Geophysics for Karstic Terrains...Geophysics for Karst Terrains 1 Department of Infrastructure,...

Geophysics for KarsticTerrains

Prepared by Anthony Knapton

Department of Infrastructure, Planning & Environmenti

Technical Report No. 12/2002

ISBN 0 7245 8246

The report both as hardcopy and in digital form (as pdf), may be obtained from the DarwinOffice of the Department of Infrastructure, Planning and Environment. Inquiries should beaddressed to:

Director Resource Assessment BranchDepartment of Infrastructure, Planning and EnvironmentPO Box 30Palmerston NT 0831Australia

Phone: (08) 89994414Fax: (08) 89993666

Department of Infrastructure, Planning & Environmentii

SUMMARYDuring May and June 2000 geophysical surveying was completed as part of a study of thesinkholes in Katherine and its’ surrounds. The works were completed to delineate sub-surfacefeatures associated with sinkhole development.

Sinkhole development (geology and physical properties). Sinkholes are found to developprimarily in the Tindal Limestone.

Karst features which may lead to sinkhole formation can have three modes of occurrence withrespect to physical properties. These are:

• voids filled with air, above the water table

• voids filled with water

• voids filled with infill material (usually soil).

Detailed pole-dipole resistivity, EM34 and self potential measurements were used to takeadvantage of the expected physical properties of the sinkhole. Two lines of ground penetratingradar were completed. One on Hickey Line 2 and another at Cutta Cutta Line 2.

Results indicate that the EM34, pole-dipole and to a limited extent the GPR (response fromabove the water table) can map the fresh limestone sub-surface topography and areas of soilinfill can be determined.

Fractures in the limestone due to faulting are evident in the pole-dipole (as abrubt changes inresistivity values) the EM34 (manifested as localised lows or negative response) and GPR(manifested as diffraction patterns).

Zones of vertical groundwater movement can be delineated by the SP method.

The combination of electrical (particularly the resistivity sections) and SP techniques can beused to determine likely locations of sinkhole development.

Department of Infrastructure, Planning & Environmentiii

Table of Contents

SUMMARY....................................................................................................................................................................................II

TABLE OF CONTENTS.......................................................................................................................................................... III

LIST OF TABLES ........................................................................................................................................................................V

1.0 INTRODUCTION..............................................................................................................................................................1

1.1 AIM ....................................................................................................................................................................................11.2 SCOPE ................................................................................................................................................................................1

2.0 SITE CHARACTERIS ATION.......................................................................................................................................2

2.1 LOCATION .........................................................................................................................................................................22.1.1 Hickey.....................................................................................................................................................................22.1.2 Cutta Cutta ............................................................................................................................................................22.1.3 Kintore....................................................................................................................................................................2

2.2 GEOMORPHOLOGY ...........................................................................................................................................................22.3 GEOLOGY...........................................................................................................................................................................22.3 SINKHOLES IN THE KATHERINE REGION.......................................................................................................................3

2.3.1 Collapse Sinkholes ...............................................................................................................................................32.3.2 Suffosion Sinkholes...............................................................................................................................................3

2.4 HYDROLOGY OF KARST LANDSCAPES...........................................................................................................................32.4.1 Karst aquifer..........................................................................................................................................................3

3.0 GEOPHYSICAL TECHNIQUES ..................................................................................................................................5

3.1 GEOPHYSICAL PROPERTIES OF ROCKS..........................................................................................................................53.1.1 Electrical Properties of Rocks............................................................................................................................53.1.2 Rock Densities.......................................................................................................................................................63.1.3 Magnetic properties of Rocks.............................................................................................................................63.1.4 Natural Gamma Emissions..................................................................................................................................6

3.2 NATURAL POTENTIAL .....................................................................................................................................................73.3 GALVANIC RESISTIVITY..................................................................................................................................................7

3.3.1 Resistivity Inversion.............................................................................................................................................73.4 GROUND CONDUCTIVITY................................................................................................................................................73.5 GROUND PENETRATING RADAR ....................................................................................................................................83.6 DOWNHOLE GAMMA LOGGING......................................................................................................................................93.7 CONCEPTUAL GEOPHYSICAL MODEL OF KARSTIC TERRAINS...................................................................................9

4.0 PREVIOUS WORKS ...................................................................................................................................................... 10

4.1 MAGNETICS AND RADIOMETRICS DATA ....................................................................................................................104.2 GRAVITY DATA..............................................................................................................................................................104.3 GROUND GEOPHYSICS AT TINDAL AIR BASE AND TURKISH BATH CAVE NEAR KATHERINE.............................10

5.0 SURVEY PARAMETERS ............................................................................................................................................ 11

5.1 NATURAL POTENTIAL ...................................................................................................................................................115.2 EM34-4 GROUND CONDUCTIVITY METER................................................................................................................11

5.2.1 Hickey EM34...................................................................................................................................................... 115.2.2 Cutta Cutta EM34 ............................................................................................................................................. 115.2.3 Kintore EM34..................................................................................................................................................... 115.2.4 Beginners Cave EM34...................................................................................................................................... 12

5.3 POLE-DIPOLE RESISTIVITY...........................................................................................................................................125.3.1 Hickey Pole-dipole............................................................................................................................................ 125.3.2 Cutta Cutta Pole-dipole.................................................................................................................................... 135.3.3 Kintore Pole-dipole........................................................................................................................................... 13

5.4 GROUND PENETRATING RADAR ..................................................................................................................................135.4.1 Hickey.................................................................................................................................................................. 135.4.2 Cutta Cutta ......................................................................................................................................................... 13

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6.0 RESULTS........................................................................................................................................................................... 14

6.1 SELF POTENTIAL ............................................................................................................................................................146.1.1 Hickey SP Results .............................................................................................................................................. 146.1.2 Cutta Cutta SP Results...................................................................................................................................... 146.1.3 Kintore SP Results............................................................................................................................................. 14

6.2 EM34................................................................................................................................................................................146.2.1 Hickey EM34 Results ........................................................................................................................................ 156.2.2 Cutta Cutta EM34 Results................................................................................................................................ 156.2.3 Kintore EM34 Results ....................................................................................................................................... 156.2.4 Beginners Cave EM34 Results ........................................................................................................................ 15

6.3 POLE-DIPOLE RESISTIVITY...........................................................................................................................................166.3.1 Depth of Investigation....................................................................................................................................... 166.3.1 Hickey Pole-dipole Results .............................................................................................................................. 166.3.2 Cutta Cutta Pole-dipole Results...................................................................................................................... 176.3.3 Kintore Reserve Pole-dipole Results.............................................................................................................. 176.3.1 Finite Difference Inversion Results ................................................................................................................ 17

6.4 GROUND PROBING RADAR ...........................................................................................................................................176.4.1 Hickey Line 2...................................................................................................................................................... 176.4.2 Cutta Cutta Line 1 ............................................................................................................................................. 17

6.4 DOWNHOLE GAMMA LOGGING....................................................................................................................................18

7.0 INTERPRETATION...................................................................................................................................................... 19

7.1 HICKEY PROPERTY ........................................................................................................................................................197.2 CUTTA CUTTA ................................................................................................................................................................197.3 KINTORE RESERVE .........................................................................................................................................................207.4 COMPARISON BETWEEN EM34 AND RESISTIVITY ....................................................................................................207.5 COMPARISON BETWEEN GPR AND ELECTRICAL METHODS....................................................................................20

