Department of Primary Industries

DEPARTMENT OF PRIMARY INDUSTRIES

VICTORIAN INITIATIVE FOR MINERALS & PETROLEUM SWAN HILL 1:250 000 AND PARTS OF BALRANALD AND DENILIQUIN

1:250 000 MAP AREAS : A GEOLOGICAL INTERPRETATION OF THE GEOPHYSICAL DATA

VIMP REPORT 84

D.H. MOORE

September 2005 Bibliographic reference: MOORE, D.H., 2005. Swan Hill 1:250 000 and parts of Balranald and Deniliquin 1:250 000 map areas: a geological interpretation of the geophysical data. Victorian Initiative for Minerals and Petroleum Report 84. Department of Primary Industries.

ISSN 1323 4536 ISBN 1 74146 375 0

This report may be purchased from: Information@dpi, 1 Spring Street Melbourne Vic. 3000 Australia. Telephone: (61 3) 9658 4440 Facsimile: (61 3) 9658 4760 Email: [email protected]

For further technical information contact: Manager Minerals GeoScience GeoScience Victoria Department of Primary Industries GPO Box 4440 Melbourne Victoria 3001 Australia Website: www.dpi.vic.gov.au/minpet/index.htm

Acknowledgements: Ken Sherry prepared this report for publication and drafted most of the figures. John Dunleavy compiled the GIS data and prepared the accompanying map.

Disclaimer: This publication may be of assistance to you, but the state of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequences which may arise from you relying on any information in this publication.

All photographs, images, maps, charts, tables and written information in this publication are copyright under the Copyright Act and may not be reproduced by any process whatsoever without the written permission of the Department of Primary Industry. SWAN HILL - INTERPRETATION 1

Contents

Abstract 2 1 Introduction 3 2 Previous work 3 3 Regional Interpretation 5 3.1 Introduction 5 3.2 Cambrian to Ordovician seafloor formation and sedimentation 5 3.3 The Benambran Orogeny 6 3.4 Early Devonian granites 7 3.5 Devonian sedimentary rocks 7 3.6 The Tabberabberan Orogeny 7 3.7 Tabberabberan granites 9 3.8 Kanimblan deformation 9 3.9 Permo-Carboniferous sedimentation 10 3.10 Mesozoic volcanism 10 3.11 Palaeocene to Recent – the Murray Basin 10 4 Conclusions 14 References 15 Appendix 1 18 Newly named units on SWAN HILL 18

List of Figures 1 Location of the SWAN HILL region 23 2 Total magnetic intensity of the SWAN HILL region 24 3 Bouguer Gravity of the SWAN HILL region 25 4 Radiometrics of the SWAN HILL region 26 5 Digital elevation model of the SWAN HILL region 27 6 Summary of the geology of the SWAN HILL region 28 7 Interpreted cross sections of the SWAN HILL region 29 8 Cambrian mafic volcanic rocks along major faults 30 9 Comparison of magnetic data from three surveys 31 10 Magnetics of SW NSW and northern Victoria 32–33 11 The Lalbert Batholith 34 12 Devonian sedimentary rocks on DENILIQUIN in southern NSW 35 13 Bore hole section along the Murray River 36 14 Mineralisation in the Murray Basin 37 15 Eroded Parilla Sand in the Leaghur area 38

List of Tables 2.1 Significant public domain reports over the SWAN HILL region 4 2.2 Public domain airborne geophysical surveys over the SWAN HILL region 5 3.1 Age determinations on intrusions of the Lalbert Batholith on CHARLTON 6 3.2 Age determinations on the granites on SWAN HILL 8 3.3 Kerang–Cohuna brown coal resource 11 3.4 Heavy mineral sand resources in the SWAN HILL region 11 3.5 Stratigraphy of the Cainozoic rocks in the SWAN HILL region 13 2 SWAN HILL - INTERPRETATION

Abstract This report is the first to outline the Palaeozoic (basement) geology of the Swan Hill region and the associated map the first to give an overall interpretation of the Palaeozoic geology at 1:250 000 scale. Previous work has concentrated on the Cainozoic Murray Basin cover sequences. The oldest rocks interpreted are Cambrian ocean floor basalts of the Dja Dja Wrung Supergroup, which are present along the major faults, particularly the Governor, Log Landing and Griminal faults. These basalts are overlain in the south and west by the Cambrian St Arnaud Group and the Ordovician Castlemaine Group, and in the northeast by the Ordovician Tueloga beds. All were probably deformed in the Benambran Orogeny. A major period of granite intrusion followed. The granites may have been dextrally strained whilst still plastic, giving the Lalbert Batholith its unusual magnetic pattern. If so, it is one of the few Bindian events recorded in western Victoria. In the Devonian, a second cycle of sedimentation took place northeast of the Governor Fault system. This was followed by Tabberabberan deformation and then by intrusion of granite at about 360 Ma. The subsequent Kanimblan Orogeny seems to only have affected the southern part of the Governor Fault system, the Lake Charm and associated faults. There is little direct evidence of further sedimentation on The SWAN HILL region until the Cainozoic, but it is possible that Permian sediments from the Numurkah Trough may be present, particularly in the east. About 120 basaltic plugs were intruded, but the surficial deposits associated with these were probably eroded to provide some of the detritus for the Late Jurassic to Early Cretaceous Otway Group. Eocene to Recent Murray Basin sediments cover almost the entire area. The sediments can be conveniently divided into four sequences. The oldest is the Eocene to Oligocene Olney Formation of the Renmark Group, which is entirely fluvial and contains abundant plant material. It is topped by the Mologa Surface, which may record a time of monsoonal weather patterns. Overlying this is the Oligocene to Miocene Murray Group, which includes the fluvial Calivil Formation and the marginal marine Geera Clay. Above this are the Late Miocene to Pliocene Bookpurnong beds, Parilla Sand and Shepparton Formation time equivalents recording the offshore marginal marine and onshore facies. All lie below the Karoonda Surface. The present cycle is all fluvial (Coonambidgal Formation), lacustrine (Blanchetown Clay and unnamed lunettes) or windblown sand (Woorinen Formation, Lowan Sand). Because of the depth of cover, most exploration has concentrated on the Murray Basin. Brown coal deposits are present in Olney Formation in the Kerang-Cohuna area, but they are covered by about 100 m of overburden and contain high levels of sulphur and ash. Both sheet and strand line style heavy mineral deposits are present, with one strand line deposit, at Wemen, having been mined. Traces of uranium are known in the Lake Boga Granite and may also be present around Lake Tyrrell. SWAN HILL - INTERPRETATION 3

1 Introduction The SWAN HILL1 region lies about 300 km north-northwest of Melbourne (Fig. 1). It is in the southern part of the Riverine Plains (Butler et al., 1973, Joyce et al., 2003), the flat expanses along the Murray River. The land is mainly used for cropping and grazing, with irrigation from the Murray River a significant water source. Apart from the area near the Murray River, the region has an extensive road network. This report is the first to outline the Palaeozoic (basement) geology of the region at 1:250 000 scale. The only previously published map of the Palaeozoic basement is the 1:1 million map in VandenBerg et al. (2000). The three outcrops of Palaeozoic rocks in the area interpreted are all of granite, and so provide little information about the stratigraphy and structure of the basement. Fortunately about 30 drill holes have penetrated to the basement and these provide a useful control on the interpretation and the depth of cover. The body of the text is largely an extended summary of the geological history of the region. Where supporting material is required, it is generally separated from the text body as extended figure captions, tables and appendices. Hopefully this format will make the report more user-friendly by allowing readers to access the text at different levels of detail and also by separating the observations from the inferences. 2 Previous work As shown in Table 2.1, the paucity of Palaeozoic outcrop has meant that almost all of the previous work has concentrated on the Cainozoic Murray Basin cover sequence. Much of this was on the hydrology and heavy mineral sands, although CRA also considered coal exploration as well. They also drilled several basaltic plugs looking for diamondiferous kimberlite. On COHUNA and KERANG there has been a small amount of exploration for gold, looking north of the Bendigo gold field. Exploration in the extensive Cainozoic cover sequence has lead to the discovery of several heavy mineral sand deposits, the most prominent of which are mentioned in Table 2.1. Much of the exploration history of these deposits is synthesised in Dickson (1999). Perhaps the most significant deposit in the region is at Wemen, where mining commenced in 2002, but was later stopped because of metallurgical problems. In a more recent release to the Australian Stock Exchange, Reliance Mining (2005) announced the discovery of a strand line HMS deposit near Meering West (about 25 km southwest of Kerang) which included intersections containing up to 2.1% of coarse heavy minerals with a suite of 12% rutile, 19% zircon, 19% ilmenite, and 25% leucoxene. Table 2.2 outlines the airborne geophysical surveys. The gravity station coverage in the Victorian part of the region is nominally 1.5 km, although this declines close to the Murray River where access is poor. In New South Wales, the coverage is nominally 11 km, although there are several detailed traverses in the general area of the Numurkah Trough. Images of the data are included as Figures 2, 3, 4 and 5. In 2004, the GSV released most of the available data on the Murray Basin on two CDs. These are obtained through 1 Spring Street Melbourne (phone 136 186, email [email protected]) or through the Minerals and Petroleum Online Store at www.dpi.vic.gov.au/minpet.

