VIMP Report 39
A geological interpretation of the geophysical data for the Ouyen 1:250 000 map sheet area
D.H. Moore
July 1997 Bibliographic reference: MOORE, D.H., 1997. A geological interpretation of the geophysical data for the Ouyen 1:250 000 map sheet area. Victorian Initiative for Minerals and Petroleum Report 39. Department of Natural Resources and Environment.
© Crown (State of Victoria) Copyright 1997 Geological Survey of Victoria
ISSN 1323 4536 ISBN 0 7306 9417 8
Keywords Ouyen 1:250 000, aerial magnetic surveys, magnetic interpretation, geophysical interpretation, Palaeozoic, Cainozoic, granite, greenschist facies, amphibolite facies, basalts, turbidites, Lachlan Fold Belt, Glenelg Complex, Netherby Trough, Murray Basin, gold, copper.
This report may be purchased from: Business Centre, Department of Natural Resources and Environment, Ground Floor, 115 Victoria Parade, Fitzroy, Victoria 3065
For further technical information contact: Manager, Geological Survey of Victoria, Department of Natural Resources and Environment, P O Box 2145, MDC Fitzroy, Victoria 3065 GEOLOGICAL INTERPRETATION - OUYEN 1
Contents
Abstract 2 1 Introduction 3 2 Access and physiography 5 3 Previous work 6 3.1 Regional studies 6 Geology 6 Geophysics 7 3.2 Mineral exploration 8 3.3 Petroleum exploration 10 4 Regional interpretation 12 4.1 Pre-Delamerian and Delamerian 12 General 12 Glenelg Zone 12 Delamerian intrusions 16 Stawell Zone 17 Devonian granites 19 Carboniferous-Permian 19 Mesozoic and Cainozoic 20 5 Conclusions 23 6 References 25 Appendix 1 29 Specifications of the Horsham airborne survey 29 Appendix 2 30 Geophysical domains - Ouyen 1:250 000 map sheet area 30 Victorian Initiative for Minerals and Petroleum (VIMP) report series 41
List of figures 1 Location map Ä OUYEN 4 2 OUYEN magnetic image 8 3 OUYEN gravity image 9 4 Thermal history of the Murray Basin 10 5 Geophysical domains Ä OUYEN 13 6 OUYEN digital elevation image 21
List of tables 1 Aeromagnetic surveys over OUYEN 7 2 Summary geological history for OUYEN 14
List of maps 1 Magnetic interpretation of basement geology (scale 1:250 000) 2 Magnetic interpretation of post-cratonic features (scale 1:250 000) 3 Calculated depths to magnetic basement (scale 1:250 000) 2 GEOLOGICAL INTERPRETATION - OUYEN
Abstract The Grampians Group was deposited mostly on the Dimboola Subzone basement, in the In 1994, as part of the Victorian Initiative for Netherby Trough, some time between the end Minerals and Petroleum, the Ouyen 1:250 000 of the Delamerian Orogeny and the intrusion of map sheet area (OUYEN) was flown with a ?400 Ma granites. These Early Devonian high quality aeromagnetic and radiometric granites intruded both the Grampians Group survey. This report presents a geological and the Stawell Zone. The Netherby Trough interpretation which combines the new also contains significant amounts of the information with older gravity data and the Carboniferous to Permian Urana Formation. geology from drill holes, and is consistent with the regional geology. It contains the first Many of the point magnetic sources have been comprehensive maps of the Palaeozoic attributed to Upper Cretaceous to Eocene basement geology of the area, the interpreted basaltic plugs. post-tectonic features, and depths to basement computed from the magnetic data. The area is generally covered by from 200 m to 500 m of Murray Basin sediments. The The magnetic basement of OUYEN has been shallowest parts are in southwestern and divided into the eastern Stawell Zone and the southeastern OUYEN, and the deepest parts western Glenelg Zone. The geological and cover the Netherby Trough. The present tectonic framework established for the Glenelg interpretation of the radiometric, magnetic and Zone on HORSHAM has been continued digital elevation data in the eastern part of the northwards. The boundary between the area shows a significantly larger area of Stawell and Glenelg Zones is the northern Loxton-Parilla Sands than on previous maps. extension of the Moyston Fault. Both the Loxton-Parilla Sands and a younger palaeolake system show indirect evidence of On OUYEN, the Glenelg Zone has been late Cainozoic faulting. subdivided into the Dimboola, Upson and Ozenkadnook Subzones based on the Recently RGC have announced the discovery of interpreted rock units, metamorphic grades and two potentially economic heavy mineral sand deformation histories. The Dimboola Subzone deposits east of the town of Ouyen. The area is mostly oceanic island arc and ocean floor contains several small occurrences hosted by rocks that have been weakly metamorphosed the Parilla Sand. No presently economic and simply deformed. There is little metalliferous mineral deposits are known, but information on the Upson Subzone, but it there has been no exploration, probably because includes low grade metasediments and mafic of the Murray Basin cover and a lack of volcanic rocks that have previously been understanding of the basement geology. Gold correlated with the Kanmantoo Group. The could possibly be targeted in the Stawell Zone. Ozenkadnook Zone includes rocks that have Copper-gold deposits may be associated with been metamorphosed to amphibolite facies and the intrusions in the southwest corner of the show complex deformation. Other lower area. metamorphic grade rocks have been fault emplaced over the amphibolite grade rocks.
The Glenelg Zone was deformed and intruded during the Late Cambrian to Early Ordovician Delamerian Orogeny. The Ozenkadnook Subzone may also have been deformed by an earlier orogenic event.
The turbidites and oceanic basalts of the Stawell Zone are typical of much of the Lachlan Fold Belt in western Victoria, although more metamorphosed. They are weakly magnetic, with most trends striking north to northwest. The Stawell Zone was undeformed before about 440 Ma. GEOLOGICAL INTERPRETATION - OUYEN 3
1 Introduction
This report is the second of a series that gives new interpretations of the basement geology of northwestern Victoria and which are part of the Victorian Initiative for Minerals and Petroleum (VIMP). Large areas have now been flown with high quality magnetic and radiometric surveys. Major gravity surveys are also being carried out on a 1.5 x 1.5 km grid, with several traverses at 250 m station spacing.
The new interpretations combine the available geological and geophysical data to give a coherent interpretation of the "basement" beneath the Murray Basin. While other publications have generally described the surface geology of the region, this report is the first to detail the OUYEN1 basement and to provide a comprehensive basement map. Section 4 is a synthesis of the geology as it is now understood, and includes discussion on both the basement and "cover". Appendix 2 gives formal descriptions of domains not previously described in the earlier report on HORSHAM.
Three 1:250 000 scale maps are included with the report. One outlines the domains, and gives an interpretation of the basement geology. A second map outlines the post-cratonic rocks and includes a reinterpretation of the surface geology based on the radiometric and digital terrain data collected. Twyford (1997) has outlined the depth of the Murray Basin cover as calculated on the magnetic data using the Naudy method. A 1:250 000 enlargement of the Ouyen part of her image is also included.
The report also includes a brief discussion of the previous work carried out in the region.
The technical details of the flying undertaken over OUYEN are included as Appendix 1. The images and digital data from the surveys used to make the interpretation can be purchased from Minerals and Petroleum Victoria.
1 All 1:250 000 map sheet areas in this report are referred to by capitalising their names. Thus the Ouyen 1:250 000 map sheet area appears as OUYEN. 4 GEOLOGICAL INTERPRETATION - OUYEN
Figure 1 Location map Ä OUYEN. GEOLOGICAL INTERPRETATION - OUYEN 5
2 Access and physiography
OUYEN lies about 400 km northwest of Melbourne. Access is via the Western and Henty Highways (Fig. 1). Within the sheet area, access is variable, ranging from very good in the southeastern parts to highly restricted within the Big Desert Wilderness Park. Extensive flooding from winter rains also causes problems away from formed roads.
The area is a plain which slopes gently from about 140 m ASL in the southwest to about 50 m ASL in the northeast. On this plain are parabolic dunes with up to 20 m relief and east- west dune chains with up to 10 m local relief (Lawrence, 1975). The larger parabolic dune fields form the Big Desert and Little Desert.
Salinas and ephemeral swamps are present in low interdune areas. Lake Hindmarsh and Lake Albacutya are more permanent, filling successively from the Wimmera River. Lunettes are common on the eastern sides of the larger lakes.
Prior to settlement, most of the area was covered with mallee gum. More luxuriant tree growth was present along Outlet Creek, an ephemeral extension of the Wimmera River. Much of the area outside the parabolic dune fields has now been cleared.
Annual rainfall is generally less than 350 mm. 6 GEOLOGICAL INTERPRETATION - OUYEN
3 Previous work Other significant hydrological studies include those by Thorne et al. (1990) and Jayatilaka et al. (1993). 3.1 Regional studies Although the regional Palaeozoic basement Geology does not crop out, evidence of it can be extrapolated from outcrops to the south and east on BALLARAT, HAMILTON and All of OUYEN is covered by sediments of the ST ARNAUD, and from the recent geophysical Cainozoic Murray Basin. The basement to the interpretation of HORSHAM. Several authors, Murray Basin does not crop out; it is known including Gibson and Nihill (1992) and Gray only from 7 drill holes. Five are recorded as et al. (1988), have subdivided the basement having penetrated Cambrian St Arnaud Group further south into two zones, the Glenelg Zone rocks or their equivalents. The other two to the west and the Stawell Zone to the east. intersected either Ordovician to Silurian Rocks of the Glenelg Zone have been affected by Grampians Group or Carboniferous to Permian the 500 Ma Delamerian Orogeny. In the Urana Group rocks. Logs of these holes are in westernmost Lachlan Fold Belt, the St Arnaud Knight et al. (1995). Group rocks of the Stawell Zone contain Delamerian age zircons, (Williams et al., 1994) The thickness of Murray Basin sediments and have been deformed no earlier than 450 Ma drilled varied between 487 m in Gunamalary 2 (Foster et al., 1996). The oldest intrusions and 252 m in Tyenna 1. Drilling on HORSHAM known are 413±3 Ma (Arne et al., 1996). indicates that at least some areas in the southeastern corner of OUYEN might have less On BALLARAT, Cayley and Taylor (in prep.) than 200 m of Murray Basin cover. have placed the boundary at the Moyston Fault1 . As the fault is approached from the east, the Lawrence (1975 & GSV, 1974) mapped the rocks increase in metamorphic grade to Murray Basin sediments on OUYEN. The amphibolite facies. The enveloping surface of oldest outcropping unit is the marginal marine the folding changes from flat to east-dipping. Pliocene Parilla Sand, although the Eocene Both imply that progressively deeper levels of Renmark Group and several Late Oligocene to the Lachlan Fold Belt are exposed. West of the Miocene units are present in the near Moyston Fault, the sequence is only weakly subsurface. The Parilla Sand was shown as metamorphosed, but has been regionally only as isolated outcrops in the southwestern deformed prior to the intrusion of the Bushy half of the map sheet area, although his cross Park Granodiorite at 495 Ma (Stuart-Smith, section showed subcropping Parilla Sand in prep.). extending across the entire map sheet area. Cayley and Taylor interpreted almost all of the The remaining units were mapped as Lachlan Fold Belt rocks of the Stawell Zone as Quaternary. These included the east-west belonging to the St Arnaud Group. These are trending dunes and sheet sands of the turbidites, somewhat more carbonaceous and Woorinen Formation, parabolic dunes of the finer in the Beaufort and Warrak Formations, Lowan Sand, lunette deposits, evaporites of the and coarser in the Pyrenees Formation. On Yamba Formation, and river and lake deposits structural grounds they considered the Group of the Coonambidgal Formation and Shepparton Formation.
Brown and Stephenson (1991) integrated 1 Lawrence's work with other studies elsewhere Others have placed the boundary between the Lachlan and Delamerian Fold Belts further west at Yarramyljup on the Murray Basin. This caused much of the Creek (Gibson & Nihill, 1992), or in the Black Range (Gray stratigraphy to be redefined. The et al., 1988). VandenBerg (1978) and Stump et al. (1986) hydrogeological map of Robinson et al. (1992) placed another zone between the two; it broadly supplemented the Geological Survey of encompassed The Grampians but could have extended as far east as the Stawell-Ararat Fault Zone. The present Victoria's (1974) map with significant new study shows the complexity of the region. Many major information on the distribution and depth of faults have been identified that bound significant rock water-bearing units within the Murray Basin. packages. Their relationships may become clearer with It includes structure contours to the top of the more geological interpretation and drilling. Parilla Sand and the pre-Tertiary basement. GEOLOGICAL INTERPRETATION - OUYEN 7
Table 1 Aeromagnetic surveys over OUYEN
SURVEY NAME YEAR OPERATOR CONTRACTOR SURVEY TRAVERSE REFERENCE ALTITUDE SPACING
Murray River Basin 1956 Frome Broken Hill Worldwide 1500 ft 5 mile Frome Broken Aerial Surveys Hill (1956) Murray Basin 1962 Planet Oil Aero Service 1500 ft 5 mile Crosby (1963) Ouyen 1981 BMR BMR 150 m 3 km Bureau of Mineral Resources (1982) Horsham 1994 GSV Kevron 80 m 400 m Willocks (1995)
From Willocks (1987) and Willocks (1995) was deposited largely in the Cambrian. Below subdivided the Glenelg Zone into three the St Arnaud Group is a sequence of tholeiitic subzones, from the west the Ozenkadnook, and boninitic volcanic and associated Miga and Dimboola Subzones. sedimentary rocks (Crawford, 1988), which were formed in ocean floor or oceanic island arc The Ozenkadnook Subzone has been complexly settings. These are generally correlated with deformed, and may include the structural other Victorian Cambrian greenstones. equivalents of the Rocky Cape Block in northwestern Tasmania (Moore, 1997). The Geophysics Miga Subzone includes metasediments and volcanic rocks that have been deformed in the Table 1 outlines the airborne magnetic and Delamerian Orogeny, forming relatively simple radiometric surveys carried out over OUYEN. north-south-trending structures. The Dimboola Only the 1994 data were used in the present Subzone strikes at about 330° and cuts across interpretation as they supersede older data. the Ozenkadnook and Miga Subzones, but More details of this survey are included as again has been deformed in the Delamerian Appendix 1. Figure 2 is an image of the Orogeny. The rocks are highly magnetic and OUYEN magnetic data. may be a different suite of volcanics to those in the Miga Subzone. The eastern boundary of the In 1973, the BMR completed a gravity survey of Dimboola Subzone is the Moyston Fault. the sheet area with a nominal station spacing of 11 x 11 km (BMR, 1980). In 1984, the BMR The Stawell Zone lies east of the Moyston Fault. also completed a traverse with a station spacing It includes both the metasediments of the of 500 m along the Ouyen Highway, in the St Arnaud Group and the mafic volcanic rocks northern part of OUYEN. These surveys which underlie them. showed the eastern half of the area to have a relatively flat gravity response from the An extensive area of Grampians Group basement sediments of the St Arnaud Group. sedimentary rocks overlie parts of the Dimboola The western half showed a gravity high and and Miga Subzones. The rocks appear to be adjacent gravity low. Ramsay and VandenBerg thickest in the eastern parts of the Dahlen (1986) called the gravity high the Stavely Domain (the central domain of the Dimboola Gravity Ridge; the low is now known to be a Subzone), and relatively thin elsewhere. These response from the Upper Palaeozoic Netherby rocks seem to be present near the base of the Trough. Figure 3 is an image of the present Netherby Trough. gravity data. Warraquil 3, in the northern part of On HORSHAM, Moore (1996a) used magnetic, HORSHAM, intersected Permian tillite. This gravity and drilling data to extrapolate the was interpreted as occupying a small graben Moyston Fault (the mapped boundary between containing possible Urana Group sediments. the Lachlan Fold Belt and the Glenelg Zone) north to the southern edge of OUYEN. He 8 GEOLOGICAL INTERPRETATION - OUYEN
Figure 2 OUYEN magnetic image; histogram equalised colour image with residual filtered intensity ("black and white") layer.
3.2 Mineral exploration present from 10 to 26 m below the surface. Outside of national parks, the map sheet area is Until recently, there had been minimal now completely covered by exploration licences exploration on OUYEN. To October 1996, only and applications. 29 exploration licences had been granted, and of these, 8 were current. All expired licences were Previously, about 20 km south of Hopetoun, used for heavy mineral sand exploration. Aberfoyle Resources Ltd. defined two Exploration for other commodities was probably mineralised strand lines (Painter, 1990). The deterred by the thickness of Murray Basin eastern strand contained a coarse ilmenite sediments and a lack of information about the sand, whilst the western strand was finer Palaeozoic basement. grained and contained about equal proportions of ilmenite, leucoxene and zircon. Both could be In February 1997, RGC announced they had traced over about 50 km. The occurrences are intersected a high grade mineral sand deposit, generally along strike from the WIM 150 the Woornack Deposit, close to the OUYEN deposit. They also found a third mineralised sheet edge and east of the town of Ouyen. They strand about 15 km northeast of Hopetoun. indicated that this occurrence contained up to This could be traced over about 5 km and was 16% heavy mineral, with a preliminary relatively rich in leucoxene and zircon, but was mineralogy of about 18% rutile, 13% zircon and low grade and contained abundant haematite 35% ilmenite. The grain size is coarse enough and goethite. Later exploration by BHP to be separated by a conventional heavy Minerals Ltd. (Davis, 1990) showed that the mineral plant and the mineralised zones were GEOLOGICAL INTERPRETATION - OUYEN 9
Figure 3 OUYEN gravity image; histogram equalised colours; white cirlces are gravity stations. To allow for easier comparison with Figure 2, the image has residual filtered magnetics as the intensity layer. The gravity data used to compile the image includes the latest VIMP data, which were not available at the time of the interpretation. The new data cover the eastern third of the area. general zone continued southeast on to The only mineral production has been from ST ARNAUD. gypsum deposits. Significant agricultural gypsum deposits are at Koonda, Cowangie, and CRA Exploration defined three areas of interest west of Hopetoun. Total recorded production in just west of the Henty Highway and between 8 the year 1995/96 was about 50 000 tonnes. and 25 km south of Ouyen (Waterfield, 1992). In each area the lower Parilla Sand was Salt (NaCl) deposits are present in several mineralised. The best result came from the lakes in the north, but most are in parks where Gypsum area, where drill hole OY133 extraction is prohibited. intersected 32.1% heavy minerals with a grainsize between 1 mm and 75 µm at depths of 8 to 9 m. However the results were considered difficult to correlate and part of the area was considered too deep for effective exploration and exploitation.
