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Record 2018/12 | eCat 117201 Geological Survey of New South Wales Record GS2018/0202

Laurelvale 1 borehole completion record Southern Thomson Project I. C. Roach, K. F. Bull, C. B. Folkes, P. Gilmore, R. Hegarty, S. L. Jones, and D. B. Tilley

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Laurelvale 1 borehole completion record Southern Thomson Project GEOSCIENCE AUSTRALIA RECORD 2018/12 GEOLOGICAL SURVEY OF NEW SOUTH WALES RECORD GS2018/0202

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I. C. Roach , K. F. Bull , C. B. Folkes , P. Gilmore , R. Hegarty , S. L. Jones , and D. B. Tilley

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Geoscience Australia. Geological Survey of New South Wales. Formerly Geological Survey of New South Wales.

Department of Industry, Innovation and Science Minister for Resources and Northern Australia: Senator the Hon Matthew Canavan MP Secretary: Dr Heather Smith PSM Geoscience Australia Chief Executive Officer: Dr James Johnson Department of Planning and Environment, New South Wales Minister: The Hon Don Harwin MLC Secretary: Ms Carolyn McNally Geological Survey of New South Wales Director: Dr Chris Yeats This paper is published with the permission of the CEO, Geoscience Australia and the Director, Geological Survey of New South Wales.

© Commonwealth of Australia (Geoscience Australia) 2018 and State of New South Wales (Geological Survey of New South Wales) 2018. With the exception of the Commonwealth Coat of Arms and where otherwise noted, this product is provided under a Creative Commons Attribution 4.0 International Licence. (http://creativecommons.org/licenses/by/4.0/legalcode) Geoscience Australia has tried to make the information in this product as accurate as possible. However, it does not guarantee that the information is totally accurate or complete. Therefore, you should not solely rely on this information when making a commercial decision. Geoscience Australia is committed to providing web accessible content wherever possible. If you are having difficulties with accessing this document please email [email protected]. ISSN 2201-702X (PDF) ISBN 978-1-925297-82-9 (PDF) eCat 117201 Bibliographic reference: Roach, I. C., Bull, K. F., Folkes, C. B., Gilmore, P., Hegarty, R., Jones, S. L., Tilley, D. B. 2018. Laurelvale 1 borehole completion record: Southern Thomson Project. Record 2018/12. Geoscience Australia, Canberra. Geological Survey of New South Wales Record GS2018/0202. http://dx.doi.org/10.11636/Record.2018.012 Version: 1701

Contents

1 Introduction ............................................................................................................................................1 1.1 The Southern Thomson Project .......................................................................................................1 2 Borehole rationale, location and construction .......................................................................................3 2.1 Rationale and location .....................................................................................................................3 2.2 Borehole construction ......................................................................................................................6 3 Borehole lithology and stratigraphy .......................................................................................................9 3.1 Introduction ......................................................................................................................................9 3.2 Lithology .........................................................................................................................................10 3.3 Basement rock petrography ...........................................................................................................12 3.4 Stratigraphy ....................................................................................................................................13 3.5 Synthesis within the regional stratigraphic framework ...................................................................14 4 Borehole and drill core rock properties ................................................................................................16 4.1 Introduction ....................................................................................................................................16 4.2 Rock properties measurements .....................................................................................................16 4.3 Results ...........................................................................................................................................17 4.3.1 Natural gamma .........................................................................................................................17 4.3.2 Induction conductivity ...............................................................................................................17 4.3.3 Magnetic susceptibility .............................................................................................................18 4.3.4 Bulk density and apparent porosity ..........................................................................................20 4.4 Rock properties data package .......................................................................................................20 5 HyLogger data .....................................................................................................................................21 5.1 HyLogger data acquisition and processing ....................................................................................21 5.2 Results ...........................................................................................................................................22 5.2.1 Laurelvale 1 mud rotary chips ..................................................................................................22 5.2.2 Laurelvale 1 diamond drill core ................................................................................................22 5.3 Comparison with other logging ......................................................................................................24 5.4 HyLogger data package .................................................................................................................24 5.5 HyLogger data reprocessing ..........................................................................................................24 6 Groundwater ........................................................................................................................................27 7 Acknowledgments ...............................................................................................................................28 8 References ..........................................................................................................................................29 Appendix A Borehole construction .........................................................................................................31 Appendix B Drilling activities and consumables .....................................................................................33 Appendix C Petrophysical equipment details .........................................................................................35 C.1 Borehole wireline logging equipment ............................................................................................35 C.2 Hand-held magnetic susceptibility logging equipment ..................................................................35 C.3 Analytical balance equipment (density determination) ..................................................................35 Appendix D Petrophysical data acquisition and processing...................................................................36 D.1 Data acquisition .............................................................................................................................36 D.2 Equipment calibration ....................................................................................................................36 D.3 Data processing 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Appendix E Lithological and stratigraphic log.........................................................................................38 Appendix F Deviation survey ..................................................................................................................40 Appendix G Borehole log........................................................................................................................41

