NTGS Geophysical & Remote Sensing Program: Acquisition &

Accessibility

Tania Dhu, Belinda Smith, Pierre-Olivier Bruna, Roger Clifton, &

Lachlan Hallett

Outline

• NTGS gravity acquisition program – 2013 Acquisition program – 2014 Acquisition program

• Industry geophysical data submissions • Accessing HyLoggerTM hyperspectral data • Collection of rock property data • Three-dimensional modelling project

2013 Gravity Acquisition Program • Prior to 2013 approximately

45% of the Territory was covered by 4 km spaced gravity or better

• Two regional surveys, funded through the Creating Opportunities for Resource Exploration (CORE) Northern Territory Government Initiative, were undertaken in 2013 to bring the coverage to greater than 52% of the Territory

• Southern Wiso Basin Gravity Survey

• 3,857 stations at 4 km x 4 km spacing

• Southern McArthur Basin Gravity Survey

• 4,618 stations at 4 km x 4 km spacing

• Industry funded infill of 1,657 stations at 2 km x 2 km spacing

Southern Wiso Basin Gravity Survey: Geology

• Intracratronic sedimentary basin faulted against the Palaeoproterozoic metamorphic rocks of Aileron Province to the south

• Unconformably overlies Palaeoproterozoic rocks of the Tanami Region to the west and Tennant Region to the east

• Sediments are generally less than 300 m thick however thicken to 2000-3000 m thick in the Lander Trough

• No basement outcrop and very little exploration

Southern Wiso Basin Gravity Survey: TMI

• Total Magnetic Intensity (TMI) shows shallow northwest-southeast trending features in the southeast of the survey area that extend into the Tennant Region to the east

• There are a number of broader wavelength magnetic anomalies along the southern boundary of the survey

Southern Wiso Basin Gravity Survey: Bouguer Anomaly

• Dominated by northwest-southeast trending linear features

• Bouguer anomaly low in the south coincident with the Lander Trough

• The depocentres can now be redefined based on this data

Southern McArthur Basin Gravity Survey: Geology

• Large Palaeo-Mesoproterozoic sedimentary basin with minor volcanics that has undergone polyphase deformation

• Unconformably overlies the Palaeproterozoic Murphy Province to the south • Overlain by sedimentary rocks of the Mesozoic Carpentaria Basin • Stratigraphy of the McArthur Basin is exposed in the Batten Fault Zone • Sediment thickness varies widely and is up 12 km thick in some areas

Southern McArthur Basin Gravity Survey: TMI

• Much of the magnetic signal is masked by the Cambrian Antrim Plateau Basalts

• Image suffers from poor resolution, 1500 m line spacing on the western boundary, 3000 m line spacing in the central portion, 500 m or better elsewhere

1500 m 3000 m 500 m or less

Southern McArthur Basin Gravity Survey: Bouguer Anomaly

• Bouguer anomaly is predominantly high in the northeast, low in the southwest • Fault traces reveal structural complexity within the Batten Fault Zone • The minimum extent of the Beetaloo Sub-basin depocentre is bounded by this sharp northwest-

southeast boundary indicative of structural controls on basin formation • The northwest-southeast trending boundary between the regions of high and low response aligns

with the strike of the Mallapunyah and Calvert Hills faults • The Daly Waters Arch, a basement topographic high, is visible as a relative anomaly high

Daly Waters Arch

Beetaloo Sub-basin

Mallapunyah Fault

Calvert Hills Fault

Resolving gravity anomalies – do you need to infill?

• Simplified geological cross-section: – Tilted basement (grey)/basin (peach)

interface with density contrasts of +0.13 and -0.27 respectively

– Target body (brown), approximately 2 km wide, with density contrast of +0.33

– Shallow (<150 m) regolith cover (yellow), with density contrast of -0.47

• “Real” Bouguer anomaly (sampled at 100 m spacing)

• Response measured at 4 km spacing, slight displaced anomaly resolved

• Response measured at 2 km spacing, sharper though offset anomaly resolved

• Response measured at 1 km spacing, anomaly well resolved in both wavelength and location

• Aim for minimum station spacing of approximately 1/3 the wavelength of the anomaly caused by the target body

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Actual response 4 km spacing

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2 km spacing 1 km spacing

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Daly Waters Arch

Southern McArthur Basin Gravity Survey: Falcon Oil & Gas Australia Limited 2km infill • Pre 2013 survey the Daly

Waters Arch is visible as a discontinuous north-south ridge

• 4 km data reveals continuity and thinning of ridge and an offset in the south

• 2 km data delineates two anomalies either side of the thinned ridge and improves the resolution within the southern anomaly

Pre 2013 Survey 4 km data 2 km data

Daly Waters Arch

Beetaloo Sub-basin

• Pre 2013 survey there is a smooth transition at the boundary of the Beetaloo Sub-basin

• 4 km data improves the definition of this boundary

• 2 km data reveals detailed structure within both the Beetaloo Sub-basin and the transition zone

Beetaloo Sub-basin

Southern McArthur Basin Gravity Survey: Santos Limited 2km infill

Pre 2013 Survey

4 km data 2 km data

• Industry will be offered the opportunity to infill where possible

• Companies that infill benefit through land access, contract management and quality control being managed by the NTGS and will often receive a per station cost saving due to the size of the survey while the NTGS benefits from a higher resolution dataset

• West Amadeus Gravity Survey to commence June 2014, covering approximately 45,000 square km

• Proposed Northern McArthur Basin Gravity Survey dependant on initiative funding planned for late 2014

