Ramping-up Exploration Value from Aeromagnetic Surveys - More Geological Input Needed!

Transcription

1 Ramping-up Exploration Value from Aeromagnetic Surveys - More Geological Input Needed! Dave Isles Southern Geoscience Consultants AIG Geoscientists Symposia Bali May 2013 EAST ASIA: Geology, Exploration Technologies and Mines

2 Acknowledgements Society of Exploration Geophysicists Shell Sponsorship Leigh Rankin Geoscience Australia & State Surveys Fugro Airborne Surveys Besra Gold Inc

3 (Harrison) Mineral discovery mystery & murder!

4 GEOLOGICAL INTERPRETATION of AEROMAGNETIC DATA a NEW e-book by Dave Isles and Leigh Rankin INTEGRATION OBSERVATIONS AEROMAGNETICS Published by ASEG and the Society of Exploration Geophysicists Australian Society of Exploration Geophysicists GEOLOGY Scheduled for release in June

5 NEW AEROMAG WORKSHOP AEROMAGNETICS, GEOLOGY AND EXPLORATION a 5-day field workshop presented by Dave Isles, Leigh Rankin and Jack Hallberg Kalgoorlie October (Mon-Fri) 2013 Handout with workshop flyer available here

6 What is meant by exploration value? Achieving exploration goals Robust assessment of AOI Definition & rating of target areas Decisions on exploration action

7 How often is good value achieved from an aeromagnetic survey? - less than 50%? Why is this? -not enough effort in interpretation

8 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.

9 using aeromagnetics to find ore bodies -here are 6 tier-one examples! Epithermal Au Haematite Fe Greenstone Au 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! Finding the major deposits in each of these frames requires careful observation, integration and application of geological and exploration themes IOCG (U, REE) BHT Ag, Pb (Zn) Sed hosted Pb, Zn /Epig _ Cu

10 Ramping-up Exploration Value from Aeromagnetic Surveys - More Geological Input Needed! TOPICS Interpretation Methodology Golden Dyke Study Mt Leyshon Goldfield study Bau Goldfield study (very briefly) Concluding Comments

11 Aeromagnetics- what does it do? MAP GEOLOGY!!!!!!! MOST geological environments reveal critical exploration & mapping information through the eye of the magnetometer

12 Uses of Aeromagnetics Mapping geology?.. what attributes? Lithology ( rock type ) Structure (geometry) Alteration Metamorphism Mineralisation All of these attributes may be seen in aeromagnetics

13 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)

14 Aeromagnetics- how do we use it? Plan Fly & Compile Process & Enhance INTERPRET

15 Data Acquisition and Processing High quality, high resolution acquisition is the norm Data Processing methodologies are robust/adequate Grants Austirex pic NO BIG PROBLEMS

16 Filtering and Image Enhancement many choices ---->???too many choices Imaging by Andy Roberts AND THERE ARE MANY MORE!!

17 Filtering and Image Enhancement Our capabilities and efforts in acquisition, processing & enhancement are excellent! But what about INTERPRETATION? SELECTIONS choose to suit the purpose TMI RTP RTP 1VD/2VD RTP 2VDagc ANSIG KEEP IT SIMPLE MAINTAIN GEOLOGICAL FOCUS TAILOR MAKE YOUR IMAGERY

18 Interpretation Methodology Gather and Digest all available GEOLOGY Careful OBSERVATION on Aeromagnetic Imagery OBSERVATION LAYER Ample RECORDING of observations (draft) SOLID GEOLOGY LAYER INTEGRATE Geology (and all other relevant data, e.g. spec, EM, grav, etc) INTEGRATED INTERPRETATION LAYER 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

19 Interpretation Methodology - mineral exploration example GOLDEN DYKE AREA, Pine Creek Inlier, NT Australian aeromagnetic grid courtesy of GADDS- Australian Government Geoscience Portal

20 Interpretation Methodology Golden Dyke GEOLOGY 1:100,000 scale mapping by Geoscience Australia (formerly BMR) Area is 7kms x 10kms AEROMAGNETIC PROFILES Data courtesy WGC, NTGS and Geoscience Australia 200m lines at 60m mtc Total of 385 line kms in example area

21 Interpretation Methodology Golden Dyke QUICK INTERPRETATION (hours) FILLS THE GAPS ADDS STRUCTURE/ CONTINUITY LOOKS OK CAN WE DO BETTER THAN THIS? + =

22 Interpretation Methodology Golden Dyke STEP 1 - WORKHORSE IMAGES CAREFUL OBSERVATIONS TIME Imaging by A Roberts Southern Geoscience Consultants

