The Y2 project (2001 – 2004)
pmd CRC
Domes and basins and their role in
fluid flow
P. Henson & Y2 project team
Boxwork alteration (Penny Dam)
predictive
redictive mineral
ineral discovery
iscovery
Y2 Research location
• Introduction- brief deformation history
• What do the low angle reflectors
represent
• Identification of domical structures
• Gravity inversion modelling & seismic
(domes)
•Fluid focussing
•Conclusions
pmd CRC
predictive
redictive mineral
ineral discovery
iscovery
Introduction
pmd CRC
Deformation history
Swager, 1997
This study
DE
N-S? extension
DE
N-S extension
D1
N-S contraction
D1
N-S? contraction
D2a
E-W contraction
D2e
E-W extension
D2E
E-W extension
(‘late basins’)
D2
E-W contraction
D2b
E-W contraction
D3
~N-S contraction
D3
E(NE)-W(SW) contraction
D4
E(NE)-W(SW) contraction
D4
E-W regional contraction
D5
E-W regional contraction
Orogenic
Surge
Domes
predictive
redictive mineral
ineral discovery
iscovery
Low angle reflectors,
LASH’s
pmd CRC
Upper crust
Middle crust
Lower crust
• Three levels of crustal deformation operate independently
• Brittle-ductile transition marks the Upper-middle crustal
boundary (low-angle detachment/LASH)
• Lower crust displays only horizontal reflectors and is assumed
to be entirely plastic deformation
predictive
redictive mineral
ineral discovery
iscovery
The detachment as a seismic
brittle-ductile transition?
Magistrale, 2002
pmd CRC
predictive
redictive mineral
ineral discovery
iscovery
The detachment as a seismic
brittle-ductile transition?
pmd CRC
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predictive
redictive mineral
ineral discovery
iscovery
Is the detachment a 10 km
palaeodepth indicator?
pmd CRC
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predictive
redictive mineral
ineral discovery
iscovery
Is the detachment a 10 km
palaeodepth indicator?
pmd CRC
B/=
B0=
B1=
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D1
D2a
D2b+
Simpler
Flatter
Younger
~10 km
predictive
redictive mineral
ineral discovery
iscovery
The detachment as a seismic
brittle-ductile transition?
pmd CRC
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predictive
redictive mineral
ineral discovery
iscovery
Identification of domical structures
Seisimic reflection lines in
the Kalgoorlie region
pmd CRC
predictive
redictive mineral
ineral discovery
iscovery
Identification of domical structures
Seisimic reflection lines in
the Kalgoorlie region
pmd CRC
predictive
redictive mineral
ineral discovery
iscovery
Dome and basin geometries
Fmubmrfcwdmpk=
pmd CRC
predictive
redictive mineral
ineral discovery
iscovery
Correlation between UBC inversion and seismic
Domes interpreted
from seismic lines
20km
W
pmd CRC
Red lines =
regional faults
Kanowna Belle
EGF01
seismic line
E
predictive
redictive mineral
ineral discovery
iscovery
Geologically constrained gravity
inversion
100km
Resulting model for spatially-constrained inversion using the starting model of Figure 5 and a local volume as outlined
above. Density range covers greenstones to 3.0g/cc (+0.3g/cc on base) down to granitic rocks of 2.6g/cc (-0.1g/cc)
pmd CRC
predictive
redictive mineral
ineral discovery
iscovery
Combining and comparing UBC gravity
pmd
inversion with seismic in 3D space
E
W
30km
EGF01
seismic line
CRC
predictive
redictive mineral
ineral discovery
iscovery
W
Kanowna Belle
E
pmd CRC
Penny Dam
Penny Dam
EGF01
N
W
E
30km
2 identical images
looking from
underneath
Kanowna
Belle
EGF01
N
30km
predictive
redictive mineral
ineral discovery
iscovery
Fluid focussing
pmd CRC
What is the significance of
identifying domical
structures?
The presence of cross
folding (domes) are of
paramount importance in
determining the locations of
Au deposition (Ellis, 1939)
Plan view of domical structures in the
Southern Cross province
predictive
redictive mineral
ineral discovery
iscovery
Oil analogy for trapping
fluids in domes
• Fluid is focussed into anticlines and
structural traps
• Oil deposition needs a source rockmigration path and trap
•Concentration and hydrocarbon
migration are often related to inversion
• Are ore fluids (Au) concentrated by the
pre-existing structures and geometries ?
pmd CRC
predictive
redictive mineral
ineral discovery
iscovery
Delivering a focussed fluid
Fault geometries &
fluid concentration
pmd CRC
Au
Fracture induced
permeability!
• Hot fluids rise (less dense)
• Fluid pathway geometries
(critical !)
• Domical structures, focus fluid
• Localised zones of dilation
Orthogonal view
predictive
redictive mineral
ineral discovery
iscovery
Breached domes, focussed fluids pmd CRC
and orogenic gold analogy
• Fracture induced permeability
• Au deposits located close to the
apex of large domes (Golden Mile,
St Ives, Telfer, Stawell etc.)
• Dome and basin geometries
produced by orthogonal
deformations provide a good
regional focussing architecture
Orthogonal view
Golden
Mile
Kanowna
Belle
10km
predictive
redictive mineral
ineral discovery
iscovery
Conclusions
Three levels of fluid focussing
pmd CRC
• Fluid focussed at the boundary of the middle and
upper crust and this boundary is domical
• Focussed fluid is released via breaching faults
• Upper crust geometries and favourable host rock
short wavelength
allow Au precipitation
upper crust
Orthogonal view
long wavelength
middle crust