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The Regolith of the Bendigo 1:100 000 Map Area

VIMP Report 77

The regolith of the 1:100 000 map area

A. Kotsonis and E.B. Joyce

March 2003

Bibliographic reference: Disclaimer: KOTSONIS, A. AND JOYCE, E.B., 2003. The regolith of This publication may be of assistance to you but the the Bendigo 1:100 000 map area. Victorian Initiative State of and its employees do not guarantee for Minerals and Petroleum Report 77. Department that the publication is without flaw of any kind or is of Primary Industries. wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or © Crown (State of Victoria) Copyright 2003 other consequences which may arise from you relying Geological Survey of Victoria on any information in this publication.

ISSN 1323 4536 ISBN 07306 9499 2

Keywords: Bendigo, 7724, regolith, regolith–landform mapping, geomorphology, gold, landform, landscape evolution, weathering.

This report may be purchased from: Minerals Business Centre, Department of Primary Industries, 8th floor, 240 Victoria Parade, East , Victoria 3002

For further technical information contact: Manager, Geological Survey of Victoria, Department of Primary Industries PO Box 500, East Melbourne, Victoria 3002

Authorship and acknowledgements The authors wish to acknowledge the Geological Survey of Victoria for their support of regolith studies in Victoria including this report. Much of the work here is sourced from ongoing Ph.D. research conducted at the University of by Kotsonis. Stephen Carey, Martin Hughes and Stafford McKnight are gratefully acknowledged for their support of the post-graduate project. Neville Rosengren from La Trobe University provided expert knowledge on the geology and regolith of the Bendigo area. This report includes airborne geophysical data from the Geological Survey of Victoria and Geoscience .

The report was edited by Linda Bibby and David Taylor and formatted by Gayle Ellis. David Higgins drafted the figures. Tavis Beer and John Dunleavy produced the accompanying map.

Author contacts Andrew Kotsonis School of Science The University of Ballarat Victoria 3353

Bernie Joyce Senior Research Fellow School of Earth Sciences The University of Melbourne Victoria 3010 Email: [email protected]

BENDIGO REGOLITH 1

Contents

Abstract 3 1 Introduction 5 2 Geology 8 2.1 Geological evolution 8 –Jurassic 8 Jurassic–middle Cainozoic 8 Middle Cainozoic–Quaternary 8 2.2 Geological structure 8 Neotectonics 10 3 Geomorphology 13 3.1 Landscape subdivisions 13 Western Uplands 13 Riverine Plain 13 Lava flows 15 3.2 Drainage 15 Drainage development 15 4 Regolith–landform units 18 4.1 Transported units 18 Alluvial 18 Colluvial 24 Marine 24 Glacial 25 Human activity 25 4.2 Volcanic units 26 4.3 In situ units 28 Deep marine turbidites (Castlemaine Group) 28 Contact metamorphosed turbidites (Castlemaine Group) 30 (Harcourt Batholith) 30 5 Regolith resources 32 5.1 Gold 32 5.2 Clay 32 5.3 Sand and gravel 33 5.4 Other resources 34 Crushed rock 34 Dimension stone 35 6 Synthesis 36 6.1 Discussion 36 In situ units 36 Transported units 36 6.2 Landscape evolution 38 7 Conclusions 41 References 42 Appendix 1 46 Full list of RTMAP codes for regolith–landform units Appendix 2 48 Regolith–landform unit summary data Appendix 3 57 Regolith excursion guide

List of figures 1. Regolith–landform map of BENDIGO 6 2. Regional geological map of Victoria showing the location of BENDIGO 7 3. Simplified geology of BENDIGO 9 4. Simplified geological structure of BENDIGO 11 2 BENDIGO REGOLITH

5. Digital terrain model of BENDIGO with major geomorphic subdivisions 15 6. Drainage map of BENDIGO 16 7. A: radiometric ternary ratio image of BENDIGO. B: single channel radiometric images 20–21 8. Radiometric ternary ratio image of northwestern BENDIGO 22 9. Aap. Thin layer of mining residue preserved above floodplain alluvium 22 10. Aep. Gravels flanking mineralised bedrock rise 23 11. ACer. Joints in silicified quartz conglomerate 24 12. OMep. Typical profile developed on marine sands 25 13. Faf. Mining residue over an old soil profile 25 14. VFvl, VFep. Soil profiles. A: old flow with little soil. B: young flow with thick soil 27 15. SMel1. Moderately weathered bedrock exposed in the Sugarloaf Range 29 16. SSeh3. Typical profile of slightly weathered saprock and thin lithic soil profile 30 17. SHel2. Typical profile showing highly weathered granite saprolite 31 18. Secondary gold. Scanning electron microscope images 33 19. Sand and gravel resources. TMI image of part of BENDIGO showing potential resources 34 20. Crushed rock resources 34 21. Landscape evolution diagram for BENDIGO 39 22. Simplified relationships between the transported regolith units in BENDIGO 47 23. Aam. Typical profile 47 24. Aam. Aerial photograph showing Spring and Bullock creeks 47 25. Aap. Typical profile 48 26. Aep. Typical profile 48 27. Aep. Regolith profile at Mackenzies pit 49 28. ACer. Typical profile 49 29. ACer. Duricrust developed in quartz conglomerate 49 30. Cfc. Typical profile 50 31. Cfc. Colluvium exposed near Nuggetty mine 50 32. OMep. Typical profile 51 33. Faf. Typical profile 51 34. VFep. Idealised cross section of the area around the 52 35. VFep. Typical profile 52 36. VFep. Boundary between a flat-topped lava residual and the slope down to the lateral stream 52 37. Idealised cross section for the Bald Hill and surrounds, showing regolith relationships 53 38. VFvl. Typical profile 53 39. Idealised cross section for BENDIGO 54 40. SMel1, SHel1, SVer1. Typical profile over the bedrock units 54 41. SSeh3. Typical profile 55 42. SSeh3. Soil profile over slightly weathered, contact metamorphosed Castlemaine Group 55 43. Idealised cross section through the Harcourt Batholith and its contact aureole 55 44. SHel2. Typical profile 56 45. Simplified regolith–landform map of BENDIGO showing excursion sites 58