2014 Gravity Acquisition Program

Ground gravity or Airborne Gravity Gradiometry (AGG) • Vertical gravity (gD) from AGG

systems is derived via spatial transformation

– Outputs are gridded rather than point located

– There are several methods and settings that can be used to derive vertical gravity resulting in different versions being created

• Data are low pass filtered to remove noise which broadens anomalies while long wavelengths are not recovered

• At regional-scale ground gravity is more cost effective however AGG can be acquired quickly and in areas of difficult access

• At this stage NTGS will endeavour to collect regional-scale ground gravity across the Territory unless land can not be accessed

Lane R, 2003. Enhancing exploration opportunities at

Broken Hill with airborne gravity gradiometry: Exploration NSW Geoscience Information Release

Benda Bluff: Equivalent Source gD

Benda Bluff: Fourier Transform gD

Tee Dee: Equivalent Source gD

Tee Dee: Fourier Transform gD

Tee Dee

Benda Bluff

Outline

• NTGS gravity acquisition program – 2013 Acquisition program – 2014 Acquisition program

• Industry geophysical data submissions • Accessing HyLoggerTM hyperspectral data • Developing a rock properties dataset • Three-dimensional modelling in the McArthur Basin

• Over $3,000,000 of airborne geophysical data was submitted by industry in 2013

• Standard processing of airborne magnetic, radiometric and electromagnetic surveys, and ground gravity surveys is being undertaken

• New data submissions are being processed to assist with quality control

• Historic data are being processed in alignment with current projects

Industry Geophysical Data Submissions

Airborne magnetic data

• Total Magnetic Intensity (TMI) pseudocolour image with sunshade

• Total Magnetic Intensity First Vertical Derivative (TMI 1VD) greyscale image

• Reduced to Pole Total Magnetic Intensity (TMI RTP) pseudocolor image with sunshade

• Reduced to Pole Total Magnetic Intensity First Vertical Derivative (TMI RTP 1VD) greyscale image

• Digital Elevation Model (DEM) pseudocolour image with sunshade

TMI

TMI 1VD

TMI RTP

TMI RTP 1VD

DEM

CR2008-0054

Airborne radiometric data

• Potassium (K) pseudocolour image

• Thorium (TH) pseudocolour image

• Uranium (U) pseudocolour image

• Total Count (TC) pseudocolour image

• Ternary (RAD) image, potassium is red, thorium is green, uranium is blue

CR2008-0054

TC RAD

U K TH

Other geophysical data

• Ground gravity data: – Bouguer anomaly (BA) pseudocolour with sunshade image – Bouguer Anomay First Vertical Derivative (BA 1VD) greyscale image

• Airborne EM pseudocolour images of the x-component time decay • Data is released as ERMapper grids, ERDAS Enhanced Compression

Wavelet and GeoTIFF • Metadata document outlining gridding specifications and image display

CR2009-0199

BA BA 1VD

Outline

• NTGS gravity acquisition program – 2013 Acquisition program – 2014 Acquisition program

• Industry geophysical data submissions • Accessing HyLoggerTM hyperspectral data • Developing a rock properties dataset • Three-dimensional modelling in the McArthur Basin

HyLogger Data Packages (HDP) • The HyLogger acquires high resolution

spectral data and imagery with thousands of individual spectra across 872 channels

• Over 200 holes in the Northern Territory have been scanned (black points)

• Approximately 150 of these have been processed and can be accessed by industry (blue points)

• HyLogger Data Packages (HDP) have been developed to assist in understanding the volume of data that is produced by the HyLogger program

• The HDP contains high resolution imagery, The Spectral Geologist (TSG) format datasets and an accompanying interpretative summary that gives users an insight into the major findings

• Currently 5 HDP released with another 12 in various stages of publication

HyLogger Data Packages (HDP)

• HDP interpretations include a comparison of logged stratigraphy (as published) with dominant mineralogy in the Short Wave Infrared (second row), Thermal Infrared (third row) and core colour (bottom row)

Image from HDP0004: BB2 (Bing Bong Prospect)

HyLogger Data Packages (HDP)

• Scalar plots that highlight observations of geological significance are individually tailored for each drillhole to address the specific geological setting and can illustrate mineralogical changes such as variation in carbonate wavelength (shown below), white mica composition or silica abundance

Image from HDP0005: McA5 (McArthur Basin)

Outline

• NTGS gravity acquisition program – 2013 Acquisition program – 2014 Acquisition program

• Industry geophysical data submissions • Accessing HyLoggerTM hyperspectral data • Developing a rock properties dataset • Three-dimensional modelling in the McArthur Basin

Rock Properties

• Geophysical modelling is a mathematical solution to a mathematical problem

• Without real world constraints there is an infinite number of solutions

• Modelling uncertainty will be decreased through linking geological bodies with geophysical responses through rock properties

Measured Response

Surface

Rock Properties

• Historic work in the Tanami Region and Georgina Basin

• Current work focused on the McArthur Basin

• Measuring bulk density, magnetic susceptibility and gamma

• Industry submitted data will also be compiled

Outline

• NTGS gravity acquisition program – 2013 Acquisition program – 2014 Acquisition program

• Industry geophysical data submissions • Accessing HyLoggerTM hyperspectral data • Developing a rock properties dataset • Three-dimensional modelling in the McArthur Basin

Three-dimensional modelling

• Record data in one- and two- dimensions that reflect characteristics of three-dimensional geology

• Synthesise disparate datasets in a single environment to build an interpretation that is consistent with all data

• Iterative process due to undersampled data, especially at the regional scale

• Input data and model realisations will be released allowing users to “nest” their own data within the model

Example of modelling the base of Barney Creek Formation in the McArthur Basin