CRA Exploration also explored the Hopetoun region for brown coal. The best result was a 3.7 m intersection at 225 m below the surface. 10 GEOLOGICAL INTERPRETATION - OUYEN
Figure 4 Thermal history of the Murray Basin in northeastern Victoria and southeastern South Australia, from apatite fission track analysis and vitrinite reflectances. (From Gibson et al., 1996).
3.3 Petroleum exploration included a large gravity survey over the Netherby Trough. There has been little petroleum exploration on OUYEN. However part of the area is presently Most previous exploration in the Victorian part held under PEP 121 by Continental Resources of the Murray Basin is summarised in Knight Pty Ltd. Much of the information from their et al. (1995). This records 10 drill holes, but the program is still confidential. Their program only hole specifically targeted for hydrocarbons, Big Desert 1, is still confidential. The other GEOLOGICAL INTERPRETATION - OUYEN 11
drill holes were either stratigraphic holes or deep water bores.
Of these, only Gunamalary 2 and Koonda 1 were logged as containing other units than the Early Palaeozoic basement or the Murray Basin. Gunamalary 2 (T.D. 717 m) intersected 84 m of Upper Carboniferous shales, siltstones and diamictites of the Urana Group (Orth, 1986). It bottomed in 146 m of sandstones and mudstones, probably of the Grampians Group.
Gibson et al., (1996) completed apatite fission track analyses and vitrinite reflectance studies on three samples from holes in the region. Their conclusions are summarised in Figure 4. The results from Gunamalary 2 indicated a maximum palaeotemperature of ≥ 110°C prior to cooling which began between 360 Ma and 280 Ma. A second heating event to about 85°C took place before cooling between 250 Ma and 120 Ma. Other drill holes in the region constrain this onset of cooling to between 200 Ma and 150 Ma. A third cooling event started between 100 Ma and 60 Ma. The Cainozoic Murray Basin section seems to be near its maximum temperature since deposition. They considered that the Grampians Group rocks were at least mid-mature for oil generation whilst the younger rocks were immature.
The bottom 74 m drilled in Koonda 1 (T.D. 551 m) intersected Devonian to Carboniferous sandstone and siltstone with bands of white clay (Nott, 1989). It is uncertain how these rocks correlate with other rocks in the region, although Cayley (pers comm., 1996) believed, from regional structural evidence, that they were unlikely to be part of the Grampians Group. 12 GEOLOGICAL INTERPRETATION - OUYEN
4 Regional interpretation appear discordant to all trends in the Dimboola Subzone and;
4.1 Pre-Delamerian and - the Ozenkadnook Subzone, where the strike Delamerian directions of the magnetic trends are more complex. General Overlying these zones are the Netherby Trough rocks, comprising the early to middle Palaeozoic The basement has been subdivided into 31 Grampians Group and the upper Palaeozoic domains using the available magnetic and equivalents of the Urana Group. Mesozoic to gravity patterns (Figs 2 & 3), drill hole Cainozoic mafic plugs are common throughout information and mapping in the region. Each the area. All units are overlain by the domain represents a sequence of rocks with a Cainozoic Murray Basin sediments. The drill similar geophysical response and is interpreted hole depths to lower or middle Palaeozoic rocks to be a single rock package with a specific range from 270 m in the northeast to 490 m in geological history. the Netherby Trough. Automated Naudy calculated depths to magnetic basement on the Individual descriptions of each domain not line data imply that depths of 200 m or less already described in Moore (1996a) form may be present in the southeast. Appendix 2. All domains are shown in Figure 5 and are detailed on Map 1. Map 2 is an interpretation of the postcratonic features. Glenelg Zone Map 3 shows the computed depths to magnetic basement. The methods used are described in Ozenkadnook Subzone Shi and Boyd, (1993), Moore et al. (1996) and Twyford, (1997). Table 2 gives a summary of Three domains are present in the Ozenkadnook the geological history. Subzone. The Yanipy Domain continues north from HORSHAM, whilst the Willoby and The interpretation relied mainly on the Wallowa Domains are described first on interpretation completed on HORSHAM to infer OUYEN. No drill hole has penetrated to units on OUYEN. Limited basement control "basement". Basement depths to the Subzone has been provided by the five drill holes that are probably about 200 m in the south and penetrated to pre-Silurian basement and had 300 m in the north. identifiable basement lithologies recorded. The regional magnetic response of the rocks is The domains are grouped on geophysical and higher than that of the Upson Subzone to the structural criteria into the Glenelg and Stawell north, but lower than that of the Dimboola Zones. The boundary between the two is the Subzone to the east. The Subzone shows a northern extension of the Moyston Fault. The strong magnetic gradient. In the north, the Stawell Zone is the westernmost part of the regional response is about 59 700 nT, whilst in Lachlan Fold Belt. the south the regional response is about 150 nT higher. The gradient is partly caused by a All the rocks in the Glenelg Zone have been strongly magnetic body centred in the affected by the Delamerian Orogeny. On northwestern corner of HORSHAM. However OUYEN, the domains of the Glenelg Zone have the Willoby and Wallowa Domains are also been grouped into three subzones. From east to generally less magnetic than the Yanipy west these are: Domain.
- the Dimboola Subzone, where the prominent The three Domains have quite different magnetic layering generally strikes magnetic responses. The Willoby Domain has northwest and the basement rocks are the lowest regional response, about 59 720 nT. strongly magnetic; The Yanipy Domain has the highest regional response and shows only the faintest - the Upson Subzone, a series of broadly northwesterly trends. Residual filters generally north-striking convex-west domains that give a felted texture to the images. This texture is consistent with the presence of strongly folded (?metamorphosed) rocks, where the GEOLOGICAL INTERPRETATION - OUYEN 13
LEGEND: Stawell Zone 1. Woornack Domain 2. Ouyen Domain 3. Tiega Domain 4. Galah Domain 5. Paignie Domain 6. Warracknabeal Domain 7. Crymelon Domain 8. Willenabrina Domain 9. Corker Domain 10. Tarranyurk Domain 11. Boinka Domain 12. Caringa Domain 13. Glenbro Domain 14. Dart Dart Domain 15. Wyperfeld Domain 16. Pallarang Domain Glenelg Zone, Dimboola Subzone 17. Kalkee Domain 18. Cowangie Domain 19. Kurnbrunin Domain 20. Little Billy Domain 21. Dahlen Domain 22. Ni Ni Domain Upson Subzone 23. Goongee Domain 24. Carina Domain 25. Panitya Domain 26. Gunamalary Domain 27. Alphildale Domain 28. Ngallo Domain Ozenkadnook Subzone 29. Willoby Domain 30. Wallowa Domain 31. Yanipy Domain
Figure 5 Geophysical domains - OUYEN. folding has produced magnetic units that are most like the Kalkee Domain, which includes too short to be resolved. Whilst individual mafic to acid volcanic rocks, possibly of oceanic responses would be aliased, consistent magnetic island arc origin. The Willoby Domain probably trends might still be visible as a felted pattern. includes similar volcanic rocks to the Wallowa The Yanipy Domain probably has a basement of and Kalkee Domains, but may include a much high grade metamorphic rocks, although thin higher proportion of metasediments as the layers of younger ?Kanmantoo age rocks may regional response is much lower than that from overlie it. the Wallowa Domain.
By contrast, the Willoby and Wallowa Domains Many of the magnetic trends in the Wallowa show strong northwest trends of 10 to 70 nT. and Willoby Domains have a pronounced The Wallowa Domain has a magnetic character pattern that could be interpreted as a sequence 14 GEOLOGICAL INTERPRETATION - OUYEN
Table 2 Summary geological history for OUYEN TIME Ma 0-60 Murray Basin sedimentation; minor faulting 60-80 Basaltic volcanism ~300 Urana Group sedimentation and faulting 400-410 Granite intrusion; cratonisation of Stawell Zone ~440 Deformation Stawell Zone
Grampians Group sedimentation Glenelg Zone 485-500 Delamerian deformation, intrusion and cratonisation Sedimentation Ozenkadnook Upson Subzone Dimboola Subzone Subzone Volcanism and Volcanism and sedimentation sedimentation ??520 Deformation Unknown Deposition; possible deformation
that has been disrupted by many layer-parallel, after 500 Ma, and may correlate in part with southwest-dipping faults. However the the 520 Ma intrusive and deformation event in southwestern edge of the Wallowa Domain is southeastern south Australia (Gravestock et al., strongly convex southwest, compatible with a 1995). northeast-dipping basal fault. These two fault patterns can be reconciled if the early The gravity response of the Subzone has a southwest-dipping faults have been cut by a strong gradient. Values of about -30 µms-2 are later low angle northeast-dipping fault. present in the northern parts of the Subzone, whilst to the south the few values are closer to Elsewhere in the Subzone, the structural and -80 µms-2. However the calculated depths to tectonic patterns are also consistent with an basement from the magnetic data show little early history of southwest-dipping faults variation in depth to basement. The two followed by later shallow northeast-dipping observations imply an increasing thickness of faults. The northeast-dipping faults are relatively dense non-magnetic cover rocks to probably low angle thrust faults, although some the north. This would require the presence of a may also have had components of normal non-magnetic layer above the Wallowa and movement. The timings of the movements are Willoby Domains, either Grampians Group or unknown, but at least some took place before non-magnetic Kanmantoo Group. the intrusion of a large ?mafic body into the Alternatively, the previously noted deep Subzone, whilst other movements seem to be magnetic body in the northern part of later. Both sets seem to be cut off by the HORSHAM could be a granite that extends far Escondida Fault, which forms the eastern enough north to influence the gravity readings boundary of the Subzone. On regional grounds on OUYEN. Since deep magnetic granites deformation is unlikely to have taken place appear to be present on OUYEN, the latter explanation is preferred. GEOLOGICAL INTERPRETATION - OUYEN 15
The western boundary of the Subzone is not greenschist facies, since a thin section from the seen on OUYEN. core was described as sericitic phyllite. They tentatively correlated the sequence with the No mineralisation is known to be present. In Heatherdale Shale or Fork Tree Limestone the near future, the 200 m of cover is likely to from the lower part of the Upper Proterozoic to mean that only potentially major orebodies Cambrian Kanmantoo Trough. Similar would be of interest to explorers. lithologies may be present elsewhere in the Upson Subzone. Upson Subzone The Skriety Fault forms the eastern edge of the The Upson Subzone lies in the northwest corner Goongee Domain, the easternmost Domain of of OUYEN, and extends onto RENMARK and the Subzone. This fault may have a steep west PINNAROO. It lies west of the Dimboola dip and have overthrust younger units in the Subzone and north of the Ozenkadnook Dimboola Subzone. The eastern side of the Subzone. Goongee Domain has a more convex-west shape. The other Domains in the Subzone Most of the rocks appear to be weakly to repeat this convex-west pattern, a pattern non-magnetic. Four of the domains (the Ngallo, which is probably the result of a west-directed Panitya, Carina and Alphildale Domains) are Delamerian thrust fault set. The movement bounded by a unit with a response generally sense is quite different to the faults in the about 10 to 20 nT higher than the adjacent Dimboola Subzone, which often show areas. This unit has been named the movements consistent with dextral extension Gunamalary Domain. The regional responses along a 340° trend. are dominated by edge effects from the much more magnetic Dimboola Subzone, which raises If the rocks are correlates of the Kanmantoo the background by over 200 nT in the eastern Trough, they may have similar mineral parts of the Subzone. potential. In South Australia, Morris (1988) considered that units significantly above the The Goongee Domain, is also weakly magnetic, Heatherdale Shale were prospective for sedex with a response typically of about 50 nT above styles of mineralisation. Even if similar rocks the regional background. were present on OUYEN, a depth of cover of at least 300 m is likely to deter exploration in the The results of Automag depth to basement near future. calculations on the magnetic data show basement depths of less than 300 m over parts Dimboola Subzone of the Gunamalary Domain. Elsewhere the Subzone seems deeper, generally over 400 m. Six domains are present in the Dimboola Subzone, the easternmost part of the Glenelg The gravity response of the Subzone has a Zone. The Kalkee, Dahlen and Ni Ni Domains strong gradient. In the south, it reaches above have been extended north from HORSHAM. 10 µms-2, whilst to the north the response is These are considered to be tholeiitic island arc about -110 µms-2, even where not apparently rocks. The Cowangie, Kurnbrunin and Little influenced by granites. This gradient may be Billy Domains have been first recognised on due to an increasing thickness of weakly OUYEN. Depths to magnetic basement sources consolidated Cainozoic sediments to the north. vary from possibly less than 200 m on the It is also at least partly due to the increasing southeastern edge of the Kalkee Domain to over influence of the less dense Netherby Trough, 1 000 m for much of the Dahlen Domain. which covers the Subzone in the northwest. All the Domains are characterised by a highly Peebinga 1, in the southwestern corner of magnetic basement. The regional response RENMARK, is the only drill hole known to generally exceeds 60 000 nT, or 200 nT above intersect the Upson Subzone basement. Rankin the Stawell Zone and Upson Subzone regional et al. (1991, p. 35) reported that the hole responses. In the north, the most magnetic intersected "a total of 55.47 m of approximately parts of the Kalkee, Little Billy and Dahlen equal proportions of metabasic rock Domains rise above 60 300 nT. (interpreted as basalt), limestone, and black shale (with tuffaceous horizons)". The grade of Responses from individual horizons are metamorphism may have been lower typically less than 100 nT, but rise to 1000 nT 16 GEOLOGICAL INTERPRETATION - OUYEN
in parts of the Kalkee Domain. Generally they faults which controlled the major dextral are broader than those on HORSHAM because extensional fault system noted in the Dimboola of the thicker Murray Basin cover. Subzone on HORSHAM (Moore, 1996). Other major faults also show movements consistent As on HORSHAM, the gravity response is with dextral extension along a 340° trend. generally high over the eastern domains and low over the Dahlen Domain. This lower The eastern edge of the Subzone is the Moyston response is interpreted to be from thicker Fault. In the south, the western boundary is Grampians Group or younger cover sequences. the Escondida Fault. On the magnetic images both the Moyston Fault and Escondida Fault None of the Dimboola Subzone rocks crop out or can be traced over 250 km. In the north, the have been drilled. The closest intersection has western edge of the Subzone is the Skriety been about 12 km south of the map sheet Fault, which separates Dimboola Subzone rocks border, in Warraquil 1, which bottomed in from the Upson Subzone. quartz feldspar porphyry. Further south, mapping on BALLARAT and other drilling on As no drill hole has intersected the Dimboola HORSHAM indicate that basement rocks Subzone on OUYEN, it is difficult to rank its include low-Ti, high-Mg andesites, gabbros and prospectivity. Exploration is most likely to other similar rocks with oceanic island arc follow success in shallower areas on affinities. Serpentinite may also be present in HORSHAM. The most likely target appears to some of the strongly magnetic layers, be a volcanic hosted massive sulphide deposit. particularly those inferred along the Moyston Fault. As similar magnetic and gravity Delamerian intrusions responses continue along strike onto OUYEN, similar rocks are probably present. No information has been published for any of the igneous rocks on OUYEN. However The Dahlen and Cowangie Domains have few granites from areas further south and west shallow magnetic sources, and may be have been dated and analysed and, together Cambrian volcanic rocks overlain by with the known tectonic relationships, these non-magnetic Grampians Group and younger have been used to constrain age estimates and rocks. In the Dahlen Domain, Gunamalary 2 other characteristics. intersected 230 m of Urana Formation and Grampians Group, bottoming in the latter. The Several S-, I- and A-type granites crop out on gravity signature over the Dahlen Domain is up HAMILTON. White and Chappell (1988), Gray to 150 µms-2 lower than that of the Cowangie (1990), and Turner et al. (1993) all record only Domain, implying that the middle Palaeozoic Delamerian dates. Indeed Gray and and younger sequence is much thinner in the Gravestock et al. (1995) record no younger Cowangie Domain. granites anywhere between the Dimboola Subzone and Adelaide. On OUYEN, many At the southern end of the Cowangie Domain, intrusions west of the Moyston Fault have been the texture of the residual magnetic image interpreted as being cut by faults. These changes from a flat, even texture to one that is intrusions are generally considered to be of more felted. This texture, of short strike length Delamerian ages. subparallel responses, is often seen over areas of highly deformed and metamorphosed rocks. One significant body intrudes the Wallowa and Because of this, the Kurnbrunin Domain has Willoby Domains. The body is clearly intrusive been separated out as a different domain. but, unlike granites, is associated with a gravity high of up to 50 µms-2. Other phases may give a The shallow sources in the Little Billy Domain slight gravity low. The body has an area of separate deeper sources in the Dahlen and about 350 km2. It is cut by the Escondida Cowangie Domains. The western boundary Fault, but one phase stitches the northeast fault of the Little Billy Domain can be traced dipping fault on the western edge of the south onto HORSHAM, where the Little Billy Wallowa Domain. The body may be at least Domain and then the western part of the partly gabbroic, and may be part of the same Kalkee Domain cut out against the fault. intrusive suite as the Black Hills Norite, Further south, on BALLARAT, the fault is considered to be Delamerian by Gravestock et mapped as the Mehuse Fault. The Mehuse al. If so, this would mean that the Fault and Moyston Fault appear to be master northeast-dipping faults were formed no later GEOLOGICAL INTERPRETATION - OUYEN 17
than the Delamerian Orogeny. The magnetics Boinka, Glenbro, Dart Dart, and Pallarang show evidence of differentiation within the Domains) are interpreted as either turbidites or body, implying the possible presence of metaturbidites. All are considered to be platinoids. The depth of cover of about 400 m is extensions of the St Arnaud Group. likely to preclude exploration in the near future. They are very weakly magnetic, with a regional response typically between 59 780 nT and Another important intrusive complex sits at the 59 820 nT where not influenced by external northern end of the highly magnetic Dimboola deep bodies. Individual responses are usually Subzone. This complex also appears to have less than 5 nT. The most magnetic domains are phases of varying densities, although none of the Woornack and Glenbro Domains, whilst the the small amount of the densest phase is least magnetic is the Willenabrina Domain. The present on OUYEN. Again, most of the relatively high regional response from the complex is considered to be of Delamerian age, Glenbro domain may reflect a less since most of it seems to be cut by faults. mineralogically mature sediment provenance or However some bodies are cut by faults that are increasing metamorphic grade as the Moyston in turn cut by later bodies. These younger Fault is approached. The high response of the intrusions may well be of Early Devonian age. Woornack Domain may partly result from the influence of a large magnetic granite complex in Many other intrusions are present in the the western part of SWAN HILL. Five Glenelg Zone. Most are less than 10 km2 in non-magnetic granites are interpreted to locally area, and appear to have been faulted. They lower the regional response by up to 20 nT. are usually strongly magnetic, with similar responses to oxidised I-type granites of the The detailed magnetic responses also vary Mt Cole Suite on ST ARNAUD. slightly between domains. Some, like most of the Ouyen Domain, show very little internal Perhaps the most interesting targets for character. Rare trends of about 2 nT are the mineral exploration are the tops of the strongly only features visible. Whitehead (1995) showed magnetic granites in the southwest corner of that, in the Dunolly 1:100 000 map sheet area, the map sheet area. These may be prospective similar responses were probably from for Olympic Dam styles of mineralisation. pyrrhotitic black slates. Moore (1996) suggested that the Dergholm Granite, on HAMILTON, has some similarities Other areas near domain edges, like the eastern to Olympic Dam analogues. parts of the Galah and Warracknabeal Domains, seemed to have more magnetic 4.2 Post-Delamerian trends. These could be interpreted as sediments containing more volcanic material and representing lower parts of the Stawell Zone stratigraphy.