1 All 1:250 000 map sheet areas in this report are in CAPITALS. All 1:100 000 map sheet areas are in SMALL CAPITALS. The term ‘SWAN HILL region’ used in this report means the SWAN HILL, COHUNA, ROBINVALE, WEIMBY and the southwestern quadrant of the MATHOURA map sheet areas. 4 SWAN HILL - INTERPRETATION

Table 2.1 Signiﬁ cant public domain reports over the SWAN HILL region at 1 January 2005 Who Principal contribution(s) REGIONAL GEOLOGICAL Butler et al., (1973) Geomorphic map of Murray Basin and surrounds Lawrence (1974)a First map of SWAN HILL Lawrence (1974)b First map of parts of BALRANALD and DENILIQUIN Lawrence (1975) Described the hydrogeology of the region; first compilation of drill holes intersecting basement Nott (1989) Summarised deep drilling for hydrological assessment of the Mallee/Wimmera region Brown and Stephenson (1991) Major compilation of the Murray Basin O’Rorke et al., (1992) Mapped hydrogeology on SWAN HILL, with particular reference to the Murray Basin Williams & Woolley (1992) Mapped hydrogeology on DENILIQUIN, with particular reference to the Murray Basin Kellett (1994) Mapped hydrogeology on BALRANALD, with particular reference to the Murray Basin VandenBerg et al., (2000) First regional interpretation of the basement geology MINERAL EXPLORATION Macumber (1969) Described Parilla Sand west of Kerang containing a 1 m thick heavy mineral band Tioxide Australia - Austiex JV (1977) Discovered coarse heavy mineral deposit on the Tyrrell Ridge Allnutt (1988), CRA Exploration (1990) Exploration for gold, heavy mineral sands, coal, diamond. Discovered the Goschen group of fine grained heavy mineral sand deposits Bush et al., (1995) Summarised previous exploration history Brown et al., (1995) Summarised exploration history for coal RZM & Aberfoyle Resources (1995), (Mason, 1999) Discovered the Wemen coarse heavy mineral sand deposit Macpherson (1999) RGC discovered the Woornack coarse heavy mineral sand deposit Zephyr Minerals/ WMC/ Ashburton Minerals Basement aircore drilling apparently along strike from Bendigo GeoScience Victoria (2004) Compiled all Murray Basin heavy mineral sand drilling data onto a CD Reliance Mining (2005) Discovered a strand line HMS deposit near Meering West SWAN HILL - INTERPRETATION 5

Table 2.2 Public domain airborne geophysical surveys over the SWAN HILL region at 1 January 2005 GSV Year Name Type Client Contractor Line spacing Magnetometer Line km SurveyNo. (m) terrain clearance: sample spacing

371 1974 Deniliquin - Magnetic/ BMR BMR 3000 460:n/a 6100 Jerilderie Radiometric 191 1980 Kerang B Magnetic/ CRA Exploration Geometrics 250 80:50 43 600 Radiometric 197 1981 Balranald Magnetic/ BMR BMR 3000 150:55 5735 Radiometric

220 1981 Swan Hill Magnetic/ BMR BMR 3000 150:55 5740 Radiometric 377 1988 Deniliquin -Hay- Magnetic/ BMR/NSWGS BMR 3000 150:55 48 720 Narrandera- Radiometric Jerilderie 3019 1994 Mildura Magnetic/ GSV World 400 80:7 49 561 Radiometric Geoscience 3020 1994 Horsham Magnetic/ GSV Kevron 200, 400 80:7 73 755 Radiometric 2003 Murray-Riverina Magnetic/ NSW DMR Fugro 400 60:7 160 500 Radiometric/ Digital elevation

3 Regional Interpretation 3.1 Introduction The Palaeozoic geology of the region is summarised in Figures 6 and 7. The surface geology is summarised in VandenBerg (1997a and b). The paucity of Palaeozoic outcrop has meant that almost all of the previous work has concentrated on the Cainozoic Murray Basin cover sequence, with only minor interest directed at the Palaeozoic basement. 3.2 Cambrian to Ordovician seaﬂ oor formation and sedimentation The oldest rocks interpreted are slivers of Cambrian ocean floor basalt of the Dja Dja Wrung Supergroup (VandenBerg et al., 2000), which are present along major faults (Figs 6, 7, 8). Near granites, these basalts are more magnetic, apparently due to contact metamorphic effects. Most basalt is concentrated along the Mount William and Governor faults, but some responses are along the Log Landing and Griminal faults in southern New South Wales (Figs 6, 7, 12). In Victoria, faults with ocean-floor rocks in the hanging wall are major structures since the rocks must have come from several kilometres depth; similar faults in New South Wales may also be regionally significant. The basalts along the Mount William Fault are apparently conformably overlain by the Middle Cambrian Knowsley East Shale, which provides a minimum age for the basalt (VandenBerg et al., 2000). Chert and black shale may lie above the basalt, but neither have been seen in outcrop or intersected in drilling. Perhaps the most likely place where they might be found is in the hangingwall of the Avoca Fault, where St Arnaud Group unit b has been interpreted. Metamorphosed turbidites are the dominant basement lithology interpreted throughout the region. In Victoria these seem to be mostly very weakly to non-magnetic. By contrast, in southern New South Wales most of the metaturbidites interpreted have a distinct 1-2 nT response (Figs 2, 9). Possible reasons for the difference include the much more recent (and hence better quality) data in New South Wales (Table 2.2), different processing streams and a slight change of facies across the border. The rocks west of the Avoca Fault also generally seem to be more magnetic than those further east. This is not a data problem or related to the depth of cover. Newer and more detailed surveys over outcrops on BENDIGO show little response compared to older surveys in the west of the region that have some 200 m of cover over the Palaeozoic basement. There are three areas where the magnetic responses are much stronger. In the southwest, between the Tyrrell and Percydale faults, a linear belt of rocks with responses of 10 nT can be correlated with similar features to the south, on ST ARNAUD. As on ST ARNAUD, the package has been labelled εaδ (Moore, 2004). A second package, near the Avoca Fault, has been similarly labelled, although the correlation is not as strong. This area has responses to 50 nT where outside the aureole of the Lake Boga Granite 6 SWAN HILL - INTERPRETATION

and to 70 nT inside it. Both packages are presumed to be pyrrhotite-rich mudstones similar to those on DUNOLLY (Whitehead, 1995). Two other moderately magnetic units (Otb and Otg) are part of the Tueloga beds (Ot) in New South Wales. These are interpreted as metasediments. Unit Otb is positively magnetised, whilst Otg is reversely magnetised. It is possible that the two are the same unit but differently orientated and with different responses caused by the effects of remanence. Both show responses varying as much as 30 nT from the regional background. Similar responses are present in northern HORSHAM, where VIMP 14 intersected nonmagnetic altered and deformed metasediments (Maher et al., 1997). Subsequent drilling by MPI Mines Ltd intersected a small lens of basalt, but the known length of this lens is significantly less than that required to account for the remanently magnetised body. Leviathan Resources Ltd. (2004, 2005) attributed part of the response to the surrounding chlorite-altered black mudstone, suggesting the unit intersected in VIMP 14 may correlate with the sulphide-rich black mudstone of the Albion Formation of Squire and Wilson (2005). Thus the remanently magnetised unit on HORSHAM may well be sedimentary and, by inference, the units Obt and Otg are interpreted as sedimentary too. 3.3 The Benambran Orogeny Until recently, the entire sedimentary pile east of the Moyston Fault has been considered to have been deformed in the Benambran Orogeny. Some workers (e.g. VandenBerg 1999) in the Stawell Zone considered the deformation to be episodic – about 455 to 440 Ma in the west and perhaps 20 million years younger east of the Avoca Fault. Foster et al. (1999) argued that the deformation across the region was more or less continuous. However more recent age dates by Miller et al. (2004) show that the first deformation in the westernmost parts (the Moornambool Metamorphic Complex) was largely complete by the end of the Delamerian Orogeny (490 Ma). This raises doubts on the ages of the major deformation of many of the outcropping rocks further east and so the timing of deformation under cover to the north is even less certain. Because of the uncertainties in the boundary and the likelihood that much of the deformation took place between 455 and 440 Ma, the term Benambran has been used throughout. In most of the southern parts of the region, the metaturbidites generally trend about 350º, like most of the St Arnaud Group in western Victoria (Figs 2, 6). Near the Governor Fault system2 (section 3.6) the rocks of the Castlemaine and St Arnaud groups swing into the plane of the faults and so trend about 320˚to 340˚. Further to the north west of the area interpreted, the St Arnaud Group rocks tend to swing to 005˚, and further north, on BOOLIGAL, the rocks along strike from the St Arnaud Group trend at about 090˚ (Fig. 10). East of the Griminal Fault the Tueloga beds (Ot) also trend at about 005˚. The reasons for the variations of strike are not clear. Some of them may well be due to oblique slip in the Governor Fault system, but other causes may also be present. The Durham Ox High3 may also be involved. Most of the unexplained variation lies in New South Wales and it is perhaps more likely that the answers also lie there.

Table 3.1 Age determinations on intrusions of the Lalbert Batholith on CHARLTON Intrusion Age (Ma) Method By Hemsleys 400±6 K/Ar on Richards & Granite biotite Singleton (1981) Wycheproof 399±8 K/Ar on Richards & Granite muscovite Singleton (1981) Wycheproof 405±8 K/Ar on Bowen (1975), Granite muscovite McKenzie et al., (1984) Wycheproof 407±6 K/Ar on McKenzie et al., Granite muscovite (1984)

2 The term Governor Fault system has been used to include the Governor Fault, the Lake Charm Fault and the linking faults between them (Figs 6, 7).