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Figures

Figure 1.1: Location of the Thomson Orogen in eastern Australia. The red box encompasses the Southern Thomson Project area. .......................................................................................................1 Figure 1.2: Location map of all boreholes drilled as part of the Southern Thomson Project. Background: TOPO 250K topographic map mosaic, Geoscience Australia. ...........................................2 Figure 2.1: Location map of the Laurelvale 1 borehole. Background: TOPO 250K mosaic of Australia, Geoscience Australia. ..............................................................................................................4 Figure 2.2: Location map showing the Laurelvale 1 borehole and solid geological basement interpretation from Purdy et al. (2014) and Purdy et al. (2018), over a first vertical derivative of total magnetic intensity (1VD TMI) image of the Magnetic Map of Australia 2015. .................................5 Figure 2.3: The Laurelvale 1 borehole site prior to clearing and drilling, looking west. Significant or culturally-sensitive vegetation such as the leopardwood tree (Flindersia maculosa, front right) was cordoned-off using warning tape to avoid accidental damage during operations. ...........................6 Figure 2.4: The drilling site at Laurelvale 1 showing equipment and sump layout prior to commencement of drilling, looking northeast. The protected leopardwood tree Figure 2.3 is visible in the background behind the drilling rig and rod sloop.................................................................7 Figure 3.1: Mud rotary chip sample layout at the Laurelvale 1 borehole site. Samples are laid out on plastic starting in the top left corner, moving right in runs of 10 m, with the sample from the deepest part of the borehole in the foreground at bottom left. Note the colour change in chips from the surface weathering zone (back) to unweathered Eromanga Basin rocks in the foreground. ...............................................................................................................................................9 Figure 3.2: Laurelvale 1 lithological and stratigraphic graphic log. Lithology is summarised from the detailed lithological log attached in Appendix E. ..............................................................................11 Figure 3.3: Dry (above) and wet (below) field photos of typical diamond drill core from Laurelvale 1. ...........................................................................................................................................12 Figure 3.4: Representative thin-section photomicrographs of basement rock sampled from the Laurelvale 1 borehole at ~367.1 m DL. ..................................................................................................13 Figure 4.1: Lithology, stratigraphy, rock properties and borehole construction data for Laurelvale 1. The legend for lithology types and stratigraphy is the same as in Figure 3.2. For more detail on borehole construction refer to Appendix A. .......................................................................................19 Figure 5.1: Mineral spectra summary plot of Laurelvale 1 mud rotary chips. ........................................22 Figure 5.2: Mineral spectra summary plot of Laurelvale 1 diamond drill core........................................23 Figure 5.3: White mica, chlorite and K-feldspar abundance in Laurelvale 1 compared with albedo. The evidence suggests that this part of the drillhole has undergone sericite/chlorite alteration. ................................................................................................................................................23 Figure 5.4A: Comparison between spectral mineralogy, interpreted stratigraphy and borehole rock properties data from Laurelvale 1. The spectral mineralogy legends in the upper part of the log refer to the mud rotary drilled portion of the borehole < 336 m DL, and in the lower part to the diamond drilled portion to EOH. .......................................................................................................25 Figure 8.1: Laurelvale 1 borehole construction. .....................................................................................32

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Tables

Table 2.1: Details for the Laurelvale 1 borehole.......................................................................................3 Table 3.1: Interpreted stratigraphy of the Laurelvale 1 borehole. ..........................................................14 Table 4.1: Laurelvale 1 natural gamma interval statistics. .....................................................................17 Table 4.2: Laurelvale 1 induction conductivity stratigraphic interval statistics. ......................................18 Table 4.3: Laurelvale 1 magnetic susceptibility stratigraphic interval magnetic susceptibility statistics. .................................................................................................................................................20 Table 4.4: Bulk density measurements on diamond drill core from Laurelvale 1...................................20 Table 8.1: Laurelvale 1 drilling times and production rates. ...................................................................33 Table 8.2: Laurelvale 1 drilling consumables used. ...............................................................................34 Table 8.3: Borehole wireline data acquisition steps in Laurelvale 1 ......................................................36 Table 8.4: Deviation survey data for Laurelvale 1 ..................................................................................40

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1 Introduction

1.1 The Southern Thomson Project The Thomson Orogen is a major component of the Paleozoic Tasmanides of eastern Australia that extends through large portions of central and southwest Queensland and northwest New South Wales (Figure 1.1). Much of the Thomson Orogen is buried under younger sedimentary basins (some up to several kilometres thick) and regolith cover, making it one of the most poorly understood elements of Australia’s geology. As a result, the mineral potential of the region is also poorly defined. The Southern Thomson Project (the Project) is a collaborative investigation between the Commonwealth of Australia (Geoscience Australia) and its partners the State of New South Wales (Department of Planning and Environment, Geological Survey of New South Wales – GSNSW) and the State of Queensland (Department of Natural Resources, Mines and Energy, Geological Survey of Queensland – GSQ).

Figure 1.1: Location of the Thomson Orogen in eastern Australia. The red box encompasses the Southern Thomson Project area.

The Project aims to better understand the geological character and mineral potential of the southern Thomson Orogen region, focusing on the border between New South Wales and Queensland, by acquiring and interpreting multi-disciplinary geophysical, geochemical, geological and geochronological data. The primary intended impact of this work is to provide the mineral exploration

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industry with pre-competitive data and knowledge that reduces risk and encourages mineral exploration in the region. The pre-competitive data collection culminated in a drilling program of 12 boreholes within the project area of New South Wales and Queensland (Figure 1.2), targeting strategic basement rocks that will improve the understanding of the mineral potential of the southern Thomson Orogen and its geodynamic setting within the Tasmanides of eastern Australia.

Figure 1.2: Location map of all boreholes drilled as part of the Southern Thomson Project. Background: TOPO 250K topographic map mosaic, Geoscience Australia.