List of enclosures Bendigo 1:100 000 regolith–landform map BENDIGO REGOLITH 3

Abstract largely due to time since formation and position in the landscape. Over 697 t of gold has been won from the area around The landscape history of BENDIGO prior to the early and under Bendigo and until recently, mining at Palaeogene is poorly understood. Minor occurrences Fosterville produced 30 000–40 000 ounces annually. of Permian glacial deposits, which are subsurface Both of these goldfields occur in areas of exposed beneath Cainozoic sediments near the Leichardt bedrock and are surrounded by a generally thin cover , indicate Permian glaciation has affected the of transported and volcanic material that effectively landscape. Mesozoic deep weathering is not shields a large area of highly prospective bedrock preserved in BENDIGO; the deep weathering on the from historical exploration. Understanding the bedrock RLUs is probably post-Mesozoic and distribution and origin of regolith materials is of associated with an eroded early Cainozoic fundamental importance when designing and, palaeoplain that developed prior to late Eocene uplift importantly, interpreting the results of, geochemical of the Western Uplands. The soil cover now exposed sampling programs. on the bedrock RLUs is young and not connected with This report summarises the results of this deep weathering. However, a ferruginous regolith–landform mapping of the Bendigo 1:100 000 duricrust developed on the bedrock (Castlemaine map area (BENDIGO) in central Victoria, and Group) is preserved on the margins of the Uplands provides a synthesis for the development of the beneath a thin veneer of transported regolith, and regolith and the evolution of the landscape. may represent part of the original soil cover at the time of deep weathering. The regolith in BENDIGO can be divided into three groups of regolith–landform units (RLUs): Palaeozoic The transported units are not extensive in the bedrock units, Cainozoic transported units, including Western Highlands, but their distribution, landscape transported mining residue that has accumulated position and regolith development provide important from the 1850s onwards, and Cainozoic basaltic lava clues for reconstructing the drainage development flows. and landscape evolution of the area. The broad architecture of the drainage has been little changed Bedrock units with predominantly in situ regolith since the Paleocene in much of BENDIGO. occur over metasedimentary rocks of the Castlemaine Group, contact metamorphic aureole The oldest preserved transported unit is the White rocks and granitoids of the Harcourt Batholith. Hills Gravel, which delineates the earliest known Weathering profiles are dominated by saprolite of drainage system in the region and is now preserved variable thickness mantled by lithic gradational and on hill tops and on the upper slopes of bedrock ridges. duplex soils. The nature of the regolith now These deposits are cemented with a duricrust of preserved on the bedrock RLUs has been controlled silcrete, argillans, and minor ferricrete, and were by Cainozoic erosion and landscape evolution, with formed as the end product of erosion of the Mesozoic deep weathering interpreted to have begun in the palaeoplain after extensive dissection, and Cretaceous to early Palaeogene. Evidence exists for weathering continuing until the middle Cainozoic late Cainozoic movement along all the major bedrock (upper age limit of late Miocene). structures within BENDIGO. Movement along these Erosion and weathering continued throughout the structures has affected weathered profiles and soils early and middle Cainozoic. All the buried leads and preserved on bedrock units, displaced buried deep leads, and the clay rich alluvial deposits at auriferous leads, and affected modern drainage and Fosterville, formed at this time as a systems. response to rapid erosion and downcutting of valleys Transported RLUs are poorly preserved in the following late Eocene uplift in the Western Uplands. Western Uplands, but form a flat-lying composite The source rocks (and gold) for this unit came from fluvio-lacustrine plain to the north, the Riverine the erosion of the White Hills Gravel and mineralised Plain. Although these units are transported relative bedrock. Intense weathering of these sediments and to the bedrock units, they also have weathering the surrounding bedrock resulted in kaolinisation profiles on them formed during post-transport in situ with no ferricrete, and is associated with Miocene weathering. weathering. The youngest RLU developed in BENDIGO is Rising sea levels in the late Miocene–early Pliocene composed of residue produced by puddling machines in the Murray Basin backfilled and buried much of and mine tailings, associated with historic gold the drainage system with marine quartz sands of the mining. It is found blanketing the present Parilla Sand. The environment of deposition for this floodplains along creeks draining the historic gold unit suggests shallow marine with estuarine fields of BENDIGO. embayments reaching Huntly and possibly to Epsom. Syn- and post-depositional weathering formed a Regolith profiles over the basaltic lava and scoria of pisolitic ferricrete (Karoonda Regolith) now the Newer Volcanic Group can be found around Bald preserved in the Parilla Sand and the exposed Hill and along the Campaspe and Coliban rivers. surface of the Formation. During and The differing regolith profiles in these two areas is after retreat of the sea, weathering and erosion 4 BENDIGO REGOLITH

continued, along with deposition of the fluvial and fluvio-lacustrine Shepparton Formation. Gold liberated from the bedrock and from older transported regolith was deposited as shallow leads. Extrusion of the Newer Volcanics also occurred at this time, around Bald Hill and in the Campaspe and Coliban river valleys. Today a volcanic plain surrounds the Bald Hill volcano, but greater dissection in the southeastern part of BENDIGO has reduced the lava flows along the Campaspe and Coliban rivers to flat-topped lava residuals bounded by lateral streams. Quaternary regolith development has been minimal, with incision of narrow sinuous streams and the widespread deposition of clayey and calcareous aeolian dust that mantles much of BENDIGO. These dust mantles are associated with Quaternary aridity and now form surficial calcareous soil horizons with disseminated fine earth, nodule and rhizomorph carbonate. Minor swamp deposits and aeolian dunes also formed at this time. There is increasing evidence for supergene gold enrichment in the weathering zone in Victoria, including BENDIGO. Secondary gold is documented at Fosterville where oxidised quartz–gold–stibnite veins show significant refinement of primary gold and deposition of supergene gold. The timing and extent of secondary gold in the landscape is unclear, but the evidence from Fosterville demonstrates localised gold movement within in situ regolith developed on mineralised metasedimentary bedrock. There is potential for further primary and secondary gold resources in BENDIGO. In addition to gold, the area is prospective for other regolith-related commodities, including clay suitable for a range of purposes, sand and gravel, crushed rock and dimension stone. BENDIGO REGOLITH 5

1 Introduction that can yield potentially larger exploration targets than the mineralisation itself. This is of particular This report summarises the results of relevance in the Victorian Gold Province where gold regolith–landform mapping conducted in the Bendigo mineralisation is typically narrow and has a small 1:100 000 map area (BENDIGO) in central Victoria areal distribution. Secondly, and more importantly, (Fig. 1). It includes descriptions of the regolith regolith processes may result in economically features based on field observations and historical significant mineral deposits, such as the oxide zone data, complemented by interpretation of geophysical at Fosterville. data and aerial photographs. It draws on A large body of information on the regolith is information in the geological map and report for contained in publications recording the mining BENDIGO of Cherry and Wilkinson (1994). The history of the Bendigo region (geological records, importance and implications of regolith development bulletins, proceedings, etc. of the Geological Survey are also discussed, in particular the relationship of Victoria). This resource is usually used exclusively between weathering, landscape evolution, and for documenting the occurrence of gold and yields secondary gold. from the mines. However, many of these reports Bendigo is one of the world’s richest goldfields, contain invaluable information on the surficial having produced over 697 tonnes of gold since its geology and regolith, often recorded in passing or in discovery in 1851 (Phillips & Hughes, 1996; Fig. 2). off-hand reference, including depth of weathering Although the field has not produced any significant (usually described as a change in the character of the gold since the closure of the last mine in 1954, the bedrock) and the nature and thickness of the surficial region still rates as a world class gold producer and is deposits. This type of information is particularly currently held by Bendigo Mining N.L., who are useful as it provides a three dimensional perspective exploring for auriferous quartz veins below the old for the regolith. workings. The other major goldfield in BENDIGO is Radiometric and magnetic data greatly assisted the Fosterville, which is held by Perseverance mapping. Geophysical data is an important tool in Corporation Ltd and, until recently, produced geological mapping and over the last 10 years its use between 30 000 and 40 000 ounces annually has become increasingly valuable in regolith (Perseverance Corporation Ltd, 1998). Both of these mapping. Airborne gamma-ray spectrometry can goldfields occur in areas of exposed bedrock. quantify the radioelement content of the upper Elsewhere in BENDIGO thin transported and 25 mm of the land surface (Darnley et al., 1995), and volcanic units cover large amounts of this highly can provide high quality surficial geological prospective bedrock, effectively shielding it from information (Wilford, 1992, Wilford et al., 1997). The historical exploration. radioelements potassium (K), thorium (Th) and Bendigo is now primarily a regional city, and a major uranium (U) have a general association with certain agricultural producing centre in central Victoria. rock types, and their mobilities vary under different The character and nature of the regolith plays an weathering conditions, allowing for the important role in the economic viability of this discrimination of different regolith materials and the industry: agricultural produce from the Bendigo partial quantification of mechanical and chemical region brought in $67.6 million in 1993 (City of dispersion (Anand, 2001). The digital topographic Greater Bendigo Economic Development Unit, 2001). data obtained in conjunction with the geophysics was The main products include livestock such as pigs ($44 useful in recognising and differentiating landform million), eggs ($10.9 million) and crops, consisting of patterns. vegetables, cereal grain and hay ($12.7 million). This The RLU codes on the map follow the RTMAP system does not include the Harcourt area, which produced set up by Geoscience Australia (formerly AGSO; Pain over $2 million from its apple industry in 1988–89 (R. et al., 2001). The codes comprise up to two upper case Luke, Department of Agriculture, in Cherry & letters, followed by up to two lower case letters, with Wilkinson, 1994). number qualifiers (Appendix 2; Chapter 4). The The surficial geology and regolith of the Bendigo upper case letters refer to the main type of regolith region is complex, and is further complicated by an developed over an area, with the lower case letters extensive mining and agricultural history that dates denoting the main landform type. The numbers refer back to the 1850s (Kotsonis & Joyce, 2002; Fig. 1). to subdivisions based on the bedrock lithology. Many areas have been extensively reworked, both Unlike other areas of Australia, the host rocks in through the removal of regolith to recover gold, and Victoria exert an important control on both through the deposition of mining residue in the mineralisation and the landforms, so their landscape. discrimination is an important part of the regolith description. This study highlights the importance of recognising historical and cultural impacts on the landscape. This is particularly relevant to exploration for gold in the Bendigo region. Regolith formation and development may result in dispersion of elements 6 BENDIGO REGOLITH

Figure 1 Regolith–landform map of BENDIGO. BENDIGO REGOLITH 7

Figure 2 Regional geological map of Victoria showing the location of BENDIGO (after VandenBerg, 2000). 8 BENDIGO REGOLITH

2 Geology Cainozoic eventually formed the Calivil Formation. These younger palaeoplacers were deposited within a channelised river system that had developed within 2.1 Geological evolution pre-existing broader valleys of the earlier landscape.