3 The Durham Ox High is a region of raised magnetic and gravity response in northern Victoria and southern New South Wales, perhaps caused by duplexing of the ocean floor basalts which underlie the turbidite sequence; (Moore, 2004). SWAN HILL - INTERPRETATION 7

3.4 Early Devonian granites The basement to the south central part of the region is almost entirely granites of the Lalbert Batholith (Fig. 11). Several of these have been assigned different names; other discrete intrusions may also be present but are so far unrecognised. None of the intrusions crop out in the area interpreted, but several have been intersected in drilling and other similar intrusions crop out to the south, on CHARLTON (Bibby & Moore, 1998). By analogy with these and other outcropping granites well west of the Avoca Fault and east of the Moyston Fault, all are likely to have been intruded at about 400 to 410 Ma (Table 3.1). Most are zoned and have magnetic phases with responses to at least 100 nT, implying they are oxidised and probably I-types. Often the inner parts are nonmagnetic, implying fractionation has progressed far enough that all the available Fe2+ can be accommodated in biotite and hornblende crystal lattices. Unlike most areas of the granite, the Lalbert Batholith seems to have little effect on the Bouguer Gravity response compared to its size (compare Figs 3 and 6). Possible reasons for this include: • Although it covers a large area, the batholith is very thin, • The intrusions might be more mafic than most granitic rocks, • The Durham Ox High, and • Significant amounts of Cambrian metavolcanics have been brought closer to the surface along the Avoca Fault. The Loddon Vale Granite (G320) lies in the southeastern corner of SWAN HILL (Figs 2, 5). Although it does not crop out, White and Chappell (1988) considered it to be part of the Mount Cole Suite on the basis of its magnetic character. These granites have a distinctive peraluminous, high-Na chemistry and often contain hornblende, sphene and allanite or monazite (White and Chappell 1988). The magnetic granites form a strong alignment at about 020° and this alignment of magnetic granites continues northwards across the Governor Fault system into New South Wales. If these northern granites were of the Mount Cole Suite, it would place a significant constraint on the movement of the Governor Fault system. All the age dates so far in outcropping Mount Cole Suite intrusions cluster at about 400 Ma or slightly older and so any significant movement on the Governor Fault that diverged from 020° would have to predate this. A prominent feature of the Lalbert Batholith is the apparent dextral shear sense shown by the Narraport pluton (G607, see Fig. 11). This shear sense is not apparent in the surrounding sedimentary rocks, but may reflect movements on faults at the time of intrusion of the pluton. If so, it implies faulting slightly older than 400 Ma, coeval with the end of the Bindian Orogeny in eastern Victoria. If this is so, it represents one of few examples of Bindian movement west of the Governor Fault. 3.5 Devonian sedimentary rocks A well-defined nonmagnetic sedimentary sequence is interpreted north of the Governor Fault on DENILIQUIN (Fig. 12). These rocks clearly sit unconformably above the magnetic Tueloga beds, and have been contact metamorphosed by the Perricoota pluton (G659). This intrusion is considered to be Late Devonian (Fig. 6), giving a younger age limit to the nonmagnetic sedimentary rocks. It is possible that at least some of the sequence is derived from erosion of rocks in the hangingwall of the Governor Fault. On BALRANALD, the equivalent sequence (about 500 m below the surface) seems to be weakly magnetic, with responses to 10 nT (Fig. 8). These weakly magnetic rocks seem to cover some interpreted granites, but not others, placing them in a similar stratigraphic position to those to the south east. Just north-east of the area interpreted, Brown and Stephenson (1991) recorded that Balranald 1 bottomed in Devonian sedimentary rocks. Tol Tol 2 (about 7 km southeast of Robinvale) is the only drill hole in the Victorian part of the region that has been logged as intersecting Devonian rocks (Nott, 1986). Examining thin sections show that even these rocks seem to have undergone basal greenschist metamorphism, suggesting they are somewhat older than initially logged and are more likely to be part of the St Arnaud Group. 3.6 The Tabberabberan Orogeny The Tabberabberan Orogeny is the only deformational event to have effected the entire Tasman Fold Belt (Coney et al., 1990). In areas to the southeast, the Governor Fault separates the Melbourne Zone, which was only deformed in the Tabberabberan Orogeny, from the Tabberabbera Zone, where Benambran and 8 SWAN HILL - INTERPRETATION

Bindian deformation also took place. Tabberabberan deformation is significant in the Melbourne Zone but not at all obvious in regions to the west. As described in section 3.3, there are significant strike variations across the SWAN HILL region, quite dissimilar to the outcropping areas of the Stawell and Bendigo zones. Some of this may have taken place in the Benambran Orogeny, but some may also have taken place in the Tabberabberan. Whilst much of the deformation recorded in the Melbourne Zone seems to be from east-west compression (e.g. Fig. 3.39 in VandenBerg et al., 2000), the fault pattern mapped near the southern boundary of SWAN HILL is consistent with a strong north-south component as well. In the northern outcrops of the Melbourne Zone, north-south compression is more obvious, with east-west fold axes common. On WANGARATTA, seismic sections of the Numurkah Trough show the Governor Fault as dipping shallowly north (VandenBerg et al., 2000, Wong, 2001). It seems unlikely that the Governor Fault system, with significant north-south movement to the east of the Mount William Fault, could be completely absent west of the Mount William Fault. Where was the north-south strain taken up?

Table 3.2 Age determinations on the granites on SWAN HILL Granite Number Age Method On Reference (Ma) Lake Boga G321 356±5 K/Ar Biotite Richards & Singleton 1981 349±6 K/Ar Biotite 358±6 K/Ar Biotite 357±6 K/Ar Muscovite 363±6 K/Ar Muscovite 362±6 K/Ar Muscovite 358±5 Preferred age 360±7 Muscovite Bowen 1975, 366±7 Muscovite McKenzie et al., 1984 Pyramid Hill G295 360±5 K/Ar Muscovite Richards & Singleton 1981 368±3 Rb/Sr Whole rock 367±4 Rb/Sr Whole rock, Muscovite 368±2 K/Ar Whole rock, Muscovite 362±5 K/Ar Biotite, Muscovite 361±3 Preferred age 372±6 K/Ar Biotite, Bowen 1975 Muscovite McKenzie et al., 1984

One possibility is that the Mount William Fault has taken up the strain and continues into New South Wales. This seems unlikely since the distinctive magnetic Cambrian Heathcote metavolcanic package, which sits in the immediate hangingwall of the Mount William Fault, swings west and is interpreted to be truncated by the Governor Fault (Figs 8, 10). It is even possible that some of the Tabberabberan north-south strain on the region may have given rise to the antiformal stack in the Heathcote Volcanic Group (the southern edge of Fig. 10 and in Edwards et al., 2001). The amount of north-south shortening accommodated by the antiformal stack could be as much as 17 km. If so, it would indicate a similar amount of north-south strain taken up west of the Heathcote Volcanic Group. Another possibility is that all the strain has been taken up along small-scale displacements. As described above, some of this has probably happened, notably along the Heathcote Volcanic Group and perhaps even as far south as WEDDERBURN (Moore 2004). However this does not explain the changes in strike direction that seem to characterise the area where the Governor Fault might be expected to pass through. SWAN HILL - INTERPRETATION 9

Nor does it explain why the strikes continue to rotate clockwise further north, until on BOOLIGAL they seem to trend about 090° (Fig. 10). This gives the magnetic and gravity data in southern New South Wales a distinctly concentric pattern. A variation on the two previous possibilities is that much of the strain has been taken up along the Governor Fault and then the Log Landing and Griminal faults. Again this is possible, as both seem to be significant faults since they are interpreted to have slivers of ocean floor basaltic rocks in the hangingwalls. Both are interpreted to have had complex movement histories. As well, both seem to extend well north of the interpreted area, implying some capacity to be able to transmit the requisite amounts of strain. However neither seem to cut the east-west-striking layers on BOOLIGAL, suggesting that this is at best only a partial explanation. Since both the magnetic and Bouguer gravity data show this concentric pattern, it implies that the rocks in the region also show this pattern, wrapping around a pre-existing core that has later been disrupted along the Bearii Fault (Fig. 10). This seems to imply that the semicircular pattern had been established before the Tabberabberan Orogeny, since almost all regions in southern Australia were deformed at least once before then4. In the Tabberabberan Orogeny, the subcircular block is interpreted to have moved south and collided with the Selwyn Block, (the northward continuation of western Tasmanian geology beneath the Melbourne Zone, see Cayley et al., 2002) and the less well cratonised basement to the west. In the Bendigo Zone, the strain was mostly taken up between the Governor and Lake Charm faults (Figs 6, 7). West and north along this system, the movement direction became closer to strike-slip and so more difficult to discern from the magnetic and gravity data. This suggestion seems to satisfy the observed facts, both at the local and regional scales, and partly returns to Scheibner’s (1985) suggestion of a thin plate of continental crust between the Curnamona Craton and southern Victoria. 3.7 Tabberabberan granites There are only three outcrops of Palaeozoic rock in the region. These are of the Lake Boga (G321) and Pyramid Hill (G295) granites. All are of highly fractionated rocks, consistent with observations elsewhere in western Victoria that the most fractionated parts of granites are most likely to crop out (e.g. VandenBerg et al., 2000). The Lake Boga Granite is sufficiently fractionated to contain anomalous amounts of uranium although the thorium radiometric response is barely above the local background of the adjacent alluvium (Thomas 1958, Chambers 1958). Both intrusions yielded age dates of about 360 Ma (Table 3.2), which places them amongst the youngest Palaeozoic intrusions known in Victoria. Although they are nonmagnetic, they may still be I-types, since the many I-type intrusions in the adjacent Melbourne Basement Terrane are similarly nonmagnetic. The outcrops are strongly fractionated, and so are more difficult to classify. Both the Perricoota (G659) and Social Bend (G658) plutons lie in the hangingwall of the Governor Fault system. As described above, the Perricoota pluton is interpreted to have intruded Devonian sediments. The Social Bend pluton seems to postdate the Governor Fault itself, consistent with a Late Devonian age. Both intrusions are nonmagnetic, like others that have probably been derived from within the Selwyn Block. 3.8 Kanimblan deformation Both the Lake Boga and Pyramid Hill granites have been cut by north-west trending faults with apparent displacements of about 1 km (Fig. 6). Since these movements postdate the granites and seem to be older than formation of the Murray Basin, they have tentatively been given a Kanimblan (350 to 325 Ma) age. Because the faults were relatively easy to trace in the magnetic data, they were particularly helpful in defining parts of the Lake Charm Fault, the southwestern edge of the Governor Fault system. As the Governor Fault is stitched by the Social Bend pluton and the Lake Charm Fault cuts the Pyramid Hill Granite, the leading edge of the Governor Fault system is interpreted to have moved southwards at this time (Fig. 8). In eastern Victoria, movements elsewhere along the Governor Fault show that east-west stress caused sinistral deformation in the Upper Devonian-Carboniferous basins of the Howitt Province. In the area