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2 Borehole rationale, location and construction

I. C. Roach and R. Hegarty

2.1 Rationale and location The Laurelvale 1 borehole was drilled approximately 78 km SSW of Wanaaring, New South Wales (NSW), adjacent to the through-road between Tongo and Tilpa (figures 1.2, 2.1, Table 2.1). The borehole was designed to test the geology of indistinct, linear aeromagnetic anomalies in the basement rocks (Figure 2.2), test the electrical conductivity properties of cover and basement rocks to validate airborne electromagnetic (AEM) data, and to test pre-drilling geophysical cover thickness estimates (see Goodwin et al., 2017). The Laurelvale 1 borehole was drilled as a sloping borehole to recover structural information from the oriented diamond drill core. Drilled Lengths (DL) of features in the borehole are converted to True Vertical Depth (TVD) in the text and tables below unless otherwise labelled. Table 2.1: Details for the Laurelvale 1 borehole. Hole ID

Laurelvale 1

Site ID*

Goorimpa 2*

Contractor

DRC Drilling Pty Ltd

Drilling rig

Sandvik DE880

Landholder

Laurelvale Station

Title

EL 8441

Status

Closed, cemented to surface, cement cap installed, site remediation earthworks completed on 23.11.2017

Location

Longitude (GDA94): 143.944082° Latitude (GDA94): -30.388867° Easting (MGAZ55S): 206351 m Northing (MGAZ55S: 6634160 m Elevation (ellipsoidal): 91 m

Drilled length

386.8 m

Casing

0-6 m DL steel 168.28 mm outside diameter (OD), cemented 0-336.9 m DL steel 114.3 mm OD, removed prior to hole closure 336.9-386.8 m DL (end of hole - EOH) open hole

Casing cut-off depth

0.5 m below surface

Grouting

Cement, from EOH to surface

Mud rotary drilled length 0-336.0 m DL (336.0 m DL) Diamond drilled length

336.0-386.8 m DL (50.8 m DL)

Commencement date

10.08.2017

Completion date

15.08.2017

Deviation

Rig mast oriented -75°/206° magnetic

Deviation survey date

12.07.2017 (Appendix F)

GA Boreholes ENO

621618

*Project pre-drilling internal reference to site.

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Figure 2.1: Location map of the Laurelvale 1 borehole. Background: TOPO 250K mosaic of Australia, Geoscience Australia.

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Figure 2.2: Location map showing the Laurelvale 1 borehole and solid geological basement interpretation from Purdy et al. (2014) and Purdy et al. (2018), over a first vertical derivative of total magnetic intensity (1VD TMI) image of the Magnetic Map of Australia 2015.

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2.2 Borehole construction The Project team at this site included scientists from Geoscience Australia and the GSNSW, a licensed water bore driller, and the contractor’s drilling team. The borehole was drilled as an inclined mud rotary borehole using two small inter-connected sumps (approximately 3 x 5 x 1.5 m) to catch mud rotary drill cuttings to 336.0 m DL before switching to a diamond drilling operation, extending the borehole to 386.8 m DL using the original 2 sumps to catch cuttings in the diamond drilling fluids. A third 3 x 5 x 2 m sump was dug to take the sludge from the mud mixing tank as the site was being abandoned. Before commencement the Project team reviewed the standing water levels in the area to assess the likelihood of artesian groundwater conditions within the borehole by assessing bore cards for local water bores (Figure 2.1) available from the NSW Department of Primary Industries Office of Water (http://allwaterdata.water.nsw.gov.au/water.stm). At this site the Project team assessed the standing water levels of the surrounding water bores and concluded that there would be little to no likelihood of accidental groundwater escape due to the fact that water levels were all sub-artesian. Thus, the borehole plan included a short guard casing cemented into the top of the borehole to prevent near-surface collapse, and the remainder of the borehole drilled using threaded SFJ (114.3 mm OD) casing into competent basement rocks before commencement of diamond drilling operations. The casing was inserted to prevent swelling clays in the Eromanga Basin sequence from closing the borehole, to prevent potential groundwater escape, to prevent potential groundwater mixing between aquifers and to prevent drilling fluids from contaminating groundwater in accordance with the requirements of the Minimum Construction Requirements for Water Bores In Australia (National Uniform Drillers Licensing Committee, 2011). The threaded casing was removed prior to borehole completion and abandonment, and the borehole was fully cemented to surface on completion. More information regarding borehole construction and drilling consumables is available in Appendix A and Appendix B and images of the site before, during and after drilling are included in Figures 2.3 to 2.6.

Figure 2.3: The Laurelvale 1 borehole site prior to clearing and drilling, looking west. Significant or culturallysensitive vegetation such as the leopardwood tree (Flindersia maculosa, front right) was cordoned-off using warning tape to avoid accidental damage during operations.

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Figure 2.4: The drilling site at Laurelvale 1 showing equipment and sump layout prior to commencement of drilling, looking northeast. The protected leopardwood tree Figure 2.3 is visible in the background behind the drilling rig and rod sloop.

Figure 2.5: Image showing the commencement of rehabilitation of mud sumps at Laurelvale 1. Sumps, shown here with temporary fencing partially erected, were subsequently fenced by the landholder with wire fencing until such time as they dry out before backfilling with the original soil, looking west.