8.0 CONCLUSIONS .............................................................................................................................................................. 21

9.0 REFERENCES ................................................................................................................................................................. 22

APPENDICES ............................................................................................................................................................................. 23

INITIAL INTERPRETATION RESULTS ......................................................................................................................... 23

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List of TablesTABLE 3.1 ELECTRICAL RESISTIVITY OF COMMON ROCKS. ................................................................................................5TABLE 3.2 DIELECTRIC PERMITTIVITY OF COMMON ROCK TYPES. ....................................................................................6TABLE 3.3 DENSITY RANGES OF COMMON ROCKS. ..............................................................................................................6TABLE 4.4 MAGNETIC SUSCEPTABILITY OF COMMON ROCKS. ...........................................................................................6TABLE 5.1 GPR SURVEY PARAMETERS FOR HICKEY LINE 2..............................................................................................13TABLE 5.2 GPR SURVEY PARAMETERS FOR CUTTA CUTTA LINE 2..................................................................................13TABLE 6.1 NOMINATED DEPTH OF INVESTIGATION FOR EM34 RESULTS.......................................................................15TABLE 5.2 MEDIAN DEPTH OF INVESTIGATION (ZE) FOR THE POLE-DIPOLE ARRAY. (LOKE, 1999)...........................16TABLE 7.1 DRILL HOLE LOCATIONS AT HICKEY SITE..........................................................................................................19TABLE 7.1 DRILL HOLE LOCATIONS AT HICKEY SITE..........................................................................................................19

Geophysics for Karst Terrains

Department of Infrastructure, Planning & Environment1

1.0 Introduction

1.1 AimThe geophysical works undertaken were to determine if geophysics can delineate featuresassociated with sinkhole development and therefore, be used to predict future sinkholedevelopment.

1.2 ScopeThis report discusses the geophysical works undertaken. It describes the project methodology,the survey techniques employed and survey parameters. The results and processing of thesurvey data are presented. The results are interpreted in terms of features associated withsinkhole development.



2.0 Site Characterisation

2.1 LocationThe sinkhole study was conducted in the region around Katherine in the Northern Territory.Three geologically different areas with known sinkhole development were selected for thegeophysics surveys.

• Terrain without soil cover (located at the Katherine Rural College)

• Terrain with soil cover of between 0-5 metres (located in Katherine North)

• Terrain with soil cover greater than 5 metres (located in the Cutta Cutta Nature ParkReserve)

The surveys have been named according to the properties they are situated on. These aredesignated the Kintore Area, Hickey Area and Cutta Cutta Area in Figure 2.1.

2.1.1 HickeyThe first survey site was on the Hickey property. Two 500 metre, south-west to north-east lineswere surveyed approximately 200 metres apart. Line 1 was located north of bore RN22288thought to have intersected a cavity feature. Line 2 was located adjacent to several sinkholes,which have been studied previously (Karp, 2001).

2.1.2 Cutta CuttaThe second survey site is located at a large recently formed sinkhole in the Cutta Cutta CavesReserve, south of Katherine. Two 200 metre lines were located adjacent to the sinkhole andorientated perpendicular to the regional geology. Figure 2.3 shows the location of the surveylines in relation to the sinkhole and fences. A third EM34 traverse was conducted severalkilometres north of the Cutta Cutta survey at the “Beginners” cave.

2.1.3 KintoreThe third investigation site is located adjacent to a sinkhole in the Kintore Reserve, north ofKatherine. Two 200 metre lines were situated either side of the sinkhole and orientatedperpendicular to the interpreted geological strike of the area. Figure 2.4 depicts the location ofthe lines in relation to the sinkhole.

2.2 GeomorphologyThe study areas are typified by Karst terrain, which is extensively developed in the TindalLimestone. Internal drainage through the Tindal Limestone generates karstic ridges, towers,sinkholes, pavements and cave systems. Terrain ranges from extensive rugged exposures toisolated residuals. Tindal Limestone caves are commonly horizontal with wide, low, randomlyorientated passages (controlled by lithological variation related to original bedding) or mazecaves with narrow, high passage oriented according to the local joint pattern. All are shallow,generated under vadose conditions above the water table (at 30-40 mBGL).

(Lauritzen and Karp, 1993)

2.3 GeologyThe geology of the study area is described in the Geological Map Series Explanatory Notes ofthe Katherine geological sheet SD 53-9 (Kruse et al, 1994). The areas under investigation areunderlain by the Tindal Limestone unit of the Daly River Group. This is described as flat lyingmassive, grey, mottled, oncoid, ribbon and bioclastic limestones with minor intercalations of



maroon-green siltstone or dark grey mudstone. The regional geology is seen in Figure 2.5,which shows the geophysical survey locations.

The main aquifers are associated with secondary porosity of the limestone. Good quality andquantity of water is derived from the Tindal unit.

Jointing, fractures and faults have been shown to be orientated primarily in a NW-SE direction.Secondary jointing is in a NE-SW orientation.

2.3 Sinkholes in the Katherine RegionThree types of sinkhole were observed in the study area:

• Collapse sinkholes

• Suffosion sinkholes

• Solution sinkholes

Only a few sinkholes observed could be classified into one of these categories. That is, as purecollapse, suffosion or solution type. In reality, the vast majority of sinkholes in the Katherineregion are hybrids of the above three forms. Diagrams of a collapse sinkhole formation areshown in Figure 2.6.

2.3.1 Collapse SinkholesThe type of collapse shown in Figure 2.6 can be associated with the oscillation of the watertable between wet and dry seasons. Temporary backing-up of water in conduits due to flashfloods also produces rapid changes in stress patterns in karstified limestone. Seasonal watertable fluctuations of up to 13m are known in the Katherine area. Sinkholes so-formed developfrom a combination of undermining from below (e.g. cave formation) and periodic removal ofbuoyant support.

2.3.2 Suffosion SinkholesIn cases described by Figure 2.7, the water table is below the soil-bedrock contact. Collapsesare usually caused by an increase in downward movement of surface water. Stage 1 in Figure2.7 shows surface runoff concentrated in drains and impoundments increasing the downwardpressure of water.

This results in the piping of saturated soil into openings in the limestone. Stage 2 shows thecollapse of soil arches due to loading of the surface by ponded water or vibration of the surfaceassociated with blasting or road transport.

2.4 Hydrology of karst landscapesThe most important factor affecting karst landscapes is the general hydrologic setting. One ofthe characteristic features, also observed in the study area, is the absence of perennial surfacestreams. Drainage networks in karst are developed principally in the subsurface region. Theyconsist of interconnected systems of caves, enlarged vertical fractures and smaller cavitiesdeveloped along bedding planes. The Katherine River originates outside (east) of the karstlandscape but flows across the Tindall Limestone as a perennial stream. This river serves asthe major discharge point for groundwater emanating from the Tindall Limestone.

2.4.1 Karst aquiferA conceptual model of a karst aquifer in Figure 7.3 (Doeflinger and Zwahlen, 1995) can be usedto characterise the Tindall Limestone aquifer. Karst aquifers are described as anisotropic. Thisimplies that they include a network of conduits with high hydraulic conductivity (K > 10-1 m/s)surrounded by a large volume of low permeability fractured and fissured rock (K between 10-3



and 10-7 m/s). Additionally, the karst network can drain water out of surrounding rock oralternatively, recharge it according to the hydrodynamic state of the aquifer. This model shownin Figure 2.8 is based on specific geomorphologic and hydraulic karst phenomena. Theseinclude:

• A general absence of surface drainage.