The Stawell Zone is interpreted as the Alternatively, they may be caused by magnetic basement to the eastern half of OUYEN. The parts of the Beaufort Formation. Krokowski de Zone has been subdivided into sixteen domains, Vickerod et al. (1997) noted a similar magnetic eight of which were first recognised on OUYEN. package on the hanging wall of the Percydale The other eight domains, which generally lie in Fault in the St Arnaud 1:100 000 map sheet the centre of the map sheet area, continue area. On structural grounds, these are also northward from HORSHAM. One, the likely to be lower parts of the St Arnaud Group. Warracknabeal Domain, has been modified from the HORSHAM interpretation to take It is also possible that the prograde better account of features seen on OUYEN. metamorphic effects of faulting may have As on HORSHAM, the western boundary of the increased the amount of magnetite present in Stawell Zone has been placed at the interpreted the adjacent rocks. Layer parallel dykes may position of the Moyston Fault. On OUYEN this also give rise to linear responses. lies along the western edges of the Dart Dart or Wyperfeld Domains. Choosing between the various alternatives is not always possible. However it is considered The rocks of nine domains (the Woornack, likely that magnetic trends in hanging wall Ouyen, Galah, Warracknabeal, Willenabrina, slates will parallel significant faults. Trends in 18 GEOLOGICAL INTERPRETATION - OUYEN
thicker, more competent, volcanic-derived the hanging wall slates. It is therefore more arenites are more likely to be oblique to an likely that the rocks present are volcanic- adjacent bounding fault. Thus the eastern derived sedimentary rocks, rather than parts of the Galah and Warracknabeal Domains pyrrhotitic black slates. may be volcanic derived arenites, whilst the western edge of the Woornack Domain may be The other domains often show linear trends up slates. to 10 km long with responses of 30 to 50 nT. These become less diffuse and stronger in the In the south, residual filtered images of the western Tarranyurk, Caringa and Wyperfeld total magnetic intensity of the Stawell Zone Domains. Local reversely magnetised units are show subtle changes in the "texture" of their present in the Crymelon and Corker Domains. responses. To the east, the Woornack, Ouyen, These five Domains are all interpreted to Galah and Warracknabeal Domains all have include mafic volcanic and sedimentary rocks. many linear basement responses about 10 km On BALLARAT the outcropping mafic volcanic long, and even where individual responses units along the Avoca Fault and the Stawell- cannot be identified there is a distinct linearity Ararat Fault are tholeiitic basalts or related in the background "noise". Further west, this ultramafic rocks (see for example Ramsay et al., becomes less prominent. Next to the Moyston 1992). It is probable that units broadly along Fault, the Dart Dart Domain shows basement strike with similar magnetic character have linear features less than 5 km and the textural similar geochemistry. character has a more even, felted appearance. In the south, the gravity contours (Map 1) of the One possible explanation for this change is that Stawell Zone show two distinct responses. West metamorphic grades increase to the west in the of the Willenabrina Domain these are typically Stawell Zone. Increasing metamorphism and above -40 µms-2. To the east of this boundary, folding may reduce the strike length of the the response gradually falls to about -140 µms-2. small proportion of magnetic units. Although This decrease in gravity response generally individual units may not always be visible in corresponds to the interpreted decreasing the filtered data, consistent magnetic trends in proportion of volcanic material in the eastern the rocks may show up as a layered pattern of part of the Stawell Zone. It also corresponds to aliased responses. This would be more a possible decreasing metamorphic grade. noticeable at the shallower basement depths in the south than further north. All the western domains of the Stawell Zone trend at about 330°, whilst those further east The remaining seven domains (the Tiega, trend closer to 360°. This fanning was Paignie, Crymelon, Corker, Tarranyurk, accommodated by the presence of three more Caringa and Wyperfeld Domains) are more Domains (Tiega, Galah and Paignie) in the magnetic. They lie between the domains north. All three are cut off by the eastern edge interpreted as metasedimentary basement and of the Warracknabeal Domain, implying that are considered to have a higher content of this boundary fault has a different (easterly?) volcanic rocks. In the northeast, the regional dip to the other boundaries of the Domains. response of the Paignie and Tiega Domains is typically 10 to 15 nT higher than the adjacent Each of the patterns described above is metasedimentary domains. Further west, the consistent with a sequence of oceanic volcanics difference between responses with the adjacent which grade upwards into the St Arnaud metasedimentary domains rises generally to Group. The sequence was then metamorphosed about 30 nT, but with local differences of over and deformed so that the folded and 100 nT. fault-repeated sequence soled out to the west against the Moyston Fault. The same pattern There is also significantly more local variation has been mapped by Cayley and Taylor (1996) in the domains. Residual filtered magnetic on BALLARAT. images highlight the general presence of features with responses of 1 to 10 nT in the less Moore (1996) described the gold potential and magnetic Tiega and Paignie Domains. These outlined exploration criteria for HORSHAM. trends are slightly oblique to, and are cut off by, OUYEN has similar potential, but basement the domain-bounding faults. Mapping in the depths generally over 200 m will constrain St Arnaud 1:100 000 map sheet area has shown exploration in the short term. that the major faults tend to parallel layering in GEOLOGICAL INTERPRETATION - OUYEN 19
Grampians Group classified the Rocklands Rhyolite as I-type and the other intrusions in the area as either I-type Map 2 shows the distribution of the Grampians or A-type granites. Group, which overlies the Glenelg Zone. Both magnetic and non-magnetic granites are Knight et al. (1995) considered that present in the Stawell Zone. Like those in the Gunamalary 2 was the only drill hole on Glenelg Zone, many of the magnetic granites OUYEN to intersect Grampians Group rocks, show more magnetic rims and less magnetic mature sandstones with rare pebbly and cores. Again, this implies that the intrusions mudstone units. The present interpretation are oxidised and fractionated I-type or A-type extends the Grampians Group to cover the granites. Similar patterns are also seen further Dahlen and Cowangie Domains in the Dimboola south, on BALLARAT and ST ARNAUD, where Subzone. This has been inferred from the Wyborn (written comm., 1996) also classified non-magnetic character and a gravity response most of the granites as oxidised I-type granites; higher than the overlying units but lower than S-types were rare. the basement. The Grampians Group is now believed to be present throughout the Netherby In eastern OUYEN, the Stawell Zone includes Trough. Gravity modelling from data collected sub-circular areas where the magnetic intensity along the Ouyen Highway in the northwestern falls by about 20 nT and the gravity by up to part of the map sheet area is consistent with a 50 µms-2. These are probably deep thickness of up to 1.8 km of Grampians Group non-magnetic intrusions. rocks. The Stawell Zone granites are undeformed and To the south, on HAMILTON, Cayley and so are younger than the age of deformation. To Taylor (in prep.) have mapped the Grampians the south, on BALLARAT, Ar-Ar dating by range, and concluded that the Grampians Foster et al. (1996) placed the deformation at Group is younger than the Delamerian about 440 Ma. The few intrusions on Orogeny, and older than 410 Ma. The present BALLARAT dated by Arne et al. (1996), using interpretation is consistent with this, since U-Pb (SHRIMP) methods, have ages of about granites and many large faults cut the 400 to 410 Ma or 370 Ma. K-Ar ages tend to be Grampians Group. slightly younger. The 400 to 410 Ma age is favoured for the intrusions on OUYEN, since Devonian granites none are aligned with possible late structural trends. Both the Stawell and Glenelg Zones include granites younger than Delamerian. In the Despite the depth of cover, gold exploration Glenelg Zone, rare intrusions appear to intrude might be feasible. Moore (1996b) correlated Grampians Group rocks, or to stitch relatively some of the gold deposits in the Stawell Zone young faults. Most of the intrusions are with the edges of non-magnetic granites and magnetic. Some show zoning with more with more magnetic sediments. Similar magnetic rims and less magnetic cores, techniques could be used on OUYEN to pick indicating an oxidised magma that has structurally favourable sites. This approach is fractionated. likely to be tried first where cover is least, in These late granites have been tentatively the southeastern part of the area. assigned a Lower Devonian age, since none are aligned with the interpreted Middle Devonian Carboniferous-Permian granites on HORSHAM. However on HORSHAM, granites are present which stitch Gunamalary 2 is the only drill hole on OUYEN the Mehuse Fault and the Grampians Group. known to have intersected Carboniferous On OUYEN, the Mehuse Fault is interpreted to sediments. From 487 m to 571 m, it intersected cut a granite which intrudes Grampians Group claystone, mudstone and tillite, which Orth rocks. Either the Mehuse Fault has a complex (1986) correlated with the Carboniferous Urana history, or the granites are of different ages. Formation.
At least some of the intrusions may correlate Using Gunamalary 2 as a control, other areas with the Rocklands Rhyolite on HAMILTON, in the Netherby Trough with similar low where Fanning (1991) obtained a U/Pb zircon gravity response have been interpreted as age of 410±3 Ma. Chappell et al. (1991) containing Urana Formation. On the detailed 20 GEOLOGICAL INTERPRETATION - OUYEN
gravity traverse along the Ouyen Highway, increase to about 500 m in the northern Knight et al. (1995) modelled the thickness of Netherby Trough. Late reactivation of faults Urana Formation at 140 m. may have given locally thinner or thicker sections. Late faults are clearly seen in the A second area to the east, named the Koonda eastern parts of Map 3, where northeast Basin by Knight et al. (1995), has also been trending faults appear to have vertical offsets of defined using the magnetic and gravity hundreds of metres on magnetic units within responses. Koonda 1 bottomed in 74 m of the Stawell Zone. By comparison, Nott (1989) sandstone and siltstone of unknown age. The showed the Danyo Fault, in the northwest, to present study has tentatively interpreted this have a vertical offset of at least 150 m at the as Carboniferous. Gravity modelling and base of the Cainozoic. automatic depth to magnetic basement calculations indicate that the Koonda Basin In the same paper, Nott showed that the Danyo could have a thickness of over 200 m of Fault was a growth fault, with the offset of pre-Tertiary sediments. The gravity and about 50 m at the top of the Middle to Late magnetic images show the Basin has Miocene Bookpurnong Beds. The present study dimensions of about 70 x 20 km. was not able to show other examples of growth faults in the Murray Basin, although they are Mesozoic and Cainozoic probably present.
Over 200 small magnetic sources have been A few of the near-surface units within the identified beneath the Murray Basin. These Murray Basin have distinctive magnetic, range in size from less than 200 m up to about radiometric or digital elevation model 2 km in diameter and have magnetic responses signatures, and so could be remapped by the up to 100 nT. Sources within the Netherby present study. Map 2 includes a new surface Trough seem to be larger than those elsewhere, geological interpretation overlaid on an RGB although this may in part be due to greater radiometric image. depths of burial. CRAE drilled many similar features on HORSHAM, and intersected basalt Southwest trending dendritic magnetic features and nephelinite (CRA, 1990). of about 1 nT have been ascribed to the Late Miocene to Pliocene Calivil Formation. These Generally the basalt plugs overprint faults, are present in the east, and were interpreted as even those with late movements. However palaeochannels. None are known to crop out in some plugs are cut by faults, implying that the area. there may have been more than one age of intrusion. The few age dates quoted by Price The oldest unit seen at the surface is the Late et al. (1988) on similar rocks elsewhere in Miocene to Pliocene Loxton-Parilla Sands. It western Victoria have ages from 80 Ma to has a distinctive linear pattern, with broadly 18 Ma. All the plugs seem to be covered by the arcuate, northwest trending, convex-east Murray Basin sediments, implying a late features about 0.5 to 1 km apart in the southern Cretaceous to Eocene age. This also fits with parts of the magnetic (Fig. 2), radiometric the apatite fission track evidence from (Map 2) and digital elevation (Fig. 6) images. Gunamalary 2 (see Section 3.3), which gave the The more magnetic linear zones correspond most recent cooling event in the region as with topographic lows, showing palaeoswales in starting between 100 Ma and 60 Ma. the Loxton-Parilla Sands. They may reflect the retreating shorelines of the Pliocene Murray Murray Basin sediments cover the entire sheet Basin sea. area. Depths are mostly about 200 m in the southeastern and southwestern parts, but GEOLOGICAL INTERPRETATION - OUYEN 21
Figure 6 OUYEN digital elevation image with sun from 270°; linear stretch, with magenta lower than 60 m and white higher than 150 m, corrected to true elevation.
The linear patterns show subtle discordances. to be outcropping Loxton-Parilla Sands. The To the west of 142°00'E 37°00'S, most swales unit is also host to the WIM 150 deposit on fan between 320° and 335°. East from here to HORSHAM and probably to the recent 142°15'E 36°30'S, the swales trend between Woornack discovery near Ouyen. 330° and 345°. Further east, they trend between 320° and 340°. These may reflect The digital elevation image clearly outlines the small changes in the slope of the Basin caused presence of two large subcircular palaeolakes. by faulting. The western discordance is close to The most prominent, is in the northwestern the mapped position of the Hindmarsh Fault part, and has a diameter of 50 to 60 km. The (GSV, 1974). However it does not correspond Pink Lakes are probably the modern remnants with any single basement fault, and it is likely of this much larger lake. The shoreline is at that the Hindmarsh Fault is made up of several about 100 m on the southern edge, and about discrete faults which together give the 90 m on the northwestern edge. The height movement sense seen. difference appears to be real, since it can also be seen on the Danyo 1:100 000 topographic To the north, the linear features are generally map (first edition). It implies that the lake edge present only on the magnetic images and as has been tilted after it was formed. subtle changes in the digital elevation images, implying that the Loxton-Parilla Sands are The other lake system is centred on Wirrengren mostly covered by younger units. Plain, at the northern end of the Wimmera All of the presently known heavy mineral sand River topographic low. To the east and occurrences are within the area now considered southeast, Loxton-Parilla Sand ridges are 22 GEOLOGICAL INTERPRETATION - OUYEN
clearly cut off by two northeast-trending ridges. Sands swales, those of the lunettes show up as The system is probably the ancestral final magnetic and radiometric highs. They can be outflow of the Wimmera River. easily distinguished from the Loxton-Parilla Sands by having a shorter wavelength, more Where the lake system has eroded Loxton - arcuate shapes and locations east of lakes. In Parilla Sands containing heavy minerals, new some areas they appear to overlie the Lowan deposits may have formed. These are likely to Sand, although it is more likely that the two be higher grade but smaller than those in the units interfinger. Loxton-Parilla Sands. The 1974 Ouyen geological map shows many Both palaeolakes are covered by Quaternary gypsum and evaporite deposits in the northern sediments and are younger than the Upper part of the area. These are generally present in Miocene to Lower Pliocene Loxton-Parilla topographic lows in areas of Woorinen Sands. They may be time equivalents of the Formation. Often they have a raised potassium older parts of the Shepparton Formation that and uranium radiometric response. The were deposited in wet climates. worked gypsum deposits cluster either in these areas or just outside the area covered by Lowan The Quaternary Woorinen Formation shows a Sand. confused radiometric and digital elevation response, probably because the main dune direction is east-west (Lawrence, 1975), parallel to the flight line direction. Radiometric images show the Woorinen Formation lapping onto the lower areas of the Parilla Sand both south and north of the Big Desert. The radiometric and digital elevation data are more consistent with large areas of the southeastern part of the sheet having subcropping Parilla Sand than with Lawrence's interpretation of Woorinen Formation.