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Figure 2.6: Panoramic view of the Laurelvale 1 borehole site post-rehabilitation. The sumps have been back-filled and slightly mounded to allow for settling, the topsoil has been furrowed to catch seeds and rain, and dead vegetation has been formed into windbreaks by the landholder. The annotations describe the use of different parts of the site during the drilling operation. Photo courtesy of Leon Zanker.

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3 Borehole lithology and stratigraphy

I. C. Roach, R. Hegarty, C. B. Folkes and P. Gilmore

3.1 Introduction Cuttings and drill core from Laurelvale 1 were logged on site by GSNSW and GA geologists. Cuttings were collected from the mud rotary-drilled cover sequence and the top of basement at 1 m intervals to 336.0 m DL, after which diamond coring commenced through to 386.8 m DL. The sampling of some intervals was incomplete due to problems with the drilling fluid mixture; however, the overall cutting quality and volume was high. Most 1 m intervals were represented by an amount of cuttings sufficient to fill a chip tray and a 250 ml sample vial for future analysis. Cuttings were laid out to partially dewater (Figure 3.1) before washing, lithological logging, sampling and analysis with a hand-held magnetic susceptibility meter. Key parameters of grainsize, colour and organic matter content, and any other major textural changes, were recorded. The basement diamond drill core interval (336.0 m DL to 386.8 m DL) was also logged and photographed on site.

Figure 3.1: Mud rotary chip sample layout at the Laurelvale 1 borehole site. Samples are laid out on plastic starting in the top left corner, moving right in runs of 10 m, with the sample from the deepest part of the borehole in the foreground at bottom left. Note the colour change in chips from the surface weathering zone (back) to unweathered Eromanga Basin rocks in the foreground.

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3.2 Lithology Laurelvale 1 penetrated 284.3 m TVD of cover sediments and sedimentary rocks before entering competent slate rocks of the basement. Lithological types observed in the hole are described below and in Figures 3.2 and 3.3. Modern regolith at the Laurelvale 1 site includes fine, red-brown, unconsolidated silt and fine sand from 0 m DL to 1 m DL. This overlies ~5 m DL interval of indurated red-brown hardpan with dominantly sub-horizontal calcrete laminae up to 5 mm thick filling cracks within the hardpan. Below this, the regolith comprises mixed red-brown silt and grey clay to ~8.5 m DL. Below this the borehole encountered a dominantly grey coloured hard band of ferruginous silcrete with abundant hematite and limonite coatings to 22 m DL. From 22 m DL the borehole penetrated 8 m DL of pallid to whitecrimson-grey, mottled, interbedded siltstone and claystone before entering white-light grey-crimson mottled, puggy, plastic claystone at 30 m DL to ~57 m DL. Below 57 m DL the borehole penetrated a series of interbedded quartz sandstones, commencing with clay-rich silts from 57 m DL to 65 m DL, interbedded fine- and medium-grained quartz sandstones from 65 m DL to 92 m DL and a siltstone bed from 89 m DL to 90 m DL. The siltstone-sandstone units are light grey-white toned and it is difficult to assess the length to the base of surface weathering, which may lie between 69 m DL and 92 m DL, based on colour or tone changes noted in the field log. Below 92 m DL, the borehole penetrated fresh, grey rocks consisting of interbedded mudstone with hard shale bands at 139 m DL, 169 m DL and 179 m DL, grey silty mudstone between 98 and 185 m DL, dark grey, puggy siltstone with carbonaceous bands between 193 m DL and 205 m DL, grey claystone with carbonaceous bands between 205 m DL and 234 m DL, and grey-brown-white mottled claystone between 245 m DL and 245 m DL. Below this to 250 m DL sample recovery was poor through to the basement intersection due to a blocked drill bit and balled mud blocking the borehole annulus. The hole was flushed and drilling recommenced in firm to hard, white-pink clay between 250 m DL and 251 m DL. From 251 m DL to 268 m DL the borehole encountered mixed mid-grey mudstone rock chips, quartz grains, brown-cream coloured soft clay, and dark brown carbonaceous clay. From 268 m DL to 291 m DL the sample returned consisted of buff-coloured clay containing variable amounts of quartz grains and lithic fragments. Below 291 m DL no obvious quartz grains could be seen in the returned samples, which were dominated by clay and increasing amounts of grey-green mudstone lithic fragments towards the base of the borehole, before mud rotary drilling refusal at 336 m DL in competent basement rocks. Proximity to basement was indicated by a sharp increase in the abundance of coarse, angular cuttings consisting of light green to grey mudstone fragments with a smooth bedding parting from ~305 m DL before the mud rotary drilling bit refused to penetrate further. Basement rocks (Figure 3.3) consist of dark grey- to grey-toned metasedimentary rocks consisting of siltstone or shale with light grey sandy interbeds and prominent pyrite-filled veins and fractures and pyrite-replaced thin beds in the rock. The rocks feature prominent soft-sediment deformation structures including rip-up clasts, dewatering structures, flame structures, slump folds and possible bioturbation features such as sandy veins penetrating shale layers.

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Figure 3.2: Laurelvale 1 lithological and stratigraphic graphic log. Lithology is summarised from the detailed lithological log attached in Appendix E.

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Figure 3.3: Dry (above) and wet (below) field photos of typical diamond drill core from Laurelvale 1.