• Sinkholes

• The existence of networks of karst solution conduits.

• Water levels that may change rapidly and substantially in response to heavy rains.Fluctuations in the water levels are of two categories - seasonal and pulse. Seasonallythe water level drops during the dry season reaching a minimum inNovember/December. It starts rising in January to reach a maximum in March.

Sinkholes play an important role in karst hydrology. They act as collecting basins for surfacerunoff and transfer surface water collected in the depressions drains, vertically through the soilinto bedrock fractures. The groundwater recharge in the Tindall Limestone occurs primarilythrough sinkholes and solution enlarged joint sets.



3.0 Geophysical TechniquesGeophysics is the study of the Earth by quantitative physical methods. It employs themeasurement of specific physical parameters, such as, variations in the Earth’s gravitational ormagnetic fields, to derive an understanding of the distribution of the causative source material inthe sub-surface. The afore mentioned variations, for example, are due to changes in thedensity and magnetic susceptability of different rocks. Density and magnetic susceptabilitychanges can be attributed to particular rock types, and an interpretation of the source materialcan be inferred.

There are a number of important advantages over other sampling methods commonly used ingeotechnical studies:

• geophysical methods are intrinsically non-invasive and non-destructive.

• surface measurements provide efficient means of rapid spatial mapping with good sub-surface resolution.

• either bulk properties or layer boundaries (such as depth of water table) may be directlyinferred from surface measurements.

• geophysical data can be acquired at a fraction of the cost of drilling.

3.1 Geophysical Properties of RocksThe physical properties of the rocks expected in the survey area must be characterised so thata meaningful interpretation of the data can be determined.

3.1.1 Electrical Properties of RocksResistivity/Conductivity

The bulk conductivity (inverse of resistivity) measured by electrical and electromagneticmethods in relation to the resistivity of the ground is controlled by several factors as defined byArchie, 1947. These factors include: porosity, lithology, permeability, clay content (cationexchange capacity) and pore fluid conductivity.

Rock Type Range(ςm)

Soil 50-300

Clay 1-100

Loose Sand 500-5000

Limestone 500-10,000

Granite 200-100,000

Basalt 50-200,000

Table 3.1 Electrical resistivity of common rocks.

Dielectric permittivity

The dielectric permittivity is the measure of the electrical polarisation resulting from an appliedelectrical field. The primary form of polarisation is due to ionic displacement. Groundprobing/penetrating radar uses reflections of electromagnetic waves at the contact of materialswith contrasting dielectric permittivity as the basis for it’s operation.

Rock Type DielectricPermittivity



Water 80

Soil 3.9-29.4

Clay 7-43

Sand (Dry) 3-5

Sand(Saturated)

20-30

Limestone 4-8

Granite 4-6

Basalt 12

Table 3.2 Dielectric permittivity of common rock types.

3.1.2 Rock DensitiesThe density of rock is described as the mass per unit volume of a material and is oftenexpressed as g/cm3 or kg/m3.

Average density ranges for common rocks are given in Table 4.2.

Rock Type Range(g/cm3)

Average(g/cm3)

Soil 1.2-2.4 1.92

Clay 1.63-2.6 2.21

Sand 1.7-2.3 2.35

Limestone 1.93-2.9 2.55

Granite 2.5-2.81 2.64

Basalt 2.7-3.3 2.99

Table 3.3 Density ranges of common rocks.

3.1.3 Magnetic properties of RocksMagnetics susceptability is the measure of the degree to which a substance may bemagnetised.

Table 4.4 Magnetic susceptability of common rocks.

3.1.4 Natural Gamma EmissionsNatural radioactivity results from the presence of small amounts of uranium, thorium andpotassium 40. It is usually lowest in basic igneous rocks (ie basalt) and highest in sedimentaryunits, especially clays and shale, although clean mature sands and clay free limestone canproduce very low counts (The Tindal limestone being an example). The γ-ray log, therefore,reflects mainly the clay content because radioactive elements tend to concentrate in clays andshale.



3.2 Natural PotentialThe natural potential or self potential method measures d.c. voltage distributions in the groundthat arise from natural and artificial sources. Natural sources include electrochemical reactions,which occur as a result of interaction between conductive mineral deposits and ground water.Thermoelectric effects arise from differential heating of the ground by sources such as magma.The most common source is from the electrokinetic effect from the interaction of fluids in theground and its constituent matrix. The streaming effect is the most important component ofelectrokinetics, in which an electric field is generated by the movement of water through porousor fissured material.

Field equipment involved with SP data collection include a pair of non-polarizing electrodes,calibrated wire and reel and a high impedance multimeter. The electrodes are generally of thecopper/copper sulphate type. In the long wire mode, a base electrode is buried in a region ofminimal SP activity and used as a reference station. The survey line is then run with a rovingelectrode inserted into the ground at regular intervals, and the difference in potential betweenthe two electrodes is measured in millivolts. Reference to SP surveying.

3.3 Galvanic ResistivityGalvanic resistivity methods are used to determine the distribution of electrical properties,primarily the resistivity (inversely the conductivity) in the sub-surface. The basic resistivitymeasurement involves the injection of current into the ground using a dipole consisting of twogrounded electrodes. During current injection a second dipole is used to measure the resultantpotential at the surface. The electrode geometry, current and resultant potential measurementscan be used to define the apparent resistivity of the ground. It is termed the apparent resistivitysince it is the value of resistivity that a homogeneous and isotropic earth would be if under thesame conditions.

The depth of investigation depends on the geometry of the array, but in general the penetrationdepth increases with increasing electrode separation.

3.3.1 Resistivity InversionInversion methods essentially try to find a model for the sub-surface whose response agreeswith the measured data. The program uses an iterative method whereby starting from an initialmodel, the program tries to find an improved model whose calculated apparent resistivity valuesare closer to the measured values. The RES2DINV is designed to operate in an automatic androbust manner with minimal input from the user.

3.4 Ground ConductivityThe conductivity meter is used to define the bulk conductivity of the soil to within a few metresof the surface. A time varying EM current is generated in the transmitter coil, which in turninduce eddy currents in the ground. The instrument measures the ratio of the secondarymagnetic field induced by the eddy currents to the primary magnetic field, a ratio linearlyproportional to electrical conductivity except in areas of high conductivity (> 300 mS/m). TheEM31 has a coil spacing of 3.7 metres, the measured value nominally represents the integratedconductivity of the uppermost 6 metres, with roughly 50% of the response derived from theupper most 2.5 metres. The EM34 data can be collected at 10, 20 and 40 metre coilseparations in horizontal and vertical dipole modes. In the horizontal mode conductivitiesrepresent the integrated conductivity of to a nominal depth of 75% of the inter-coil spacing. TheEM34 uses variations in acquisition parameters to allow variation in the depth of exploration andthe data collected can be interpreted as a crude sounding. The relative contribution to theresponse from a particular depth is seen below.



0.0 0.5 1.0 1.5 2.0

Z (depth divided by intercoil spacing)

0.0

0.4

0.8

1.2

1.6

2.0

Re

lativ

e R

espo

nse

Horizontal Dipole

Vertical Dipole

It can be seen that the horizontal dipole (coils perpendicular to the ground) response is stronglydependent on the near surface conductivities, whilst the vertical dipole’s (coils laid on theground) response is due to features in the sub-surface with very little contribution from the nearsub-surface. From this it can be seen that the vertical dipole response will be the mostindicative of conductive zones such as saturated soil infill or saline ground water.