Middle Cainozoic–Quaternary Ordovician–Jurassic In the Pliocene, a marine incursion into the Murray The oldest rocks in BENDIGO are Ordovician Basin deposited marginal and near-shore marine turbidites of the Lachlan Belt, which consist of quartz sands (Parilla Sand of Brown & Stephenson, predominantly mudstone, shale and sandstone of the 1991; Bagshot Formation of Cherry & Wilkinson, Castlemaine Group (Fig. 3). The sequence was 1994). Deposition of fluvio-lacustine deposits of the regionally metamorphosed and deformed during the Shepparton Formation continued within the Silurian Benambran Deformation into north–south highland valleys and after marine retreat on the trending regional folds and faults (VandenBerg et al., exposed surface of the Murray Basin. Within the 2000), and intruded by post-orogenic Late highland valleys gold was eroded from the bedrock granitoids of the Harcourt Batholith. Gold and older palaeoplacers and concentrated within emplacement is believed to have occurred during, or gully deposits and shallow leads of the present just after the final stages of regional deformation highland valleys. Erosion of the bedrock also (Ramsay et al., 1998; Bierlien et al., 2001). resulted in the deposition of colluvium flanking Glaciation modified the landscape in the Permian, bedrock rises and within gullies. leaving behind deposits of tillite. Permian glacial Volcanic activity (Newer Volcanic Group) within the deposits are not exposed in the map area, but glacial Bendigo map area occurred at Bald Hill in the west erratics occur within the Cainozoic fluvial deposits, and along the Coliban and Campaspe rivers in the indicating that the region was affected by Permian southeast (Coliban ; Edwards et al., 1998). glaciation (Cherry & Wilkinson, 1994). More The Bald Hill volcano and associated basalt flows extensive Permian glacial deposits are exposed to the have a lower age limit of 1.64 Ma (Webb, 1989). The east, around in HEATHCOTE. source of the Coliban and Campaspe flows is This was followed by an inferred period of tectonic uncertain. Several eruption points have been stability, with Mesozoic deep weathering, planation suggested, such as Green Hill near Malmsbury for and erosion resulting in the formation of a deeply the lava flow (Cherry & Wilkinson, weathered Mesozoic palaeosurface (Hills, 1975), 1994), and an eruption point on the Coliban River which is not preserved in BENDIGO. near Metcalfe for the Coliban River lava flows (Coceani, 1999). Jurassic–middle Cainozoic Fluvio-lacustrine deposition occurred throughout the Quaternary. Fluvial sediments of the Coonambidgal Lamprophyre dykes intruded both the Ordovician Formation (Lawrence, 1966) represent the present metasediments and the Harcourt Batholith in the drainage system. They have been deposited on the Jurassic. In the late Mesozoic, Gondwana began to incised, older fluvial deposits of the Shepparton break up (Jenkin, 1988), and by the Cretaceous, an Formation (Lawrence, 1966), which form narrow east–west trending range, the Great Divide, began to floodplain terraces. Minor aeolian and swamp develop parallel to the break-up margin. Sometime deposits also formed at this time, with many near the Late Cretaceous–early Cainozoic boundary, controlled by prevailing westerly winds. Historic the Murray Basin began to subside as Antarctica gold mining activity has created additional separated from Australia, and was infilled with sediments that form a thin blanket along many of the fluvio-lacustrine sediments derived from the erosion larger alluvial plains exiting the Bendigo goldfield. of Palaeozoic bedrock. The quartz gravels of the White Hills Gravel are the earliest recognised drainage system from this time and are now 2.2 Geological structure preserved in BENDIGO on hill tops and high level terraces (Williams, 1983). Gold released from the North–south trending regional folds and faults in the erosion of mineralised Palaeozoic bedrock was Ordovician Castlemaine Group dominate the carried by streams and deposited within the White structure of BENDIGO (Fig. 4). Cainozoic units Hills Gravel. Ongoing weathering ferruginised the occasionally show neotectonic fault offsets along gravel, creating a distinctive deep weathering profile reactivated portions of some of the Palaeozoic faults. that includes pallid zones in the underlying bedrock. The Castlemaine Group is faulted by several major This profile has been called the Hard Hills surface north–south trending, west-dipping regional faults (Hills, 1975) and the Norval Regolith (Hughes & that extend beyond the map area. These faults Carey, 1998). include the Muckleford and Whitelaw faults, which Continued erosion of both the White Hills Gravel and have displacements in excess of a kilometre (Harris the metasedimentary bedrock in the early to middle & Thomas, 1934; Harris, 1934). The northern BENDIGO REGOLITH 9

Figure 3 Simplified geology of BENDIGO (after Edwards & Slater, 2001). 10 BENDIGO REGOLITH