4 The only exceptions known are the Melbourne Zone, underlain by the Selwyn Block, and eastern Tasmania, which may also be underlain by Precambrian crust (Drummond et al., 2000). 10 SWAN HILL - INTERPRETATION

mapped, the strain direction is less obvious, with apparent sinistral, dextral and vertical movements all present along the contact of the Pyramid Hill Granite. 3.9 Permo-Carboniferous sedimentation Although no Permo-Carboniferous sediments are recorded in the area interpreted, it is possible that some are present. The outlined area of the Numurkah Trough lies just east of the area, but its western edge is poorly constrained. The 250 µmms-2 gravity low associated with the Pericoota pluton is probably partly due to younger sediments overlying the less fractionated (and more easily eroded) outer parts of the pluton (VandenBerg et al., 2000). On BENDIGO, the outcrops of Permo-Carboniferous sediments are weakly lithified periglacial units (Bowen & Thomas 1976). Tickell (1977) and O’Brien et al., (2003) describe these sediments as having been deposited in periglacial environments. O’Brien et al. (2003) gave an age range from Auselian to Samarkian (298 to 283 Ma). O’Brien et al. (2003) also discounted the possibility of the sediments containing coaly units, as do sediments of the Oaklands Basin to the east. These periglacial sediments would be particularly difficult to recognise in drill cuttings, and it is possible that some holes on SWAN HILL previously considered to have intersected basement or overlying Olney Formation may have intersected Permo-Carboniferous rocks. Meering 12 bottomed in white to pale green mudstone and granite. The magnetic and gravity responses do not support the proposition that the granite was in situ, but it may have been a Permian erratic in a periglacial sequence. 3.10 Mesozoic volcanism About 120 subcircular bodies with magnetic responses to 200 nT are interpreted to be from bodies in the basement below the Murray Basin sediments. Only two of these on SWAN HILL have been drilled by CRA Exploration, intersecting basaltic volcanic rocks, but other drill holes on HORSHAM and ST ARNAUD have intersected similar rocks. Moore (2004) correlated those on ST ARNAUD to the volcaniclastic sediments in the Otway Basin, implying an Upper Jurassic or Cretaceous minimum age. Somewhat more mafic rocks are also known from subsurface exposures at Bendigo; K/Ar dates by McDougall and Wellman (1976) gave ages of 146±4 Ma and 155±4 Ma. Brown and Stephenson (1991) gave Late Cretaceous ages for the few mafic volcaniclastic rocks preserved in the Renmark and Wentworth Troughs. If Moore’s (2004) correlation is correct, the comparative lack of volcaniclastic rocks below the Murray Basin might be explained by a gentle regional southwards gradient, which allowed the volcanic detritus to be carried south into the Otway Basin. This gradient could have been caused by extension as the Australian–Antarctic break-up took place (Norvick & Smith, 2001). 3.11 Palaeocene to Recent – the Murray Basin The Murray Basin covers virtually the entire region. In the area interpreted this post-cratonic sequence is dominantly non-marine, although marine incursions took place in the Late Miocene, probably also in the Middle Miocene and perhaps in the Early Oligocene as well. The basin is characterised by slow subsidence rates, minimal compaction and hence slow sedimentation rates. The stratigraphy and boundary relationships are summarised in Table 3.5 and Figure 13. Holdgate (2003) drew a section about 30 km south of the Murray River which showed a maximum thickness of about 400 m, while O’Rorke et al. (1992) showed a maximum thickness of over 350 m just east of the Tyrrell Fault. The oldest unit recorded in the basin is the Warina Formation, an arkosic sand deposit from a braided stream environment. Whilst this has not been noted on SWAN HILL, it may be present in the valleys of the Loddon and Avoca rivers. Several bore holes bottomed in ‘granite’ (e.g. Bael Bael 3, Meran 23), but neither the magnetic nor the gravity data support this interpretation. An alternative is that the holes bottomed in arkosic sand derived from the Wedderburn Granite or the Lalbert Batholith and that this sand lies at the same stratigraphic level as the Warina Formation. The oldest unit logged in the region is the Oligocene to Eocene Olney Formation, a fluvial to lacustrine and paralic siltstone to claystone (Lawrence and Abele 1988). Drilling by CRA Exploration encountered a major brown coal resource within the Olney Formation in the Kerang-Cohuna area, with seams up to 40 m thick (Table 3.3), but the seams had unacceptably high ash and sulphur contents and the deposits had at least 100 m of overburden. Other coal deposits were found in the Torrumbarry-Tandarra and Echuca areas. SWAN HILL - INTERPRETATION 11

Figure 13 shows the Olney Formation has a roughly constant thickness of 100±25 m over the 90 km between drill holes Tyntynder North 1 and Kerang 4. By contrast, the overlying Murray Group and lateral equivalents vary between 40 m and 160 m, generally thickening to the west. One way of interpreting this is that the Norval Regolith at the top of the Olney Formation was relatively flat and that many of the thickness variations in the overlying Murray Group are due to syn-depositional or post-depositional faulting in the region. This fits with the observations of Brown et al. (1995) that the Olney Formation coals must have been deposited on a flat surface and that many of the contacts of this formation with the overlying Calivil Formation are erosional. Brown & Stephenson (1991) believed that the 100 m of Geera Clay in drill hole Piangil West 2 was mostly deposited in a marginal marine environment, but included intertidal flat and estuarine deposits. Holdgate’s (2003) section showed about 10 m of ‘Middle Renmark Group’ just below this. To the southeast, Tyntynder North 1 showed similar stratigraphy and slightly thicker Geera Clay, but Tyntynder West 2 (only 9 km further southeast) showed the Geera Clay as interfingering with lateral equivalents of the Calivil Group. This fits well with Vail et al.’s (1977) sea level curves that predict flooding at this time. Similarly the lacuna at the top of the Geera Clay-Calivil Formation coincides with a lowering sea level.

Table 3.3 Kerang-Cohuna brown coal resource Resource at 10 m thickness cut-off 12 Bt Resource at 5 m thickness cut-off 20 Bt Moisture 56% Ash 10.8% Sulphur (dry basis) 1.5% Specific energy (net wet) 8.9 MJ/kg Oil yield (6 Fischer assays) 95 L/t

From Brown et al., 1995

If the Geera Clay is the marginal marine equivalent of the sand and gravel of the Calivil Formation, it implies a strong sorting between the grain sizes of the two units. Some authors (e.g. Cherry & Wilkinson, 1994) have argued that the Calivil Formation was deposited as a result of strong uplift, but this would not have allowed the sorting to have taken place. It seems more likely that intense weathering caused the regolith to form on the Mologa Surface, perhaps in a monsoonal environment. The outcropping Palaeozoic rocks were mostly weathered into the clay that formed the Geera Clay, but the quartz vein material survived as the sand and cobbles of the Calivil Formation. Gentle uplift allowed the fines to be winnowed out whilst the coarser material was washed only as far as the water courses. This would also account for the abnormally high volume of clay when compared to the coarser facies, which would normally be the thicker sequence (Fig. 13).

Table 3.4 Heavy mineral sand resources in the SWAN HILL region Name Tonnes Grade % Rutile Zircon Ilmenite Data from (Mt) HMS % % % Kulwin 24 11.5 16.7 10.1 30.8 Macpherson (1999) Wornack- 40.5 9.3 17.8 9.3 29.7 Macpherson (1999) Rownack Wemen 9.16 5 28 12 44 Mason (1999)

The marine Bookpurnong beds, paralic Parilla Sand and part of the fluvial Shepparton Formation group together as sequence equivalents within the Whungnu Group. As such, they record another flooding event. However, unlike the lacuna at the top of the Geera Clay and the Calivil Formation, the upper parts of the sequence have mostly been preserved. 12 SWAN HILL - INTERPRETATION