Results are interpreted as variations in conductivity along the line. These variations can beassociated with lithological variation or ground water quality. Some estimate of conductivityversus depth can be determined by using a combination of Tx-Rx separations.

In the case of vertical conductors encountered by the system, coupling effects generally causethe vertical dipole response to go negative (or very low) at the edges of the feature, if the widthof the feature is greater than the Tx-Rx separation. A single low/negative feature may result ifthe vertical conductor has a width less than the Tx-Rx separation and a depth less than half theTx-Rx separation.

3.5 Ground Penetrating RadarGround penetrating radar (GPR) is a high resolution electromagnetic technique for the rapidmapping of lateral variations of bedding and lithology (upto 20 m deep). Although the groundrapidly attenuates high frequency EM signals, adequate penetration can often be obtained inthe megahertz frequency range to successfully address shallow geological and geotechnicalproblems. Commercially available GPR systems generally use broadband impulse techniqueswith separate transmitter and receiver bowtie antennas. The transmitter pulse is typicallyseveral hundred volts but only a few nanoseconds long.

The GPR technique can be considered to be the electromagnetic equivalent of a seismicreflection pulse. A pulse of EM energy generated at the surface can be transmitted through theunderlying materials in a manner comparable to the release of elastic energy from a seismicsource. Layer depths and bulk rock properties are revealed by the propagation characteristics.When an EM wave is incident on the interface between two separate layers a proportion of theincident energy is transmitted through the boundary and the remainder is reflected. In thisrespect the behaviour of EM energy is directly comparable with optical systems and stronglyresembles the behaviour of seismic waves

Changes in the electromagnetic properties (dielectric permittivity see section 3.1.1) for differentgeological layers can provide sufficient impedance contrast to generate detectable reflections.



The received waveforms are typically 200 - 1000 nanoseconds long and are recorded usingequivalent time sampling techniques. Thus an image of sub-surface structure can be rapidlyrecorded without the need for expensive drilling or excavation. Since the radar antennas do notneed to be inserted into the ground, survey speed can be rapid compared to other electrical andseismic geophysical techniques.

Modern GPR systems are designed for maximum mobility. Control systems are extremely light-weight and utilise digital sampling and waveform stacking. Fibre optic cables are used for datatransmission with all control and data storage on a laptop computer. The control equipment canbe backpacked by an operator or mounted on a trolley (subject to ground condition). Theantennas are advanced by a field hand at the completion of each stack or can be traversed atconstant velocity. Depending on the depth of penetration and the resolution required, differentnominal frequencies are used ranging from 200 MHz (shallow), through 100MHz, and down to25MHz ( 20m + penetration).

It must be noted that to obtain interpretable data the location of the survey line(s) should be asfar as possible from trees and cultural features such as power lines.

3.6 Downhole Gamma LoggingThis was to differentiate lithological character and provide objective correlation of borestratigraphy throughout the study area. The gamma logs are of particular interest when RABdrilling in cavernous limestone terrain where poor or no sample return due to loss of circulationis common. The information provides lithological determination and can be used to show thedepth of the limestone. The clean or clay free limestone is characterised by low gamma countsper second (the measure of natural radiation)

3.7 Conceptual Geophysical Model of Karstic TerrainsFrom the hydrogeological mode of occurrence and the geophysical properties of rocks aconceptual model of the karstic terrain can be determined. Essentially the area can besummarised by three modes of occurrence with respect to physical properties:

• voids in limestone filled with air, above the water table

• voids in limestone filled with water

• voids in limestone filled with infill material (usually soil either saturated or unsaturated).

The geophysical models are seen in Figure 3.1, 3.2 and 3.3.

During and for a time after the wet season moisture will move downwards through permeablestrata associated with sinkholes, in the form of fractures in the limestone or through infill soilmaterial. Negative Self Potential anomalies for both modes are expected, with the greaterresponse coming from the water moving vertically down through the soils.



4.0 Previous WorksPrevious geophysics work conducted in the Katherine area has been confined to regionalairborne magnetics, radiometrics and gravity surveys.

4.1 Magnetics and Radiometrics DataIn 1975, as part of the nation wide survey, magnetics and radiometrics were flown over theentire Katherine Sheet at 1.5km line spacing and 150 metre ground clearance. Major featuresare identifiable from these datasets, although resolution is poor due to the relatively low sampledensity. Both data-sets provide information about regional geological structures. Theseregional features are dominated by the faults bounding the Daly Basin.

4.2 Gravity DataGravity data were acquired on a nominal 11km sampling grid. Again resolution is poor due tothe low sampling density. Gravity data can be seen in Figure 4.2.

4.3 Ground geophysics at Tindal Air Base and Turkish Bath Cave nearKatherineIn 1988 geophysical investigations for sub-surface cavities at RAAF Base Tindal wereconducted the results of this work and presented by Creswell, 1988. Techniques used includedmicrogravity and resistivity profiling. Generally it was found that the techniques were too slowand costly for the amount of information gathered.

Calvert, 1995 describes examples of GPR response in surveys conducted near Katherine. Partof this work was completed over known cave features (Turkish Bath Cave) to characterise theresponse expected. Generally the results of this work were successful in delineating cavefeatures. The collected data quality is excellent showing little interference from trees andcultural features with depth of penetration approaching 15 metres in some cases ..



5.0 Survey ParametersGround based geophysical works were completed at the three sites (a single line of EM34 wasalso conducted at a fourth site). The main objective of the survey was to delineate geologicalstructure and to infer cave features. A total of 6 lines were traversed using self-potential, EM34-4 (7 lines) and pole-dipole resistivity. Two lines were located at Hickey 2km north-west ofKatherine, two at Cutta-Cutta 25km south-east of Katherine and two lines at Kintore Reserve20km north-west of Katherine. A single line of EM34 was also completed centred on the“Beginners” cave system to the south of Katherine.

Geological and hydrogeological conditions indicate that sinkholes develop in the vadose zone,which is confined to the upper 30-40 metres of the sub-surface. Resistivity and EM data werecollected to provide information to at least this depth. The EM34 provides information toapproximately 40 metres depth and the resistivity to approximately 20 metres depth.

5.1 Natural PotentialSP voltages were collected using a fixed remote reference electrode (located approximately1km from each survey area) with a roving potential electrode at 5 metre spacings (along line)using a digital multimeter accurate to 0.1 mV. A line of 500 metres was completed in 30 to 45minutes with repeat readings taken at the first four stations of each line. This was to give anindication of drift due to telluric currents and a estimate of noise.

5.2 EM34-4 Ground Conductivity MeterEach line was completed with 10, 20 and 40 metre Tx-Rx separations with along line stationspacings of 5 metres, horizontal and vertical modes were used at each station. Themeasurements were recorded onto a palm-top computer and down loaded for processing at theend of each survey day. A 500 metre line (100 stations per line) took approximately 6 hours tocomplete the full suite of readings.

5.2.1 Hickey EM34Two 500 metre lines were completed on the Hickey property. The lines were located close tosome known karstic features and drill holes and oriented perpendicular to the regionalgeological strike.