3.3 Basement rock petrography Two representative thin-sections of basement rocks were taken at ~367.1 m DL and ~368.4 m DL. The rock is described as a meta-siltstone. The basement rocks predominantly consist of fine-grained siltstone/mudstone layers with constituent grains forming a fabric at a low angle to bedding (formed by mica grains; Figure 3.4). Some layers are carbonaceous and there are also frequent coarser layers of coarse siltstone to very fine-grained sandstone that show minor soft-sediment deformation textures. Disseminated opaque grains are now mostly iron-oxides but a small number are yellow in reflected light, suggesting they are pyrite. All layers contain variable amounts of detrital muscovite and biotite that has often been partially altered to chlorite.

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Figure 3.4: Representative thin-section photomicrographs of basement rock sampled from the Laurelvale 1 borehole at ~367.1 m DL.

3.4 Stratigraphy The stratigraphy in the Laurelvale 1 borehole (Table 3.1) is interpreted based on geological mapping on the WHITE CLIFFS (Cornish et al., 1964) and YANTABULLA(Wallis and McEwan, 1962) 1:250,000 geological maps, interpretations from regional water bores and regional stratigraphic drill holes described by Hawke and Cramsie (1984). The upper unit encountered between the surface and 6 m DL in the borehole is described by Cornish et al. (1964) as ‘Qrd, dune deposits of red and brown clayey sand’, which is in keeping with the aeolian red-brown fine sand and silt sheets that cover the region and are part of the present-day Murray-Darling hydrogeological basin. Much of this is derived from the nearby Paroo River overflow and can be regarded as source-bordering dunes (Qrd). A well-developed red-brown hardpan with horizontal and vertical fracture-fills of regolith carbonate is found in the lower 5 m DL of this unit.

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Below this unit, from 6 m DL to 57 m DL, the borehole is interpreted to have passed through remnant Wallumbilla Formation rocks consisting of interbedded clay, claystone and siltstone. These rocks are weathered quite heavily at the top to form ferruginous silcrete. Table 3.1: Interpreted stratigraphy of the Laurelvale 1 borehole.

Province

Stratigraphic unit

Top depth Bottom depth True (m TVD) (m TVD) thickness (m TVD)

No province

Quaternary sand sheet, regolith carbonate hardpan

0.00

5.80

5.80

Eromanga Basin

Wallumbilla Formation

5.80

55.43

49.63

Eromanga Basin

Wyandra Sandstone Member

55.43

89.73

34.30

Eromanga Basin

Cadna-owie Formation

89.73

284.27

194.54

Thomson Orogen

Basement – Tongo Formation

284.27

378.74 EOH

94.47

At 57 m DL the borehole enters a sandy mudstone, then clean quartz sandstone of 34.30 m true thickness, which is interpreted to be the Wyandra Sandstone Member, the major aquifer in the local area. Below this, sedimentary rocks become grey to dark grey, clayey or puggy, carbonaceous and with interbedded mudstone lithic chips and quartz grains, which are interpreted to be part of the Cadna-owie Formation, which is a paralic, mixed-source package of terrestrial to shallow-marine rocks (Hawke and Cramsie, 1984; Cook et al., 2013). The Cadna-owie Formation continues to the basement-cover contact, however the actual location of this contact is difficult to interpret. This is given that the basement and cover have similar lithology in mud rotary samples, being composed of clay with lithic and quartzose fragments, and that mud rotary samples were lost in this interval. The basement-cover interface is interpreted at 290 m DL (284.27 m TVD) in the borehole. Basement rocks in Laurelvale 1 consist of light grey- to light green-coloured slate, meta-siltstone and sandstone (Figure 3.3). Rocks in the drill core are hard, jointed and have a single foliation. Pyrite-filled tension gash arrays occur, and pyrite can occur in oblique fractures or bedding-parallel fractures or as replacements in some beds. The rock contains numerous sedimentary structures indicating original depositional structures (graded bedding, scours and rip-up clasts), and soft-sediment deformation (dewatering structures, flame structures, slump folds) as well as possible bioturbation features such as sandy veins penetrating shale layers. Facing directions of depositional structures in the basement core indicated that bedding was steeply dipping, but not overturned.

3.5 Synthesis within the regional stratigraphic framework According to the most recent basement interpretation map of Purdy et al. (2018), this borehole is located in the currently mapped extent of the Tongo Formation described as ‘possibly magnetised metasedimentary rocks’. There is very little information on this unit that comprises a moderately magnetic, ~150 km by 15 km zone, so this diamond drill core provides important information into a regionally extensive rock package. Similar basement material to that sampled by the Laurelvale 1 borehole was sampled by the Eugene borehole (Dick and Simpson, 2010), described as an ‘alternating grey-black, quartz-rich, siltstone that parts along cleavage planes which are predominantly parallel to bedding. Darker units are more carbonaceous with little variation in grain size throughout the unit’. The basement lithology sampled by the Laurelvale 1 and Eugene boreholes appear to provide representative rocks of the currently mapped extent of the Tongo Formation.