extension of the Muckleford Fault (north of the Guildford Plateau Mining Company, northwest of Harcourt Batholith) coincides with the Leichardt Guildford in CASTLEMAINE. The north-trending Fault, and a fault breccia zone within the Harcourt Muckleford Fault has displaced west-trending Batholith indicates post-Devonian reactivation of auriferous lead by 20 m vertically, and the overlying this fault system (Rabone, 1973). by 15 m, indicating at least two periods of movement on the fault during the Cainozoic. The Sebastian Fault lies between the Muckleford and Thomas (1935) commented “along the fault affecting Whitelaw faults, and coincides with the Myers Creek the Tertiaries about 15 cm coarse gravel may be seen valley. It is unlike the other major faults in the representing auriferous wash caught up during the Bendigo map area in that it is downthrown to the faulting movement as colours of gold may be obtained west, forming a horst in the area between the by panning”. Sebastian and Whitelaw faults. Borehole data to the north of Raywood suggests that the horst continues At , the Leichardt Fault has been shown to into the Murray Basin (Cherry & Wilkinson, 1994). influence the continuity and nature of the deep lead The geometry of the Sebastian Fault is very poorly (an area of approximately 75 km2 west of Marong and constrained. The west-side down movement sense, bounded by Lat. 36º42’–36º46’; Long. 144º02’–144º08’; the regolith distribution and maximum stress Canavan, 1988). Rich shallow leads trending to the direction data for southeastern Australia (Hillis et west passed under basalt of the Bald Hill lava flows, al., 1999; Sandiford, 2003) support an easterly dip, but deep boring up to about 1907 failed to find any raising the possibility that it is a reactivated deep channel either to the north, south or west that backthrust off the Whitelaw Fault. could represent an outlet channel. The absence of an outlet is explained by the original extension of the Neotectonics lead valley being on the upthrown block of the Leichardt Fault, with the buried scarp clearly visible There is significant evidence for post-Palaeozoic in the depth-to-bedrock contours (Canavan, 1988; movement along some of the major bedrock faults in Cherry & Wilkinson, 1994). The strike of the fault is BENDIGO. A zone of brecciation 100 m wide and about 345º with the west side upthrown by several kilometres long in the Harcourt Batholith approximately 45 m. However, there is insufficient along the Muckleford Fault indicates post-Devonian evidence to determine whether movement occurred movement (Rabone, 1973; Cherry & Wilkinson, before, during or after the formation of the lead 1994). There is also significant evidence for (Canavan, 1988). Cainozoic movement on bedrock faults in the Bendigo region (Kotsonis et al.,1998; Hughes et al.,1998) and Other evidence for Cainozoic tectonism in the in other areas in the Victorian Highlands (Mulvany, Bendigo region includes a drop ranging from 8 m to 1939). 22 m across the Whitelaw Fault at White Hills (O’Dwyer, 1879, in Cherry & Wilkinson, 1994; Historical evidence from gold mining records, Stirling, 1898) where the Huntly deep lead was particularly those associated with deep lead mining, downthrown to the east. A sudden drop of 15 m was show displacement of leads across extensions of also recorded from the alluvial workings in the area known bedrock faults, and it was not uncommon for (Cherry & Wilkinson, 1994). There is little evidence a sudden drop in elevation to occur within the deep for early Cainozoic tectonism along the Whitelaw leads as they crossed these features. An extremely Fault, although drainage associated with the White good run of alluvial gold at Sebastian, northwest of Hills Gravel at White Hills was deflected from a Bendigo, was traced for over a quarter of a mile west north-northwesterly direction from Heathcote to an of Frederick the Great Company’s main shaft to east-northeast direction down the Bendigo Creek Myers Creek, where “a sudden drop of 70 feet (20 m), valley (Williams, 1983; Hughes & Carey, 2002), from 30 feet (10 m) to 100 feet (30 m), was indicating that the fault scarp had enough relief to encountered” (Whitelaw, 1899). This ‘drop’ is on the influence drainage orientation. northern extension of the Sebastian Fault within the Myers Creek valley, with White Hills Gravel to the At Wilsons Hill near Marong, recent movement of west of Myers Creek lying topographically low in the approximately 45 m is also indicated along a possible landscape and close to the present river, suggesting continuation of the Leichardt Fault (Canavan, 1988; these sediments have been downthrown on the Cherry & Wilkinson, 1994). western side of the Sebastian Fault. The change in Valley asymmetry can also indicate neotectonic drainage patterns at the mouth of the Myers Creek influences on the landscape. North–south valleys are valley and in the Riverine Plain also suggests recent asymmetric regionally in the map area and movement along the Sebastian Fault. surrounds, resulting from differential weathering Displacement of sub-basaltic gravels by up to 50 m on and erosion of valley slopes caused by solar radiation the Muckleford Fault near Guildford, south of (Kane, 1978; Section 3.1). However, east–west BENDIGO, indicates the last movement on the fault trending creeks and gullies across the bedrock divide was late Cainozoic (Cherry & Wilkinson, 1994). between Myers and Bendigo creeks show differences Thomas (1935; also in Canavan, 1988) also recorded in incision, with streams on the west-facing slopes evidence of movement on the Muckleford Fault at the and draining towards Myers Creek steeper and more BENDIGO REGOLITH 11

Figure 4 Simplified geological structure of BENDIGO (modified after Cherry & Wilkinson, 1994 and Slater, 2002). 12 BENDIGO REGOLITH

deeply incised than those on the east-facing slopes and draining into Bendigo Creek. This difference in incision reflects a topographic change between the Myers Creek valley to the west and the Bendigo Creek to the east, a difference in level of approximately 20 m, with Myers Creek lying below Bendigo Creek. One possible explanation proposed for the asymmetric incision of streams is wind erosion and deflation of material from the western side and its deposition on the lee (eastern) side (Cherry & Wilkinson, 1994). Cherry and Wilkinson (1994) noted dunes on the east and northeast of deflated areas, indicating westerly and south westerly prevailing winds, but both authors agreed that the absence of dunes in all the incised areas suggest that the hypothesis does not hold true for all west facing gullies in the Bendigo region. Another possible explanation could be late Cainozoic reactivation of the Whitelaw Fault. The drainage divide separating deeply incised gullies to the west and shallow ones to the east to the north of Bendigo coincides with the northward extension of the Whitelaw Fault. Incised gullies and creeks on west- facing slopes that flow into Myers Creek either cross the fault or have their headwaters to the west of the fault, whereas the shallow gullies are to the east of the fault and flow into Bendigo Creek. The deep incision of gullies to the west of the fault may have resulted from the Cainozoic movement of the Whitelaw Fault, with uplift of the western side initiating incision and erosion of the creeks draining into Myers Creek. The streams on the eastern side would not have been adversely affected by the tectonic displacement, and have therefore undergone very little modification. The modification of drainage to the east and west of the Whitelaw Fault is consistent with Cainozoic re-activation and uplift along the fault. The Sebastian Fault also appears to have undergone reactivation, although the movement sense is the opposite to that of the Whitelaw Fault, resulting in the uplift of the area between the two faults. We have named the uplifted block the Alexander Horst, after Mount Alexander, the highest point in the horst (Section 6.2). Hence the timing of the movement on the Sebastian Fault is likely to have been concurrent with movement on the Whitelaw Fault in the late Cainozoic. BENDIGO REGOLITH 13

3 Geomorphology highlands and Southern Uplands in Victoria, NSW and ACT (Woods, 1989), suggesting that there is a regional cause of asymmetry. In the northern 3.1 Landscape subdivisions hemisphere, valley asymmetry is the inverse of that observed in the southern hemisphere, suggesting it is The geomorphology of BENDIGO comprises two largely due to solar radiation, resulting in broad divisions, the Western Uplands and the differential weathering and erosion of valley slopes. Riverine Plain (Fig. 5). The Western Uplands can be This in turn leads to differences in vegetation type subdivided on the landforms developed over the and density, soil texture and permeability and slope different geological units: metasedimentary bedrock, processes, with more significant run-off on drier, less the contact metamorphic aureole around the vegetated north-facing slopes (Kane, 1978). Harcourt Batholith, and the Harcourt Batholith Contact metamorphic aureole itself. The Riverine Plain is a broad fluviolacustrine Prominent ridges around the north and south sides of plain that extends into the northern parts of the Harcourt Batholith mark the contact BENDIGO. metamorphic aureole around the batholith. The The Newer Volcanic Group flows only form a small ridges are generally topographically higher than the part of the landscape in the Western Uplands and adjacent rocks. The elevations of the ridges are consists of residual lava flows along the Campaspe commonly over 350 m, with Mount Tarrengower the and Coliban rivers, and the volcano and associated highest peak at 571 m. The aureole is characterised stony rises forming a lava plain around Bald Hill. by a steep slope near the contact with the granite, Cherry and Wilkinson (1994) give a broad outline of and a gentler slope towards the turbidites outside the the landscape and major geomorphic subdivisions of aureole. BENDIGO, which is summarised in Figure 5. Harcourt Batholith The Harcourt Batholith forms rolling hills with Western Uplands 100–250 m relief. Fresh granite outcrop with tors is common in higher relief areas, whereas in Metasedimentary bedrock topographically lower areas fresh granite is Ranges with up to 250 m relief over the Castlemaine commonly capped with thin soil and colluvium. In Group turbidites form a dissected plateau sloping to the west the Harcourt Batholith forms a basin the north (Cherry & Wilkinson, 1994). This landform surrounded by the topographically higher landforms is generally deeply weathered to saprolitic clay, of the contact metamorphic aureole. However, the ferricrete and residual reef quartz. Bedrock ridges highest range in the Bendigo area is developed on the tend to follow the northerly strike of bedding and are Harcourt Batholith, with peaks including Mount modified by faulting and jointing. Barker (550 m), Mount Prospect (560 m) and Mount Drainage is oriented in two main directions, with Alexander (742 m). This is probably due to relatively streams west of the Whitelaw Fault draining north recent movement on the Sebastian and Whitelaw (Bullock, Myers and catchments) and faults, which appear to have upthrown the eastern those east of the Whitelaw Fault draining east and part of the batholith (Section 2.2). Drainage within northeast (Bendigo Creek and tributaries; Fig. 6). the area of the batholith is largely confined by the Northeast of Bendigo, in the north-draining topographically higher contact metamorphic catchments, the valleys have asymmetric cross aureole—Bullock, Spring and Bradford creeks are sections, with the east-facing slopes being steeper the only streams to drain through the aureole into and more deeply incised in comparison to the west- the Riverine Plain. East of Maldon, the Muckleford facing slopes. In some areas this has been attributed Creek drains southward through a gap in the to aeolian deflation by prevailing westerly winds, aureole. with material being eroded from the western side and deposited on the eastern (lee) side (Cherry & Riverine Plain Wilkinson, 1994), but a more likely explanation is late Cainozoic movement along the Whitelaw Fault The Riverine Plain fringes the Uplands and includes (Chapter 2). gently sloping alluvial valleys that drain towards the north, where they branch out and form a broad, flat- To the south of Fosterville along the Campaspe River lying and generally uniform, aggradational fluvio- and its tributaries, many east–west valleys are lacustrine plain. This plain includes the alluvial asymmetric, with the northern valley side (i.e. south valleys which drain the Uplands, from west to east: facing slope) typically steeper and often cliffed Bullock Creek, Myers Creek, the broad valley compared to that of the southern side of the valley between Raywood–Summerfield–Neilborough East, (i.e. north facing slope). Similar valley asymmetry and Bendigo Creek and its tributaries and the has been mapped on Permian glacial deposits in Campaspe River. The surficial sediments of this HEATHCOTE to the east of BENDIGO by the senior plain belong to the Shepparton Formation (Lawrence author (unpublished data). It has also been observed 1966, 1975), with prior streams and traces of in the Adelaide Hills, Mount Lofty Ranges, the lower meandering stream systems dominating the Flinders Ranges, parts of , and the 14 BENDIGO REGOLITH

