Ramping-up Exploration Value from Aeromagnetic Surveys ... · Dave Isles . Southern Geoscience...
Transcript of Ramping-up Exploration Value from Aeromagnetic Surveys ... · Dave Isles . Southern Geoscience...
Dave Isles Southern Geoscience Consultants
AIG Geoscientists Symposia
Bali
May 2013
Ramping-up Exploration Value
from Aeromagnetic Surveys
- More Geological Input Needed!
EAST ASIA: Geology, Exploration Technologies and Mines
Acknowledgements Society of Exploration Geophysicists
Shell Sponsorship
Leigh Rankin
Geoscience Australia & State Surveys
Fugro Airborne Surveys
Besra Gold Inc
(Harrison)
Mineral discovery
mystery & murder!
GEOLOGICAL INTERPRETATION of
AEROMAGNETIC DATA
a NEW e-BOOK by Dave Isles and Leigh Rankin
GEOLOGY
Australian Society of
Exploration Geophysicists
AEROMAGNETICS
OBSERVATIONS
INTEGRATION
Scheduled for
release in June
Published by ASEG
and the Society of Exploration Geophysicists
NEW AEROMAG WORKSHOP
AEROMAGNETICS, GEOLOGY AND EXPLORATION
a 5-day ‘field workshop’
presented by
Dave Isles, Leigh Rankin and Jack Hallberg
Kalgoorlie October 21-25 (Mon-Fri) 2013
Handout with workshop flyer
available here
What is meant by ‘exploration value’?
‘Achieving exploration goals’
• Robust assessment of AOI
• Definition & rating of target areas
• Decisions on exploration ‘action’
How often is ‘good value’ achieved
from an aeromagnetic survey?
- less than 50% ?
Why is this?
-not enough ‘effort’ in interpretation
Motherhood Statement
Integration of aeromag with geology provides a basis for ‘reading’ exploration themes and models into the interpretation. Without this we cannot clearly identify ‘geologically anomalous’ features and differentiate them from ‘routine’ geological features that may be geophysically ‘anomalous’.
using aeromagnetics to find ore bodies -here are 6 ‘tier-one’ examples!
Finding the major deposits in each of these frames
requires careful observation, integration and
application of geological and exploration themes
NONE of the major ORE BODIES
in these images is a
‘STAND-OUT’ MAGNETIC ANOMALY
but all could be FOUND
with the HELP of AEROMAGNETICS!
Epithermal Au Haematite Fe Greenstone Au
IOCG (U, REE) BHT Ag, Pb (Zn) Sed hosted Pb, Zn /Epig _ Cu
Interpretation Methodology–
Golden Dyke Study
Mt Leyshon Goldfield study
Bau Goldfield study (very briefly)
Concluding Comments
TOPICS
Ramping-up Exploration Value
from Aeromagnetic Surveys
- More Geological Input Needed!
Aeromagnetics- “what does it do?”
MAP GEOLOGY !!!!!!!
MOST geological environments reveal
critical exploration & mapping information
through the eye of the magnetometer
• Mapping geology? .. what attributes?
– Lithology (‘rock type’)
– Structure (geometry)
– Alteration
– Metamorphism
– Mineralisation
Uses of Aeromagnetics
All of these attributes may be seen in aeromagnetics
Mapping geology… why/how is it possible?
– Magnetic minerals are present in (almost) all ‘rock types’
(0.0003% ‘magnetite’ is detectable)
– Magnetometers can measure tiny ‘geological’ signals
(0.05nT is achievable with care)
– Airborne platforms allow rapid & inexpensive coverage (e.g 50km x 50km flown with 200 m line spacing- ~<15,000line kms- could be
flown and processed in 6 week time frame and cost ~<$250,000)
Aeromagnetics- how do we use it?
• Plan
• Fly & Compile
• Process & ‘Enhance’
‘INTERPRET’
• High quality, high resolution acquisition is ‘the norm’
• Data Processing methodologies are robust/adequate
NO BIG PROBLEMS
• High quality, high resolution acquisition is ‘the norm’
• Data Processing methodologies are robust/adequate
NO BIG PROBLEMS
Data Acquisition and Processing Data Acquisition and Processing
Grants
Austirex
pic
Filtering and Image Enhancement Filtering and Image Enhancement
Imaging by Andy Roberts
many choices ----> ???too many choices
AND THERE ARE MANY MORE !!