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Although there are currently no age constraints on the Tongo Formation, the preservation of primary features, a low regional metamorphic grade, lack of evidence for contact metamorphism and only one fabric preserved, suggest these rocks are different to the metasedimentary rock units of the Warratta Group and the basement rocks intersected by the Euroli 1 drillhole (Roach et al., 2018a). This suggests that the Tongo Formation is younger than the Warratta Group. However, the Tongo 1 granodiorite (preliminary age of 421 Ma; Roach et al., 2018b) appears to intrude the Tongo Formation, so this would seemingly provide a minimum age for the Formation. The Tongo Formation is proposed to be overlain by non-magnetic sedimentary rocks equivalent to the Cobar Supergroup, suggesting that the Tongo Formation is Silurian or older (Purdy et al., 2018). However, although the source of moderately-magnetic linear trends (Purdy et al., in prep.) was sampled in the Laurelvale 1 borehole, the proposed overlying non-magnetic sedimentary rocks (Cobar Supergroup equivalents) were not sampled. Geochemical and geochronological (Cross et al., in prep) analyses will be forthcoming and will better help to place the rock unit sampled in the Laurelvale 1 borehole in a regional context.

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4 Borehole and drill core rock properties

I. C. Roach, R. Hegarty and S. L. Jones

4.1 Introduction Rock properties data provide the petrophysical link between observed geophysics and under-cover geology. Rock properties data may be used to help constrain models and inversions of potential fields (magnetic, gravity) geophysical data, resulting in more accurate predictions of geology from geophysics. Electrical conductivity rock properties data can also be used to constrain inversions of airborne electromagnetic (AEM) data for regional geological and groundwater resources mapping.

4.2 Rock properties measurements Rock properties measurements were performed in situ using borehole wireline logging tools, using hand-held equipment on mud rotary drill chips and diamond drill core in the field, using hand-held and laboratory equipment in the GSNSW core repository at Londonderry, New South Wales, and at the Coffey Services Pty Ltd laboratory in Fyshwick, Australian Capital Territory. Rock properties measurements include: •

dual channel induction (electrical) conductivity (borehole wireline)



natural gamma (borehole wireline)



magnetic susceptibility (borehole wireline on uncased basement rocks and hand-held on mud rotary drill chips and diamond drill core)



bulk rock density (drill core only).

Borehole wireline logging was performed in stages, where possible, between drilling and subsequent borehole casing installation owing to the necessities of safely drilling and casing boreholes through the Great Artesian Basin, and preventing the uncontrolled escape of artesian groundwater. Every attempt was made to obtain borehole wireline rock properties measurements from open, uncased sections of each borehole. This was in order to obtain induction conductivity data to help validate airborne electromagnetic data collected in 2014 and 2016, detailed by Roach (2015) and Brodie et al. (in prep). Details of the equipment used are provided in Appendix C. No in situ density measurements were obtained. Data acquisition, processing and quality control details are included in Appendix D and an enlargedscale graphic log is presented in Appendix G.

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4.3 Results 4.3.1 Natural gamma Natural gamma data were obtained along the full length of the borehole (Figure 4.1), from uncased sections in stages as they became available, and through casing at the completion of drilling. The statistics included in Table 4.1 are taken from a composite of data from the uncased borehole. Natural gamma data are processed according to the description in Appendix D and are presented using American Petroleum Institute (API) units. Natural gamma emissions are relatively subdued in the Quaternary cover, but are variable in the Wallumbilla Formation rocks of the Eromanga Basin. Slight variations are attributed to small differences in source materials and leaching due to surface weathering in the modern regolith profile. There is a strong correlation between low natural gamma and low induction conductivity adjacent to the silcrete layer in the top of the borehole. Natural gamma emissions in the Wyandra Sandstone Member are subdued, reflecting the quartz-rich nature of this unit, but increase towards the base together with induction conductivity, suggestive of a gradual increase in clay content. In the Cadna-owie Formation, natural gamma emissions are reasonably steady until ~190 m DL, where changes in lithology and source materials result in highly variable natural gamma signal reflective of finely interbedded materials. Natural gamma emissions in the base of Cadna-owie Formation have the characteristic increase seen in many boreholes approaching the basement-cover interface (Hawke and Cramsie, 1984; Habermehl, 2001; Roach et al., 2017). Basement rocks in Laurelvale 1 have overall elevated natural gamma emissions when compared to the rest of the borehole. A gradual reduction in leaching in the palaeoweathering profile is noticeable as a gradual increase in emission from the basement–cover interface at 290 m DL to ~330 m DL, and an attenuation in gamma emissions at ~340 m DL to 344 m DL can be attributed to a quartz sand-rich layer in the borehole at this level. Table 4.1: Laurelvale 1 natural gamma interval statistics. Strat unit

Minimum (API) Maximum (API) Average (API) SD (API)

Quaternary

56.79

138.51

78.31

11.77

Wallumbilla Formation

19.66

168.64

69.46

23.63

Wyandra Sandstone Member

8.46

94.96

45.94

17.62

Cadna-owie Formation

20.16

320.42

101.36

44.54

Basement

134.39

326.61

219.24

30.18

4.3.2 Induction conductivity An almost complete profile of induction conductivity logging is available for Laurelvale 1. A small data gap exists in the top of the borehole where casing was inserted to prevent loose sand from falling into the borehole (0 m DL to 6 m DL), and another occurs where several metres of cuttings filled the bottom of hole before the commencement of diamond drilling at ~ 336 m DL (Figure 4.1). Electrical conductivity statistics for stratigraphic units encountered within Laurelvale 1 are presented in Table 4.2. Negative values are attributed to a slight miscalibration of the induction conductivity tool.