Figure 5 Digital terrain model of BENDIGO with major geomorphic subdivisions. BENDIGO REGOLITH 15

landscape (Bowler 1967). Younger river systems northeast flowing Bullock and Myers creeks, and incised into the Riverine Plain (Coonambidgal northwest flowing Bendigo and Axe creeks. Bullock Formation; Lawrence, 1966) carry the rivers and Creek drains into the Loddon River to the west of major streams in the Bendigo region. BENDIGO, via Hird Swamp near Cohuna, whereas Myers Creek forms a number of distributary Lava flows channels and dissipates across the Riverine Plain. Axe Creek joins the Campaspe River to the north of Evidence of volcanic activity (Newer Volcanic Group) Axedale. Bendigo Creek joins Piccaninny Creek, within BENDIGO is confined to Bald Hill and along then drains into Mount Hope Creek and ultimately the Campaspe and Coliban rivers (Coliban Basalt; into Kow Swamp to the east of Gunbower. Edwards et al., 1998). The Bald Hill lava flows form an undulating surface with areas of stony rises Drainage development around Bald Hill, a complex volcano comprising a composite cone with two vents, one of predominantly Many of the bedrock hillslopes, particularly those scoria and the other a lava dome (Cherry & lower in the landscape, are mantled with Cainozoic Wilkinson, 1994). The Bald Hill volcano and basalt deposits of varying age and origin. All are relatively flows have been dated at 1.64 Ma (K/Ar; Webb, 1989). low relief features that represent relatively small areas, and are defined by lithology and landscape Basalt flows crop out along the Campaspe and position. Although many of these deposits have been Coliban rivers, but the source of the flows is dissected and now lie scattered in the landscape, uncertain. Four lava flows outcrop at Barfold Gorge their remnants provide important clues to the and Turpins Falls along the Campaspe River, drainage development as the landscape has evolved, whereas two lava flows occur along the Coliban River particularly in the Cainozoic. As such, they have (Coceani, 1999). The youngest lava flow in the been important in reconstructing the Cainozoic Campaspe River valley is 3.12 Ma (Wallace & Ollier, landscape evolution of the area (Chapter 6). 1990) and the third oldest flow is dated at 4.49–5.57 Ma (Webb, 1989; 1990). The Coliban River The oldest recognisable Cainozoic landscape lava flows are undated. Cherry and Wilkinson (1994) elements are fluvial conglomerates of the White Hills proposed Green Hill near Malmsbury as a possible Gravel now preserved as erosional plains on hilltops source of these lavas. Green Hill itself has not been and upper slopes of bedrock ridges throughout dated, although Wallace and Ollier (1990) compared BENDIGO. The White Hills Gravel was deposited by it to Kangaroo Hill, which has been dated at 2.62 Ma. the earliest recognisable drainage systems in the Petrographic and geochemical evidence indicates region, possibly in the Paleocene–Eocene (Hughes & that the Campaspe River lava flows and Coliban Carey, 2002). The present day drainage has been River lava flows are different, and were not sourced inherited, and further developed from, this earlier from Green Hill, or other young eruption points such fluvial system, since the distribution of the present as Pattens or Kangaroo Hill (Coceani, 1999). The drainage still approximates this older system, except presence of lava dykes and outcrop of scoriaceous to the east of the Whitelaw Fault. Remnants of material on the southernmost exposures near White Hills Gravel in this area indicate that the old Metcalfe in CASTLEMAINE suggests a local river flowed north-northwest along the Heathcote eruption point on the Coliban River since eroded Fault in its headwaters, then west to White Hills away (Coceani, 1999). where it was deflected by the Whitelaw Fault (Williams, 1983), before turning east-northeast to 3.2 Drainage follow the Bendigo Creek valley (Hughes & Carey, 2002). BENDIGO is located along on the northern margin of Near Fosterville and at Axedale to the east of the Western Uplands, with drainage mainly oriented Bendigo, fluvial gravels and clays possibly younger north towards the Riverine Plain (Fig. 6). There are than the White Hills Gravel are exposed. They form no large rivers in the map area, with Bullock, isolated hilltop cappings or flank bedrock rises, and Bendigo and Axe creeks forming the largest drainage consist predominantly of kaolinitic clays and minor systems. quartz gravels. Lawrence (1975) mapped them as the Torrumbarry Clay and correlated them with the There is an east–west drainage divide to the north of Calivil Formation. Cherry and Wilkinson (1994) Maldon, and a north–south drainage divide between interpreted these deposits as White Hills Gravel; Raywood, Bendigo and Mount Prospect and Mount Edwards et al., (1998) noted the ambiguous Barker. The drainage divide around Maldon occurs stratigraphic relationships. These sediments have a along Mount Tarrengower, Nuggetty Hills, Mount different regolith profile to the White Hills Gravel Gaspard and Porcupine Hill, with creeks draining to and are significantly more clay rich. the south. These creeks eventually drain into Cairn Curran Reservoir and the Loddon River. Remnants of Pliocene siliceous marine deposits (Parilla Sand) and colluvium consisting of gully The drainage divide between Raywood–Bendigo and alluvium and material transported by gravity from Mount Prospect–Mount Barker separates the higher areas is a minor component of BENDIGO. 16 BENDIGO REGOLITH

Figure 6 Drainage map of BENDIGO and part of MITIAMO. BENDIGO REGOLITH 17

The presence of marine sands reflects the extent of the Pliocene marine incusion, and a change from fluvial to marine conditions. After the retreat of the sea the fluvial system was reestablished. 18 BENDIGO REGOLITH

