Ramping-up Exploration Value from Aeromagnetic Surveys ... · Dave Isles . Southern Geoscience Consultants . AIG Geoscientists Symposia Bali . May 2013 . Ramping-up Exploration Value

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




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?


‘WORKHORSE’

IMAGES

‘WORKHORSE’

IMAGES

CAREFUL OBSERVATIONS CAREFUL OBSERVATIONS

Imaging by A Roberts

Southern Geoscience Consultants

TIME


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


(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


+

(draft) SOLID GEOLOGY (draft) SOLID GEOLOGY STRUCTURAL

INTERPRETATION

STRUCTURAL

INTERPRETATION

mineralisation

STEP 3 – INTEGRATED INTERPRETATION STEP 3 – INTEGRATED INTERPRETATION

TIME

+


QUICK INTERPRETATION

(hours)

LIMITED EXPLORATION VALUE

Important detail in aeromag

has been overlooked



has been overlooked THOROUGH INTERPRETATION

(days)

HIGH EXPLORATION VALUE

Detail in geology and aeromag

integrated and interpreted




‘END POINT’ – EXPLORATION TARGETING ‘END POINT’ – EXPLORATION TARGETING

QUICK INTERPRETATION

(hours)



has been overlooked



has been overlooked THOROUGH INTERPRETATION

(days)







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

Google

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


shale / sst Triassic

granodiorite

host limestone

Miocene dacite

porphyries



‘workhorse’

aeromagnetic

images

100m 045° 80m agl

‘Dighem’ Survey

‘workhorse’

aeromagnetic

images

Without robust RTP

sensible (structural) interpretation

is not achievable



‘workhorse’

aeromagnetic

images



Interpretation

step1

Observations

‘shallow’



‘shallow’

observations

provide

‘extra’ geology



In this area

there is a

clearly defined

‘deeper’ set of

magnetic rock ‘units’



applying a 1st VD

to the

spectral window

refines the definition

of deep geometry



Interpretation step ‘1b’

-a separate set

of observations

is needed

to describe

this deep geometry



the deep geometry

and structure

adds greatly to the

geological picture



Combining

shallow and deep

observations

adds complexity,

but it is REAL GEOLOGICAL

complexity



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

???



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….




Documents

Ramping-up Exploration Value from Aeromagnetic Surveys ... · Dave Isles . Southern Geoscience Consultants . AIG Geoscientists Symposia Bali . May 2013 . Ramping-up Exploration Value