Lawrence (1975) divided the Quaternary Lowan Sand into two units, parabolic dunes and longitudinal dunes. The parabolic dunes tend to be in the centre of the dune fields while the longitudinal dunes are at the eastern (leading) edges of the sand body. The RGB radiometric image clearly shows the Lowan Sand as a unit with low response; the longitudinal dunes have slightly higher responses in all three channels. The general pattern conforms closely with that given by Lawrence. It also shows that the Lowan Sand overlies the Woorinen Formation.
The lake and river deposits of the Coonambidgal Formation generally have a high radiometric response, although the highs are more subdued in areas adjacent to Lowan Sand. Along the rivers and major creeks in the eastern part of the map sheet area, the Coonambidgal Formation deposits can be interpreted as both underlying and overlying the Lowan Sand. Both the stratigraphic relationships and the merging of radiometric character imply the units interfinger.
Lunettes are present on the eastern sides of many of the salinas. Like the Loxton-Parilla GEOLOGICAL INTERPRETATION - OUYEN 23
5 Conclusions styles of mineralisation. Another large intrusive complex is present at the northern end of the Dimboola Subzone. The magnetic basement of OUYEN has been divided into 31 geophysical and structural The Stawell Zone rocks are turbidites and ocean domains. They can be grouped into two zones, floor or oceanic island arc basaltic rocks typical the western Glenelg Zone and the eastern of the Lachlan Fold Belt in central and western Stawell Zone. The boundary is the northern Victoria. They have probably been extension of the Moyston Fault, which marks metamorphosed to as high as amphibolite facies the eastern limit of rocks affected by the and faulted along north- to northwest trending Delamerian Orogeny. It thus forms the faults. In the exposed areas of the Lachlan Fold boundary between the Lachlan and Kanmantoo Belt in western and central Victoria, significant Fold Belts. gold deposits cluster where weakly magnetic sediments are present near gravity lows Other significant faults separate each domain. associated with granites. Similar responses These faults can be traced for up to 250 km. could be used to target gold exploration beneath the Murray Basin cover in the Stawell Zone The Glenelg Zone has been subdivided into the rocks. Dimboola, Upson and Ozenkadnook Subzones. To the south, the Dimboola Subzone is Sedimentary rocks of the Netherby Trough dominated by Cambrian volcanic rocks that overlie rocks of the Cowangie and Dahlen probably have oceanic island arc affinities and Domains in the Dimboola Subzone. They that have been only weakly metamorphosed. include the pre-Devonian fluvial to marginal Similar rocks are probably present on OUYEN. marine Grampians Group and the The Subzone appears to been subjected to Carboniferous Urana Group tillite and dextral extensional faulting along master faults associated rocks. Gravity models give a that trend approximately 340°. thickness of 1.8 km of sediments in the northern part of the Netherby Trough. The Upson Subzone lies in the northwestern part of the area. It is poorly known, as it does Magnetic and non-magnetic granites intrude not crop out and only a small number of drill the Stawell Zone. Both are considered to have holes are known to have intersected it, all of ages of about 400 Ma, and may be spatially them outside the map sheet area. The rocks associated with gold mineralisation. intersected include phyllite, black shale, limestone and metabasalt. It is likely that the Over 200 ?Cretaceous to ?Eocene basaltic and various arcuate domains reflect east-dipping nephelinitic plugs have been intruded in the fault sets. sheet area. Most stitch faults, but a small number appear to be faulted. These may reflect The Ozenkadnook Subzone lies west of the either a range of ages of intrusion or faulting. extension of the Escondida Fault. The Yanipy Domain may be complexly folded, highly The entire map sheet area is covered by the metamorphosed Proterozoic rocks. The sediments of the Murray Basin. The thickness Wallowa and Willoby Domains are more likely of sediments ranges from about 200 m in the to be rocks that have ultimately been emplaced southeast and southwest to over 500 m above above the Yanipy Domain on northeast-dipping the Netherby Trough. In the short term these faults, but they show evidence of older sediments are likely to inhibit exploration in southwest-dipping faults. There is no direct the underlying basement, although highly evidence of the rocks present in these domains, profitable major mineral deposits may still be but they have been tentatively inferred to attractive. include metavolcanic and metasedimentary rocks. The new datasets show generally similar patterns to the 1974 OUYEN surface geological The Glenelg Zone includes 500 Ma intrusions. map. However much of the eastern part of the The largest body, a mafic and felsic complex of map sheet area appears to be underlain by about 350 km2, has intruded the Ozenkadnook Loxton-Parilla Sands. Interpretation of the Subzone. Other bodies seem to be present in magnetic, radiometric and digital elevation the southwestern subsurface. The tops of these data show the Loxton-Parilla Sands as a series could be prospective for Olympic Dam Cu-Au of strand lines spaced at about 0.5 to 1 km 24 GEOLOGICAL INTERPRETATION - OUYEN
across the sheet area. These trend between 320º and 345º and are consistent with a Murray Basin sea shoreline retreating to the southwest. Both Wirrengren Plain and the Pink Lakes are remnants of much larger upper Tertiary to lower Quaternary lake systems. Both the lake systems and the Loxton-Parilla Sands show indirect evidence of faulting in the upper Cainozoic. The Woorinen Formation appears to be older than the other Quaternary units on the map sheet, principally the Coonambidgal Formation and the Lowan Sand. GEOLOGICAL INTERPRETATION - OUYEN 25
6 References CRA EXPLORATION PTY LTD., 1990. Murray Basin project drilling of bulls-eye anomaly drill holes. 1:100 000 map ARNE, D.C., BIERLEIN, F.P., sheets 7123, 7223, 7224, 7323, 7324, MCNAUGHTON, N.J., WILSON, C.J.L., 7325, 7424, 7425, 7524, 7525, 7526, and MORAND, V.J., AND RAMSAY, W.R.H., 7625 (4 volumes). Department of Natural 1996. Timing of felsic magmatism in Resources and Environment, Victoria, Victoria and its relationship to gold expired mineral exploration reports. mineralisation. In Hughes, M.J., Ho, S.E., and Hughes C.E., (eds.) Recent CRAWFORD, A.J., 1988. Cambrian. In J.G. developments in Victorian geology and Douglas and J.A. Ferguson (eds.) Geology mineralisation. Australian Institute of of Victoria. Victorian Division, Geological Geoscientists Bulletin 20, pp. 43-48. Society of Australia Inc., pp. 37-62.
BROWN, C.M., AND STEPHENSON, A.E., 1986. CROSBY, R.O., 1963. Interpretation report of Murray Basin, Southeastern Australia: airborne magnetometer survey of Murray Subsurface Stratigraphic Database. Basin, New South Wales-Victoria. Bureau of Mineral Resources, Geology Unpublished report for Planet Oil and Geophysics, Report 262. Company N.L. Department of Natural Resources and Environment, Victoria, BROWN, C.M., AND STEPHENSON, A.E., 1991. expired petroleum exploration report. Geology of the Murray Basin southeastern Australia. Bureau of DAVIS, R.P., 1990. Exploration Licence 1888, Mineral Resources, Geology and Beulah, Victoria report for the six months Geophysics Bulletin 235. ending September 1990 and final report. BHP-Utah Minerals International BUREAU OF MINERAL RESOURCES, 1982. Ouyen Unpublished Company Report 7181. 1:250 000 map of total magnetic intensity Department of Natural Resources and contours. Environment, Victoria, expired mineral exploration report. BUREAU OF MINERAL RESOURCES, 1980. Ouyen 1:250 000 map of Bouguer anomalies. FANNING, C.M., 1991. Single and multi-grain U-Pb zircon dating of the Rocklands CAYLEY , R.A., AND TAYLOR, D.H., 1996. Rhyolite. Geological Survey of Victoria Geological evolution and economic Unpublished Report 1991/6. potential of The Grampians area, Victoria. In Hughes, M.J., Ho, S.E., and FOSTER, D.A., GRAY, D.R., AND OFFLER, R., Hughes C.E., (eds.) Recent developments 1996. The western subprovince of the in Victorian geology and mineralisation. Lachlan Fold Belt, Victoria: structural Australian Institute of Geoscientists style, geochronology, metamorphism and Bulletin 20, pp. 11-18. tectonics. Specialist Group in Geochemistry, Mineralogy, and Petrology, CAYLEY , R.A., AND TAYLOR, D.H., (In prep.) Field Guide 1. Geological Society of Ararat 1:100 000 map geological report. Australia Inc. Geological Survey of Victoria Report 115.
FROME BROKEN HILL, 1956. Report on Murray CHAPPELL, B.W., ENGLISH, P.M., KING, P.L., River Basin aeromagnetic survey by WHITE, A.J.R., AND WYBORN, D., 1991. Worldwide Aerial Surveys Pty. Ltd. for Granites and related rocks of the Lachlan Frome Broken Hill. Department of Fold Belt. (1:1250 000 scale map) Bureau Natural Resources and Environment, of Mineral Resources. Victoria, expired petroleum exploration report.
GEOLOGICAL SURVEY OF VICTORIA, 1974. Ouyen 1:250 000 geological map.
GIBSON, G.M., AND NIHILL, D.N., 1992. Glenelg River Complex: western margin of the 26 GEOLOGICAL INTERPRETATION - OUYEN
Lachlan Fold Belt or extension of the JAYATILAKA, C.J., LAKEY, R.C., ELDER, G.M., Delamerian Orogen into western ROBINSON, K.J., SHUGG, A.J., Victoria? In C.L. Fergusson and R.A. HEISLERS, D.S., AND BARNETT, S.R., 1993. Glen eds. The Palaeozoic eastern margin South Australian/Victorian Mallee region of Gondwanaland: Tectonics of the groundwater model stage 1 completion Lachlan Fold Belt, southeastern Australia report. Department of Conservation and and related orogens. Tectonophysics 214, Natural Resources Victoria. pp. 69-91. KNIGHT, L.A., MCDONALD, P.A., FRANKEL, E., GIBSON, H.J., MOORE, M.E., MOONEY, R.A., AND AND MOORE, D.H., 1995. A preliminary KEIRAVILLE KONSULTANTS, 1996. appraisal of the pre-Tertiary infrabasins Thermal history reconstruction of Murray beneath the Murray Basin, northwestern Basin wells Gunamalary-2, Sunset-1, Victoria. Victorian Initiative for Minerals Warraquil-1, Wallpola-1, Olney-1 in and Petroleum Report 16. Department of Victoria and Nadda-1 in South Australia, Agriculture, Energy and Minerals. using apatite fission track analysis and vitrinite reflectance. Geotrack Report KROKOWSKI DE VICKEROD, J., MOORE, D.H., #558 (unpublished). AND CAYLEY, R.A., 1997. St Arnaud 1:100 000 map geological report. GRAVESTOCK, D.J., ALLEY, N.F., BENBOW, M.C., Geological Survey of Victoria Report 110. COWLEY, W.M., FARRAND, M.G., FLINT, R.B., GATEHOUSE, C.G., KREIG, G.W., AND LAWRENCE, C.R., 1975. Geology, PREISS, W.V., 1995. Early and Middle hydrodynamics and hydrochemistry of Palaeozoic. In Drexell, J., and Preiss, the southern Murray Basin. Geological W.V., (eds.) The geology of South Survey of Victoria Memoir 30. Australia Volume 2. Mines and Energy South Australia. MOORE, D.H., 1996a. A geological interpretation of the geophysical data for GRAY, D.R., ALLEN, R.L., ETHERIDGE, M.A., the Horsham 1:250 000 map sheet area. FERGUSON, C.L., GIBSON, G.M., MORAND, Victorian Initiative for Minerals and V.J., VANDENBERG, A.H.M., WATCHORN, Petroleum Report 24. Department of R.B., AND WILSON, C.J.L., 1988. Agriculture, Energy and Minerals, 34 p. Structure and Tectonics. In J.G. Douglas and J.A. Ferguson (eds.) Geology MOORE, D.H., 1996b. Geophysical signatures of of Victoria. Victorian Division, Geological gold deposits in western Victoria. In Society of Australia Inc., pp. 1-36. Hughes, M.J., Ho, S.E., and Hughes C.E., (eds.) Recent developments in Victorian GRAY, C.M., 1990. A strontium isotopic geology and mineralisation. Australian traverse across the granitic rocks of Institute of Geoscientists Bulletin 20, southeastern Australia: Petrogenetic and pp. 43-48. tectonic implications. Australian Journal of Earth Sciences 37, pp. 331-350. MOORE, D.H., 1997. New data, new insights: an example from western Victoria. GRAY, D.R., AND WILLMAN, C.E., 1991. Exploration Geophysics 28, pp. 270-275. Deformation in the Ballarat Slate Belt, central Victoria, and implications for the MOORE, D.H., TWYFORD, R., SHI, Z., AND crustal structure across southeast WILLOCKS, A., 1997. Automatic depth Australia. Australian Journal of Earth estimation in regional magnetic surveys: Sciences 38, pp. 171-201. a case study from north west Victoria. In Shalley, M. (ed.) Australian Society of Exploration Geophysicists 12th Conference and Exhibition Conference Handbook, Preview No. 66, pp. 69-70. GEOLOGICAL INTERPRETATION - OUYEN 27
MORRIS, B.J., 1988. Review of lead-zinc ROBINSON, M., et al. Victorian Rural Water mineralisation in South Australia: Corporation, 1992. Ouyen Kanmantoo Trough. Department of Hydrogeological Map (1:250 000 scale). Mines and Energy, South Australia Bureau of Mineral Resources, Geology Report Book 88/22. and Geophysics, Canberra.
NOTT, R.B., 1989. Preliminary hydrogeological SHI, Z., AND BOYD, D., 1993. AUTOMAG - an assessment of the Mallee/Wimmera automatic method to estimate thickness region of northern Victoria: Summary of of overburden from aeromagnetic profiles. data from the deep drilling program Exploration Geophysics 24, pp. 789-794. 1986-1988. Groundwater Assessment and Policy Branch, Department of Water STUART-SMITH, P.G, (in prep.) Willaura Resources. 1:100 000 map geological report. Australian Geological Survey ORTH, K., 1986. Well completion report Organisation, Canberra. Gunamalary 2. Petroleum Development Branch, Victorian Department of STUMP, E., WHITE, A.J.R., AND BORG, S.G., Industry, Technology and Resources, 1986. Reconstruction of Australia and W 940. Antarctica: evidence from granites and recent mapping. Earth and Planetary PAINTER, J.A.C., 1990. Exploration Licence Science Letters 70, pp. 348-360. 1626 "Hopetoun" progress report on exploration for the six-monthly period THORNE, R., HOXLEY, G., AND CHAPLIN, H., ended 23rd April 1990. Aberfoyle 1990. Nyah to the South Australia Resources Ltd. Department of Natural border hydrogeological project. Rural Resources and Environment, Victoria, Water Commission of Victoria, expired mineral exploration report. Investigations Report 1988/5.
PRICE, R.C., GRAY, C.M., NICHOLLS, I.A., AND TURNER, S.P., ADAMS, C.J., FLÖTTMANN, T., AND DAY, A., 1988. Cainozoic volcanic rocks. FODEN, J.D., 1993. Geochemical and In J.G. Douglas and J.A. Ferguson (eds.) geochronological constraints on the Geology of Victoria. Victorian Division, Glenelg River Complex, western Victoria. Geological Society of Australia Inc., Australian Journal of Earth Sciences 40, pp. 439-452. pp. 275-292.
RAMSAY, W.R.H., STANLEY, J.M., HUGHES, M., TWYFORD, R., 1997. A methodology for depth to MORAND, V., AND CARROLL, R.P., 1992. basement estimates for the Murray Basin The Pitfield-Avoca Fault system: the area, north west Victoria. Geological locus of a cryptic-discontinuous Survey of Victoria Technical Record greenstone belt in central-western 1997/2. Department of Natural Victoria. Geological Society of Australia Resources and Environment. Abstracts 32, pp. 233-235. VANDENBERG, A.H.M., 1978. The Tasman Fold RAMSAY, W.R.H., AND VANDENBERG, A.H.M., Belt system in Victoria. 1986. Metallogeny and tectonic Tectonophysics 48, pp. 267-297. development of the Tasman Fold Belt System in Victoria. Ore Geology Reviews WATERFIELD, D.W., 1992. E.L. 3220 Ouyen 1, pp. 213-257. Block, Victoria final report. CRA Exploration Pty. Ltd. unpublished report RANKIN, L.R., CLOUGH, B.J., FARRAND, M.G., number 18438; Department of Natural BARNETT, S., LABLACK, K., Resources and Environment, Victoria, GATEHOUSE, C.G., AND HOUGH, L.P., expired mineral exploration report. 1991. Murray Basin transect project: 1990 well completion reports. Department of Mines and Energy, South Australia Report Book 91/15. 28 GEOLOGICAL INTERPRETATION - OUYEN
WATCHORN, R.B., AND WILSON, C.J.L., 1989. Structural setting of the gold mineralisation at Stawell, Victoria, Australia. Economic Geology Monograph 6, pp. 292-306.
WHITE, A.J.R., AND CHAPPELL, B.W., 1988. Granites. In J.G. Douglas and J.A. Ferguson (eds.) Geology of Victoria. Victorian Division, Geological Society of Australia, pp. 427-439.
