3D Integration of seismic, petrophysical and lithogeochemical data 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 Seismic Reflection: regional conformable alteration zone felsic host rocks mafic cover rocks massive sulphide ore sulphide stringer ore
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 W E FW basalt Threehouse basalt S Balloch rhyodacite Balloch basalt N Balloch rhyodacite Lalor HW mafic rocks sericite-pyrite-biotite kyanite quartz-biotite-kyanite ρ 3? ρ 1 ρ 2 100 m 10 Lens 20 lens Massive sulphides Mg-Ca association K-Fe-Mg assocation K association anthophyllite-cordieritegarnet-biotite-staurolite carbonate-chlorite with Ca-Mg amphiboles Gold zone Mg-Fe association Less intense alteration Caté et al. 2013
1075 1075 Seismic detection of sulphide ore Crossline 1000 1175 1350 1000 Inline 1 km 1150 1000 Inline H3 FW HW 21 10, 11, 20 F1 H7 H6 H5? 1 km 1150 F2 H5? 1000 1175 1350 Crossline time slice at 283 ms (approx. 835 m)
Seismic synthetics Near-vertical incidence synthetic seismic trace. T/D T-D Chart DUB245 (2 Points) Log Velocity (m/s) Density (g/cm) 3 5800 60005000 70002.62.9 3.2 AI RC 20000-0.1 0.1 Wavelet Extracted Ref. log Synthetic Trace Synthetic Borehole (Density) (+) (-) Lalor_3D_DMOMIG Inline:1088, Crossline:1196-400 0 0.10 0.20 500 and geological model (Inline 1085 DMO-poststack Synthetic seismic trace overlayed on seismic migrated volume). SW Ore zone Synthetic trace NE 0.30 1000
History of VMS footwall rocks 1. 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 6 1 5 2 4 3 Subsurface Knowledge Unified Approach
3D modelling of geologic surfaces to define the geometry of the curvilinear grid Unit contacts from geologic map (Bailes et al, 1993) lithostratigraphic markers from drill logs (Bailes 2012) lithofacies recoded from Hudbay drill logs strike/dip s 0 restored from bedding-core angles (Bailes, 2012) NE SW 3D geologic surface model Lalor deposit
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 Dulac 2008 Subsurface Knowledge Unified Approach uvt transform Mallet 2004 (Mallet, 2003) Numerical grid modelling, including structural analysis (characterization of spatial autocorrelation) is conditioned by the modelled geological structure
Methods for filling the uvt grid kriged lithofacies kriged density kriging variance simulated density 1 simulated density 2 simulated density 3
3D grid modelling to interpret relationships lithology, alteration & seismic amplitude SW 3D geological surface model 3D Lithofacies model 3D curvilinear grid 3D CCPI alteration model
Lithofacies modelling, input drill hole data 82 rock classes 15 rock classes Zr/TiO 2 <= 0.013 basalt mafic fragmentals - tuff mafic gneiss/schist 0.013< Zr/TiO 2 < 0.019 dacite dacitic fragmetals - tuff interm. gneiss./schist Zr/TiO 2 >=0.019 rhyolite/rhyodacite felsic fragmetals - tuff felsic gneiss schist sulphide ore argillite diorite/gabbro
Lithofacies modelling, systematic classification COHERENT VOLCANIC ROCKS COARSE VOLCANICLASTIC ROCKS (FRAGMENTALS) FINE VOLCANICLASTIC ROCKS (LAPILLI TUFF / TUFF) GNEISS / SCHIST (UNRECOGNIZABLE PROTOLITH) REMAINING CLASSES Zr/TiO 2 < =0.013 0.013 < Zr/TiO 2 < 0.019 Zr/TiO 2 >= 0.019 Zr/TiO 2 < =0.013 0.013 < Zr/TiO 2 < 0.019 Zr/TiO 2 >= 0.019 Zr/TiO 2 < =0.013 0.013 < Zr/TiO 2 < 0.019 Zr/TiO 2 >= 0.019 Zr/TiO 2 < =0.013 0.013 < Zr/TiO 2 < 0.019 Zr/TiO 2 >= 0.019 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
Can we see the effects in 3D lithofaciesseismic amplitude model? W E Cate et al., 2013 strongest intensity of hydrothermal alteration Zr/TiO 2 <= 0.013 basalt mafic fragmentals - tuff mafic gneiss/schist 0.013< Zr/TiO 2 < 0.019 dacite dacitic fragmetals - tuff interm. gneiss/schist Zr/TiO 2 >=0.019 rhyolite/rhyodacite felsic fragmetals - tuff felsic gneiss schist
Impedance contrast hanging wall unaltered versus footwall altered rocks hanging wall rocks altered footwall rocks Ỵ-Ỵ density g/cm 3 Ỵ-Ỵ density g/cm 3 Zr/TiO 2 <= 0.013 basalt mafic fragmentals - tuff mafic gneiss/schist 0.013< Zr/TiO 2 < 0.019 dacite dacitic fragmetals - tuff interm. gneiss./schist Zr/TiO 2 >=0.019 rhyolite/rhyodacite felsic fragmetals - tuff felsic gneiss schist
Vp-density plots borehole geophysical logs Vp (m/s) Y-Y density Vp seismic velocity log sample, n = 67657 rock sample, n=42 ϒ-ϒ density (g/cm 3 )
Co-locating geophysical borehole logs with lithogeochemistry samples and lithology logs geophysical log datum HOLEID Depth ρ Vp Vs Zr/TiO 2 CCPI AI Lithology DUB202 831.3 2.49 5421 3289 0.009 87 55 basalt flow DUB202 831.5 2.52 5345 3560 0.009 87 55 basalt flow ALTERATION INDICES AI = 100 (K 2 O + MgO) (K 2 O + MgO + Na 2 O + CaO) Drill path CCPI = 100 (MgO + FeO) (MgO + FeO + Na 2 O + K 2 O) 1259 of 67657 geophysical log samples (1.9 %) are co-located with geochemical samples within 30 cm
V p - density plot felsic-intermediate rocks, FW
V p - density plot mafic rocks, footwall
Seismic Impedance vs. Alteration Box Plot hanging wall footwall seismic impedance (kg.m -2.s -1 x 10-6 )
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