The Parilla Sand is host to the main economic interest in the region, the heavy mineral sands. Perhaps the most significant deposit found so far is that at Wemen, which was briefly mined. Mining stopped because of metallurgical problems with clay. The arcuate foredunes of the Parilla Sand are prominent in the southwest, where they host the heavy mineral sand deposits of the Tyrrell Ridge and the Kulwin-Boorongie-Ronack-Wornack group (Fig. 14). Also present are the Birne, Goschen North, Goschen Central and Goschen South WIM or sheet style deposits. Although the sheet style deposits are considered to have formed offshore, and so to the west of the strandline deposits, several sheet style deposits are present east of the easternmost mineralised strandline. Furthermore, the easternmost outcrops of Parilla Sand (near Leaghur) show none of the characteristic arcuate ridge topography of the Parilla Sand outcrops to the west. This suggests that the topmost parts of the Parilla Sand have been eroded away since deposition. Erosion would not be unexpected, since on HORSHAM and ST ARNAUD there is strong evidence of both syn-depositional and post-depositional movement in the basin (Moore, 1996, 2004). Despite this erosion, not all the strand line deposits have been lost. In a release to the Australian Stock Exchange, Reliance Mining (2005) announced the discovery of a strand line HMS deposit near Meering West (about 25 km southwest of Kerang) which included intersections of up to 2.1% of coarse heavy minerals with a suite of 12% rutile, 19% zircon, 19% ilmenite, and 25% leucoxene. The most recent depositional cycle has been entirely terrestrial. It includes the Blanchetown Clay (the sediments deposited in Lake Bungunnia), the Recent fluvial sediments of the Coonambidgal Formation, and the windblown deposits of the Woorinen Formation and Lowan Sand. Along the lower part of the Avoca River near Leaghur, the Coonambidgal Formation is clearly lower than the nearby Parilla Sand (Fig. 15), consistent with erosion in response to the Kosciuszko Uplift (Sandiford, 2003). Thus the Leaghur Fault may not exist, since the main lines of evidence for its existence can be interpreted in other ways. This is not to deny the existence of recent fault movements elsewhere in the region. In particular, the Tyrrell Fault seems to have moved. Lake Tyrrell, immediately on its eastern side, is some 10 m below the height of the Murray River and forms the lowest part of the region studied. It is also about 10 m below the floor of Lake Bungunnia which otherwise is quite flat, the only other features being lunettes and later dunes. As well, the base levels for the Parilla Sand dunes are about 10 m higher in the south than where they are covered by later sediments further north. SWAN HILL - INTERPRETATION 13 Tyrrell along the Figures 4, 5, 11; Murray River Murray River Figures 4, 5 Lake Tyrrell Murray River Figures 4, 5, 14, 15; HILL southwest of SWAN Figures 4, 5, 14 Loddon River valley of Kerang West Southeast of Kerang Loddon River Valley Radiometric response Typical example Often high K, Th, especially when sourced from K- or Th- enriched rocks lowVery Patchy low response from K, Th Low south of the Figures 4, 5, 11; LowTh high where subsequently lateratised or where mineralised north of Figures 4, 5, 11; Figures 4, 5, east of the 1 nT Low east of Lake Figures 4, 5, 11; ≤ response Typically response response response response No detectable response response No detectable response Minor magnetic highs correlate with topographic lows response channels have responses to 15 nT lakes Fills low areas covered by Lake Bungunnia Dendritic river channels draining north; fills broad lows Upper surface broad convex-west arcuate ridges In palaeotopographic lowsIn palaeotopographic lows No detectable Minor areas where Karoonda Surface Mologa Surface, Norval Regolith . (2004). et al Conformably overlies other units Arcuate ridges on the lee sides of Conformably overlies other units Fills active river valleysConformably overlies other units No detectable Convex-west arcuate dunes No detectable Sequence equivalent of Bookpurnong beds and Shepparton Fm and Parilla Sand Offshore equivalent of Calivil FmUnconformable on Palaeozoic basement, upper contact erosional No detectable contact conformable Onshore sequence equivalent of Parilla Sand south blown sand sand and silt sand dunes nonmarine clay fluvial to paralic silt, clay; minor lignite shoestring sand Nonmarine Fluvial sand and mud, coarsening to the Coonambidgal Fm Fluvial mud and Lowan Sand FmWoorinen sand Wind-blown Conformably overlies other units sand Wind-blown Irregular to subparabolic dunesParilla Sand No detectable Marginal marine Bookpurnong beds Marine mud Sequence equivalent of Shepparton Fm Geera Clay Marine to Formation?Warina Arkosic sand Underlies the Olney Formation No detectable Shepparton Fm Fluvial mud and and ‘Middle Renmark Group’ Renmark Olney Formation Carbonaceous Murray Calivil Formation Quaternary Lunettes of wind- Table 3.5 Stratigraphy of the Cainozoic rocks in the SWAN HILL region HILL 3.5 Stratigraphy of the Cainozoic rocks in SWAN Table Age Group Formation Lithologies Boundary relationships Topography Magnetic Eocene to Palaeocene PliocenePliocene to Late WunghnuMiocene Blanchetown Clay Lacustrine clay Basal contact partly erosional; upper Miocene to Late Eocene Data mostly from Brown & Stephenson (1991), Holdgate (2003) and 14 SWAN HILL - INTERPRETATION

4 Conclusions The region has seen three major episodes of sedimentation and two major episodes of deformation and granite intrusion. The oldest sediments interpreted were deposited directly on the Cambrian oceanic crust inferred to underlie the entire area, but which is only seen as isolated fragments along the Governor Fault. Both Cambrian and Ordovician metaturbidites are present. There is no clear break between the two, but from the evidence on ST ARNAUD, the magnetic rocks have been inferred to be from the St Arnaud Group whilst the nonmagnetic rocks east of the Avoca Fault are considered to be from the Castlemaine Group. The equivalent rocks north of the Governor Fault are consistently magnetic and so perhaps contain slightly more pyrrhotite than those that crop out in the Bendigo and Stawell Zones. They have been separated out into a new unit, the Tueloga beds. The entire region was deformed in various phases of the Benambran Orogeny, after which there was a major period of granite intrusion at about 400 to 410 Ma. Neither is known to have given rise to any economic mineralisation on SWAN HILL, but exploration has been minimal due to the depth of cover. The second sedimentary package is probably Devonian, since it is younger than the Benambran deformation and older than the 360 Ma granites. It is nonmagnetic and has only been interpreted north of the Governor Fault. Drilling near the SWAN HILL region also intersected Devonian sedimentary rocks. This was followed by the Tabberabberan Orogeny and intrusion of the late Devonian granites. The deformation was probably largely restricted to the Governor Fault system, since the older rocks had been cratonised by previous events. The 360 Ma granites stitch the Governor Fault itself, but are cut by other faults further south, implying that the locus of movement on the system had moved south by the Kanimblan Orogeny. The Lake Boga Granite contains the only potentially economic Palaeozoic mineralisation known in the area, traces of uranium (Thomas, 1958; Chambers, 1958). There are few deposits recording the geological history from the Carboniferous to the Eocene. Thin Permo-Carboniferous sediments of the Numurkah Trough may be present, but have not been recorded. About 120 ?Jurassic plugs have been interpreted, but much of the surficial deposits erupted now probably form the sediments of the Otway Group. The third significant sedimentary cycle formed the Cainozoic Murray Basin. This is largely nonmarine on SWAN HILL, but includes marginal marine deposits in the Geera Clay and the Parilla Sand. Sedimentation seems to have been controlled by a subtle combination of tectonic activity and changes in sea levels. The Olney Formation has been prospected for brown coal, the Parilla Sand contains potentially economic concentrations of heavy minerals and uranium seems to be leaching into Lake Tyrrell. SWAN HILL - INTERPRETATION 15

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VANDENBERG, A.H.M., WILLMAN, C.E., MAHER, S., SIMONS, B.A., CAYLEY, R.A., TAYLOR, D.H., MORAND, V.J., MOORE, D.H. & RADOJKOVIC, A., 2000, The Tasman Fold Belt System in Victoria. Geology and mineralisation of Proterozoic to Carboniferous rocks. Geological Survey of Victoria Special Publication. Department of Natural Resources and Environment.

WHITE, A.J.R., & CHAPPELL, B.W. 1988. Granites. In Douglas, J.G. & Ferguson, J.A. eds., Geology of Victoria, pp. 427–439. Geological Society of Australia, Victorian Division, Melbourne.

WHITEHEAD, M.L. 1995. Geological interpretation of geophysical data over the Dunolly 1:100 000 sheet. Victorian Initiative for Minerals & Petroleum Report 7. Department of Agriculture, Energy & Minerals Victoria.

WILLIAMS, R.M & WOOLLEY, D., 1992. Deniliquin Hydrogeological map (1:250 000 scale). Australian Geological Survey Organisation and Department of Water Resources N.S.W.

WONG, D., 2001. A preliminary interpretation report on the MEMV96 seismic survey Murray Basin, Victoria, Australia. Department of Natural Resources and Environment. 18 SWAN HILL - INTERPRETATION

Appendix 1 Newly named units on SWAN HILL Solid red lines show the outlines of granites at the base of the Murray Basin. Dashed red lines imply deeper boundaries.