WHITEHEAD, M.L., 1995. Geological interpretation of geophysical data over the Dunolly 1:100 000 sheet. Victorian Initiative for Minerals and Petroleum Report 7. Department of Agriculture, Energy and Minerals Victoria.
WILLOCKS, A.J., 1987. Interpretation of the aeromagnetics and gravity on the Horsham 1:250 000. Geological Survey of Victoria Unpublished Report 1987/13.
WILLOCKS, A.J., 1995. An appraisal of the new airborne surveys over the North West VIMP area. Victorian Initiative for Minerals and Petroleum Report 6. Department of Agriculture, Energy and Minerals.
WILLIAMS, I.S, CHAPPELL, B.W., CROOK, K.A.W, AND NICOLL, R.S. 1994. In search of the provenance of the early Palaeozoic flysch in the Lachlan Fold Belt, southeastern Australia. . Geological Society of Australia Abstracts 37, p. 464.
WILSON, C.J.L., WILL, T.M., CAYLEY, R.A., AND CHEN, S., 1992. Geologic framework and tectonic evolution in Western Victoria. In C.L. Fergusson and R.A. Glen eds. The Palaeozoic eastern margin of Gondwanaland: Tectonics of the Lachlan Fold Belt, southeastern Australia and related orogens. Tectonophysics 214, pp. 93-127. GEOLOGICAL INTERPRETATION - OUYEN 29
Appendix 1
Specifications of the Horsham airborne survey
Location Horsham (part), St Arnaud (part) and Ouyen 1:250 000 map sheet areas Duration August-December, 1994 Km flown 71 274 km Acquisition and processing Kevron Geophysics Flight line direction East-west Flight line spacing 200 m (part HORSHAM only) and 400 m Tie line spacing 4 km Flight height 80 m above ground level Magnetometer Scintrex CS-2 Cs vapour (±0.001 nT resolution) Time sample interval 0.1 sec Ground sample interval Approx. 7 m Gamma spectrometer Exploranium GR820 (256 channels, calibrated radiometrics) Crystal volumes Downward array 33.8 l Upward array 4.2 l Time sample interval 1.0 sec Ground sample interval Approx. 70 m Navigation Ashtech XII GPS receiver, real time differential Contract and client Geological Survey of Victoria, Department of Agriculture, Energy and Minerals Geological Survey of Victoria 3020 reference number 30 GEOLOGICAL INTERPRETATION - OUYEN
Appendix 2 A complex, circular feature about 12 km in diameter with response about 40 nT which cuts across the Domain; intruded by a later, more Geophysical domains - Ouyen magnetic body with responses to 200 nT. (The 1:250 000 map sheet area early body has an associated gravity high of at least 40 µmsec-2.); magnetic mafic intrusions. The following domain descriptions characterise regions that have similar magnetic pattern, Circular to sub-circular features less than 1 km gravity response and basement geology, and in diameter and generally 10 to 150 nT; both which have first been outlined on OUYEN. The normally and reversely polarised; basaltic new domains are described generally in order plugs. from west to east. The domain boundaries are shown in Figure 2 and Map 1. Comments are Gravity response: included on magnetic features that are High?; the few stations over the domain gave superimposed on the established fabric, such as readings from about -20 µmsec-2 to -40 µmsec-2. those from younger igneous rocks or the Murray Basin. Boundaries: East - Faulted; a linear magnetic low of about Descriptions for domains previously described 50 nT. on HORSHAM are in Moore (1996). All domain names and descriptions have been registered West - Faulted?; taken as the western edge of a with the Central Register of Stratigraphic linear magnetic unit with response about 20 nT Names. higher than the Yanipy Domain.
Glenelg Zone - Ozenkadnook Subzone Lithologies: Unknown; the magnetic character is most like Wallowa Domain the volcanics of the Kalkee Domain, implying the possibility of calc-alkaline acid to mafic Named from: volcanic rocks. Wallowa Downs, a homestead (5112000E 60257000N)1 within the Domain. Correlations: Uncertain; possibly with other Cambrian Regional magnetic response: volcanic rocks of the region. Generally about 59 780 nT to 59 800 nT, with a Willoby Domain strong linear character disrupted by many layer-parallel faults. Named from: Detailed magnetic responses: The parish of Willoby, on the southern edge of Features are characterised by the Domain.
- lengths of up to 10 km and responses of Regional magnetic response: up to 70 nT, Low; typically between 59 700 nT and 59 750 nT, although this is probably at least - being discordant with other features partly influenced by residual effects from the within the Subzone, deep magnetic source in the Dimboola Subzone. - having strong lows on their northeastern Extreme layer-parallel faulting seems to be sides, implying shallow southwestern present in the northern part of the Domain. dips, Detailed magnetic response: - general convex-west shape, implying Minor linear features with responses to 80 nT. antiforms which plunge to the west, and - each apparently dying out rapidly to the Superimposed magnetic features: west, implying a limited depth extent. Gridding artefacts; the northeast-trending Superimposed magnetic features: features of about 1 nT may be caused by the gridding routine being unable to completely resolve successive northwest-trending 1 These numbers give the approximate AMG Zone 54 grid responses. reference for the locality after which each domain is named. GEOLOGICAL INTERPRETATION - OUYEN 31
Regional gradient; the deep body in the Boundaries: Dimboola Subzone causes a regional low of East - Possibly faulted against the Gunamalary about 50 nT to 100 nT. and Carina Domains.
A complex of variably magnetic features (from West - Largely outside OUYEN; to the south flat responses to 400 nT) which cuts across the possibly faulted against the Gunamalary Domain. (The complex has an associated Domain. gravity high of up to 50 µmsec-2); magnetic mafic intrusions. Lithologies: Uncertain; possibly metasediments. Two circular features about 1 km in diameter with responses of 10 and 100 nT; basaltic plugs. Correlations: Uncertain; possibly of similar age to the Minor narrow, parallel shallow linear trends St Arnaud Group or Kanmantoo Group. about 5 km long, weakly arcuate (concave west) of about 1 nT, striking about 320°; interdune Ngallo Domain heavy mineral concentrations. Named From: Gravity response: Ngallo Parish, which the includes the northern High; typically from -30 µmsec-2 to -15 µmsec-2; part of the Domain. slightly lower than adjacent domains. Regional magnetic response: Boundaries: Low; typically 59 750 nT to 59 780 nT, but as East - Faulted; probably the northern extension low as 59 700 nT along the western edge. of the Escondida Fault. Detailed magnetic response: West - Faulted; a linear magnetic low of about Away from the western faulted boundary, 50 nT. essentially flat, but possible minor, weak linear features with responses of about 0.5 nT Lithologies: trending at about 340°. Uncertain; possibly metasediments within faulted volcanic rocks. Superimposed magnetic features: Gridding artefacts?; the northeast-trending Correlations: features of about 2 nT next to the western Uncertain; probably with other Cambrian boundary may be caused by the gridding sedimentary and igneous sequences in the routine being unable to completely resolve region. successive northwest-trending responses.
Glenelg Zone - Upson Subzone Minor narrow, parallel shallow linear trends about 5 km long, weakly arcuate (concave west) Panitya Domain of about 0.5 nT, striking about 330°; interdune heavy mineral concentrations. Named from: Panitya Siding (4992000E 61005000N) within Gravity response: the Domain. High? (possibly from -10 to -40 µmsec-2); few data points. Regional magnetic response: Low; typically from 59 700 nT to 59 800 nT . Boundaries: East - Faulted against the Gunamalary Detailed magnetic response: Domain. Generally featureless; a 0.5 nT to 2 nT response parallels the eastern edge of the Domain. West - Faulted, probably by an extension of the Escondida Fault. Lithologies: Gravity response: Uncertain; possibly sediments metamorphosed Moderate to high?; the only data is from a to at least upper greenschist facies. detailed traverse across the Domain, which gave responses of from -110 to -70 µmsec-2. Correlations: 32 GEOLOGICAL INTERPRETATION - OUYEN
Uncertain; possibly of similar age to the Uncertain; possibly sediments metamorphosed St Arnaud Group or the Kanmantoo Group. at least to upper greenschist facies.
Carina Domain Correlations: Uncertain; possibly of similar age to the Named from: St Arnaud Group or the Kanmantoo Group. The village (5083000E 60984000N) and railway siding within the Domain. Gunamalary Domain
Regional magnetic response: Named From: Generally low, but complicated by the effects of Gunamalary Parish, which lies at the north regional gradients and magnetic granites. eastern end of the Domain.
Detailed magnetic response: Regional magnetic response: No internal character visible that is definitely A series of convex-west linear features of not from either intrusions or the adjacent similar response (up to 80 nT) which divide the domains. largely non-magnetic Upson Subzone into different domains. At the southern end of the Superimposed magnetic features: Upson Subzone, the Domain forms the Regional gradient; the deep body in the boundary between the Dimboola Subzone and Dimboola Subzone causes a regional gradient of the Ozenkadnook Subzone. about 300 nT. Detailed magnetic response: Elliptical features from 3 to 20 km in diameter The linear features are a series of en echelon with responses of up to 400 nT; of at least two responses, typically about 10 km long. ages, since some stitch interpreted faults that cut other interpreted intrusions; magnetic Superimposed magnetic features: granites. Regional gradient; the deep body in the Dimboola Subzone causes a regional gradient of Crudely elliptical areas of about 10 km up to 400 nT. diameter, with flat, low magnetic character; non-magnetic granites. An elliptical feature about 4 km in diameter with response about 40 nT which cuts across Circular to sub-circular features about 1 km in the Domain; lower in the centre, higher on the diameter and with responses of about 20 nT; eastern edge where contact metamorphic effects basaltic plugs. may be present; magnetic granite.
Minor narrow, parallel shallow linear trends Gravity response: about 3 km long, weakly arcuate (concave west) Unknown; no stations lie within the Domain. of about 0.5 nT, striking about 330°; interdune heavy mineral concentrations. Boundaries: Probably faulted. Gravity response: Varies from -80 µmsec-2 to -160 µmsec-2 , caused Lithologies: by varying thicknesses of less dense cover Unknown; possibly mafic volcanics or sequences; non-magnetic granites may also be serpentinite; may include magnetic mylonite. present, lowering the response. Correlations: Boundaries: Possibly with the Cambrian tholeiitic basaltic East - Probably faulted against the Goongee volcanics of western Victoria. Domain. Alphildale Domain West - Probably faulted against the Gunamalary Domain. Named from: Alphildale Homestead (5060000E 60790000N), North - Intrusive. which lies within the Domain. Lithologies: Regional magnetic response: GEOLOGICAL INTERPRETATION - OUYEN 33
Very weakly magnetic; dominated by regional A series of linear trends about 5 km long, with a gradient effects from a deep body in the consistent convex-west shape. Dimboola Subzone. Superimposed magnetic features: Detailed magnetic response: Regional gradient; the deep body causes a Minor features 2 to 5 km long and subparallel regional gradient of about 600 nT. to the Domain boundaries with responses of less than 2 nT. Circular feature 3 km in diameter, faulted along the eastern edge of the Domain, but Superimposed magnetic features: stitching the western edge; response to 100 nT Regional gradient; the deep body in the and with slightly lower response in the centre; Dimboola Subzone causes a regional gradient of magnetic granite. from 100 to 400 nT. Circular to sub-circular features 0.5 to 2 km in Circular feature about 1 km in diameter with a diameter with responses of 20 to 200 nT; response of 15 nT; basaltic plug. basaltic plugs.
Minor narrow, parallel shallow linear trends up Gravity response: to 3 km long, weakly arcuate (concave west) of The domain lies on the boundary between two about 0.5 nT, striking about 330°; interdune quite different gravity regions. To the east and heavy mineral concentrations. south, the regional field is typically between -170 and -110 µmsec-2. To the west, the Gravity response: regional field is as high as +10 µmsec-2. On this High to very high, ranging from +40 µmsec-2 in gradient, the domain might be a local gravity the southern part to -60 µmsec-2 in the north. high of about 5 µmsec-2.
Boundaries: Boundaries: East - Probably faulted against the Goongee East - A major fault, which bounds the Domain. Netherby Trough.
West and north - Probably faulted; the West - Probably faulted. A major change in boundary forms an arcuate, concave east magnetic response, with no evidence of units outline defined by magnetic units of the which cross the boundary. If faulted, the Gunamalary Domain. movement must predate at least some movement on the eastern side of the Domain, Lithologies: since the intrusion which stitches the western Uncertain; possibly sediments metamorphosed side is cut off by the eastern side. to at least upper greenschist facies. Lithologies: Correlations: Uncertain; possibly intermediate to mafic Uncertain; possibly sediments of similar age to volcanic rocks. the St Arnaud Group or the Kanmantoo Group. Correlations: Goongee Domain Uncertain; either upfaulted from the Dimboola Subzone or a tholeiitic basaltic package similar Named from: to those below the St Arnaud Group. The locality (5168000E 61180000N) within the Domain and the parish which covers the greater part of the Domain.
Regional magnetic response: A prominent north-south-trending linear feature about 3 km wide of 5 to 100 nT which is discordant to the regional trends to the east and west, and which marks the probable boundary of a deeper, highly magnetic body.
Detailed magnetic response: 34 GEOLOGICAL INTERPRETATION - OUYEN
Glenelg Zone - Dimboola Subzone Faint, weak, short strike length, subparallel features are present, implying possible aliased Little Billy Domain responses.
Named from: Superimposed magnetic features: Little Billy Parish, which straddles the Domain. Sub-circular feature about 1 km in diameter and with response about 2 nT; basaltic plug. Regional magnetic response: A strongly magnetic package, most magnetic in Parallel, narrow, shallow linear trends up to the southern parts of OUYEN and north of 10 km long, weakly arcuate (concave west) of 35º20', where it becomes the most magnetic about 0.5 nT, striking about 340°; interdune unit within the map sheet area with a response heavy mineral concentrations. above 60 400 nT. Gravity response: Detailed magnetic response: No stations within the Domain. Strong linear features present, typically 5 to 10 km long with responses to 150 nT. Boundaries: East - Faulted against the Kalkee Domain. Superimposed magnetic features: Circular features with diameters of about 2 km West - Faulted against the Kalkee Domain. and responses which may exceed 200 nT. Some seem to be cut by later faults, others seem to Lithologies: overprint the faults; magnetic granites. Uncertain; possibly metasediments over Kalkee Domain acid to basic volcanics. Circular to sub-circular features 0.5 to 2 km in diameter and responses less than 50 nT, which Correlations: seem to lie along faults and are shallower than The magnetic character is most like that of the the general magnetic basement; basalt plugs. St Arnaud Group metasediments.
Gravity response: Cowangie Domain Moderate to very high (-75 to +40 µmsec-2); lower to the north, where cover sequences are Named From: thicker. The village (5345000E 61006000N) and railway siding of Cowangie within the Domain. Boundaries: East - Faulted against the Kalkee and Regional magnetic response: Cowangie Domains. Dominated by a strong deep source which deepens to the east; no shallow sources. West - Faulted against the Dahlen Domain. Detailed magnetic response: Lithologies: None from rocks of the Domain. Uncertain; possibly intermediate to mafic volcanic and intrusive rocks. Superimposed magnetic features: Elliptical magnetic features up to 5 x 3 km with Correlations: responses to 300 nT and which cut across other A Cambrian igneous sequence of uncertain features; magnetic granites. affinities. Circular to sub-circular features of two different Kurnbrunin Domain types;
Named from: - less than 1 km in diameter and with The locality (5724000E 60322000N) within the responses less than 20 nT; shallow Domain. basaltic plugs, or - 1 to 3 km in diameter and with responses Regional magnetic response: of 10 to 150 nT; basaltic plugs below Dominated by a deep magnetic source. thicker Murray Basin sediments. Narrow, parallel, shallow linear trends up to Detailed magnetic response: 15 km long, weakly arcuate (concave west) of GEOLOGICAL INTERPRETATION - OUYEN 35
less than 2 nT, striking about 330; interdune Boundaries: heavy mineral concentrations. East - Possibly faulted against the Dart Dart Domain. Gravity response: High (mostly -10 to 70 µmsec-2), but often West - Faulted against the Kalkee Domain. slightly lower than the adjacent Kalkee May connect to the Moyston Fault to the Domain. southeast.
Boundaries: Lithologies: East - Probably faulted , either against the Uncertain; probably mafic metavolcanics. Kalkee Domain or rocks of the Stawell Zone. Correlations: West - Probably faulted. Probably with the tholeiitic mafic volcanic rocks seen elsewhere in central and western Victoria. Lithologies: Milmed 8001 bottomed in pre-Cainozoic shale Pallarang Domain (Brown & Stephenson, 1986). Named from: Correlations: Pallarang (5298000E 61160000N), a place name The upper, non-magnetic layer probably with within the Domain. the Grampians Group. The lower, dense, magnetic layer is probably mafic igneous rocks, Regional magnetic response: possibly of the Kalkee Domain. This A near-surface weak response is masked by a interpretation is consistent with that proposed the response from a deep, strongly magnetic by Cayley and Taylor (1996) for the Grampians. body. This produces a strong easterly gradient of about 100 nT. Stawell Zone Detailed magnetic response: Wyperfeld Domain Rare responses of up to 5 nT and about 5 km long trend about 045º. Named from: The Wyperfeld National Park, in which the Superimposed magnetic features: Domain lies. Circular to sub-circular features less than 1 km Regional magnetic response: in diameter and responses of about 5 nT; Two distinct areas of layered magnetic rocks basaltic plugs. just east of the interpreted position of the. northern extension of the Moyston Fault. Gravity response: Responses of from 59 820 nT to 59 950 nT in the Moderate?; stations from -85 µmsec-2 to southern area and 59 970 nT to 60 100 nT in -105 µmsec-2, but strongly influenced by broad the northern area are affected by a strong regional gradients and poor station distribution. easterly gradient from a deeper body. Boundaries: Detailed magnetic response: East - Probably faulted against the east-dipping Subparallel linear magnetic responses up to Caringa Domain. 10 km long and locally up to 100 nT. West - A north-trending 40 nT high; probably a Superimposed magnetic features: layer of mafic volcanics within a fault zone. A roughly rectangular body about 10x3 km, with a response of about 40 nT; magnetic South - Uncertain, may be faulted; taken at the granite. last northeast-trending unit.