Laurelvale 1 borehole completion record

17

Induction conductivity data reveal that the cover at the borehole site is electrically conductive, and that basement is electrically resistive, partially confirming the results of AEM surveying over the site in 2016 (see Brodie et al., in prep). It is not known how electrically conductive or resistive the Quaternary sands are at the top of the borehole because of casing, but the prominent silcrete layer between 8 m DL and 13 m DL is relatively resistive, correlating with the leached, silica-rich mineralogy of this unit. Rocks of the Wallumbilla Formation and Wyandra Sandstone Member are variably electrically conductive, and it is suggested that the Wyandra Sandstone Member contains brackish groundwater in this area resulting in high bulk electrical conductivity despite the quartz-rich nature of the rock. Waterbore GW004336, ~3.9 km ESE of Laurelvale 1, contains groundwater of between 3000 ppm Total Dissolved Solids (TDS) and 7000 ppm TDS. Bulk electrical conductivity is relatively high but quite variable throughout the upper portion of the Cadna-owie Formation to ~220 m DL, where low bulk electrical conductivity is correlated with high but variable natural gamma emission signifying a major change in the sediment source supplying material to the Cadna-owie Formation, most likely to the local country rocks, and perhaps a freshening of groundwater resulting in low overall bulk electrical conductivity at the base of this unit. Basement rocks have low bulk electrical conductivity, confirming the results of AEM data in the local area. Negative values in the statistics in the basement (Table 4.2) are attributed to a slight miscalibration of the borehole tool. Table 4.2: Laurelvale 1 induction conductivity stratigraphic interval statistics. Strat unit

Minimum (mS/m) Maximum (mS/m) Average (mS/m) SD (mS/m) Medium channel

Quaternary

NA

NA

NA

NA

Wallumbilla Formation

221.15

1197.73

574.82

193.44

Wyandra Sandstone Member

525.26

1086.05

796.03

164.47

Cadna-owie Formation

26.05

1087.14

379.10

257.82

Basement

-3.57

37.64

14.03

8.10

Deep channel Quaternary

NA

NA

NA

NA

Wallumbilla Formation

293.11

1197.73

647.76

184.20

Wyandra Sandstone Member

622.55

1092.17

874.26

133.88

Cadna-owie Formation

35.90

1092.29

427.77

276.62

Basement

-10.48

42.99

17.69

11.41

4.3.3 Magnetic susceptibility The Laurelvale 1 borehole was logged using a borehole wireline magnetic susceptibility tool in the upper part to 336.2 m DL only. Hand-held magnetic susceptibility data were acquired along the entire length of the borehole from the mud rotary drilled chips at 1.0 m intervals and the diamond drill core at 0.5 m intervals. The handheld data were used to calibrate the borehole wireline magnetic susceptibility data and to produce a final composite magnetic susceptibility log of the borehole (Figure 4.1). Magnetic susceptibility stratigraphic interval statistics for Laurelvale 1 are summarised in Table 4.3.

18

Laurelvale 1 borehole completion record

Figure 4.1: Lithology, stratigraphy, rock properties and borehole construction data for Laurelvale 1. The legend for lithology types and stratigraphy is the same as in Figure 3.2. For more detail on borehole construction refer to Appendix A.

Laurelvale 1 borehole completion record

19

The Laurelvale 1 borehole was drilled to test a subdued magnetic anomaly in the “Tongo Association”, which is a belt of magnetic rocks with not surface outcrop or borehole intersections. Magnetic susceptibilities in the borehole are elevated in the surface Quaternary cover, related to maghemite and hematite in the sand sheet covering the site. Several relatively strong magnetic anomalies occur in the Cadna-owie Formation, and the basement rocks are similarly magnetised, thus it is not clear whether the magnetic anomaly at this site is due to magnetised cover, or basement, or both, based on this evidence alone. Targeted Magnetic Inversion Modelling (TMIM) at the site gave cover thickness estimates of between 272 m and 378 m (Goodwin et al., 2017), suggesting that magnetised basement is responsible for the magnetic anomaly at the borehole site. Table 4.3: Laurelvale 1 magnetic susceptibility stratigraphic interval magnetic susceptibility statistics. -5

-5

-5

-5

Minimum (SI x 10 ) Maximum (SI x 10 ) Average (SI x 10 ) SD (SI x 10 ) Quaternary dunes

7.00

50.00

12.39

10.16

Wallumbilla Formation

2.66

76.00

10.46

10.36

Wyandra Sandstone Member

4.17

21.60

9.34

1.59

Cadna-owie Formation

0.00

93.66

9.18

4.75

Basement

0.00

37.44

12.27

6.76

4.3.4 Bulk density and apparent porosity Samples of diamond drill core were submitted to the Coffey Services Australia Pty Ltd laboratory in Fyshwick, Australian Capital Territory, for determination of dry bulk density, saturated bulk density, grain density and apparent porosity according to Australian Standard AS 1141.6.1-2000, presented in Table 4.4. Table 4.4: Bulk density measurements on diamond drill core from Laurelvale 1. From (m DL)

To (m DL)

n samples

Mean dry bulk Mean Mean grain density saturated bulk density 3 3 3 (g/cm ) density (g/cm ) (g/cm )

Mean apparent porosity (%)

351.25

351.51

3

2.71 ± 0.004

2.73 ± 0.002

2.78 ±0.006

0.96 ± 0.13

384.4

386.8

4

2.65 ± 0.03

2.66 ± 0.03

2.69 ± 0.02

0.51 ± 0.30

380.4

380.6

1

2.69

2.71

2.74

0.68

± error is calculated as 1 standard deviation of the sample population

4.4 Rock properties data package Rock properties data for Laurelvale 1 are compiled as a Log ASCII Standard (LAS) file available for free download from the Geoscience Australia website and through the Rock Properties Explorer discovery tool (http://www.ga.gov.au/explorer-web/rock-properties.html). Rock properties data are also included in a Web Mapping Service (WMS) and Web Feature Service (WFS) from GA (http://www.ga.gov.au/data-pubs/web-services/ga-web-services).