6036000N

6075000N

6032000N

6075000N 6070000N

6028000N

6065000N 6070000N E E E E E E 000 000 000 000 000 000 665 660 720 723 760 755 Benjeroop Granite (G656) Bourka pluton (G652) Cannie pluton (G655)

6040000N

6125000N

6035000N 6060000N

6100000N

6030000N 6055000N E E E E E E 000 000 000 000 000 000 715 710 675 650 770 765 Macorna Granite (G317) Manangatang Granite (G316) Meatian pluton (G650)

6070000N 6060000N

6075000N

6055000N 6060000N

6070000N E E 6050000N 000 000 680 675 6050000N Moah pluton (G651) E E E E E 000 000 000 000 000 760 765 770 700 710 Murnungin pluton (G649) Murrabit Granite (G657) SWAN HILL - INTERPRETATION 19

6125000N

6100000N

6040000N

6050000N

6075000N 6036000N

6025000N 6032000N

6050000N E E E E E E E 000 000 000 000 000 000 000 300 325 275 700 675 265 260 Percoota pluton (G659) Polisbet Granite (G319) Social Bend pluton (G658)

6050000N 6040000N

6080000N

6040000N 6030000N

6030000N 6020000N

6070000N E E E E 000 000 000 000 680 670 710 700 Toort pluton (G662) Towma pluton (G654) E E 000 000 770 780 Tueloga beds 6060000N

6060000N 6050000N

6050000N 6040000N E E E E 000 000 000 000 680 670 690 680 Tungie pluton (G663) Wortongie pluton (G653) 20 SWAN HILL - INTERPRETATION Part of the Lalbert Batholith On the northeastern edge of Lalbert Batholith Lalbert Batholith Intersected in Kerang 99 below 2 low in 2 in the 2 low 2 below regional 2 lower than 2 gravity high in the gravity high On the northeastern edge of 2 2 south and east Largely defines the regional 100 µm/s To surrounds in the north and west but less than 20 µm/s 10 µm/s A northeast, but a 50 µm/s the south 10 µm/s A About 10 µm/s the regional To 80 µm/s To Typically about 2 Typically but units may nT, may reach 30 nT; be remanently magnetised Granite; variably magnetic, to 80 nT Nonmagnetic about 5 µm/s Gravity low, Distinctly magnetically layered, with alternating nonmagnetic and magnetic (to 80 nT) layers Strongly magnetic, to 300 nT above surrounds Magnetic response to 150 nT but with nonmagnetic core Magnetic response shows strong zoning, with both nonmagnetic parts and other areas to 60 nT Mostly north of the Governor Fault System. Subsurface, mostly south and west of Manangatang southeast from Kerang for about 12 km An irregularly shaped intrusion about 10 km west of Meatian and about 35 km east of Sea Lake subcircular A intrusion about 4 km in diameter under the town intrusion about 6 km in diameter and about 5 km northeast of Sea Lake A 75km long A intrusion that extends from northwest of to Nyah West southeast of Sea Lake Station Manangatang, a town Macorna Parish Subsurface; Murnungin Parish Meatian, a minor town and parish Moah Parish subcircular A Polisbet Parish, which lies at the northern end of the Granite Name bedsTueloga Railway Tueloga Named after Distribution Magnetic response Gravity response Comments Manangatang Granite (G316) Macorna Granite (G317) Murnungin pluton (G649) Meatian pluton (G650) Moah pluton (G651) Polisbet Granite (G319) SWAN HILL - INTERPRETATION 21 On the northwestern edge of Lalbert Batholith On the eastern edge of Lalbert Batholith Part of the Lalbert Batholith below 2 low on a regional 2 lower than surrounds 2 2 Gravity low, approximately 50 Gravity low, µm/s gravity low 50 µm/s A surrounds 100 µm/s but Probably a weak low, obscured by more regional effects 10 µm/s A gradient Magnetic response to 150 nT but with nonmagnetic core Strongly magnetically zoned with an outer response to 150 nT above the surrounds and a nonmagnetic core Largely nonmagnetic but with outer rim to 100 nT Strongly magnetic (response to 300 nT) and shows distinct layering An 100 nT high, showing magnetic zoning elliptical intrusion about 5 km west of Quambatook intrusion about 5 km in diameter and about 5 km northwest of Sea Lake; a second smaller intrusion is grouped with this pluton crudely A elliptical 18x10 km intrusion about 10 km south east of Sea Lake elliptical intrusion about 15 km north of Birchip Aligned in the foliation of the Governor Fault system about 30 km north of Kerang Cannie Parish 5x14 km A Bourka Parish subcircular A Wortongie Parish Towma ParishTowma 6x17 km A Benjeroop Parish and Benjeroop 1 which intersected the granite Cannie pluton (G655) Name Bourka pluton (G652) Named after Distribution Magnetic response Gravity response Wortongie pluton (G653) Comments Towma pluton Towma (G654) Benjeroop Granite (G656) 22 SWAN HILL - INTERPRETATION Near the eastern edge of Lalbert Batholith Near the western edge of Lalbert Batholith higher than higher in the 2 2 low low on the edge of 1 Intersected in Murrabit West 2 2 gravity low, (is partly gravity low, 2 A 20 µm/s A About 60 µm/s A 20 µm/s A the Pericoota pluton caused by overlying Numurkah Trough surrounding plutons east than the west 150 µm/s About 20 µm/s Nonmagnetic, but has contact metamorphosed nearby mafic volcanic rocks Confused magnetic response, but generally high in the west and nonmagnetic in the east Mostly nonmagnetic, but with magnetic phase in the southeast to 50 nT nonmagnetic, but with magnetic contact metamorphic rim to moderately Weakly magnetic core (responses mostly less than 30 nT) surrounded by strongly magnetic rim (responses to 200 nT); Stiches the Governor Fault west of the Pericoota pluton; intrudes the Pericoota pluton about 10 km east of Cohuna shaped intrusion about 25 km southeast of Sea Lake foliation of the Governor fault system about 15 km northwest of Kerang North of the Governor Fault; largely overlain by the Numurkah Trough crudely A elliptical 24x15 km intrusion about 25 km northwest of Quambatook Social Bend, a locality on the Murray River ParishTungie An irregularly Murrabit Parish Aligned in the Pericoota State Forest which overlies much of the pluton parish, on Toort the western edge of the pluton Social Bend pluton (G658) pluton Tungie (G663) Name Murrabit Granite (G657) Named after Distribution Magnetic response Gravity response Comments Pericoota pluton (G659) pluton Toort (G662) SWAN HILL - INTERPRETATION 23

0Km100

S35°

Swan Hill

Kerang

S36°

Bendigo

S37°

Melbourne E144°00’ E142°30’

Figure 1. Location of the Swan Hill area interpreted, outlined in white. Main roads are shown in brown. The background image is a digital elevation model with an east-west gradient, which highlights north-south trending features. Areas of different data quality are also highlighted. Almost all of the region interpreted is covered by the arcuate Parilla Sand dunes or the magenta low area of the former Lake Bungunnia. Lake Tyrrell (west of Swan Hill and the lowest point in the region interpreted, is a remnant of this much larger Lake. East-block-down movement on the Tyrrell Fault, which lies just west of the Lake, has preserved it. New South Wales data courtesy of the Geological Survey of New South Wales. 24 SWAN HILL - INTERPRETATION Total Magnetic intensity Total

Figure 2. image of the interpreted region and surrounds. HILL of SWAN White and pink show magnetic highs, purple and magenta lows. State border in blue. New South data courtesy of the New Wales Geological Survey. South Wales E144°30' Km

050

E144°00'

E143°30'

E143°00' E142°30' S 34°30' S 35°00' S 35°30' S 36°00' SWAN HILL - INTERPRETATION 25 rst ﬁ eld. eld. ﬁ , minor -2 . Pink and white -2 Bouguer gravity of the

eld, intensity layer is ﬁ interpreted region of SWAN HILL HILL interpreted region of SWAN and surrounds. Colour layer is total vertical derivative of total contours at 20 ms Major contours at 100 ms Figure 3. are highs, purple and magenta low.

50 E144°30' Km

E144°00'

E143°30'

E143°00' E142°30' S 34°30' S 35°00' S 35°30' S 36°00' 26 SWAN HILL - INTERPRETATION Radiometics of SWAN Radiometics of SWAN Figure 4. and surrounds. Red colours HILL show predominance of potassium response, green predominantly thorium and blue predominantly The blue uranium responses. striping is caused by imperfectly levelled data.

50 5 50 E144°30'

Km K Km

0 0 0

E144°00'

E143°30'

E143°00' E142°30'

S 34°30' S

S 35°00' S

S 35°30' S

S 36°00' S SWAN HILL - INTERPRETATION 27 oor of ﬂ Digital elevation model Figure 5. region. Pink HILL of the SWAN and white colours show topograpic ASL) magenta highs, (to 120 m m and blue topographic lows (40 the The state border, ASL). The lowest Murray River is in blue. point in the area is Lake Tyrrell (142°50’E, 35°20’S), Tyrrell Lake some 5m lower than the Murray Reasons for this could River. include sediment deposition from the Murray River building up nearby areas, and/or east–block– Tyrrell down movement on the Tyrrell). Fault (just west of Lake

50 5 E144°30'

Km K

0 0

E144°00'

E143°30'

3°00' E14 E142°30'

S 34°30' S

S 35°00' S

S 35°30' S

S 36°00' S 28 SWAN HILL - INTERPRETATION Palaeozoic geology of

Figure 6. the Swan Hill region.

′

45'