Circular feature about 0.5 km in diameter and Lithologies: response of 10 nT; basaltic plug. Uncertain; metasediments? Correlations: Gravity response: Possibly equivalents of the St Arnaud Group. No stations fall within the Domain. 36 GEOLOGICAL INTERPRETATION - OUYEN
Glenbro Domain Caringa Domain
Named from: Named from: The Glenbro Homestead (5461000E Caringa Homestead (5861000E 60179000N) 61032000N) within the Domain. within the Domain.
Regional magnetic response: Regional magnetic response: Dominated by a strong easterly gradient from a A zone of discontinuous highs to 60 000 nT, deep, strongly magnetic body. In the north of with associated linear magnetic units typically OUYEN, the western edge of the domain has a about 59 850 nT. In the northern parts of the response above 59 900 nT, whilst the eastern Domain, probably dips east. edge has a response of about 59 800 nT. Detailed magnetic response: Detailed magnetic response: Individual highs to 100 nT, with linear Flat; detail is obscured by the strong gradient magnetic units up to 8 km long and 50 nT. and depth of burial. Superimposed magnetic features: Superimposed magnetic features: Sub-circular magnetic features about 3 km in A 5 km diameter body with a 500 nT response diameter, with magnetic response to about cuts the western edge of the Domain. Another 40 nT; magnetic granite. body with response to 20 nT is present at the southern end of the Domain; magnetic granite. Circular to sub-circular features less than 1 km in diameter and responses less than 10 nT; Circular areas of flat, low magnetic response basaltic plugs. adjacent to interpreted magnetic granites; non-magnetic granite. Gravity response: High?; the only station within the Domain has a Narrow, parallel, shallow linear trends up to response of -44 µmsec-2. 5 km long, weakly arcuate (concave west) of about 1 nT, striking about 330°; interdune Boundaries: heavy mineral concentrations. East - Faulted against the Boinka Domain.
Narrow, arcuate, concave west, features of West - Generally faulted against the Dart Dart about 0.5 nT; magnetic highs correspond with Domain; in the north, probably dips east. lunette swales; lunettes. Lithologies: Circular to sub-circular features less than 1 km Probably mafic volcanics. in diameter and responses less than 5 nT; basaltic plugs. Correlations: Probably similar to other tholeiitic basaltic Gravity response: sequences in central and western Victoria. Moderate, -90 µmsec-2 to -140 µmsec-2, where not influenced by areas of later less dense cover sequences. Lithologies: Uncertain; ?metasediments Boundaries: East - On regional evidence, probably faulted Correlations: against the Boinka Domain. On regional considerations, St Arnaud Group.
West - Probably faulted against either the Boinka Domain Caringa or Dart Dart Domains; contact may dip east. Named from: The village (5547000E 61042000N) and lake on the western edge of the Domain. GEOLOGICAL INTERPRETATION - OUYEN 37
Regional magnetic response: Uncertain; possibly sediments metamorphosed Variable; probably due to influences unrelated at least to upper greenschist facies. to the rocks just below the Murray Basin cover. In northern OUYEN, typically about 59 790 nT; Correlations: in the southern half, as high as 59 880 nT. Probable St Arnaud Group.
Detailed magnetic response: Paignie Domain In northern OUYEN, few distinct basement responses; in the south, many weak, short Named from: strike length, subparallel features are present, The locality (5962000E 61180000N) and probably aliased responses. channel within the Domain.
Superimposed magnetic features: Regional magnetic response: Deep magnetic bodies up to 4 km diameter with The southern and eastern parts of the Domain responses to 50 nT; magnetic granite. are moderately magnetic, with responses typically about 59 800 nT. Further north, on Sub-circular areas up to 25 km diameter where MILDURA, the regional response falls to less the magnetic response is about 10 nT lower than 59 785 nT. than the regional response elsewhere; non-magnetic granite. Detailed magnetic response: Many linear responses of about 5 nT in the Circular to sub-circular features less than 1 km more magnetic areas. Further north, few in diameter and responses less than 10 nT; responses of more than 1 nT. basaltic plugs. Superimposed magnetic features: Narrow, parallel, shallow linear trends up to Circular magnetic responses of less than 5 nT 10 km long, weakly arcuate (concave west) of and less than 1 km in diameter; basaltic plugs. about 1 nT, striking about 330°; interdune heavy mineral concentrations. Rare narrow, parallel shallow linear trends up to 5 km long, weakly arcuate (concave west) of Narrow, arcuate, concave west, features of about 1 nT, striking about 330°; interdune about 0.5 nT in an area mapped as containing heavy mineral concentrations. lunettes; magnetic highs correspond with lunette swales; lunettes. Gravity response: Low; about -140 µmsec-2 to -150 µmsec-2; Gravity response: possibly slightly lower response than adjacent Uncertain; ranges from at least -110 µmsec-2 to domains, although this could easily be -190 µmsec-2, but confused by effects from accounted for by differing thicknesses of less granitic intrusions, later less dense cover dense cover rocks. sequences, and inadequate gravity station spacing. Boundaries: East - Faulted; on OUYEN marked by an Boundaries: abrupt change from the more magnetic, linear East - At least partly faulted against the character of the Paignie Domain to the less Tarranyurk Domain, which has a response up magnetic, flat character of the Galah Domain. to 100 nT higher than the Boinka Domain; all Trends in the Paignie Domain are truncated at magnetic features in the Tarranyurk Domain the boundary. are terminated at the boundary. West - Faulted; on OUYEN, marked by a 50 km West - In the southern and central parts of long linear magnetic high of up to 10 nT, which OUYEN, faulted, generally against the Caringa separates the Paignie and Warracknabeal Domain; all magnetic features in the Caringa Domains. Domain terminate at the boundary. To the north, on regional considerations probably Lithologies: faulted; the Boinka and Glenbro Domains are Uncertain; possibly more magnetic similarly non-magnetic. metavolcanics grading upwards to sediments. Correlations: Lithologies: 38 GEOLOGICAL INTERPRETATION - OUYEN
Possibly similar lithologies to those Watchorn further south by a narrower magnetic high of and Wilson (1989) described in the Stawell about 10 nT. mine sequence. Lithologies: Galah Domain Untested.
Named from: Correlations: The settlement and railway siding (6067000E Probably part of the St Arnaud Group; the 61168000N) within the Domain. western part may be Pyrenees Formation, whilst the eastern, more magnetic, part could Regional magnetic response: either be Beaufort Formation or metasediments Weak, but showing consistent regional with a higher volcanic component. increasing from west to east and from south to north. The lowest responses are less than Tiega Domain 59 785 nT, whilst the highest responses exceed 59 810 nT. Named from: The village (6108000E 61170000N) and channel Detailed magnetic response: within the Domain. The few weak (2 nT) basement linear features are most clearly seen on the eastern side of the Regional magnetic response: southern part of the Domain. A north-south-trending zone about 2 km wide, pinching out to the south and wider to the Superimposed magnetic features: north; response about 59 810 nT, about 15 nT A 7x8 km diameter elliptical magnetic low of at higher than the Ouyen Domain to the east and least 10 nT that crosses the boundary of the about 10 nT higher than the Galah Domain to adjacent Warracknabeal Domain; non-magnetic the west. granite. Detailed magnetic response: Narrow, parallel, shallow linear trends up to Trends are slightly en echelon to the zone 10 km long, weakly arcuate (concave west) of boundaries, with sinistral to vertical apparent about 1 nT, striking about 330°; interdune movement sense; faults typically disrupt more heavy mineral concentrations. continuous trends at about 10 km intervals; individual responses about 10 nT. Generally east-west trending features of about 2 nT and showing both normal and reverse Superimposed magnetic features: polarity; palaeochannels. Rare narrow, shallow linear trends up to 5 km long, weakly arcuate (concave west) of about 1 Circular to sub-circular features less than 1 km nT, striking about 330°; interdune heavy in diameter and responses less than 10 nT; mineral concentrations. basaltic plugs. Arcuate, concave west, subparallel features in Gravity response: both digital terrain and magnetic datasets; local On the only detailed gravity traverse in the relief up to 20 m, magnetic response up to 2 nT; region, a 50 µmsec-2 high compared to the lunettes. domains either side, but part of a regional gravity low. The high may be due to local Gravity response: thickness variations in the overlying Murray About -130 µmsec-2; possibly slightly lower Basin, rather than basement response. response than adjacent domains, although this could easily be accounted for by differing Boundaries: thicknesses of less dense cover rocks. East - Probably faulted, but could be a facies change from metavolcanics to metasediments, Boundaries: or metasediments with different provenance; East - Faulted; an abrupt change in magnetic magnetic trends in the Tiega Domain are character, with magnetic trends in the Galah truncated at the boundary. Domain truncated. West - Probably faulted, but could be a facies West - Faulted; marked in the northernmost change from metavolcanics to metasediments, parts of OUYEN by a 1 km wide 5 nT high, and or metasediments with different provenance; GEOLOGICAL INTERPRETATION - OUYEN 39
magnetic trends in the Tiega Domain are East - Possibly faulted; marked by a change in truncated; regional magnetic response also magnetic character and a higher magnetic and changes, but not as much as the eastern gravity response from the Woornack Domain. boundary. West - Probably faulted; marked by distinct Lithologies: changes in character and a lower regional Uncertain; probably either metavolcanics or magnetic response than the Warracknabeal or metasediments derived from volcanics. Tiega Domains.
Correlations: Lithologies: Possibly similar lithologies to those Watchorn The only drill hole to intersect the Domain, and Wilson (1989) described in the Stawell Tyenna 1, bottomed in schist and gneiss (Brown mine sequence. & Stephenson, 1986).
Ouyen Domain Correlations: Probably correlates with parts of the Pyrenees Named from: Formation on ST ARNAUD. The town of Ouyen (6200000E 61185000N), the major town within the Domain. Woornack Domain
Regional magnetic response: Named from: A regional magnetic low, with a regional Woornack (636000E 61085000N), a place name response of about 59 800 nT, and with large within the Domain. areas below 59 780 nT in the south on the western side of the Domain. Regional magnetic response: Weak, with a subtle gradient from 59 820 nT in Detailed magnetic response: southeastern OUYEN to 59 810 nT on the Generally few magnetic responses visible. Most northern edge. Slightly higher than domains to trend about 330°, with strike lengths up to the west. 10 km long and widths up to 0.5 km. Detailed magnetic response: Superimposed magnetic features: South of 36º15' S, trends of less than 5 nT with A sub-circular area about 2 km in diameter strike length 1 to 10 km and width of about devoid of fine scale basement responses and 0.5 km. These strike 350° to 360°, parallel to with slightly lower regional response; the domain boundaries. The character may be non-magnetic granite. partly due to original bedding and partly formed during Wilson et al. (1992) dominant D2 Parallel, narrow, shallow linear trends up to event. 20 km long, weakly arcuate (concave west) of about 1 nT, striking about 345° in the south and Further north, the fine features visible are not 330º in the north. Less apparent in the north; from basement sources. interdune heavy mineral concentrations. Superimposed magnetic features: Anastomosing features showing both normal Parallel, narrow, shallow linear trends up to and reverse polarity and with responses about 5 km long, very weakly arcuate (concave west) 1 nT; palaeochannels: of about 1 nT, striking about 330°; interdune heavy mineral concentrations. Circular to sub-circular features about 0.5 km in diameter; responses mostly less than 20 nT, Anastomosing features showing both normal but rarely to 50 nT; basaltic plugs: and reverse polarity with responses about 1 nT; palaeochannels. Gravity response: Circular to sub-circular features less than 1 km Low; generally about -130 µmsec-2 but rising in diameter and response less than 20 nT; slightly to the west. The 11 x 11 km station basaltic plugs. spacing means that few stations are within the domain. Gravity response:
Boundaries: 40 GEOLOGICAL INTERPRETATION - OUYEN
Low; -130 µmsec-2 to -170 µmsec-2 and probably decreasing to the north, although defined by few stations.
Boundaries: East - Not present on sheet.
West - Possibly a fault contact, marked by a drop of about 5 nT to the background of the Ouyen Domain. Also marked by a generally lower gravity response over the Ouyen Domain.
Lithologies: Untested.