5.2.2 Cutta Cutta EM34Two 200 metre survey lines were completed parallel to the boundary fence between the CuttaCutta Cave reserve and NT Portion 3625. The lines were located as close to the sinkhole aspossible whilst trying to minimise the effects from fences (the fences were essentially groundedinfinite extent conductors, previous experience has shown that these features can dominate theEM response if closer than approximately 20 metres). Line 1 crosses two fence lines at 10 and65 metres. Line 2 crosses a fence at 150 metres.

5.2.3 Kintore EM34Two 200 metre lines were located at either side of the selected sinkhole feature andperpendicular to the fence line to the north of the survey area. The lines were centred on whatwas thought to be a fault. The EM34 gave spurious values during measurements of 40 metreTx-Rx spacing on line 1 and no further EM34 measurements were collected. This resulted in no40 metre data being collected for line 2.



5.2.4 Beginners Cave EM34A 100 metre line was completed, centred on the “Beginners” Cave system. The line was runalong the edge of the Stuart Highway. The 40 metre horizontal and vertical dipole was used at5 metre station spacing.

5.3 Pole-Dipole ResistivityThe pole-dipole method is a galvanic resistivity technique where one of the current electrodes isfixed a great distance from the other three electrodes. The spacing between the potentialelectrodes was 5 metres (the “a” spacing was 5 metres with n=0.5 to 9.5) with 10 metre currentelectrode/array move-on. The array geometry and apparent resistivity calculation for the pole-dipole method are given below:

ρa = 2π . n(n+1)a . (∆V/I)

where

ρa is the apparent resistivity

n is the offset multiplier of the potential dipole from the current electrode (n=0.5 to 9.5)

a is the potential electrode spacing in metres (a=5 m)

∆V is the measured voltage between the potential electrodes (volts)

I is the injection current (amps)

The array was chosen because it has good horizontal coverage with minimal crew and surveyequipment. The pole-dipole method does have however a drawback, in that the array isasymmetrical and over symmetrical structures the apparent resistivity anomalies in pseudo-section are asymmetrical making for more complex interpretation.

Measured parameters (voltage and current) were entered into a small palm-top computer,which calculated apparent resistivity values from the array geometry at each station and pole-dipole spacing. This provided a first pass check of data quality. Data was down loaded to alap-top computer at the end of each day and apparent resistivity pseudo-sections produced. A500 metre section (475 readings) took approximately 10 hours to complete with two personnel.

5.3.1 Hickey Pole-dipoleTwo 500 metre length pole-dipole lines were completed at the Hickey site. Each line wascompleted from SW to NE with the above mentioned survey parameters.

I∞ V

ana

Potential DipoleCurrent Electrode

Pole-Dipole Electrode Configuration



5.3.2 Cutta Cutta Pole-dipoleTwo 200 metre length pole-dipole traverses were completed at the Cutta Cutta site. Chainagesof the traverse increase from SW to NE, however, the resistivity data was collected from NE toSW such that the first current electrode was located at 197.5 metres and the potential electrodepair located at 195 and 190 metres.

5.3.3 Kintore Pole-dipoleTwo 200 metre length pole-dipole traverses were completed at the Kintore site. Chainages ofthe traverse increase from SW to NE, however, the resistivity data was collected from NE to SWsuch that the first current electrode was located at 197.5 metres and the potential electrodesstarted at 195 and 190 metres.

5.4 Ground Penetrating RadarGPR surveys were completed at Hickey lines 2 and Cutta Cutta lines 2.

5.4.1 HickeyLine 2 The data were collected at 25 MHz and 50 MHz. The survey parameters for the tworuns are given in Table 5.1

Table 5.1 GPR survey parameters for Hickey Line 2

Base Frequency 25 MHz 50 MHz

Station Spacing 0.458 metres 0.4 metres

Sample Interval 1.6 ns 1.6 ns

Antenna Spacing 2 metres 2 metres

Record Length 500 ns 400 ns

Time Zero 34 ns 20 ns

5.4.2 Cutta CuttaLine 2 The data were collected at 25 MHz and 50 MHz. The survey parameters for the tworuns are given in Table 5.2

Table 5.2 GPR survey parameters for Cutta Cutta Line 2

Base Frequency 25 MHz 50 MHz

Station Spacing 0.458 metres 0.4 metres

Sample Interval 1.6 ns 1.6 ns

Antenna Spacing 2 metres 2 metres

Record Length 500 ns 400 ns

Time Zero 34 ns 20 ns



6.0 Results

6.1 Self PotentialThe self potential data is presented as profiles. Generally the data showed little drift during thetime that line data were taken (ie due to telluric currents etc). Individual readings showed ±2mVvariation (at the time of acquisition), which is several times smaller than the magnitude of theanomalies encountered. Generally data was consistent between adjacent readings andrepeatable, suggesting that the data is reliable.

6.1.1 Hickey SP ResultsResults of the self-potential data are seen in Figure 6.1a and Figure 6.2a. The data has beenplotted with EM34 profiles for comparison.

Line 1 showed a range from of 15 mV, with noise values of less than 2 mV. The data shows aregional trend with higher values from 0 to 210 metres and relatively low values from 210 to 500metres. The section with lower values also has local relative lows at 260, 290, 360 and 420metres.

Line 2 shows a relatively constant voltage, with a low between 385 to 460 metres with adominant low of 5mV magnitude at 450 metres. There are localised lows at 0 and 100 metres.

6.1.2 Cutta Cutta SP ResultsResults of the self-potential data are seen in Figure 6.3a and Figure 6.4a. The data has beenplotted as profiles with EM34 profiles for comparison.

Line 1 has a range of 22 mV with noise of approximately ±2 mV. The data shows a relativelylow extending from 80 to 180 metres.

Line 2 shows a relatively constant voltage, with lows centred on 105 and 175 metres.

6.1.3 Kintore SP ResultsSelf potential data for Lines 1 and 2 are seen in Figure 6.5a and Figure 6.6a respectively.

Line 1 the data has a range of 25 mV along the line with lows at 25, 80, 95 and 110 metres.

Line 2 the data has a range of 35 mV with an estimated noise level of ±2 mV. 85 and 110metres, corresponding with a “regional” level change in the response from approximately 10 mVto –5 mV.

6.2 EM34The EM34 data were collected at 10, 20 and 40 metres coil separation. The data wererelatively noise free generally 1–2 mS/m. Data are plotted as profiles with the measurementtaken to be at the centre of the array.

EM34 data has also been grided and contoured to provide a pseudo-depth section forcomparison with resistivity results. The different Tx-Rx measurements were assigned nominaldepths, 75% of Tx-Rx separation, was used for the nominal depth of the vertical dipoleresponse (the vertical dipole mode is expected to yield the most information from deeper strata,due to the reasoning discussed in Section 3.2). The 10 metre horizontal dipole responseprovided an estimate of the surface conductivity. Negative values were also removed from thedata.



Tx-RxSeparation(metres)

Depth(metres)

10 (H) 0

10 7.5

20 15

40 30

Table 6.1 Nominated depth of investigation for EM34 results.

6.2.1 Hickey EM34 ResultsThe data are presented as profiles for each of the transmitter-receiver spacings (Figure 6.1 andFigure 6.2) and as pseudo-sections (Figure 6.8 and Figure 6.9).