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Laurelvale 1 borehole completion record

5 HyLogger data

D. B. Tilley and I. C. Roach

5.1 HyLogger data acquisition and processing Diamond drill cores and mud rotary chips were spectrally scanned using the CSIRO-developed HyLogger™ system at NSW Planning and Environment’s HyLogger™ facility in the W.B. Clarke Geoscience Centre, Londonderry, NSW. The resultant spectral data were analysed using The Spectral Geologist™ (TSG) software, also developed by the CSIRO. This instrument measures spectra in three different wavelength bands (Mason and Huntington, 2012): • • •

the visible-near infrared (VNIR) between 380 and 1072 nm the short-wave infrared (SWIR) between 1072 and 2500 nm the thermal infrared (TIR) from 6000 and 14,500 nm.

The HyLogger™ instrument collects spectral data and imagery of geological materials on a systematic basis. The near-continuous nature and abundance of the spectral data collected provides ideal datasets which can be processed to identify systematic changes in the overall mineral assemblage along diamond drill cores and chip trays. This can highlight shifts in the nature of individual mineral species present (particularly chlorite and white mica), and identify changes in the relative abundance of specific minerals. Prior to scanning, the diamond drill core was cleaned with a vacuum cleaner and moistened cloth to remove dust, dirt and in-tray debris. Disjointed core pieces were realigned and reconnected within sections of a tray to make a continuous core stick. Following this, the core was allowed to dry to reduce H2O spectral interference prior to scanning. In contrast, the only preparation done on the chips was that they were allowed to dry within their trays for a few days in open air. A number of specialised scalars were used for inferring changes in the composition of white mica and chlorite and for estimating their relative abundances in core and chips. For white mica composition and relative abundance The Spectral Assistant (TSA™) batch scalars White Mica Wavelength v1.2 and White Mica Intensity v1.2 were used. These scalars are based on the wavelength and depth of the Al-OH absorption feature in the short-wave infrared (SWIR) spectrum. It has been noted by Pontual et al. (2008) that the absorption minimum ranges from 2184 nm for paragonite (Na-sericite), to 2202 nm for muscovite (“normal” potassic compositions) and 2225 nm for phengite compositions (Mg-Fe substituted sericites). Also, the scalar’s batch script specifies that any identification of montmorillonite by TSA™ will provide a null result, whilst samples classified by TSA™ as bearing highly crystalline and/or illitic white micas are included in the determinations. The highly crystalline white micas include muscovite, phengite and paragonite whilst the illitic white micas include illite, phengitic illite and paragonitic illite. The depth of the feature provides an estimation of the relative abundance of white mica within core and chips. The inferred composition and relative abundance of chlorite group minerals were determined using the following TSG™ Feature Extraction (FeatEx) scalars: • •

chlorite composition: FeatEx Wvl, 2253 nm ± 10 nm chlorite relative abundance: FeatEx Depth, 2253 nm ± 10 nm.

Laurelvale 1 borehole completion record

21

These scalars were used to determine the wavelength and depth of the Fe-OH absorption feature in the SWIR spectrum. The chlorite Mg-OH feature can be affected by the presence of carbonate, which overlaps the chlorite Mg-OH absorption. Consequently, it is more reliable to use the Fe-OH absorption feature for inferring the composition of chlorite rather than the Mg-OH feature. Pontual et al. (2008) have shown that this feature varies from 2245 nm for Mg-chlorite to 2261 nm for Fe-chlorite. The depth of the feature provides an estimation of the relative abundance of chlorite within the core/chips.

5.2 Results 5.2.1 Laurelvale 1 mud rotary chips The mud rotary chips from Laurelvale 1 are composed mainly of kaolin (kaolinite), smectite (montmorillonite), white mica (muscovite), sulfate (gypsum), quartz, K-feldspar (microcline) and plagioclase (albite) (Figure 5.1). The white mica is tending to phengite (ranges from 2206 nm to 2211 nm) towards the bottom of the borehole. This is consistent with the phengitic white mica observed throughout the diamond tail. Although observed in the diamond tail, chlorite is not detectible in the mud rotary chips.

Figure 5.1: Mineral spectra summary plot of Laurelvale 1 mud rotary chips.

5.2.2 Laurelvale 1 diamond drill core The upper section (336 m DL to 350 m DL) of the Laurelvale 1 diamond drill core is composed predominantly of white mica, chlorite, quartz and Na-plagioclase (albite) (Figure 5.2), which is consistent with the siliciclastic turbidite lithology. Between 350 m DL and 358 m DL, white mica, chlorite and albite reduces in abundance while Kfeldspar (microcline) content increases. This section of the drill hole appears to have undergone sericite/chlorite alteration (Figure 5.3).

22

Laurelvale 1 borehole completion record

The lower section (358 m DL to 387 m DL) is composed mainly of quartz, K-feldspar and plagioclase with minor chlorite and white mica. Within this section, chlorite and mica is locally abundant in narrow