Lithological correlations: May correlate with parts of the Beaufort Formation on ST ARNAUD. GEOLOGICAL INTERPRETATION - OUYEN 41
Victorian Initiative for 13 BUSH, M.D., CAYLEY, R.A. and ROONEY, S., 1995. The geology and Minerals and Petroleum prospectivity of the Glenelg region, (VIMP) report series North West VIMP area. 14 SLATER, K.R., 1995. An appraisal of 1 BUCKLEY, R.W., BUSH, M.D., new airborne geophysical data over the O'SHEA, P.J., WHITEHEAD, M. and Glenelg region, North West VIMP area, VANDENBERG, A.H.M. 1994. The Victoria. geology and prospectivity of the Orbost 15 RYAN, S.M., KNIGHT, L.A. and Survey area. PARKER, G.J., 1995. The stratigraphy 2 VANDENBERG, A.H.M., WILLMAN, and structure of the Tyrendarra C., HENDRICKX, M., BUSH, M.D. and Embayment, Otway Basin, Victoria. SANDS, B.C. 1995. The geology and 16 KNIGHT, L.A., McDONALD, P.A., prospectivity of the 1993 Mount FRANKEL, E. and MOORE, D.H., 1995. Wellington Airborne survey area. A preliminary appraisal of the pre- 3 HOLDGATE, G., 1995. The exploration Tertiary infrabasins beneath the potential of the Permian Numurkah Murray Basin, Northwestern Victoria. Trough and Ovens Graben, Victoria. 17 PERINCEK, D., SIMONS, B.A., 4 BUSH, M.D., CAYLEY, R.A., ROONEY, PETTIFER, G.R. and GUNATILLAKE, R., SLATER, K. and WHITEHEAD K., 1995. Seismic interpretation of the M.L., 1995. The geology and onshore Western Otway Basin, Victoria. prospectivity of the southern margin of 18 LAVIN, C.J. and NAIM, H.M., 1995. the Murray Basin. The structure, stratigraphy and 5 ROONEY, R., 1995. Mineral petroleum potential of the Portland exploration history of the North West Trough, Otway Basin, Victoria. VIMP area. 19 SIMPSON, C.J., SIMS, J.P. and 6 WILLOCKS, A.J., 1995. An appraisal of ORANSKAIA, A., 1995. The geology the new airborne surveys over the and prospectivity of the Mt Elizabeth North West VIMP area. area, Eastern Highlands VIMP area. 7 WHITEHEAD, M.L., 1995. Geological 20 ORANSKAIA, A., 1995. A geological interpretation of geophysical data over interpretation of geophysical data over the Dunolly 1:100 000 sheet. the Mallacoota 1:250 000 sheet, Eastern Highlands VIMP area. 8 VANDENBERG, A.H.M., CALUZZI, J., NOT RELEASED WILLOCKS, A.J. and O'SHEA, P.J., 1995. The geology and prospectivity of 21 SARMA, S., 1995. Seismic the Mallacoota 1:250 000 sheet, Eastern interpretation of the offshore Otway Highlands VIMP area. Basin, Victoria. 9 SANDS, B.C., 1995. A geological 22 MEHIN, K., and LINK, A.G., 1995. interpretation of the geophysical data Early Cretaceous source rocks of the from the Orbost 1994 airborne survey. Victorian onshore Otway Basin. 10 OPPY, I.D., CAYLEY, R.A. and 23 PARKER, G.J., 1995. Early Cretaceous CALUZZI, J., 1995. The geology and stratigraphy along the northern margin prospectivity of the Tallangatta of the Otway Basin, Victoria. 1:250 000 sheet. 24 MOORE, D.H., 1996. A geological 11 CALUZZI, J., 1995. Mineral exploration interpretation of the geophysical data of history of the Tallangatta 1:250 000 the Horsham 1:250 000 map sheet area. sheet. 25 VANDENBERG, A.H.M., HENDRICKX, 12 SIMONS, B.A., 1995. An appraisal of M.A., WILLMAN, C.E., MAGART, new airborne geophysical data over the A.P.M., ORANSKAIA, A.N., ROONEY, Tallangatta 1:250 000 map area, S. and WHITE, A.J.R.,1996. The Victoria. geology and prospectivity of the Orbost 1:100 000 map area, eastern Victoria. 42 GEOLOGICAL INTERPRETATION - OUYEN
26 HENDRICKX, M.A., WILLMAN, C.E., 41 LAVIN, C. J., and MUSCATELLO, T. MAGART, A.P.M., ROONEY, S., 1997. The petroleum prospectivity of VANDENBERG, A.H.M., ORANSKAIA, the Casterton Petroleum System in the A. and WHITE, A.J.R. The geology and Victorian Onshore Otway Basin. prospectivity of the Murrungowar 42 CHIUPKA, J. W., MEGALLAA, M., 1:100 000 map area, eastern Victoria. JONASSON, K. E., and FRANKEL E., 27 BOYLE, R. J., 1996. Mineral 1997. Hydrocarbon plays and play exploration history of the Omeo fairways of four vacant offshore 1:100 000 map area. Gippsland Basin areas, 1997 acreage release. 28 HAYDON, S.J., 1996. An appraisal of airborne geophysical data from the 1995 43 MEHIN, K., and LINK, A.G., 1997. Omeo survey, Victoria. Late Cretaceous source rocks offshore Otway Basin, Victoria and South 29 MAHER, S., 1996. Mineral resources of Australia. the Dunolly 1:100 000 map area. 44 WILLOCKS, A.J., 1997. An appraisal of 30 CHIUPKA, J.W., 1996. Hydrocarbon airborne geophysical data from the Play Fairways of the Onshore Castlemaine-Woodend survey, Victoria. Gippsland Basin, Victoria. 31 MEHIN, K., and LINK, A.G., 1996. Early Cretaceous source rock evaluation for oil and gas exploration, Victorian Otway Basin. 32 SLATER, K.R., 1996. An appraisal of new airborne geophysical data over the Dargo region, Victoria. 33 McDONALD, P.A., 1996. An appraisal of new airborne geophysical data over the Corryong region, northeastern Victoria. 34 TWYFORD, R., 1996. An appraisal of airborne geophysical data from the Murrindal survey, Victoria. 35 HUTCHINSON, D.F., 1996. Mineral exploration history of the Dunolly 1:100 000 map area. 36 BROOKES, D.J. and BOYLE, R.J., 1996. Mineral exploration history of the Bairnsdale 1:250 000 map area. 37 MAHER, S., HENDRICKX, M.A., BOYLE, R.J. and BROOKES, D.J., 1996. Geology and prospectivity of the Bairnsdale 1:250 000 map sheet area. 38 McDONALD, P.A. and WHITEHEAD M.L., 1996. Geological interpretation of geophysical data over the Ararat 1:100 000 map sheet. 39 MOORE D.H. 1997. A geological interpretation of the geophysical data of the Ouyen 1:250 000 map sheet area. 40 BROOKES, D.J., 1997. Mineral exploration history, Ararat and Grampians 1:100 000 map areas. OUYEN 500000mE 520000mE 540000mE 560000mE 580000mE 600000mE 620000mE Cmup Cgm bs 35 00' S Cmue bs Dglm bs bs Cmsi bs bs GEOLOGICAL INTERPRETATION OF Cmug Cmuc Cgn bs Dglm Cmsg Cmsa Cmsl bs 6120000mN Cgm Cmsa / Dglm bs Cmuc BASEMENT GEOPHYSICAL FEATURES Dglm Cmsp Cmsr Cgm bs Cmsw bs OUYEN B bs Dglm bs bs bs Cmdk bs Cgm Cmdc LEGEND bs bs bs Cmst Cmsc Cgm bs bs bs Cgm Cmuc bs Cmso Cmsd Cmsc / bs Dgln bs Sedimentary Igneous Interpreted lithology Geophysical signature bs Cmsh bs Dglm Cmsb bs Cmse Dglm bs Dglm TERTIARY TO bs Basaltic to dioritic or nephelinitic plugs and associated volcanic rocks. Subcircular sources diameter about 0.5 km and amplitude usually less than 200 nT. bs MESOZOIC Cmuc bs bs Cmug Cmsl / Dgln Cmsk Cmsf Dgln Featureless magnetic areas often surrounded either by interpreted magnetic Cmue bs bs bs Non-magnetic granitic intrusions correlated with the Mafeking or Mt Cole bs LOWER Suites (Rb/Sr ages 380 to 400 Ma, U/Pb zircon to 410 Ma). granite or weakly magnetic contact aureoles. Gravity lows. Overprint Delamerian Cmdk faults but may be cut by later faults. DEVONIAN 2 bs Magnetic granitic intrusions correlated with the Mafeking or Mt Circular to elongate areas up to 50 km with rough magnetic texture and response of Cmsr / Dglm Dgln Cole Suites (Rb/Sr ages 380 to 400 Ma, U/Pb zircon to 410 Ma). up to 500 nT. Gravity lows. Overprint Delamerian faults but may be cut by later faults. Cmup Cmdy bs bs Cmdk Cmsg Cmuc Cmsb / bs Non-magnetic granitic intrusions mostly cut by Delamerian faults; correlated with Featureless magnetic areas often surrounded either by interpreted magnetic granite or Dgln Cgn bs intrusions of the Glenelg area and Padthaway Ridge with U/Pb zircon ages of weakly magnetic contact aureoles. Gravity lows. Generally faulted, but also overprint faults. 6100000mN Cmdk 500 to 520 Ma and K/Ar ages of 480 to 500 Ma. 2 Dglm bs Magnetic granitic intrusions generally cut by Delamerian faults; correlated with Circular to elongate areas up to 1 000 km with rough magnetic texture and response of Dglm bs bs 35 15' S CAMBRIAN TO Cgm intrusions of the Glenelg area and Padthaway Ridge with U/Pb zircon ages of up to 500 nT. Gravity lows. Generally faulted, but also overprint faults. bs ORDOVICIAN 500 to 520 Ma and K/Ar ages of 480 to 500 Ma. Cmug Dgln A bs 2 bs bs bs Cmso Cmst / bs Cgim Intermediate to mafic intrusions cut by Delamerian faults. Circular to elongate areas of about 100 km with rough magnetic texture and response of Dgln bs up to 300 nT; overprinted by faults. Gravity highs. Cmdh bs Cmsi bs bs Cmdc bs bs bs bs bs CRATONISED AT bs bs STAWELL ZONE APPROX. 440Ma Cmua Cmdc / bs Dglm MOYSTON FAULT Cmso bs Cmsw Cmue Cmsk Weakly magnetic with responses where not beneath deep cover of 1 to 3 nT trending 350 o to bs Woornack Domain: St Arnaud Group metasediments; ?lower greenschist facies. o Dglm 360 ; linear texture. Gravity response low; dominated by variations in basement depth. Cmst
Cmdk Cmdk Dgln Cmse Ouyen Domain: St Arnaud Group metasediments; ?lower greenschist facies. Essentially non-magnetic; in areas of thinner cover responses less than 3 nT striking 340 o ; Dglm Dglm Cmsi bs linear texture with most responses from cover. Gravity response low; dominated by
SKRIETY Cmsr variations in basement depth. Cmso bs Cmsb / bs Cmsd bs Cmun Dglm bs bs Cmsh Galah Domain: basal St Arnaud Group metasediments; ?lower greenschist facies. Weakly magnetic, from more magnetic rocks in the south and east to less magnetic in the Dgln west; linear texture. Gravity response moderate, but confused by effects from buried Cmsi bs Cmsc 6080000mN bs granites and thickness variations in cover. bs Cmsf Cmso bs Cmsw Weakly magnetic, with responses of less than 3 nT trending about 350 o; linear texture. Cmsr / bs bs Warracknabeal Domain: St Arnaud Group metasediments; ?lower greenschist facies. ESCONDIDA Dgln bs Cmsh / Lower gravity response than domains to the west. Cmdy bs Cmsb Dglm Cmsw/ Dgln Dgln Cmso bs Dgln Cmdc bs
FAULT Cmsi bs Dglm Cmsl bs Cmsg Willenabrina Domain: basal St Arnaud Group metasediments; ?lower greenschist facies. Generally very weakly magnetic but with responses with intensities up to 20 nT; linear Cmso texture; regional magnetic signature variable. Gravity response at similar levels to the Dglm bs bs Cmsl bs Crymelon Domain. Cgm Cgm Dglm bs Cmsb Cmob Dglm Boinka Domain: St Arnaud Group metasediments; ?upper greenschist facies or above. Very weakly magnetic, with a regional gradient imposed by more magnetic packages bs to the east and west; abundant short strike length weak subparallel (? aliased) responses. Cgm bs Cmsh 35 30' S Cmsf Gravity response probably low compared to the domains to the east and west. bs bs bs FAULT bs Cmso Cmow Cgm bs bs Dglm Glenbro Domain: St Arnaud Group metasediments; ?upper greenschist facies or above. Very weakly magnetic with little character where not influenced by other sources; abundant Cmse Dglm bs short strike length weak subparallel (? aliased) responses. Moderate gravity response. bs bs Cmsc / bs Dglm CAMBRIAN TO bs Cmsi Dgln ORDOVICIAN Cmsd bs bs Dart Dart Domain: St Arnaud Group metasediments; ?upper greenschist facies or above. Very weakly magnetic where not influenced by younger rocks; abundant short strike length bs bs Dglm weak subparallel (? aliased) responses. Gravity response moderate to very high. Cmsl / Dgln Cmug bs bs Dgln bs bs Cmsa o Cmdh bs Cmst Pallarang Domain: ?St Arnaud Group metasediments; ?lower greenschist facies. Very weakly magnetic, with minor responses less than 2 nT trending 45 ; weak bs Cmsb / linear texture. Gravity response probably moderate, but influenced by strong gradients bs Dglm 6060000mN bs from outside the domain. Cmdy bs Cmsi / bs bs Dglm Dgln bs Cmsd Cmsg Moderately magnetic with responses up to 10 nT. Gravity response low; variations MEHUSE Tiega Domain: tholeiitic basaltic volcanic and volcaniclastic rocks below the Cmdk /Dglm possibly caused by variations in basement depth. Cmow bs bs St Arnaud Group. Dglm bs Cmsc Cmsp Cgim Dglm Paignie Domain: tholeiitic basaltic volcanic and volcaniclastic rocks below the Grades from moderately magnetic responses, up to 5 nT in the west, to essentially non- Dgln bs Cmdk bs St Arnaud Group; grades west into metasediments. magnetic in the centre of the domain, with a 15 nT response forming the eastern edge. bs bs Gravity response low.
Cmsd Dglm Cmsc Crymelon Domain: tholeiitic basaltic volcanic and volcaniclastic rocks below the Weakly magnetic, with many linear responses, including some reversely polarised. Gravity Cmug/ bs Cgim bs Cmsl / Dgln Cmsw St Arnaud Group. response lower than most units to the west, higher than to the east. Dglm bs bs Cgim bs Cmdc Dglm Dgln bs Cmdy FAULT Cmsr Corker Domain: tholeiitic basaltic volcanic and volcaniclastic rocks below the basal Weakly magnetic, with rare linear responses of 10 to 50 nT, including reversely magnetised bs bs Cgim Cgim bs St Arnaud Group. responses. Gravity response higher than units to the east. bs Cmoy bs Cgm bs Cmst HOPETOUN Cmdh bs Cmsb bs Cmst Tarranyurk Domain: tholeiitic basaltic volcanic and volcaniclastic rocks below the Weakly magnetic with a broad high and local linear responses of up to 50 nT. Gravity bs bs bs Dglm 35 45' S St Arnaud Group. response high. Varies from low to very high, depending on the presence of granite intrusions Cgim bs and thickness of less dense cover. Cgim Cgim Cmdh / bs bs Dglm Cmsi Cmsi 6040000mN bs Caringa Domain: tholeiitic basaltic volcanic and volcaniclastic rocks below the Moderately magnetic, with most linear responses 10 to 50 nT, but rarely to 150 nT along the Cgim Dglm Dglm bs St Arnaud Group; may also include serpentinite along the western margin. western edge. bs Cmdc bs Cmsl bs bs Cmob/ bs Wyperfeld Domain: tholeiitic basaltic volcanic rocks and volcaniclastics below the Parallel magnetic responses of 10 to 100 nT. Cgim Cgim bs bs Cmsf Cgim Dglm bs bs St Arnaud Group. Cgim bs Cmdc / bs Cmsr Cgim bs bs Dglm bs Cmdy bs GLENELG ZONE Cgim bs bs CRATONISED BY Cmob bs 490 +_ 10 Ma UPSON DOWNS SUBZONE bs Cmst Cmse bs bs Cmdk bs bs Cmob bs bs Cmow bs Dglm o bs bs Cmun Ngallo Domain: ?metasediments. Magnetic responses of about 1 nT strike about 40 in the southern part of the domain; Cmow bs Dglm bs bs elsewhere essentially non-magnetic. High gravity response.
Cgm Cmdy Cmdb bs bs Cmsb bs Cmup bs Dglm Dglm Panitya Domain: ?metasediments. Rare weak magnetic responses of less than 2 nT, discordant to deep magnetic source. bs Cmsc / Dgln Moderate to high gravity response. bs Dglm Cmdc bs Cmsl / Dgln Dglm Cmdi bs Cmuc Dgln Cmsd Carina Domain: ?metasediments. Non-magnetic at magnetic basement where not influenced by other lithologies, but with Cmsc bs Cmoy Dgln deep strongly magnetic feature. Gravity moderate to high influenced by thickness of cover bs Cmoy bs sequence and granitic intrusions. bs bs Cmsw bs Cmdy Cmug Gunamalary Domain: ?serpentinite or mafic volcanic rocks. Linear magnetic responses to 50 nT sub-parallel to domain edges. 6020000mN bs bs bs Cmsb Cmsr bs Cmoy/ Cmdi bs bs Cmdk bs Cmst Cgm Cmdh bs bs Cmdi bs bs Cmua Rare weak magnetic responses of less than 2 nT, discordant to strong, deep magnetic bs Alphildale Domain: ?metasediments. Dglm source. High to very high gravity response. bs bs bs 140 58' E 141 00' E 36 00' S 141 15' E 141 30' E 141 45' E 142 00' E 142 15' E 142 30' E Cmue Goongee Domain: volcanic rocks, possibly faulted from Dimboola Subzone. Linear magnetic responses to 80 nT, discordant to deep magnetic body. High gravity response, but often difficult to separate from strong regional gradients.
DIMBOOLA SUBZONE GRAVITY MODELLED CROSS SECTION Strong deep magnetic sources, but no near surface responses. Gravity response high, Section scales CAMBRIAN Cowangie Domain: ?Kalkee Domain rocks below Palaeozoic sedimentary Cmdc cover sequences. but lower than Kalkee Domain. Horizontal 1:250 000 Vertical 1:100 000 A B Kurnbrunin Domain: Kalkee Domain rocks below ?St Arnaud Group metasediments Strong deep magnetic sources, but shallow basement magnetic sources less than 2 nT 59 400 Cmdb of ?upper greenschist to amphibolite facies. trending close to 360 o ;felted texture.
0 59 300 Kalkee Domain: calc-alkaline basalt, andesite and rhyolite; most magnetic units may be Abundant linear magnetic responses to 500 nT, highest along the eastern edge. Cmdk mafic volcanics; correlates with Mt Dryden volcanic rocks; may also include serpentinite High gravity response. along eastern edge. 59 200 -50 Linear magnetic sources to 150 nT, generally strongest on the western side of the domain Gravity Magnetic Cmdy Little Billy Domain: mafic to intermediate volcanic rocks of uncertain affinities. and deepening to the north. Gravity response moderate to very high; lower to the north response 59 100 response where less dense cover is thicker. (um sec -2 ) modelled gravity (nT) -100 magnetic profile Dahlen Domain: 59 000 Cmdh probably mafic volcanic rocks below Palaeozoic cover sequences. On the western edge, deep magnetic sources present that become deeper eastwards. The eastern edge is generally non-magnetic where not influenced by other lithologies. Gravity response low. -150 58 900 Ni Ni Domain: ophiolite, metaboninite and related intrusions, culture measured gravity Cmdi gabbro and dolerite; minor andesite and rhyolite. Highly magnetic, with abundant linear responses of up to 500 nT traceable up to 58 800 15 km. Gravity response high. 0 2.0 Undifferentiated Murray Basin OZENKADNOOK SUBZONE 2.3 P P Cmsr Cmsl 1 2.3 2.69 2.66 Linear magnetic responses to 50 nT, generally with little apparent depth extent. Suk Cmow Wallowa Domain: ?basaltic to acidic volcanic rocks. High gravity response. 2.4
Depth (km) 2 C C m m Mostly non-magnetic but with distinctive linear magnetic responses up to 80 nT. d s Cmob Willoby Domain: ?metasediments within faulted mafic volcanic rocks. Gravity response high, but slightly lower than adjacent domains. 3 Cmun Cmup Cmuc Cmue Cmdh Cmdy Cmdk bs Cmdc k Cmdc Cmdk Cmsf d Cmso Cmsb Cmst Dgln Cmsc Cmsw Cmsp Cmsh Cmsg Cmse Cmsk 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.705 2.66 2.66 2.66 2.69 2.65 2.665 2.66 2.66 2.66 2.66 2.66 2.66 2.67 PRECAMBRIAN TO Cmoy Yanipy Domain: correlates with amphibolite facies A regional magnetic gradient that decreases to the east; generally felted texture 4 CAMBRIAN metasediments. with rare linear responses to 30 nT trending about 310 o. Moderate gravity response.