4 Regolith–landform units 4.1 Transported units

Seventeen regolith–landform units have been Transported regolith–landform units are thin and differentiated in BENDIGO (Fig. 1), which can be discontinuous within the Western Uplands, but form divided into three groups: a composite flat-lying fluvio-lacustrine plain in the l transported regolith consisting of thin and Riverine Plain. These units were formed from the discontinuous fluvial and marine sediments in the erosion of older units, some of which can be related to Western Uplands, thick composite fluvio- source rocks in BENDIGO. The distribution of the lacustrine deposits in the Riverine Plain and transported units is largely controlled by the Late mining residue accumulated from the 1850s Cretaceous to middle Cainozoic landscape evolution, onwards; and their preservation in the landscape has been affected by middle- to late Cainozoic tectonism. l volcanic lava flows with regolith profiles largely Many of these units have been variably ferruginised, dependent on landscape position and time since silicified and/or cemented with clays, both from formation; and groundwater and from pedogenic processes. l bedrock units consisting of predominantly in situ Many of the Cainozoic units are gold bearing to some regolith, with weathering profiles controlled by degree, due to proximity to older gold bearing Cainozoic erosion and landscape evolution. transported regolith and/or bedrock mineralisation. Transported regolith consists predominantly of Historically, transported regolith in or near areas Cainozoic rocks, although it is likely that small with primary bedrock mineralisation has yielded amounts of Permian glacial deposits are concealed phenomenal amounts of gold, whereas regolith of the beneath some of these rocks. Mining residue from same character in areas where primary bedrock human activity is a recent and conspicuous mineralisation is absent has produced very little transported element, as are the basaltic units, gold. However, this does not preclude transported sourced from volcanoes. Although these units have regolith being auriferous in areas where primary post-transport in situ weathering profiles, they are bedrock mineralisation is absent. This can result considered as transported units relative to the from either the complete erosion of the primary underlying bedrock and primary gold mineralisation. bedrock mineralisation from the landscape, burial of primary bedrock mineralisation beneath younger In situ regolith is developed on the bedrock units transported regolith, or the transported regolith (sedimentary rocks, the Harcourt Batholith and containing recycled gold sourced from a known associated contact metamorphosed aureole) with goldfield some distance away. predominantly deeply weathered profiles overlying fresh bedrock. Alluvial The regolith–landform units represent specific Aam associations of regolith materials, landform, and Alluvial sediments on meander plains often bedrock geology, soils and radiometric response. Channel and overbank sediments on meander plains Regolith materials vary significantly both spatially (Coonambidgal Formation) form the youngest and compositionally, so it is often difficult to map drainage system in BENDIGO. This unit is regolith directly and consistently across an area. In diachronous with the younger parts of the alluvial addition regolith may become complex at the contact plain (Shepparton Formation) that forms the present between two distinct units, or where superimposition landsurface of the Riverine Plain (Aap). The change of regolith materials has taken place (i.e. weathering from alluvial plain to meander plain occurs where occurring on both transported and in situ regolith). the stream or creek begins to incise the alluvial plain, However, landforms and regolith are formed and is accompanied by highly sinuous meandering predominantly from the same processes, so it is often channels. Many of the incised streams are poorly possible to demonstrate a close relationship between defined in the Upland ranges, but become well regolith and landform. Once this relationship is defined on the Riverine Plain. Most stream channels understood from field inspections, then landforms are incised only a few metres, but can be up to 7 m can be used to predict regolith patterns (Pain et al., deep, with associated floodplains commonly less than 2001; Taylor & Eggleton, 2001). There is also a good 70 m wide. correlation between the surficial regolith materials and the radiometric data (Fig. 7). Soils are described The typical lithology of the channel sediments using the Northcote scheme (Northcote, 1979). consists of poorly sorted angular and sub-rounded Concurrent with regolith–landform mapping is the lithic and mineral fragments in a sandy to clayey development of landscape and regolith evolution matrix. It is slightly weathered; the floodplain model(s). terraces have grey to grey-brown sandy and clayey uniform soils (Um) developed on them. BENDIGO REGOLITH 19

Aap, Iuu significant aeolian deposit that can be depicted in the Alluvial sediments on alluvial plains; aeolian accompanying map is the lunette on the eastern side sediments forming a lunette of Priors Swamp (AMG 234500 5934500). Priors This unit includes flat-lying alluvial sediments, over Swamp has a small thin arcuate lunette consisting of bank deposits and minor lacustrine and aeolian sandy clay. Small, isolated, irregularly shaped dunes sediments that cover the present Riverine Plain. consisting of sand and clay occur in the Whipstick These sediments form a relatively uniform blanket of and Kamarooka forests (AMG 265600 5951800 and transported regolith over much of BENDIGO, which 270500 5955500), but are too small to be depicted in reach a maximum thickness of at least 60 m to the the map. Much of the present surface of the Riverine northwest (Cherry & Wilkinson, 1994). It also Plain contains a wind-blown component of loess, includes sediments in the gently sloping alluvial commonly with no geomorphic expression, consisting valleys that drain the uplands. Many of the small of pelletal calcareous clay and silt-sized quartz with gullies and creeks in the uplands contain alluvial an iron oxide coating. This aeolian mantle was sediments, which merge with bedrock-derived originally sourced from the western Murray Basin, colluvium (Cfc). The younger parts of the plain also and now occurs within the soil as either disseminated grade into the younger meander plains (Aam). calcareous fine earth or small nodules. Drainage in the upland valleys forms a distributary Most of the deposits in this regolith–landform unit pattern, but streams and creeks coalesce in the are within the Shepparton Formation (Lawrence, Riverine Plain to form an anabranching drainage 1966; 1975), one of the youngest transported system, with mostly shallow and poorly defined auriferous units in BENDIGO. Many shallow leads creeks and streams. Meander plains (Aam) have and alluvial workings that drain mineralised bedrock developed within the floodplains and form the beds of are within this unit. Gold recovered from these the rivers and major streams in BENDIGO. In many young alluvial deposits consists of both gold eroded places the sediments are mantled with a thin alluvial from the bedrock and recycled gold from older fluvial cover sourced from historic gold mining (Faf). This units. mantle of alluvium has obscured the morphology of Channel deposits and lenses of sands within the many shallow streams. plain are dominated by lithic clasts that reflect the The surface sediments are generally uniform red- source rocks. Compositional variations noted in the brown silts and clays, which at depth become weakly field, combined with interpretation of the radiometric to strongly mottled. Surface soils tend to be imagery (Fig. 8) show the plain is composed of gradational (Gc, Gn) or uniform red-brown with several distinct floodplain units, described below. occasional fine earth and nodular carbonate in the B Floodplains derived from metasedimentary bedrock horizon. These floodplains are derived from erosion of the Pisolitic ferricrete soils have been identified in the metasedimentary bedrock (Castlemaine Group) and subsurface of this unit in BENDIGO. Hughes et al. are dominated by a low radiometric response. They (1998) suggest this soil is likely to be equivalent to include (from west to east) Myers and Bendigo creeks the Karoonda Regolith developed on the marine and the broad valley system between Raywood and sediments (Parilla Sand), indicating a Neilborough East. The channel deposits are Plio–Pleistocene age. The presence of ferricrete in characterised by the presence of weathered or the Shepparton Formation (i.e. ferruginisation of ferrugunised sub-angular to angular lithic pebbles matrix, ferruginised bedrock clasts, ferricrete in and cobbles and reef quartz. soils) is indicative of the older parts of the unit. The For example, exposures at Myers Creek (AMG sediments that are at the present surface of the 248800 5937600) and at Laugoons quarry at Myers upland valleys and the Riverine Plain are Flat (AMG 251200 5933800; Fig. 9) are dominated by diachronous with other Quaternary fluvial units in sub-angular to sub-rounded clasts of pebble- and area. They lack ferricrete and are characterised by cobble-sized metasedimentary bedrock (most the presence of both nodular and fine earth soil ferruginised) and reef quartz in a loosely compacted carbonates. matrix of poorly sorted quartz sand. Swamp deposits are uncommon in BENDIGO and Floodplains derived from eroded granite only occur near or in association with areas of Several creeks and streams in BENDIGO have their stagnant drainage. The largest swamps in the region headwaters in the Harcourt Batholith, and are occur at Tang Tang and Winghee near Dingee, and characterised by the presence of granitic quartz, clay Thunder Swamp northeast of Raywood. Swamp and mica. The floodplains of these creeks and deposits are young features in the landscape, but streams are characterised by a higher total some may extend back beyond the last glacial cycle to radioelement response than the floodplain sediments older than 20 000 yr. BP. Most swamps are too small derived from metasedimentary bedrock. These to be depicted on the accompanying map. streams are (from west to east): Bradford Creek, Aeolian deposits are associated with Quaternary Spring Creek, Bullock Creek, Axe Creek and Myrtle aridity and cold climates, and include a lunette, Creek. Sediments in Bullock Creek at Lockwood dunes and aeolian dust mantle (loess). The only South (AMG 246500 5919000) and distributary 20 BENDIGO REGOLITH

Figure 7 A: radiometric ternary ratio image of BENDIGO (Red = potassium, Green = Thorium, Blue = Uranium). Regolith–landform polygon boundaries as white lines. BENDIGO REGOLITH 21

Figure 7 B: single channel radiometric images. 22 BENDIGO REGOLITH

Figure 9 Aap. A sediment-filled mine shaft and a thin layer of mining residue preserved above floodplain alluvium. Most of the clasts are comprised of ferruginised metasedimentary bedrock. Laugoons Quarry, Myers Flat, AMG 251200 5933800.

