehole

-400 0

Near-vertical incidence synthetic seismic trace.

and geological model (Inline 1085 DMO-poststackSynthetic seismic trace overlayed on seismic

migrated volume).

History of VMS footwall rocks1. Volcanic deposition 1.89 Ga

2. Hydrothermal alteration & mineralization 1.88 Ga

3. Tectonic deformation and metamorphism 1.81 Ga

All these processes effect physical rock properties. Can we isolate the effects of hydrothermal alteration?

Building a curvilinear-faulted grid

1

34

5

6

2

Subsurface Knowledge Unified Approach

3D modelling of geologic surfaces to define the geometry of the curvilinear grid

strike/dip s0 restored from bedding-core angles (Bailes, 2012)

lithofacies recoded from Hudbay drill logs

Unit contacts from geologic map (Bailes et al, 1993)

lithostratigraphicmarkers from drill logs (Bailes 2012)

3D geologic surface model Lalor deposit

NE SW

Building a curvilinear grid from geological surfaces

NE SW

Nominal cell size: 20 x 20 x 5m

Chisel-Lalor fault

Advantages of defining a curvilinear grid for modelling properties

Subsurface Knowledge Unified Approach

Mallet 2004

Dulac 2008

Numerical grid modelling, including structural analysis (characterization of spatial autocorrelation) is conditioned by the modelled geological structure

uvt transform (Mallet, 2003)

simulated density 1 simulated density 2 simulated density 3

Methods for filling the uvt grid

kriged lithofacies kriged density kriging variance

3D grid modelling to interpret relationships lithology, alteration & seismic amplitude

3D curvilinear grid

3D CCPI alteration model

3D Lithofacies model

SW

3D geological surface model

Lithofacies modelling, input drill hole data

82 rock classes 15 rock classes

Zr/TiO2 <= 0.013 basalt mafic fragmentals - tuff mafic gneiss/schist

0.013< Zr/TiO2< 0.019 dacite dacitic fragmetals - tuff interm. gneiss./schist

Zr/TiO2>=0.019 rhyolite/rhyodacite felsic fragmetals - tuff felsic gneiss schist

sulphide ore argillite diorite/gabbro

Lithofacies modelling, systematic classification

1 MAFVR mafic volcanic rock (basalt, andesite)

2 INTVR intermediate volcanic rock (dacite)

3 FELVR felsic volcanic rock (rhyolite, rhyodacite)

4 VCLCM mafic coarse-gr volcaniclastic rocks (fragmentals)

5 VCLCI intermediate coarse-gr volcaniclastic rocks (fragmentals)

6 VCLCF felsic coarse-gr volcaniclastic rocks (fragmentals)

7 VCLFM mafic fine-gr volcaniclastic rocks (tuff/lapili tuff)

8 VCLFI intermediate fine-gr volcaniclastic rocks (tuff/lapilli tuff)

9 VCLFF felsic fine-gr volcaniclastic rocks (tuff/lapilli tuff)

10 GNSCHM gneiss/schist mafic protolith

11 GNSCHI gneiss/schist intermediate protolith

12 GNSCHF gneiss/schist felsic protolith

13 ORE sulphide ore

14 ARG argillite

15 DIO feldspar-phyric diorite/gabbro intrusions

COHERENT VOLCANICROCKS

COARSE VOLCANICLASTIC ROCKS (FRAGMENTALS)

FINE VOLCANICLASTIC ROCKS (LAPILLI TUFF /TUFF)

Zr/TiO2 < =0.013

0.013 < Zr/TiO2 < 0.019

Zr/TiO2 >= 0.019

Zr/TiO2 < =0.013

0.013 < Zr/TiO2 < 0.019

Zr/TiO2 >= 0.019

Zr/TiO2 < =0.013

0.013 < Zr/TiO2 < 0.019

Zr/TiO2 >= 0.019

Zr/TiO2 < =0.013

0.013 < Zr/TiO2 < 0.019

Zr/TiO2 >= 0.019

GNEISS / SCHIST(UNRECOGNIZABLE PROTOLITH)

REMAINING CLASSES

strongest intensity ofhydrothermal alteration

Can we see the effects in 3D lithofacies-seismic amplitude model?

Zr/TiO2 <= 0.013 basalt mafic fragmentals - tuff mafic gneiss/schist

0.013< Zr/TiO2< 0.019 dacite dacitic fragmetals - tuff interm. gneiss/schist

Zr/TiO2>=0.019 rhyolite/rhyodacite felsic fragmetals - tuff felsic gneiss schist

Cate et al., 2013W E

Impedance contrast hanging wall unaltered versus footwall altered rocks

hanging wall rocks altered footwall rocks

Ỵ-Ỵ density g/cm3 Ỵ-Ỵ density g/cm3

Zr/TiO2 <= 0.013 basalt mafic fragmentals - tuff mafic gneiss/schist

0.013< Zr/TiO2< 0.019 dacite dacitic fragmetals - tuff interm. gneiss./schist

Zr/TiO2>=0.019 rhyolite/rhyodacite felsic fragmetals - tuff felsic gneiss schist

Vp-density plots borehole geophysical logsV

p (m

/s)

ϒ-ϒ density (g/cm3)

Y-Y densityVp seismic velocity

log sample, n = 67657rock sample, n=42

Co-locating geophysical borehole logs with lithogeochemistry samples and lithology logs

100 (K2O + MgO)

(K2O + MgO + Na2O + CaO)AI =

100 (MgO + FeO)

(MgO + FeO + Na2O + K2O)CCPI =

ALTERATION INDICES

Drill path

HOLEID Depth ρ Vp Vs Zr/TiO2 CCPI AI LithologyDUB202 831.3 2.49 5421 3289 0.009 87 55 basalt flowDUB202 831.5 2.52 5345 3560 0.009 87 55 basalt flowgeophysical

log datum

1259 of 67657 geophysical log samples (1.9 %) are co-located with geochemical samples within 30 cm

Vp- density plot felsic-intermediate rocks, FW

Vp - density plot mafic rocks, footwall

Seismic Impedance vs. Alteration Box Plot

seismic impedance (kg.m-2.s-1 x 10-6)

hanging wall

footwall

3D model seismic amplitude and CCPI index

CCPI (%)

footwall

Conclusions: effects of hydrothermal alteration

Protoliths: density contrasts preserved, acoustic impedance contrast and seismic reflectivity are enhanced

Dominant effect hydrothermal alteration is increase in Vp

Increase in Vp is correlated with CCPI and AI.

Effects are likely due to low density-high velocity Ca-Mg & Fe-Mg alteration minerals (dolomite, anthophyllite)

Follow-up seismic forward modelling and mineral physical property studies required

Conclusions (integration methodology)

3D data integration instrumental for ore system science

We need co-located samples of lithofacies, mineralogy, lithogeochemistry and petrophysics to calibrate, model and validate

Modelling properties of a curvilinear-faulted grid (Skua) essential to obtain realistic results in hard rock settings

We are equipped these days with sophisticated data-driven methods ….. but we are still searching for a needle in a hay stack if we do not understand how ore forming processes effect our data

We need to pool highly-specific expertise in economic geology, mineralogy, geochemistry, petrophysics and geophysics

Acknowledgements

Antoine Caté, Patrick Mercier-Langevin

Alan Bailes, Bailes Geoscience

Matt Salisbury

Randy Enkin

Craig Taylor, Peter Dueck, Hudbay Minerals

gOcad research consortium