ROCK RELATIONSHIP DIAGRAM
Qlp/Qll MAP SCALE 1:250 000 SYMBOLS Qu Qlp/Qll Qw Qc Qw Geological boundary; interpreted...... Tma OUYEN Tpp Cmsk Cmug 35 00' S BOUGUER GRAVITY metres 5000 2500 0 5 10 15 2 0 kilometres Fault; interpreted...... Cmup Cmuc Cmsg Cmsa Cmue P 3 Cmow Cmsp Suk Density = 2.67 T/m Cmdy Cmsb Cmsc Horizontal datum: Australian Geodetic Datum (1966). Unconformity (cross section only)...... Cgim Cmua Suk 2 Cmun Cmdb Contour interval: 20um/sec Transverse Mercator Projection: Australian Map Grid - Zone 54 Cmsh Cmdh Suk Grid interval: 20 000 metres. Cmob Cmsl Intrusion at depth...... Cmsd Cmso bs 41 to 80 D Cmdk D g D C Cmst Cmdi g Cmsf Cmse Strongly magnetic response...... Cmdh l g m 1 to 40 Cmoy m l l s Cgm Cgn n Cmsr Cmsw m i Weakly to moderately magnetic response...... Cmdc -39 to 0 Cmdy Cmsw -79 to -40 Reversely polarised magnetic response...... Ozenkadnook Upson Dimboola Subzone -119 to -80 Dip direction of magnetic feature...... Subzone Subzone RV E SU Y O 3 L F -159 to -120 Gravity model density, T/m (cross section only)...... A True 2.67 C V
I
I
GLENELG ZONE STAWELL ZONE C
G T
O
Magnetic L O
R O
I E -199 to -160 A
Road...... G Note : Only those units considered to be part of the magnetic basement are coloured on this diagram. The uncoloured units are described on the associated map "Ouyen geological interpretation of post-cratonic -239 to -200 geophysical features". N Town...... -280 to -240 1:250000 Geophysical Map 9 55' Gravity station OUYEN Geological interpretation of 0 30 km RESPONSIBILITIES AND ACKNOWLEDGEMENTS VICTORIA 1:250 000 MAP SHEET SERIES INDEX TO ADJOINING SHEETS 36 00' S basement geophysical features Geophysical interpretation (1996): D. H. Moore Scale 1:1 000 000 Geophysical modelling (1995-1996):P. A. McDonald Edition 2 34 S 142 30' E NEW SOUTH 141 00' E Acknowledgements - July 1998 WALES Supervising Geophysicist: A.J. Willocks Mildura RENMARK MILDURA BALRANALD Manager, Geological Survey: T.W. Dickson Refer to this map as:
N.T. Image preparation: D. H. Moore, D. Bibby MOORE D. H. & M c D ONAL D P.A., 1997. Ouyen 1:250 000 QLD. 35 S Project Cartography: D.V. Higgins (LICS P/L), D.J. Jansen Geological interpretation of basement geophysical features. The magnetic data used to compile this interpretation were obtained in 1994 by Kevron Geophysics Pty. Ltd. for the Geological Survey of Victoria. Magnetic declination 9 55' at Ouyen in 1996, Publishing Process: D.J. Jansen Geological Survey of Victoria. W.A. PINNAROO OUYEN SWAN HILL Manager Draughting: J.P. Kinder. The survey was flown at 400 m line spacing and 80 m mean terrain clearance. The gravity data used are those held in the GSV gravity database increasing at 2.5' per annum. Associated products:
Natural Resources VICTORIA as at May 1996. S.A. The base is Crown copyright and is reproduced with permission of the General OORE ONALD VICTORIA 36 S M D. H. & MD c P.A., 1997. Ouyen 1:250 000 and Environment Magnetic inclination 67 00' at Ouyen in 1996, Manager, Australian Surveying and Land Information Group, Department of SOUTH AUSTRALIA The main map is a composite of a magnetic image and the geological interpretation. The magnetic image was derived from the total magnetic Geological interpretation of post-cratonic geophysical features. N.S.W. increasing at 0.8' per annum. Administrative Services. Topographical information correct to 1978. AGRICULTURE Geological Survey of Victoria. Melbourne NARRACORTE HORSHAM ST ARNAUD intensity using a first vertical derivative. To allow comparison of the geological interpretation and data, the interpretation has been draped over the image. RESOURCES VIC Published by the Department of Natural Resources and Environment. M OOR E D. H., 1997. A geological interpretation of the CONSERVATION The interpretation shows only those features that are considered to be part of the craton or which obliterated the cratonic signatures. Those 37 S P.O. Box 500, East Melbourne, Victoria, 3002. geophysical features for the Ouyen 1:250 000 map sheet area. that are presumed to be part of the overlying sequences are shown on the associated map "Ouyen geological interpretation of post-cratonic LAND MANAGEMENT Portland Geological Survey of Victoria, Victorian Initiative for geophysical features". 144 E TAS. 141 E c CROWN (STATE OF VICTORIA) COPYRIGHT 1997. Minerals and Petroleum Report 39 .
139 30' E 142 30' E Reproduction without permission is forbidden. Department of Natural Resources and Environment.
4062-1 500000mE 520000mE 540000mE 560000mE 580000mE 600000mE 620000mE OUYEN bs 35 00' S bs P D U bs bs U P/ Dglm bs bs Dglm bs D P GEOLOGICAL INTERPRETATION OF bs bs 6120000mN D D U bs U bs POST-CRATONIC GEOPHYSICAL FEATURES U OUYEN bs D D D U Dglm bs bs bs U bs bs D bs bs P/ bs D Dglm U U bs bs D bs U D bs U U bs U D bs D bs D bs U P/ Dglm D Dglm bs U P B bs bs LEGEND bs D D U D U bs bs U D bs Suk U D bs U Sedimentary Igneous Interpreted lithology Geophysical signature U D bs bs bs Lunette deposits of sand, silt and clay (positions of Arcuate linear features east of lakes. Magnetic response to 2 nT. Qu interdunes shown on 1:250 000 scale map; colour Radiometric response generally high in all channels. Digital elevation bs to 30 m above local surroundings. 6100000mN U only shown on rock relationship diagram). D bs Dglm Qc bs Coonambidgal Formation: lacustrine and fluvial sand, No detectable magnetic response. Radiometric response highest in U bs 35 15' S silt and clay (shown only on surficial geology map and all channels for lacustrine deposits. Digital elevation shows flat areas. bs D D U U colour only on rock relationship diagram). A D Dglm U D D D U bs U U U D D bs bs bs bs Lowan Sand: parabolic dunes (shown only on interpreted No detectable magnetic response. Radiometric response lowest in all bs Qlp QUATERNARY RECENT surficial geology and rock relationship diagram) channels. Digital elevation shows a plain, gently sloping from west to bs bs bs Suk U U bs east, with dunes slightly lower than Qll. bs D D bs bs Suk D D U bs Qll Lowan Sand: longitudinal dunes (shown only on interpreted No detectable magnetic response. Radiometric response low in all U bs bs U D surficial geology and rock relationship diagram). channels but with a speckled texture. Digital elevation shows a plain bs U D gently sloping from west to east, with dunes slightly higher than Qlp. D bs U U D U P P D U bs D U No detectable magnetic response. Radiometric response moderate in Qw Woorinen Formation: wind blown sand (shown only on D surficial geology map and rock relationship diagram). all channels. Digital elevation shows a distinctive wavy pattern in the DANYO FAULT U U D D D D north that occupies relatively low areas. U U U D bs U Dglm U D U UPPER Loxton-Parilla Sand: beach strand lines (only positions Magnetic swales several km long parallel arcuate magnetic highs (about D o MIOCENE- Tpp D D bs of magnetic swales shown on 1:250 000 scale map; 10 nT) mostly trending 310 and weakly concave west. Where not covered bs bs PLIOCENE U U bs colour only shown on rock relationship diagram). swales are radiometric highs, strand lines topographic highs. U D U D bs D U D bs D U TERTIARY 6080000mN bs D D Calivil Sand?: north- and west-draining river channels Dendritic magnetic pattern, mostly highs of less than 5 nT; rarely bs U U MIOCENE Tma bs bs (positions of drainage channels shown on 1:250 000 reversely polarised. U bs U bs D bs scale map; colour only shown on rock relationship D D U bs diagram). Dgln bs D bs D D MESOZOIC D Dglm D U Basaltic to dioritic or nephelinitic plugs and associated Circular magnetic highs up to 200 nT and approximately 0.5 km in U U bs U TO bs U Dglm U volcanics. diameter. bs D TERTIARY bs bs Suk D D U U D U bs Dglm U CARBONIFEROUS Urana Formation: glacial deposits. No detectable magnetic response. Restricted to gravity lows. bs D bs U TO P U D 35 30' S bs D PERMIAN bs bs U bs bs bs D Dglm D U D D U bs U Non-magnetic granitic intrusions correlated with the Featureless magnetic areas often surrounded either by interpreted D bs Suk U Dgln bs bs Mafeking or Mt Cole Suites (Rb/Sr ages 380 to 400 Ma, magnetic granite or weakly magnetic contact aureoles. Gravity lows bs U/Pb zircon to 410 Ma). where measured. Stitch Delamerian faults but may be cut by later faults. DEVONIAN EARLY bs D bs bs 2 bs Dglm U Dglm Magnetic granitic intrusions correlated with the Mafeking Circular to elongate areas up to 50 km with rough magnetic texture or Mt Cole Suites (Rb/Sr ages 380 to 400 Ma, U/Pb and response of up to 500 nT. Gravity lows where measured. Stitch bs bs U zircon to 410 Ma). Delamerian faults but may be cut by later faults. D bs bs U bs D D bs U P D D bs U ORDOVICIAN U bs 6060000mN TO Grampians Group: terrestrial to marginal marine sandstone No detectable magnetic response; intruded by Devonian granites. bs D Suk bs bs D SILURIAN with lesser conglomerate and siltstone. D U U U bs D bs bs U U Suk bs D D U Dglm Dgln bs D bs D ? U D bs U bs U D U bs ? bs ? P bs bs bs U Dglm D bs D U INTERPRETED SURFICIAL GEOLOGY
? bs Suk bs bs
bs bs 500000mE 550000mE 600000mE bs 35 00' S D U Qll Qll ? HOPETOUN bs Qw Qll Qll bs U D D Qw/Tpp bs bs Dglm 35 45' S bs Qw bs U Qc Qu U bs D Qll Qy bs bs Qu Qy 6040000mN Qy Qy Qw Dglm bs Dglm bs U bs Suk D Tpp U bs D bs bs Qc bs U bs Dgln D D bs U D Qc Qc bs Suk/Dglm U bs U bs ? bs ? U bs D bs Qw Qw bs bs D Qy Tpp Qu Qw ? Qc Qw bs D bs bs bs bs Tpp ? bs D U Suk bs 6100000mN P U D Tpp bs bs U D bs bs Dglm bs Qll D bs D Tpp ? U D U Qll U D U U U bs U D U D D bs bs U bs Tpp D Qw bs Qlp bs Qu D Qll bs Qu U Tpp Qc Qc Dglm D D U bs D U bs Qll bs U Qu Suk/Dgln U D bs Qlp bs U D D bs Qc Tpp Tpp U bs U U Qu 6020000mN bs U Qu D bs D bs bs Qc D Suk D bs D U bs bs bs U bs D bs Suk U U Qc bs 35 30' S bs D Qlp Dglm Qlp bs bs bs Qll/Tpp 140 58' E 141 00' E Qlp/Tpp 141 30' E 36 00' S Qc Qll 141 15' E 141 45' E 142 00' E 142 15' E Qll Tpp 142 30' E Qlp Qu Qc Qc Qll/Tpp Qu Qlp Qc GRAVITY MODELLED CROSS SECTION Qlp Qc Qu Section scales Qc Horizontal 1:250 000 Qu Qu Vertical 1:50 000 6050000mN A B MAP SCALE 1:250 000 Qll 59 400 Qc Qll Tpp 0 Qc Qc 59 300 Qc Qu Qu modelled gravity metres 5000 2500 0 5 10 15 2 0 kilometres Qc Qc Qu 59 200 -50 Gravity Horizontal datum: Australian Geodetic Datum (1966). Qc Magnetic Qll Qlp Qc response 59 100 response Transverse Mercator Projection: Australian Map Grid - Zone 54 Qc -2 Grid interval: 20 000 metres. Qw (um sec ) measured gravity (nT) Tpp -100 magnetic profile Qc Tpp 59 000 Tpp Qc Qlp Qll Qlp Qu Qu -150 58 900 Qu culture Qll Qc 58 800 Tpp Tpp Qw/Tpp Qc 0 Qll Tpp Qc Qc Qu Undifferentiated Murray Basin Qw Tpp Tpp 2.0 Qll Tpp 36 00' S P 2.3 P 2.3 OUYEN 1 35 00' S BOUGUER GRAVITY 141 30' E
Scale 1 : 500 000 142 00' E 140 58' E 141 00' E Suk 142 30' E 3 2.4 C C Density = 2.67 T/m m m Cmdc Cmdk Cmsf Cmso Cmsb 2 Depth (km) s 2.66 Cmun Cmup Cmdc d 2.7 2.7 2.71 2.66 Contour interval: 20um/sec 0 20 40km Cmuc bs 2.7 d 2 2.7 2.7 Cmdk k 2.7 2.7 2.66 2.7 2.7 41 to 80 Cmue Cmdy Transverse Mercator Projection: Australian Map Grid - Zone 54 2.7 2.7 Cmdh 1 to 40 2.7 3 -39 to 0
-79 to -40
-119 to -80 ROCK RELATIONSHIP DIAGRAM SYMBOLS
Qlp/Qll -159 to -120 Qu RADIOMETRIC RGB (K,Th, U) TERNARY DIAGRAM Qlp/Qll Qw Lithological boundary; interpreted, inferred...... Qc -199 to -160 K Qw Tma Tpp Unconformity, (cross section only)...... Cmug Cmsk -239 to -200 Cmup Cmuc Cmsg Cmsa Cmue P Fault; interpreted, movement sense shown...... U Cmow Cmsp -280 to -240 Suk D Cmdy Cmsb Cmsc Cgim Cmua Suk Cmun Cmdb Intrusion at depth...... Cmsh Cmdh Suk Cmob Cmsl Gravity station Cmsd Cmso bs D Cmdk Cratonic zone boundary...... g D C Cmst Cmdi D Cmsf Cmdh l g g m Cmse 0 30 km Cmoy m l l s 36 00' S U Th Interlunette...... Cgm Cgn n Cmsw m i Cmsr Cmdc Scale 1:1 000 000 Cmdy Swale...... 141 00' E Cmsw 142 30' E Palaeochannel......
Note : Only those units considered to be post-cratonic are coloured on this diagram. The uncoloured units are described on the associated map "Ouyen geological interpretation of basement geophysical features". 3 Units with identical geophysical responses have not been separated. Gravity model density, T/m (cross section only)...... 2.67 RV E SU Y O L F A C V I
Road...... I
G C T
O
L O
R
O
I E A Town...... G
True VICTORIA 1:250 000 MAP SHEET SERIES INDEX TO ADJOINING SHEETS Magnetic 1:250000 Geophysical Map The magnetic and radiometric data used to compile this interpretation were obtained in 1994 by Kevron 35 00' S Geophysics Pty. Ltd. for the Geological Survey of Victoria. The survey was flown at 400 m line spacing 34 S and 80 m mean terrain clearance. The gravity data used are those held in the GSV gravity database in N RESPONSIBILITIES AND ACKNOWLEDGEMENTS OUYEN NEW SOUTH May 1996. WALES Geophysical interpretation (1996): D. H. Moore Mildura Geological interpretation of RENMARK MILDURA BALRANALD The 1:250 000 scale map is a composite of a magnetic image and the geological interpretation. The Geophysical modelling (1995-1996):P. A. McDonald N.T. image was derived from the total magnetic intensity using a residual ring filter. The output was STAWELL Acknowledgements- post-cratonic geophysical features ZONE 9 55' QLD. 35 S then stretched to sort most of the mid-range values towards either black or white. To allow comparison Supervising Geophysicist: A.J. Willocks Edition 1 of the geological interpretation and data, the interpretation has been draped over the image. Manager, Geological Survey: T.W. Dickson OUYEN SWAN HILL July 1997 W.A. PINNAROO Project Cartography: D.J. Jansen, D.V. Higgins (LICS P/L) The interpretation shows only those features that were considered to have formed, or faults that have GLENELG VICTORIA Publishing Process: D.J. Jansen S.A. ZONE Refer to this map as: VICTORIA 36 S moved, after cratonisation. In the Stawell Zone this is taken at about 435 Ma. In the Glenelg Zone Manager Draughting: J.P. Kinder
Natural Resources SOUTH AUSTRALIA cratonisation finished with the Delamerian Orogeny at about 490 Ma. Thus faults that moved during the N.S.W. MOORE D. H. & M c D ONAL D P.A., 1997. Ouyen 1:250 000 and Environment event that cratonised the Stawell Zone are shown as post-cratonic in the Glenelg Zone, but not in the The base is Crown copyright and is reproduced with permission of the General Melbourne NARRACORTE HORSHAM Geological interpretation of basement geophysical features. ST ARNAUD Manager, Australian Surveying and Land Information Group, Department of AGRICULTURE Stawell Zone. Basement elements interpreted are shown on the associated map "Ouyen geological Geological Survey of Victoria. VIC interpretation of basement geophysical features". Administrative Services. Topographical information correct to 1978. RESOURCES 37 S Associated products: CONSERVATION Portland The 1:500 000 scale map shows the distribution of surficial units in the area. The outlines of the units Magnetic declination 9 55' at Ouyen in 1996, Published by the Department of Natural Resources and Environment. M OOR E D. H., 1997. A geological interpretation of the 144 E LAND MANAGEMENT TAS. 141 E 36 00' S geophysical features for the Ouyen 1:250 000 map sheet area. interpreted have been placed over an RGB ternary radiometric image. This shows red intensities as 140 58' E 142 30' E increasing at 2.5' per annum. P.O. Box 500, East Melbourne, Victoria, 3002. 139 30' E 142 30' E calculated potassium concentrations, green intensities as calculated thorium concentrations, and blue Geological Survey of Victoria, Victorian Initiative for intensities as calculated uranium concentrations. The ternary diagram gives a guide to the relative Magnetic inclination 67 00' at Ouyen in 1996, c CROWN (STATE OF VICTORIA) COPYRIGHT 1997. Minerals and Petroleum Report 39 . proportions of each element but not their absolute concentrations. increasing at 0.8' per annum. Reproduction without permission is forbidden. Department of Natural Resources and Environment.
4062-2