• SELECTIONS — choose to suit the purpose
KEEP IT SIMPLE
MAINTAIN GEOLOGICAL FOCUS
‘TAILOR MAKE’ YOUR IMAGERY
• SELECTIONS — choose to suit the purpose
KEEP IT SIMPLE
MAINTAIN GEOLOGICAL FOCUS
‘TAILOR MAKE’ YOUR IMAGERY
Filtering and Image Enhancement Filtering and Image Enhancement
TMI RTP RTP 1VD/2VD RTP 2VDagc ANSIG
Our capabilities and efforts in
acquisition, processing & enhancement are
excellent!
But what about INTERPRETATION?
• Gather and Digest all available GEOLOGY
• Careful OBSERVATION on Aeromagnetic Imagery
• Ample RECORDING of observations
• INTEGRATE Geology (and all other relevant data, e.g. spec, EM, grav, etc)
• INTERPRET - develop a working hypothesis
• TEST hypothesis – e.g. map, sample & drill
• REVIEW - field tests will create new information
feed this information back into interpretation
• Gather and Digest all available GEOLOGY
• Careful OBSERVATION on Aeromagnetic Imagery
• Ample RECORDING of observations
• INTEGRATE Geology (and all other relevant data, e.g. spec, EM, grav, etc)
• INTERPRET - develop a working hypothesis
• TEST hypothesis – e.g. map, sample & drill
• REVIEW - field tests will create new information
feed this information back into interpretation
Interpretation Methodology Interpretation Methodology
OBSERVATION LAYER
(draft) SOLID GEOLOGY LAYER
INTEGRATED INTERPRETATION LAYER
Interpretation Methodology - mineral exploration example Interpretation Methodology - mineral exploration example
GOLDEN DYKE AREA,
Pine Creek Inlier, NT
GOLDEN DYKE AREA,
Pine Creek Inlier, NT
Australian aeromagnetic grid courtesy of GADDS-
Australian Government Geoscience Portal – www.geoscience.gov.au
AEROMAGNETIC PROFILES Data courtesy WGC, NTGS and Geoscience Australia
200m lines at 60m mtc
Total of 385 line kms in example area
AEROMAGNETIC PROFILES Data courtesy WGC, NTGS and Geoscience Australia
200m lines at 60m mtc
Total of 385 line kms in example area
GEOLOGY 1:100,000 scale mapping by Geoscience Australia
(formerly BMR)
Area is 7kms x 10kms
GEOLOGY 1:100,000 scale mapping by Geoscience Australia
(formerly BMR)
Area is 7kms x 10kms
Interpretation Methodology – Golden Dyke Interpretation Methodology – Golden Dyke
‘QUICK’ INTERPRETATION (hours) ‘QUICK’ INTERPRETATION (hours)
FILLS THE GAPS
ADDS STRUCTURE/ CONTINUITY
LOOKS OK
FILLS THE GAPS
ADDS STRUCTURE/ CONTINUITY
LOOKS OK
+ =
CAN WE DO BETTER THAN THIS? CAN WE DO BETTER THAN THIS?
Interpretation Methodology – Golden Dyke Interpretation Methodology – Golden Dyke
‘WORKHORSE’
IMAGES
‘WORKHORSE’
IMAGES
CAREFUL OBSERVATIONS CAREFUL OBSERVATIONS
Imaging by A Roberts
Southern Geoscience Consultants
TIME
Interpretation Methodology – Golden Dyke Interpretation Methodology – Golden Dyke
STEP 1 - STEP 1 -
CAREFUL OBSERVATIONS CAREFUL OBSERVATIONS
Structural Detail Structural Detail
Aleration Zone Aleration Zone
stratigraphic markers stratigraphic markers
‘anomalies’ ‘anomalies’
STEP 1 – OBSERVATION LAYER STEP 1 – OBSERVATION LAYER
Interpretation Methodology – Golden Dyke Interpretation Methodology – Golden Dyke
(draft) SOLID GEOLOGY (draft) SOLID GEOLOGY OUTCROP MAPPING OUTCROP MAPPING AEROMAG
OBSERVATIONS
AEROMAG
OBSERVATIONS
STEP 2 – DRAFT SOLID GEOLOGY STEP 2 – DRAFT SOLID GEOLOGY
TIME
Interpretation Methodology – Golden Dyke Interpretation Methodology – Golden Dyke
+
(draft) SOLID GEOLOGY (draft) SOLID GEOLOGY STRUCTURAL
INTERPRETATION
STRUCTURAL
INTERPRETATION
mineralisation
STEP 3 – INTEGRATED INTERPRETATION STEP 3 – INTEGRATED INTERPRETATION
TIME
+
Interpretation Methodology – Golden Dyke Interpretation Methodology – Golden Dyke
QUICK INTERPRETATION
(hours)
LIMITED EXPLORATION VALUE
Important detail in aeromag
has been overlooked
LIMITED EXPLORATION VALUE
Important detail in aeromag
has been overlooked THOROUGH INTERPRETATION
(days)
HIGH EXPLORATION VALUE
Detail in geology and aeromag
