Enabling Technologies
3D Architecture
Geophysical methods and advanced inversion methods
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A legacy for mineral exploration science
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predictive mineral discovery*Cooperative Research Centre
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A. Gradient inhydraulicpotential
B. Permeability
C. Solubilitysensitivity to P, T, C
D. Spatialgradient of P, T, C
E. Time (duration)
Key Parameter
is reflected in
ExplorationMineral System
scale-dependent translation
5 Questions1. Geodynamics2. Architecture3. Fluid
reservoirs4. Flow drivers &
pathways5. Deposition
Terrain Selection
Area Selection
Drill Targeting
Slide after: A. Barnicoat
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Gravity Profile
2D section
White more dense
Boschetti et al 1998
Other 2D sections
White more dense
Slide after: L. Ailleres
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Let us consider a set of drilling intersections
After Caumon, 2007A very conservative geologist’s interpretation.
After Caumon, 2007A conservative geologist’s interpretation.
After Caumon, 2007An optimistic geologist’s interpretation.
After Caumon, 2007A very optimistic geologist’s interpretation.
After Caumon, 2007An extremely optimistic geologist’s interpretation.
After Caumon, 2007A geophysicist’s interpretation.
After Caumon, 2007The reservoir engineers interpretation.
After Caumon, 2007
Slide after: L. Ailleres
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predictive mineral discovery*Cooperative Research Centre
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Gravity/magnetic data
Inversion
Applyconstraint
Create reference
Buildmap
3D reference model3D geological map andphysical properties
3D inversion model
???
Analyse and update Slide after: Richard Lane
Solid geologySeismicStructureDrilling(et cetera)
Potential field data - Gravity
Gravity variations → rock density
density contrast
shape of the spatial variation in the gravitational acceleration to identify the location and shape of the ore body
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gravity anomaly: variations in the background gravity field produced by local geologic structure or a model of local geologic structure
a gravimeter is any instrumentdesigned to measure spatial variations in gravitationalacceleration
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Material Density (gm/cm^3)
Air ~0Water 1Sediments 1.7-2.3Sandstone 2.0-2.6Shale 2.0-2.7Limestone 2.5-2.8
Granite 2.5-2.8
Basalts 2.7-3.1
Metamorphic Rocks 2.6-3.0
Potential field data - Gravity
Potential field data - Gravity
Factors that Affect the Gravitational Acceleration:
Temporal Based Variations - time dependent- Instrument drift- Tidal effects
Spatial Based Variations - space dependent- Latitude - Elevation - Slab - Topographic
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Gravity - Magnetics
Similarities:
both measure potential fields
Identical physical and mathematical representations can be used to understand magnetic and gravitational forces
point mass ↔ magnetic monopole
The acquisition, reduction, and interpretation of gravity andmagnetic observations are very similar.
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Gravity - MagneticsDifferences:
rock densities vary little ↔ magnetic susceptibility can vary much (amongst different rock types, within a given rock type) → difficult to determine rock types on the basis of estimated
susceptibilities
gravitational force is always attractive ↔ magnetic force can be either attractive or repulsive
Unlike point masses in gravity, single magnetic point sources (monopoles) always occur in pairs → dipoles
at least two possible sources for magnetic field (induced/remanent)
magnetic field is highly time dependent
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Potential field data - Magnetics
Magnetics measures magnetic field variations→ magnetic susceptibility→ determined by the physical properties of the magnetic
material, unitless constant
Dia- / Para- / Ferromagnetism
Magnetic anomalies are a function of 2 independentparameters:
subsurface distribution of susceptibilityorientation of the Earth's main magnetic field
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
I = кH
Potential field data - Magnetics
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Magnetized Sphere North Pole Equator Northern Hemisphere
Potential field data - MTmeasures electric and magnetic fields
main parameter derived from MT is restivity.
main factor affecting resistivity is lithology, but also pore fluid, P, T
mapping of basins, geothermal prospects, structures
data are normally integrated with whatever other informationis available (gravity, magnetics, geology, and borehole).
in lieu of seismic, in lead of seismic, in conjunction with seismic
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Potential field data
(a) Interpretation of MT data
and
(b) seismic section from Turkey
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Worms
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• edges in a "wavelet transform" of the underground terrain• an above ground 3D mirror image of a geological boundary • Irregularities - Density contrasts – points of maximum gradient
at successive heights• Position (x, y), height (z) and amplitude (w) of a gradient• Visualised over range of heights, points merge into sheet-like
surfaces (worm sheets)• Height and amplitude of worm sheet is a function of the
geological source
Worms
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
* =
* =
One unit upward continuation
Five units upward continuation
Upward continuation
Courtesy of: F. Horowitz
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
After: Holden et al 2001
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Sources(L×M×N)
Field(M×N)
Worms
Archibald et al 1998
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A legacy for mineral exploration science
Courtesy of: F. Horowitz
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Courtesy of: F. Horowitz
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Courtesy of: F. Horowitz
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Courtesy of: F. Horowitz
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Courtesy of: F. Horowitz
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Courtesy of: F. Horowitz
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
Worms -Visual interpretation
Courtesy of: F. Horowitz
Holden et al 2001
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predictive mineral discovery*Cooperative Research Centre
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Synthetic spherical/plug intrusions (A) Infinite vertical column.(B) Finite truncated parabolic
cone. (C)Infinite outward diverging
cone.
Worms - Visual interpretation Holden et al 2001
Synthetic dipping dykes
(A) Vertical dyke. (B) Dyke dipping 60o to the right. (C) Dyke dipping 30o to the right.
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Worms - Visual interpretationHolden et al 2001
Synthetic plunging folds (A)with vertical axial planeand vertical axes. (B)with vertical axial plane andaxes plunging 60o to the right.(C)with vertical axial plane andaxes plunging 30o to the
Synthetic dipping contacts on highdensity body (A) vertical contact. (B) Contact dipping to the right
with footwall high density. (C) Contact dipping to the right
with hanging wall high density.
Example
Yilgarn Gold Faults:
Existing digital coverage
Issues of quality andreliability
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Slide after: Barry Murphy
Example
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Length
Zwt Max (Height)
Worm Data
Wallaby
Sons of Gwalia
Log Zwt/Log Length10km radius of deposit
Bierlein et al 2006
predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science
ReferencesHolden, D., Archibald, N., Boschetti, F. , and Jessell, M. (2001). "Inferring
Geological Structures Using Wavelet-Based Multiscale Edge Analysis and Forward Models." Exploration Geophysics 31(4): 000-000.
Boschetti, F., Horowitz, F.G., and Hornby, P. (1998). "Ambiguity Analysis and the Constrained Inversion of Potential Fields." manuscript submitted to Geophysical Journal International: 30 p.
Archibald, N. J., Gow, P., and Boschetti, F. (1998). "Multiscale edge analysis of potential field data." Exploration Geophysics 30: 38-44.
Bierlein, F. (2006). "Distribution of orogenic gold deposits in relation to fault zones and gravity gradients: targeting tools applied to the Eastern Goldfields, YilgarnCraton, Western Australia." Mineralium deposita 41(2): 107-126.
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predictive mineral discovery*Cooperative Research Centre
A legacy for mineral exploration science