Line 1 Conductivities are lower (less than 10 mS/m) from 0 to 150 metres with an increase inconductivity from 150 to 500 metres. The 10 metre separation in the vertical dipole modeshows two negative responses of –27 mS/m and –3 mS/m at 95 and 140 metres respectively.The 40 metre dipole separation shows an overall low response in the vertical mode withnegatives at 395 and 475 metres.

Line 2 The 20 metre dipole separation shows a similar regional response to the 10 metreresponse, however, negatives of and occur at 165 and 450 metres respectively.

6.2.2 Cutta Cutta EM34 ResultsLine 1 The EM response (Figure 6.3 & Figure 6.10) is relatively subdued and constant alongthe line for all three separations at around 30 mS/m. The vertical and horizontal responses arealso similar with consistent conductivity for both modes. The vertical dipole response shows anegative feature (present for all three separations) around 10 metres, this corresponds with afence at this location. The 10 metre vertical dipole response shows a second negative feature(not evident at greater dipole separations) centred on 70 metres and corresponds to anotherfence.

Line 2 The EM response (Figure 6.4 & Figure 6.11) of all three dipole separations shows slightincreases in the conductivity to the north-east. “Noisy” data is evident at around 150 metres onthe 10 and 20 metre dipole separation, this is coincident with a fence line running perpendicularto the survey line.

6.2.3 Kintore EM34 ResultsLine 1 The EM response (Figure 6.5) shows an overall increase in conductivity to thenortheast. The response between 0 to 90 metres is around 20 mS/m in both modes for the 10and 20 metre dipole separations. The response becomes more erratic from 90 to 200 metresand the vertical and horizontal dipole modes are seen to diverge.

Line 2 The EM response (Figure 6.6) is relatively subdued. The vertical and horizontal dipolemodes show similar conductivities along the line for both the 10 and 20 metre separations. Theresponse increases with increasing chainage from approximately 15 mS/m to 40 mS/m. The 10and 20 metre vertical dipole response shows relative lows centred on 90 and 135 metres.

6.2.4 Beginners Cave EM34 ResultsThe EM34 results are seen in Figure 6.7. The response varies between 3 to 12 mS/m with anoise level of approximately ±1-2 mS/m. Even though there is a relatively high noise level,



there is a definite trend evident. The results have been smoothed using a 3 point averagingfilter (bold lines) to remove some of this noise. The horizontal dipole mode shows a peak (11mS/m compared with a background of 7 mS/m) centred on 50 to 60 metres. The vertical modeshows a low (3 mS/m compared with a background of 6 mS/m) centred on 55 to 60 metres.

6.3 Pole-Dipole ResistivityThe 6 lines of resistivity data are presented as pseudo-sections. Pseudo-depths have bedetermined using Lokes’ depth approximations (Section 6.3.1) and resistivity values have beenplotted beneath the centre of each potential dipole location. Consistent colour ranges for theresistivity contours (plotted as log apparent resistivity) have been used to provide a comparisonbetween the sections. Figure provides visual conversion between resistivity (ohm.m),conductivity (millimho/m) and log resistivity.

6.3.1 Depth of InvestigationLoke provides depth of investigation (ze) estimates for various arrays based on the “a” valueand “n” spacing. Table 5.2 cites values of investigation depth for the pole-dipole array. The “a”value for the Katherine caves work was 5 metres and the maximum n value was 9.5. Thisprovides an approximate depth of investigation of 20 metres.

n ze/a

0.5 0.34

1.5 0.73

2.5 1.12

3.5 1.51

4.5 1.90

5.5 2.29

6.5 2.68

7.5 3.07

8.5 3.46

9.5 3.85

Table 5.2 Median depth of investigation (ze) for the pole-dipole array. (Loke, 1999)

Figure 6.12 Conversion between apparent conductivity, apparent resistivity and logapparent resistivity.

6.3.1 Hickey Pole-dipole ResultsLine 1 is plotted in Figure 6.13 The section shows an overall trend of decreasing resistivity withincreasing chainage. High resistivities >100 ςm (low conductivity <10 mS/m) extend fromchainages 0 to 260 metres, lower resitivities <100 ςm (conductivity >10 mS/m) predominatefrom 260 metres to 500 metres.



Line 2 is plotted in Figure 6.14. The section shows an overall trend of decreasing apparentresistivity with increasing chainage. High resistivities >100 ςm (low conductivity <10 mS/m)extend from chainages 0 to 160 metres and lower resitivities <100 ςm (conductivity >10 mS/m)from 160 to 500 metres.

6.3.2 Cutta Cutta Pole-dipole ResultsLine 1 (Figure 6.15) shows a layered section with high resistivities (>100 ςm) at the top of thesection (from 0 to 4 metres) and lower resistivities (from 10 to 100 ςm) from 4 to 20 metres.

Line 2 (Figure 6.16) shows resistivities approaching 100 ςm between 0 to 20 metres.Resistivities of less than 100 ςm dominate from 20 to 200 metres, with resistivities increasingwith depth.

6.3.3 Kintore Reserve Pole-dipole ResultsLine 1 (Figure 6.17) shows a variable resistivity section with resistivities generally less than100 ςm. Higher resistivities occur at the beginning of the line and decrease with increasingchainage.

Line 2 (Figure 6.18) shows high resistivities (˜100 ςm) from 0 to 80 metres. Lower resistivities<100 ςm predominate from 80 to 200 metres.

6.3.1 Finite Difference Inversion ResultsThe inversion program divides the sub-surface into a number of blocks, it then uses a leastsquares inversion scheme to determine the appropriate resistivity value for each block such thatthe calculated resistivity values agree with the measured values from the field survey.

Inversion results are presented in Figures 6.13 and 6.14 for the Hickey data, Figure 6.15 and6.16 for the Cutta Cutta data and Figures 6.17 and 6.18 for the Kintore data. The inversionresults are presented with constant resistivity ranges for comparison. It can be seen thatgenerally the inversion data has the same appearance as the pseudo-sections, it should benoted that an offset is apparent for inversion features at depth in relation to their apparentlocation in the pseudo-section. This can be attributed to the asymmetry of the pole-dipolemethod.

6.4 Ground Probing RadarThe radar data for Hickey Line 2 and Cutta Cutta Line 1 are presented as TWT sections in areport by On-Line Geophysics (Beresford, 2001). The data has been processed to highlightgeological features and to remove “noise” such as reflections from trees.

6.4.1 Hickey Line 2Figure 6.19 is of the Hickey Line 2 data set. Strong diffractions are seen from 0 to 140 metresand 470 to 500 metres. There is also diffractions at 260 metres. The report states that most ofthe horizontal features are due to processing (removal of source pulse) and do not correlatewith geological features.

Note: There is a feature centred on 260 metres, which, is due to a mound of dirt on the surfacequite close to the survey line.

6.4.2 Cutta Cutta Line 1Figure 6.20 is of the Cutta Cutta Line 1 data set. A single strong reflection is seen at a TWT of130 ns (approximately 6.5 metres) at 180 metres and 180 ns (approximately 9 metres) at 600metres. Diffraction features at later times are due to trees.



6.4 Downhole Gamma LoggingGamma logging was completed in 6 of the 12 holes drilled at the Hickey investigation site and 2of the 4 holes drilled at the Cutta Cutta site. The gamma data shows the location of soil/clay inthe strata and provides an indication of limestone purity. Gamma logs can be seen in Figure7.1 and 7.2 showing the relationship with resistivity inversion results.