000 m

40 ! 35 144

45' 30 25 ′

36°00 144°45

20 60

95 000 mE 000

7 w

Ot C

000 mE 000 7

a Oc

G65

b Dx

Oc Dx

′

G75

G75 Dx

000mN

60 35°30 60

55 E 50 ′ 144°30 ′ 144°30 45

133m

C 184m

\ \ b

a b

\ \ \ 9

Ot LT

G65

FAUz

a Ot

Dx C

b Ot

G65

202m

LT 70 r FAU RIVER z

C w

L 220m

bowe

INA 9

Gun

189m Dx

GRIM G65

Ot ille

LT a a

ediments FAU

Oc Rup

a DING

Leitchv

C z 55

Ot LAN

Wee

106m

G659

y Oc

beds 205m

LEGEND LOG

Wee Wee

Keel z

a C

ian s

193m

Ot z

Oc-alpha

188m

147m

Cohuna 5

55 GOVERNOR FAULT

G29

Dgl

165m

189m

179m 45 z

Basaltic plugs

Post Tabberabben granites

Devon

Early Devonian granites Ordovician

Castlemaine Group

Tueloga Tueloga

Cambrian

St Arnaud Grou

Dja Dja Wrung Super Group Dja Dja Wrung

arra arra

drook

naw naw

98m Nor

Koon

Gan Gan 102m

LT a

83m

132m C

G29 FAU

z z

W 40

83m

124m

221m

193m

-109m a MURRAY 183m WHITELA

nes

90m

Bridge C

Mil

oint

13m 35

′ C

a Oc

95m-1

Teal P Teal

202m

Ot Macorna

84m-120m

30 90m-108m 7

000 mE 000 G32

40 C

-108m C

000 m

z 88m-127m

Zone 55

111m-12

87m

189m

88m-142m

35°00

ang

90 85 75

20 05

88m-150m

15 10 80

B 147m C 95 ′ 60 144°00 ′

144°00 CHARM

East

121m-144m 5

Ker

a 7

126m

132m

Dge Ot

G29

G31

120m D

124m

000 mE 000 7

gowel

ang

179m z

172m

Tra

Sout

108m

C LT Ker

Zone 55

FAU 65

107m

NEW

203m

WAL

SOUTH

G65

z z

KERANG

a a

Dgl

C C

C rley

Fai z

Zone 54

LAKE 214m

236m

6 194m

Dge

a 178m

della

G65

C Ot

ville

gwa

240m

Wan

Din

Lang

270m Oc

307m

168m

a 257m

Zone 54

226m

Oc Lake

Meering

a alpha

RNOR 89m

141m

a z

Oc-

a ur Ot

GOVE z

C Lake

Charm

250m

TORIA

Leagh a

243m

252m

143m

Par

VIC

Mysti

124m Dge

135m

Ot 143m

137m

a East 248m

Budgerum

Lake

Boga

C 1

163m d

192m

G32

b G32

Ot 165m

403m

Ot Dge

180m

d e

29m

a d

RIVER a

C C Ot

C G333

g d

′

mbatook Budgerum

C LT C

d FAU

128m

G631

Qua HIL

C d

SWAN a

a 199m

e d

000 mN

e d

g 11

′ 130m 143°30

e d a a C

75 rd

a a

C C

a a

a 55

40 30

70 65

35 25

61 C 45

34°30 b ′

143°30 C C

92m

a Ot

d AVOCA G655

102m

d a

282m

Beverfo

a Ot

a 190m

der

Dx C

d a

tyn

a 5

Sou

Tyn

G333

d 170m

G65

a C

LT 170m

e FAU Ot

CA C

d 244m

84m Dx

AVO a

der

126m

tyn

a C

131m

FAULT Tyn a

Dge

d C

84m

Ot d

ong

tyb

Road

e d

G61 3

aninny

Lalber

Nya

a a

Tit

Lalbert

C C

ifera Tow

MURRAY G61

222m

Vin

G61

G650

C 0

25 CHARM

176m

h We h

G65 296m

Wood

351m

Nya

ngil

Dx e

LAKE 132m

Pia

raby

G662

222m G60

Yar

ima

G64

sda North

Piangil

C z

Ult

Hay

G31

mbie

rung

138m

Pia G64

a 180m

RIVER Nar

368m

a z

120m

osa

94m

G31

Dum

232m

121m

lawil

380m a

Ot C

G31

G60

Nul

G60 C

381m 381m C

G319 e

LAKE G31

LT a G60 FAU

CHARM 9 e

G31

94m

345m

d e

e C

a a

a e d

86m

Bend

C C

a a

G31

Culgoa

Boundary

C C

G31

153m

ngil

126m

Pia

133m

336m

UTH WALES UTH

a a

00 C

90m a

C a

raport

Nar

G31

Dge

lock

G60

wil ′

z 143°00

z l

a e

Berri

Dgl

147m

G663

Jil

a C ′ 143°00 C

172m

e d

a a

G60

Dge

C C

136m

315m

90 Dge

G31

ains

Chinkapook

Dge

G e

287m

Long Pl Long C

G31

222m

G31

rell

G65

G653

G65

z Down Tyr

a 3

295m

G65 C

Dge

274m

Boigbea G65

Dge

C 182m

124m Dge BIRCHIP

e z

421m

MANANGATAN

325m

a a

z C

Dge z

C C

G31 z

G31

NEW

C 186m

d TORIA

234m C

C d

323m SEA LA SEA

6 80 z

Y C

G65

152m

VIC 65

99m

C G31

e 6

MURRA 264m

LT a

z E

FAU z

G31

285m

nabulla

a a

G31 FAULT

C C

435m

Kin

G65

C G31

Curyo

351m d

C bourie

a 60

trap

d C

L C

d 6 REL a

TYR C z

G31

ROBINVAL

a Bim

a C

Corner

Day

255m C

e L LT

G31 e

FAU a

Bannerton e

C TYRREL

wyn

d pga

C C

Kul

chu

z a

e e

a C

a a

Wat

C C

daly

Nan

210m

elang

201m

d a

Woom

z 206m

z Dam

llan

Reedy

a z d

tyack

C a

-Ca-epsil

r Mi r

Mit

a Pie

z C

LT win

60 a

FAU LE

YDA a

z z Kul

d z

a a

a PERC

Wemen

C C

e e

00'

z a

Lascelles

C e

atton z

241m

a e

Str

echee

C 40 a 6

C mE 000

a LE

z YDA C

C PERC

106m

Kurdwe

ah e

Gama

East

Beul a ′

C 142°30 a

50 40 C 000 mE 000

6 w

ant

C C

′ a ′

142°30 Wag

45 40

50 35

80 70

90 85

30 25

000 mN 35

′

70 60

20 A

000 mN

36°00 80

34°30

30'

00'

35 SWAN HILL - INTERPRETATION 29 -40 -80 0 60775 60750 60725 60700 60675 60650 60625 60600 40 -160 -120 5000 m 10000 m 0 m 0 m 60625 -120 -160 -80 -40 5000 m 10000 m 40 0 60775 60750 60725 60700 60675 60650 60600 B E a Ot b Dx Km (nT) Intensity Dgl 010 ) a Total Magnetic Total 2 Ot m/s a Dge m Ot (

G659 LT

Bouguer Gravity FAU

a LOG LANDING LOG Ot w C

RNOR a C

GOVE z a

FAULT C a Ot G295 VICTORIA NEW SOUTH WALES NEW VICTORIA g Ot z a w C C b Ot e a C a Ot a VICTORIA NEW SOUTH WALES NEW VICTORIA z C

HARM a C d a

C a LAKE CHARM LAKE C LT FAULT C FAU

FAULT a

Oc WHITELAW AVOCA LT w C

FAU d a C D e z a a C C w C a Oc e a C a C folding largely diagrammatic z a C a C a z Oc a e C a folding largely diagrammatic C G319 z a a C C e a a C C d z a C a C G631 C 0 40 0 m -40 -80 -120 -160 60750 60725 60700 60675 60650 60625 60775 60600 5000 m 10000 m G316 e

TYRRELL a FAULT C d a w C C ) 2 z a C m/s m ( regional gravity high in the Bouguer Gravity -2 a e C

ms C FAULT d μ

Cross-sections in the Swan Hill C (nT) PERCYDALE folding largely diagrammatic Intensity

z a Total Magnetic Total C oor basalt in the hanging wall of the fault. oor basalt in the hanging wall of fault. ﬂ A 0 40 -40 -80 0 m -160 -120 60775 60750 60725 60700 60675 60650 60625 60600 5000 m 10000 m Figure 7. region. Locations shown on Figure 6. Section AB region. Locations shown on Figure 6. Section shows the 60 hanging wall of the Avoca Fault. The reason for Fault. Avoca hanging wall of the but may relate to duplexing of the this is unclear, ocean However the high extends for about 50 km to The west, implying duplexing over a large area. Fault is partly Tyrrell gravity low just east of the due to the Manangatang pluton G316, but is also partly due to the Cainozoic reverse movement The gravity high over the granite in on the Fault. is due to aliasing of the data. New South Wales 30 SWAN HILL - INTERPRETATION

6050000N

C G 6025000N

P W

6000000N E E E E 000 000 000 000 775 800 825 850

Figure 8. Cambrian mafi c volcanic rocks along major faults. The image has the total magnetic intensity over fi rst vertical derivative of the magnetics. The blue line shows the course of the Murray River, pink line the limits of the map, solid white lines major faults, dashed grey lines smaller faults, red lines outline granites and magenta lines apparently unfaulted contacts with basaltic rocks. The Governor Fault (G) trends north-west across the image and is correlated with the faults associated with those mapped with the ocean fl oor basalts at Dookie, to the east on WANGARATTA. The Mount William Fault (W) and associated highly magnetic mafi c rocks swing into the Governor Fault and seem to be truncated by it. Other slivers of mafi c rocks are interpreted further west along the Governor Fault and along the Log Landing Fault (L) in the top-left of the image. Thus the east-west component of strain, mostly taken up along the Mount William Fault system, was largely translated to the Log Landing and associated faults, whilst the north-south component has been taken up along the Governor and Lake Charm (C) fault systems. The nonmagnetic Social Bend pluton (S) stitches the Governor Fault. The other nonmagnetic granites in the region have age dates of about 360 Ma, and if the Social Bend pluton is the same age, it implies little movement on the Governor Fault since then. By comparison, the Pyramid Hill Granite (P) has seen signifi cant faulting since then along the Lake Charm and associated faults. SWAN HILL - INTERPRETATION 31 E E E 000 000 000 800 825 775

6075000N

6050000N

6025000N

6000000N

Figure 9. Comparison of fi rst vertical derivatives of magnetic data from three surveys. North of the Victorian border (blue) the Murray-Riverina data were collected in 2003 for the NSW Geological Survey at 60 m mean terrain clearance on 400 m line spacing. The interpreted metaturbidites can be seen as 1 or 2 nT responses in the northeast of the image. In Victoria, the northern survey (191) was fl own in 1980 at 80 m mean terrain clearance and 250 m line spacing. The southern survey (2688) was fl own in 1994 at 100 m mean terrain clearance and 400 m line spacing. In both, the metaturbidites are weakly to nonmagnetic. Hallett and Webster (2004) suggest that the magnetic metaturbidites in New South Wales extend south into Victoria as far as Bendigo. This seems unlikely, since where the Murray-Riverina survey crosses into Victoria, the responses are also too weak to show any linear character. The Governor Fault broadly corresponds with the border (Fig. 6) and is interpreted to divide the two metaturbidite packages. A further alternative explanation, that there has been a major facies change across the border, seems less likely. 32 SWAN HILL - INTERPRETATION