Mixed-source floodplains The Loddon River floodplain is sourced from both granite and metasedimentary bedrock. It only occurs in the northwest corner of BENDIGO and has northeast oriented channels. The boundary between the Loddon River floodplain and the Bullock Creek floodplain is defined by the change in orientation of channels and streams. Similarly, feldspars have been encountered in the alluvium at in the Fosterville gold field Figure 8 Radiometric ternary ratio image of northwestern BENDIGO (Scott & van Riel, 1999), and granitic quartz along showing the variations in radiometric response of the three floodplains, the Coliban–Campaspe rivers (Coceani, 1999), caused by differing source rocks. The thinner white lines are the RLU indicating a granitic component in the alluvium of boundaries. these rivers. Aep channels at Campbells Forest (AMG Alluvial sediments on erosional plains 244500 5943500) are sourced from the Harcourt This unit is exposed to the south of Huntly (Forest Batholith and are dominated by mica and quartz deep lead; AMG 261500 5937200), Sharkeys pit at sand. Spring and Bullock creeks drain into the Fosterville (AMG 278300 5939500) and Mackenzies Loddon River floodplain, whereas Bradford Creek pit at Axedale (AMG 274200 5928400). Much more drains to the west of BENDIGO and Axe Creek and extensive deposits of this unit occur east of Axedale, Myrtle Creek drain to the east. The Coliban River to but these are to the east and outside BENDIGO. The the south-east is also sourced from the Harcourt typical profile is strongly bleached and characterised Batholith, but has no significant floodplain in by a coarser basal sub-rounded to rounded quartz BENDIGO. pebble and cobble gravel with a kaolinitic clay and quartz sand matrix, overlain by finer grained and generally uniform clay and silty clay. The basal gravels (“washdirt”) are auriferous, and there are BENDIGO REGOLITH 23

Shepparton Formation. It does not include other gold bearing leads associated with either younger or older alluvial sediments (i.e. Shepparton Formation or White Hills Gravel) that may be considered as deep leads where buried beneath thick alluvium. Examples of this include the Ironstone Hill Deep Lead, which drains into the Telegraph Lead and is considered to be a Shepparton Formation lead, and the unnamed buried lead at Myers Creek where White Hills Gravel is buried beneath floodplain alluvium (Aap). Historical records on gold grades and the geology of the Calivil Formation can be obtained from the reports on the auriferous deep leads of the Figure 10 Aep. Gravels flanking mineralised bedrock rise. This Huntly–Telegraph Lead (Murray, 1873; Stirling, exposure has now been removed by rehabilitation work. Sharkeys Pit, 1898; Brough Smyth, 1869; Smiley, 1901) and the Fosterville, AMG 276800 5934400. Forest Deep Lead (Stirling, 1898). Flake and nuggetty alluvial gold has been recovered from the several upward-fining sequences which tend to be base of Calivil Formation at Sharkey’s pit (T. less mature (sub-angular to sub-rounded poorly Jackson, pers. comm.), which is different to the sorted gravels) and only partly auriferous (Cherry & micron-sized gold found throughout Fosterville gold Wilkinson, 1994). At Osterfields pit to the east of field. BENDIGO where the sediments are similar to those Some of these deposits, particularly those at at Mackenzies pit, some of the quartz gravels at the Mackenzies and Osterfields pits, have been base of the pit appear to be of granitic origin. The interpreted as White Hills Gravel (Cherry & upper several metres of the unit consist of uniform to Wilkinson, 1994) although stratigraphic weakly laminated kaolinitic clays with minor quartz relationships are ambiguous (Edwards et al., 1998). silt or sand and are strongly bleached with minor The high clay content, extensive bleaching and mottling. Silty and clayey pale red-brown absence of ferricrete and silcrete suggests that these gradational soils (Gn) are typical. deposits are not equivalent to the White Hills Gravel At Fosterville, minor outcrops of fluvial gravels and but represent a younger fluvial system. clays form isolated hilltop cappings or flank bedrock ACer rises. At Sharkeys pit (exposure now destroyed) in Channel sediments on erosional rises the northern part of the Fosterville mine site, clays Channel sediments occur on erosional rises along the and quartz sands and gravels flank the mineralised margins of the highland ranges. The typical regolith bedrock rise (Fig. 10). On the western side of the pit, profile is bleached, cemented conglomerate overlying the mineralised bedrock was mantled by 15–20 m of very highly weathered bedrock. These profiles are clays and gravels with a steeply sloping valley side to elevated in the landscape, and often occur on the the west (towards Gunyah Creek), that define the flanking ranges along present drainage, such as margins of a palaeovalley. At Mackenzie’s pit, Myers, Bendigo and Axe creeks, indicating that in bleached clays lie on the margin of Axe Creek and many areas the modern drainage system has been appear to follow the present drainage. Similar inherited from this earlier fluvial system. In the deposits are encountered at the Osterfield’s pit Bendigo region, particularly around White Hills and northeast of Axedale and just outside BENDIGO. surrounds, the conglomerate has been worked for These deposits consist of green-grey to white gold, with the gold mostly recovered from the base of stratified kaolinitic clays and bedded quartz sands the gravels. and pebbles that overlie green-grey to white weathered Ordovician bedrock. The intense Gold mining has considerably disturbed the upper weathering of both the alluvial sediments and the surface. Soil profiles are absent, and cemented surrounding bedrock may indicate kaolinisation quartz conglomerate is typically exposed at surface. associated with post-depositional weathering. It is moderately to strongly cemented with silica, clay and lesser iron oxides, forming a duricrust several The surface exposure of the gravels is limited, but metres thick. It consists of cemented sandy quartz they are an important unit because they continue pebble and cobble conglomerate and it is quite hard— into the sub-surface and host the famous ‘deep lead’ historical mining records indicate that explosives gold deposits. They include the auriferous deep lead were commonly used to penetrate this layer. Historic deposits of the Huntly–Telegraph Lead, the Forest photos from the Bendigo gold field and other gold Deep Lead (south of Huntly), the Elysian Deep Lead producing regions in central Victoria suggest that (Neilborough–Raywood), and the Spring Creek Deep there may have not been any significant soil profile Lead (west of Marong). It is uncertain whether the developed on this unit. other deep leads in the Leichardt–Marong area (Greenways Lead) are younger leads within the 24 BENDIGO REGOLITH

quartz cobbles, with minor sandstone/quartzite cobbles, and contrasts with the dominance of ferruginised bedrock clasts within younger shallow leads mined at Myers Flat and present on the banks of Myers Creek.