7.0 Interpretation

7.1 Hickey PropertyResistivity data were inverted using Loke’s Res2DInv program, which uses finite differenceleast squares inversion to determine the distribution of resistivities in the sub-surface. Theinversion results were then compared to drilling and gamma logging results (locations are inFigure 7.1 and Table 7.1), as seen in Figure 7.2 and 7.3.

Gamma results tend to indicate that fresh limestone occurs shallower than drilling results wouldsuggest. This is reflected in the resistivity inversion data where a resistivity of approximately120 to 160 ohm.m is interpreted to represent the contact between soil cover or weatheredlimestone and hard, fracture free limestone.

The gamma response reflects the low clay content associated with the weathering of limestone.low resistivity because of the high porosity in this region. The regions of high resistivity >120ohm.m correlate with fresh limestone with low porosity/fracturing as determined from drilling.

Table 7.1 Drill hole locations at Hickey site.

RN Line Chainage Easting Northing GammaLog

31969 1 65 201545 839890731968 1 255 201683 839904131967 1 440 201810 8399173 Yes31966 1 476 201827 8399202 Yes32748 2 22 201301 839904732749 2 90 201354 839908032870 2 165 201420 839914132557 2 260 201470 8399215 Yes32746 2 330 201520 8399260 Yes32558 2 424 201590 8399326 Yes32559 2 480 201631 839936932740 2 485 201631 8399365 Yes32741 2 985 201341 8398865

7.2 Cutta CuttaThe results from the Cutta Cutta survey are inconclusive in terms of locating features which canbe associated with the sinkhole formation.

Line 2 inversion results are presented in Figure 7.4 and are compared to gamma logs at thebeginning and end of the line. The gamma response indicates clean limestone wasencountered at 10 and 17 metres. This correspond to a resistivity of 80 ohm.m in the resistivitysections. This interpretation is consistent with those encountered at the Hickey site.

Table 7.1 Drill hole locations at Hickey site.

RN Line Chainage Easting Northing GammaLog

31969 2 65 201545 8398907 Yes32741 2 985 201341 8398865 Yes



7.3 Kintore ReserveThe results from the Kintore survey indicate that the sinkhole is located over a fault feature. SP,resistivity and EM34 data show a distinct change in voltage response andresistivity/conductivity. The self potential lows, centred on this change, are associated with thedownward movement of water through the sub-surface along preferential pathways.

7.4 Comparison between EM34 and ResistivityThe EM34 and pole-dipole resistivity sections show strong correlation. The EM results,however, show interpreted fracturing in the limestone, which is not as evident in the resistivitydata. The fractures are seen as negative or low responses in the profiles. These areas offracturing dominate the regions identified as shallow limestone along both lines at Hickey.

7.5 Comparison between GPR and Electrical MethodsHickey Line 2 provides the best section for comparison between the GPR data and theresistivity data. The fresh limestone interface has been interpreted from the resistivity data andconverted to TWT data for comparison with the GPR data. Where the limestone is interpretedto be above the water table (6.5 mBGL) a velocity of 0.106 m/ns has been used. Where theinterface is interpreted to extend below the water table a velocity of 0.061 m/ns is used. Nodiffractions are evident below the water table, which has a TWT of approximately 113 nsassuming a velocity of 0.106 m/ns.

The calculated TWT to the Limestone from the resistivity is in strong agreement with the GPRdata. It should also be noted that below the water table little response is seen in the GPR data.This would seem likely since the water would attenuate the signal making the contact at depth(>7 metres) undetectable.



8.0 ConclusionsEM and resistivity provide similar information, however, the resistivity data provides bettercontrol on depth determination. Due to the survey configuration EM data was seen to have agreater depth of investigation as compared with the resistivity data.

Modelling software is more readily available for resistivity data.

Determine depth to fresh limestone.

SP correlates with features observed in EM and resistivity data and suggest water movementalong structural features.

GPR data shows the



9.0 References

Beresford, G., 2001, Katherine Sinkhole Study; Processing and Analysis of Ground PenetratingRadar Data, In-house report.

Kruse, P.D., Sweet, I.P., Stuart-Smith, P.G., Wygralak, A.S., Pieters, P.E. and Crick, I.H., 1994,1:250,000 Geological Map Series Explanatory Notes: Katherine SD53-9, Government Printer ofthe Northern Territory, Darwin.

Loke, Dr M.H., 1999, Electricl Imaging surveys for environmental and engineering studies; Apractical guide to 2-D and 3-D surveys,

Lange, A.L., McEuen, R.B. and Gustafson, E.P., 1986, The Application of Active and PassiveElectrical Methods to Ground Water Monitoring in Surface and Borehole Geophysical Methodsand Ground Water Instrumentation, National Water Well Association, Dublin, Ohio.

AppendicesInitial Interpretation Results



Line 1

Chainage Feature Comments70 Hick1 Fracture zone (may need to drill either side of feature)260 Hick2 SP Low, suggests water movement265 Hick3 Fault feature, suggested by resistivity section395 Hick4 Low resistivity feature, deep soil infill440 Hick5 Fault feature, suggested by resistivity section455 Hick6 Fracture zone (may need to drill either side of feature)475 Hick7 Fracture zone (may need to drill either side of feature)Line 2

Chainage Feature Comments0 Hick8 EM negative and SP low, suggests water filled fracture100 Hick9 Fracture zone (may need to drill either side of feature)165 Hick10 fault feature, suggested by resistivity section175 Hick11 EM negative suggests vertical fracture250 Hick12 Thick soil infill, increased depth to limestone315 Hick13 relatively shallow limestone, under soil cover415 Hick14 deep fracture zone @ 40m430 Hick15 SP Low, suggests water movement450 Hick16 EM –ve and resistivity low suggests deep, water filled

fracture485 Hick17 void @ 25m, adjacent to small sinkhole on line 2Line 1

Chainage Feature Comments15 Cutta1 Resistive feature (pole-dipole) @ 40-50m, suspect void35 Cutta2 Low resistivity feature, thick sediments over limestone –

determine thickness100 Cutta3 SP low and resistive feature @ 50m, cavity with water flow?120 Cutta4 Low resistivity feature, thick sediments over limestone –

determine thickness140 Cutta5 resistivity low @ 35m150 Cutta6 SP lowLine 2

Chainage Feature Comments10 Cutta7 conflicting cond high and resist high40 Cutta8 conductivity low80 Cutta9 fault feature90 Cutta10 increased depth to limestone?100 Cutta11 shallow limestone120 Cutta12 shallow limestone/fracture zone180 Cutta13 conductive highLine 1

Chainage Feature Comments50 Kin1 fracture – soil filled/saturated80 Kin2 shallow fracture edge of fault zone95-100 Kin3 fracture/fault120 Kin4 fracture – soil filled/saturated180 Kin5 deep fractureLine 2

Chainage Feature Comments



20-25 Kin6 fracture zone50 Kin7 void @ 40m water filled or soil filled65 Kin8 void @ 20m water filled or soil filled85 Kin9 fracture zone115 Kin10 void @ 20m water filled or soil filled140 Kin11 edge of fault155 Kin12 limestone at depth, deep soil cover/sandstone infill175 Kin13 conductive feature, EM34

Geophysics for Karstic Terrains

Department of Infrastructure, Planning & Environment26Figure 2.1 Location of Study Area

Extent of Tindal Limestone


Department of Infrastructure, Planning & Environment27Figure 2.2 Location of geophysical lines – Hickey Site

8400100mN

lOT?