Figure 10. Magnetics and gravity of a southwestern New South Wales and northern Victoria. a. TMI (colour) on an EW gradient intensity layer. b. Bouguer gravity of the same area as a ; the intensity layer is a ﬁ rst vertical derivative of the gravity. In both, white and pink are relative high values, magenta and blue low values; the pink outline shows the interpreted area for this report and the white box the area of Figure S34° 10c, a greyscale ﬁ rst vertical derivative of the magnetic data. In the east, the deep north-northwest nonmagnetic trends are parallel to the northern extension of the Kancoona Fault system (K) and so probably have the same age, (Bindiian, or about 410 Ma). This fabric seems to extend no further west than the Bearii Fault (B). Further north (south of X in c) the demagnetised zones are interpreted B to be covered by a later magnetic unit, the K Devonian Hillston Volcanic Complex. In the lower left of a, the distinct linear fabric of the St Arnaud Group is clearly visible, and S36° this can be traced clockwise on a and c to the north around a ‘nucleus‘ centred just 0km 100 north of B. The St Arnaud Group is intruded by post–deformation 410 Ma granites and has generally been deformed between 460 and 440 Ma. At X on c, this older fabric b truncates the younger 410 Ma fabric, an apparent breach of the law of superposition. Such truncation would however be possible if the ‘nucleus’ was a separate fragment of crust, which arrived at its present location as part of the deformation of the sediments to the west.

S34°

B K

S36°

0km 100 E144° E146° SWAN HILL - INTERPRETATION 33

c S33° X

S34° E144° E145°

Figure 10c. 34 SWAN HILL - INTERPRETATION

a b 6100000N 6100000N

6175000N 6075000N

6050000N 6050000N

6025000N 6025000N

6000000N 6000000N A E E E E E E E E 000 000 000 000 000 000 000 000 675 700 725 750 675 700 725 750

Figure 11. The magnetic and gravity responses of the Lalbert Batholith. a) is of the total magnetic intensity (reduced to the pole) in colour with the fi rst vertical derivative of the magnetics as the intensity; red lines show the various intrusions, blue the Victorian border. Only a small part of the batholith in the southeast crops out as Hemsleys and Wycheproof granites, but several drill holes have also intersected it, confi rming the responses as entirely from granites. The age determinations on Hemsleys Granite (400±6 Ma on biotite) are from near x and those from the Wycheproof Granite (407±6 Ma on muscovite) near Y. The distinctive elongate character of many of the intrusions seems to have been caused by dextral strain whilst the bodies were still plastic. As the ages are likely to be minima, it is possible deformation took place late in the Bindian Orogeny (418 to 410 Ma). If so, it is one of few Bindian events recorded in western Victoria. b) Bouguer gravity contours on the same area; the white lines show the major faults in the region. The Avoca Fault (A) is on the eastern edge of the image. To the west of this, the gravity contours show a prominent rise to the highest levels on SWAN HILL, perhaps implying the presence of ocean fl oor basalt on the sole of the fault. The gravity response is little effected by the northern part of the Lalbert Batholith, but further south, on ST ARNAUD, there is are two prominent lows, perhaps implying both thicker granitic intrusions and the absence of mafi c rocks at depth. The gravity high and the regional magnetic high in a) are largely, but not entirely, coincident. This could be related to the path the batholith took whilst it was being emplaced. Much of the ocean fl oor basalt in eastern and central Victoria is nonmagnetic, and so the gravity response may give a truer refl ection of the extent of the basalt. SWAN HILL - INTERPRETATION 35

6100000N

6075000N

6050000N E E 000 000 250 275

Figure 12. Devonian sediments in southern New South Wales overlying folded Tueloga beds and unnamed granites. White solid lines show major faults, grey dotted lines smaller faults, red lines granite boundaries, magenta lines edges of Cambrian metavolcanic rocks, green dotted lines edges of Devonian sedimentary rocks, pink line the edge of the map. The background image is a ﬁ rst vertical derivative of the reduced to the pole magnetics. Figure 8 covers much of the same area. The normal linear magnetic responses of the Tueloga beds are seen in the left of the image. In the centre left these are largely suppressed by an overlying nonmagnetic sequence; those on the right are completely suppressed. Thus the thickening nonmagnetic sequence has suppressed the magnetic responses of the underlying Adaminaby Group. The responses around the nonmagnetic granite in the lower right (the Pericoota pluton, G659) are interpreted to be contact metamorphic effects. If so, the host rocks must be older than the granite. The youngest granites in the region are the similarly nonmagnetic Lake Boga and Pyramid Hill granites, both about 360 Ma (Upper Devonian), whilst most other (mostly magnetic) intrusions to the south are about 400 to 410 Ma (Lower Devonian). The nonmagnetic rocks are therefore probably Devonian, and could perhaps be partly derived from erosion of the rocks in the hangingwall of the Governor Fault system.

36 SWAN HILL - INTERPRETATION

MK004

MK103

MK108

MK051

MK052

Nacorna 2 Nacorna Gunbower West 2 West Gunbower

Calivil Formation

Nacorna 3 Nacorna

Gannawarra 8 Gannawarra

Gannawarra 7 Gannawarra

Kerang 4 Kerang coal attened to the Mologa Surface, which emphasises ﬂ

Kerang Subbasin Cohuna Subbasin Subbasin Torrumburry Meram 10 Meram

d n a S

la il Mologa Surface r Palaeozoic Basement

Benjeroop 79 Benjeroop

Boga 17 Boga Boga 317 Boga ‘Middle Renmark Group’

Olney Formation

Tyntynder West 2 West Tyntynder Tyntynder North 1 North Tyntynder

l s

C d

w g

o t n

Geera Clay

e o

h n r Norval Regolith

c u

n p

l k

B o

Piangil West 2 West Piangil

Wunghnu Group Wunghnu Murray Group Murray Group Renmark cant thickness of the Geera Clay in west, implying abnormal basin thickening, possibly due to syndepositional faulting ﬁ Bore hole section along the Murray River from Swan Hill east to the edge of the map area. The section has been Bore hole section along the Murray River from Swan Hill east to edge of map area. Miocene to late Eocene Pliocene to late Miocene Eocene to Palaeocene 0 The change in the thicknesses of Renmark Group east Kerang 4, The lateral continuity of the coal intersected, particularly between Kerang and Cohuna Subbasins, The signi 100 200 300 400 metres • • • Data reworked from Holdgate & Gallagher (2003). Figure 13. SWAN HILL - INTERPRETATION 37

(a) (b)

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differential compaction over these phases. The shallow inlets so (c) formed may then have acted like shallow gold pans, concentrating the ﬁ ne heavy minerals winnowed out of the coarser deposits. Although sheet style deposits are considered to be offshore facies equivalents of the strand line style mineralisation, the sheet style 6100000N mineralisation is concentrated in the east of the image and the strands are in the west. This implies that the strand lines in the east have been eroded away in the last 6 million years.

6075000N Lake Tyrrell can be seen as the ﬂ at area in the upper centre of a). It is just a remnant of the much larger Lake Bungunnia, the area of magenta and blue, which extended west onto OUYEN for at least 100 km and north into New South Wales (Moore, 1997, 6050000N Sandiford, 2002). The present surface of the old Lake Bungunnia has been partly covered by later dunes of the Woorinen Formation and Recent lunettes. Lake Tyrrell, just east of the Tyrrell Fault, is the lowest place in the region and some 10 m below the Murray River. It also suggests that the Tyrrell Fault at present has an east- 6025000N block-down movement sense. The largest gravity low associated with the Fault is in the area of Lake Tyrrell, consistent with it having the largest Cainozoic movement there. E E E E

000 000 000 000 c). Arbitrary stretch of U channel, where white shows areas with 625 650 675 700 eU3O8 of more than 7 ppm. The highest responses are on the western side of the lake, where responses of more than 250 ppm were recorded. Figure 14. Mineralisation in the Murray Basin. a)Topography, b) magnetic responses and c) uranium responses near Lake Tyrrell. Pink line shows the extent of the interpertation. Heavy mineral sand accumulations (blue lines and stipple) are present on the western, shoreface, sides of the dunes. However not all magnetic responses are sites of mineralisation and not all mineralisation is magnetic. This suggests that the mineralisation is at least partly controlled by other factors. The sheet style mineral sand deposits seem at least partly controlled by phases in the underlying granites. This may be due to increased weathering of these phases, which has subsequently allowed 38 SWAN HILL - INTERPRETATION

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Figure 15. Eroded Parilla Sands in the Leaghur area. RGB (K, Th, U) image has an intensity layer of an east-west shaded DEM. The blue lines show the rivers and lakes. Comparison with the southwest corners of Figures 6 and 12 shows the Parilla Sand (green tones in raised areas) has much less well developed ridge structures. The Leaghur ‘Fault’ is supposed to run along the eastern side of the easternmost elevated area, but the elevated area lies between two northeast–ﬂ owing rivers that could not have been in their present locations when the Parilla Sands were laid down as they would have been offshore. It seems likely that the gentle uplift of the highlands to the south has partly rejuvenated the rivers, allowing them to cut through the Parilla Sand. The ‘fault’ scarp is thus considered to be an erosional feature.