23 Interpretation Methodology Golden Dyke STEP 1 OBSERVATION LAYER stratigraphic markers CAREFUL OBSERVATIONS Structural Detail anomalies Aleration Zone

24 Interpretation Methodology Golden Dyke STEP 2 DRAFT SOLID GEOLOGY AEROMAG OBSERVATIONS + OUTCROP MAPPING (draft) SOLID GEOLOGY TIME

25 Interpretation Methodology Golden Dyke STEP 3 INTEGRATED INTERPRETATION (draft) SOLID GEOLOGY STRUCTURAL INTERPRETATION mineralisation + TIME

26 END POINT EXPLORATION TARGETING HIGH EXPLORATION VALUE Detail in geology and aeromag THOROUGH INTERPRETATION integrated and (days) interpreted LIMITED EXPLORATION VALUE Important detail in aeromag QUICK INTERPRETATION has been (hours) overlooked

27 END POINT EXPLORATION TARGETING HIGH EXPLORATION VALUE Detail in geology and aeromag THOROUGH INTERPRETATION integrated and (days) interpreted LIMITED EXPLORATION VALUE Important detail in aeromag QUICK INTERPRETATION has been (hours) overlooked the essential ingredients in good-value interpretation are GEOLOGICAL THINKING and TIME

28 Charters Towers - Mt Leyshon Interpretation Study Ravenswood Batholith North Queensland, Australia

29 Charters Towers Region Aeromagnetics mainly 400m spacing- (GSQ/ Geoscience Australia)

30 Geology and Landuse Google Earth GSQ Geology 5 km

31 Detailed Aeromagnetic Data (200m lines m agl) ( multiclient ) courtesy Fugro Airborne Surveys

32 WORKHORSE IMAGES RTP 1VD drape RTP RTP 2VD drape 5 km

33 Interpretation Step 1a Mag Observations - breaks

34 Interpretation Step 1b Mag Observations - zonation & contacts

35 Interpretation Step 2 (draft) Solid Geology

36

37 BAU Goldfield, East Malaysia Aeromagnetic Study Data courtesy BESRA Gold Inc

38 BAU Goldfield, Sarawak Miocene dacite porphyries host limestone Triassic granodiorite shale / sst Data courtesy BESRA Gold Inc

39 BAU Goldfield, Sarawak workhorse aeromagnetic images 100m m agl Dighem Survey Data courtesy BESRA Gold Inc

40 workhorse aeromagnetic images Without robust RTP sensible (structural) interpretation is not achievable

41 BAU Goldfield, Sarawak workhorse aeromagnetic images Data courtesy BESRA Gold Inc

42 BAU Goldfield, Sarawak Interpretation step1 Observations shallow Data courtesy BESRA Gold Inc

43 BAU Goldfield, Sarawak shallow observations provide extra geology Data courtesy BESRA Gold Inc

44 BAU Goldfield, Sarawak In this area there is a clearly defined deeper set of magnetic rock units Data courtesy BESRA Gold Inc

45 BAU Goldfield, Sarawak applying a 1 st VD to the spectral window refines the definition of deep geometry Data courtesy BESRA Gold Inc

46 BAU Goldfield, Sarawak Interpretation step 1b -a separate set of observations is needed to describe this deep geometry Data courtesy BESRA Gold Inc

47 BAU Goldfield, Sarawak the deep geometry and structure adds greatly to the geological picture Data courtesy BESRA Gold Inc

48 BAU Goldfield, Sarawak Combining shallow and deep observations adds complexity, but it is REAL GEOLOGICAL complexity Data courtesy BESRA Gold Inc

49 BAU Goldfield, Sarawak Bau arch / anticline andesites, cored with granodiorite/diorite?and Miocene dacite? Major fracture systems and dykes -age? -relevance to Au? Interpretation step2 Integrate geology & aeromag (draft) Solid Geology??? Broad fracture zone with en-echelon intrusions?miocene dacites?? arc-normal fracture zone? Data courtesy BESRA Gold Inc

50 BAU Goldfield, Sarawak Bau arch / anticline andesites, cored with granodiorite/diorite?and Miocene dacite? Major fracture systems and dykes -age? -relevance to Au? Interpretation step2 Integrate geology & aeromag More time & geological input needed! (draft) Solid Geology??? Realisation of exploration value? Not yet- Broad fracture zone with en-echelon intrusions?miocene dacites?? arc-normal fracture zone? but the signs are very encouraging Data courtesy BESRA Gold Inc

51 Ramping-up Exploration Value from Aeromagnetic Surveys - More Geological Input Needed! Final Message. 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!