8398600 mN

201500 mE 202000mE 202500mE 203000mE


Department of Infrastructure, Planning & Environment28Figure 2.3 Location of geophysical lines – Cutta cutta Site

8386500 mN

8386000 mN

. Hil.O . 154.6

226500 mE 227000 mE 227500 mE 228000 mE


Department of Infrastructure, Planning & Environment29Figure 2.4 Location of geophysical lines – Kintore Site

8405500 mN

8405000 mN

8404500 mN

195500 mE 196000 mE


Department of Infrastructure, Planning & Environment30Figure 2.1 Regional Geology of Study Area

D D D []

LEGEND

Tidal Limestone

Jindu:kin Limestone

Montej inni Limestone

ToI lis Forrrul:ion

(



Figure 2.6 Schematic diagram showing mechanisms responsible for a sinkholecollapse

Figure 2.7 Schematic diagram showing mechanism of sinkhole collapse

Figure 2.8 Conceptual model of karst aquifer (Doeflinger & Zwahlen 1995)



0 50 100 150 200 250 300 350 400 450 500

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

10 metre separationLegend

VerticalDipole

HorizontalDipole

0 50 100 150 200 250 300 350 400 450 500

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

20 metre separation

0 50 100 150 200 250 300 350 400 450 500

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

40 metre separation

0 100 200 300 400 500

Chainage (metres)

-8

-4

0

4

SP

Vol

tage

(mV

)

Self Potential

LegendSP

5pt runningaverage

Station spacing 5mChainage increases to north



Hickey, EM34 - Line1

(a)

(b)

(c)

(d)

Figure 6.1 a) SP Results, b)EM34 10 metre separation, c) EM34 20 metreseparation and d) EM34 40 metre separation.



0 50 100 150 200 250 300 350 400 450 500

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)


VerticalDipole

HorizontalDipole

0 50 100 150 200 250 300 350 400 450 500

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

20 metre separation

0 50 100 150 200 250 300 350 400 450 500

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

40 metre separation

Hickey, EM34 - Line2




0 100 200 300 400 500

Chainage (metres)

-8

-6

-4

-2

0

2

SP

Vol

tage

(mV

)

Self Potential

LegendSP

5pt runningaverage

(a)

(b)

(c)

(d)




0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)


VerticalDipole

HorizontalDipole

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

20 metre separation

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

40 metre separation

0 40 80 120 160 200

Chainage (metres)

40

60

80

100

120

SP

Vol

tage

(mV

)

Self Potential

LegendSP

5pt runningaverage




Cutta Cutta, EM34 - Line 1

(a)

(b)

(c)

(d)

Fence

Fence

Fence




0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)


VerticalDipole

HorizontalDipole

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

20 metre separation

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

40 metre separation

0 40 80 120 160 200

Chainage (metres)

-40

-20

0

20

40

SP

Vol

tage

(mV

)

Self Potential

LegendSP

5pt runningaverage




Cutta Cutta, EM34 - Line2

(a)

(b)

(c)

(d)

Fence

Fence

Fence




0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)


VerticalDipole

HorizontalDipole

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

20 metre separation

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

40 metre separation

0 40 80 120 160 200

Chainage (metres)

-80

-60

-40

-20

0

SP

Vol

tage

(mV

)

Self PotentialLegend

SP

5pt runningaverage




Kintore, EM34 - Line 1

(a)

(b)

(c)

(d)




0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)


VerticalDipole

HorizontalDipole

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

20 metre separation

0 50 100 150 200

Chainage (metres)

0

20

40

60

80

App

aren

t Con

duct

ivity

(mS

/m)

40 metre separation

0 40 80 120 160 200

Chainage (metres)

0

20

40

60

80

SP

Vol

tage

(mV

)

Self PotentialLegend

SP

5pt runningaverage




Kintore, EM34 - Line 2

(a)

(b)

(c)

(d)




0 10 20 30 40 50 60 70 80 90 100

0

4

8

12

Beginers Cave - EM34 Survey

Horizontal Dipole

Vertical Dipole

Figure 6.7 EM34 40 metre separation.



Figure 6.8 Hickey Line 1 – EM34 pseudosection

Figure 6.9 Hickey Line 2 – EM34 pseudosection

Line 1

Chainage (metres)

Line 2

Ch ainage (metres)

(:Oro "C~"l)t (m3-'rnJ



Figure 6.10 Cutta Line 1 – EM34 pseudosection

Figure 6.11 Cutta Line 2 – EM34 pseudosection

Chainage (metre,)

Line 2

ChaiMge (metre5)

Conauot,v,,,, (mS/m)



Figure 6.12 Hickey pole-dipole inversion results determined fromLoke’s 2D inversion.

Figure 6.13 Hickey pole-dipole inversion results determined fromLoke’s 2D inversion



Figure 6.14 Cutta cutta pole-dipole inversion results determinedfrom Loke’s 2D inversion

Figure 6.15 Cutta cutta pole-dipole inversion results determinedfrom Loke’s 2D inversion



Figure 6.16 Kintore pole-dipole inversion results determined fromLoke’s 2D inversion

Figure 6.17 Kintore pole-dipole inversion results determined fromLoke’s 2D inversion



Figure 6.18 Hickey GPR results. Processing has suppressed the source pulse using a 21point trace mix in subtraction mode with high pass filter, AGC (30) from Beresford, 2001.

Figure 6.19 GPR results from Cutta cutta Line 2. Traces are displayed using conventionalAGC (30)

• , c

f

Hickey Line 2

Dist ~nce (metres)

Cutta Cutta Line 1 Distance (meires)



201000 mE 201500 mE 202000 mE

8398600 mN

8399100 mN

8399600 mN

RN 31966RN 31967

RN 31968

RN 31969

RN 32748

RN 32749

RN 32870

RN 32557

RN 32558

RN 32746

RN 32559RN 32740

RN 32741

Zim

in D

rv

Figure 7.1 Bore locations on Hickey Property



Figure 7.2 a) Inversion results and b) Interpreted resistivity results – Hickey Line 1.

, -10-'

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CI1aio3ge (metres)

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_ _ _ _ _ ~ _ _ _ _ D _ _ __ _ _ 5 [1l mo ,IH .0.0 1Il 0 160 32[] 00

~";'''' f ~ "'''' m



Figure 7.3 a) Inversion results and b) Interpreted resistivity results – Hickey Line 2.

, Oc~ C '" '"' • d

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£

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"" a...""II'" (rTJetres)

l EGEND

w,,, .. ," ... ,"'" ." ... , ..,,_ ~.,,",

CM"""", (metres) _ _ _ _ _ ~ _ _ _ _ D _ _ _ _ _ _ 500 ;U O <DD i OD III 0 1Ell 320 00

R'''''"'f ~ 0"'" '"



Figure 7.4 a) Inversion results and b) Interpreted resistivity results – Cutta Cutta Line 2.

, ~ L' R'~ -( ~

"-, 7 , " '" " " " " " " H" '" '" 130 140 1&1 160 170 180 190 200 .. Distance (metres)

"" '-''''' ' ' . ..... ~ . .. ...... " " ,," ..., ,,0. ~.~ ..

[);Slance (metres)

'" ---- -----~oo ' ~D ' " 00



Figure 7.5 GPR results compared with interpreted resistivity results.

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