integrated and interpreted
HIGH EXPLORATION VALUE
Detail in geology and aeromag
integrated and interpreted
‘END POINT’ – EXPLORATION TARGETING ‘END POINT’ – EXPLORATION TARGETING
QUICK INTERPRETATION
(hours)
LIMITED EXPLORATION VALUE
Important detail in aeromag
has been overlooked
LIMITED EXPLORATION VALUE
Important detail in aeromag
has been overlooked THOROUGH INTERPRETATION
(days)
HIGH EXPLORATION VALUE
Detail in geology and aeromag
integrated and interpreted
HIGH EXPLORATION VALUE
Detail in geology and aeromag
integrated and interpreted
the essential ingredients
in ‘good-value’ interpretation are
GEOLOGICAL THINKING
and TIME
‘END POINT’ – EXPLORATION TARGETING ‘END POINT’ – EXPLORATION TARGETING
Charters Towers -
Mt Leyshon
Interpretation Study Ravenswood Batholith
North Queensland, Australia
Charters Towers Region Aeromagnetics
mainly 400m spacing- (GSQ/ Geoscience Australia)
Geology and Landuse
Earth
GSQ
Geology
5 km
Detailed Aeromagnetic Data (200m lines 070° 80m agl)
(‘multiclient’)
courtesy Fugro Airborne Surveys
RTP 1VD
drape
RTP RTP 2VD
drape
‘WORKHORSE’ IMAGES ‘WORKHORSE’ IMAGES
5 km
Interpretation Step ‘1a’ – Mag Observations -’breaks’
Interpretation Step ‘1b’ – Mag Observations - zonation & contacts
Interpretation Step 2 – (draft) Solid Geology
BAU Goldfield, East Malaysia
Aeromagnetic Study
Data courtesy BESRA Gold Inc
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
shale / sst Triassic
granodiorite
host limestone
Miocene dacite
porphyries
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
‘workhorse’
aeromagnetic
images
100m 045° 80m agl
‘Dighem’ Survey
‘workhorse’
aeromagnetic
images
Without robust RTP
sensible (structural) interpretation
is not achievable
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
‘workhorse’
aeromagnetic
images
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
Interpretation
step1
Observations
‘shallow’
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
‘shallow’
observations
provide
‘extra’ geology
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
In this area
there is a
clearly defined
‘deeper’ set of
magnetic rock ‘units’
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
applying a 1st VD
to the
spectral window
refines the definition
of deep geometry
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
Interpretation step ‘1b’
-a separate set
of observations
is needed
to describe
this deep geometry
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
the deep geometry
and structure
adds greatly to the
geological picture
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
Combining
shallow and deep
observations
adds complexity,
but it is REAL GEOLOGICAL
complexity
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
Interpretation step2
Integrate
geology & aeromag
Bau ‘arch’/ ‘anticline’
andesites, cored with
granodiorite/diorite
?and Miocene dacite?
Broad fracture zone
with en-echelon intrusions
?Miocene dacites?
? ‘arc-normal’ fracture zone?
Major fracture systems
and dykes
-age?
-relevance to Au?
(draft) Solid Geology
???
BAU Goldfield, Sarawak
Data courtesy BESRA Gold Inc
Interpretation step2
Integrate
geology & aeromag
Bau ‘arch’/ ‘anticline’
andesites, cored with
granodiorite/diorite
?and Miocene dacite?
Broad fracture zone
with en-echelon intrusions
?Miocene dacites?
? ‘arc-normal’ fracture zone?
Major fracture systems
and dykes
-age?
-relevance to Au?
(draft) Solid Geology
??? More time & geological input needed!
Realisation of exploration value?
Not yet-
but the signs are very encouraging
• Your existing aeromag probably has new and important exploration clues ……………… waiting to be ‘found’
• Take more time, think more geology
• Terima Kasih.. thank you for your attention!
Final Message….
Ramping-up Exploration Value
from Aeromagnetic Surveys
- More Geological Input Needed!