Colluvial Cfc Colluvial sediments in colluvial fans and fan systems Colluvial material derived primarily from the erosion of weathered bedrock is found flanking many bedrock hills and rises. These deposits occur on most hill slopes and at the headwaters of many streams in the uplands, and are characterised by poor sorting and Figure 11 ACer. Steep joints in silicified quartz conglomerate, possibly indistinct bedding. It is poorly exposed and merges a response to movement on the Whitelaw Fault. Council quarry, White with the deposits in the alluvial plains (Aap). The Hills, AMG 230700 5959800. contact between these two units is usually delineated by a break in slope. The duricrust grades with depth to compacted and The colluvium consists of poorly sorted angular to generally uncemented sandy quartz pebble and sub-rounded lithic and mineral fragments in a sandy cobble conglomerate, with patchy silicification, to clayey matrix, and can be subdivided on the basis ferruginisation, and clay cementing. The channel of source rocks. Colluvium derived from weathered sediments themselves comprise well-rounded, or sub- metasedimentary bedrock is dominated by sub- rounded to sub-angular quartz cobbles and pebbles, angular to angular pebbles and cobbles of mudstone and minor sub-rounded to rounded sandstone cobbles sandstone and reef quartz. Colluvium derived from and pebbles. the Harcourt Batholith granite consists of quartz, feldspars and clay, with occasional pebbles and The council quarry at White Hills (AMG boulders of sub-rounded granite. However colluvium 230700 5959800) exposes north–south trending, sub- on the Harcourt Batholith near the margin with the parallel joints silicified and cemented with clay. The contact metamorphosed aureole contains a mixture joints may have developed in response to movement of sub-angular to angular hornfelsic and granitic on the Whitelaw Fault (Fig. 11). debris (AMG 238800 5905300). The colluvium can be The underlying metasedimentary rocks are several metres thick and partly cemented in places weathered to mottled and pallid saprolite. To the with iron oxides, but is often poorly consolidated. west of White Hills, where these gravels have been Soils are poorly developed and are uniform coarse stripped away, soft, moderately weathered textured (Uc) or uniform, non-cracking fine textured interbedded mudstone, siltstone and minor (Uf). Soils on colluvium derived from weathered sandstone is exposed, which is mottled and bleached metasedimentary rock consist of typically pale grey- in places. To the east, highly weathered brown silty clays with lithics throughout, whereas metasedimentary rocks crop out, which are iron those developed on colluvium derived from the indurated and contain mega-mottles. Harcourt Batholith consist of uniform red-brown Similar deposits occur throughout the Western sandy clays. Uplands, also in elevated landscape positions. These deposits are grouped into the White Hills Gravel Marine after White Hills, 3 km north of Bendigo, where bleached quartz sand and gravels form hill cappings OMep that were worked in the mid-1800s for their alluvial Marine sediments on erosional plains gold. Near White Hills several other hills capped This unit usually occurs along the margins of bedrock with cemented quartz gravel were also worked for valleys, and is limited to the west of the Leichardt alluvial gold. Fault and east of the Whitelaw Fault. It is generally flat lying, forming topographically subdued and On the western slopes of the Myers Creek valley isolated outcrops on the lower slopes of bedrock hills (AMG 247800 5937300) small, isolated outcrops of and hill margins. The typical profile over this unit is White Hills Gravel on the margin with the Riverine mottled, fine quartzose sands of marine origin Plain lie approximately 1 m above the present fluvial overlying highly weathered metasedimentary system. These gravels appear to define a narrow lead bedrock (Fig. 12). However, in many areas only a that was worked for gold, and local farmers have very thin sand cover is preserved. The typical indicated that some of the shafts in these gravels surface expression of this unit is cobbles and pebbles were deep (in excess of 5 m). Mullock from these of ferruginised, moderately to well sorted quartz shafts is dominated by rounded to sub-rounded sandstone overlying weathered bedrock. BENDIGO REGOLITH 25

dominated by silcrete or silicification, and younger exposures (<4.6 Ma) shown to be lateritic type profiles that consist predominantly of iron accumulation (Kotsonis, 1995; 1999). Younger exposures can be described as a laterite or lateritic podzol (Coaldrake, 1951; Hills, 1975; Lawrence, 1975). The change from silica to iron mobilisation within the soil environment possibly reflects a change in climate (Chapter 6).

Glacial Glacial deposits Glacial deposits are not exposed in BENDIGO, but Figure 12 OMep. Typical profile developed on marine sands overlying there appears to be some indirect evidence for turbidite bedrock. Disused quarry, Epsom, AMG 236700 5963000. subsurface Permian glacial sediments at Leichardt, Marong and Woodstock, and reworked glacigene sediments in younger deposits at Kangaroo Gully, The marine sands themselves consist of well-sorted Myrtle Creek and Big Hill (Cherry & Wilkinson, and predominantly fine quartz sand and silt, with 1994). All of these deposits are characterised by the occasional sub-rounded coarse reef quartz or very presence of either faceted or striated glacial erratics. coarse to fine conglomerate. The quartz sands are The extent of subsurface glacial deposits in typically sub-rounded to sub-angular. This unit is BENDIGO is unclear—many of these rocks may have generally massive, but weak bedding structures are been misidentified as Cainozoic fluvial deposits. sometimes visible, and it is strongly bioturbated in some areas with well-defined vertical burrows (e.g. AMG 259200 5943200), similar to Skolithos Human activity ichnofacies suggesting a shallow water and tidal flat Faf environment (Cherry & Wilkinson, 1994). This Mining residue on floodplains suggests it formed in estuarine embayments that Although not traditionally considered a feature of the reached Huntly and possibly towards Epsom (Cherry modern landscape, mining residue forms a & Wilkinson, 1994). Although coarse beds are significant component of the surficial environment in common, the presence of fine grained sands and silts BENDIGO. With the discovery of gold at Bendigo in suggest a low energy environment. the 1850s, the massive influx of miners extensively The upper surface of this unit is capped with a working creek beds and gullies resulted in enormous lateritic type weathering profile consisting of volumes of mining residue being washed down the ferricrete and/or silcrete. In BENDIGO the common creeks and gullies and into the river valleys. profile is (Appendix 2): Historically, this mining residue was termed ‘sludge’, the name given to the residue of alluvial gold mining, l a detrital pisolitic ferruginous lag at the surface; and particularly to that from the process of puddling, overlying a semi-fluid mixture of crushed rock, soil and water l a mottled red and yellow clayey and sandy B (Cole, 1994; see below). It forms a very fine grained, horizon; that grades with depth to hard setting, concrete-like ‘capping’ overlying either l mottled clayey friable sandstone (duplex soil with a red clay B horizon). The pisolites at surface tend to be rounded to sub- rounded with polished outer surfaces. Mottling in the B horizon decreases with depth, and the mottles near the surface tend to be more strongly cemented with iron oxides, suggesting that the pisolites have formed from the iron cemented mottles. The underlying sandstone is often weakly to moderately cemented with argillans (cutans), and sometimes cemented with iron oxides. This type of weathering profile is generally present where there is a thick (>1 m) sequence of marine sand. Firman (1973) named the duricrust at the top of this unit the Karoonda Surface; Kotsonis (1995) renamed Figure 13 Faf. Mining residue over an old soil profile. Myers Creek, it the Karoonda Regolith. The Karoonda Regolith is AMG 248800 5937600. The mining residue forms a layer of relatively time-transgressive and varies across the western consistent thickness; the contact is marked by the base of the hammer Murray Basin, with older exposures (>4.6 Ma) above the centre of the photograph. Hammer is 33 cm long. 26 BENDIGO REGOLITH

a well developed, well structured pedal horizon or the A puddling machine consisted of a large lined circular gravels or sands of a creek bed (Fig. 13). It varies pit 5–6 m in diameter with a horse drawn harrow. between a few centimetres and three metres in Material was washed with water and churned by the thickness (Peterson, 1996; 1997). In previous harrows, with the ‘sludge’ residue discharged though studies, the hard setting clay has been interpreted as an outlet channel (Peterson, 1995). It was estimated calcareous dust (Mikhail, 1976) or compaction of that by 1855, 2000 puddling machines were in the surface soils caused by overgrazing (Lorimer & Bendigo district (Anderson, 1978) and by 1859 the Schoknecht, 1987). Recent work has identified a problems associated with ‘sludge’ accumulation wide distribution of sludge from Bendigo, northwards culminated in a Royal Commission (Peterson, 1995). to Goornong and Elmore, and along Myers and The Commissioners noted that “even on the plains, Mount Hope creeks (Cole, 1994; Peterson, 1995; thirty or forty miles away (50–60 km) from 1997). Sandhurst (Bendigo), where the sludge flows thin, and is relieved from its heavier particles, we found it The mining residue forms a thin, flat-lying unit along baked into a perfect concrete, and in thicknesses present drainage and mantles floodplain deposits varying up to two feet (60 cm) or more” (Victoria downstream from Bendigo and is a hard setting silty Parliamentary Papers, 1859–60). The Royal clay. The lower contact is often undulating, and Commission Report estimated 500 puddling traces of bedding and laminations are common machines in the western side of the Bendigo goldfield throughout. Pisolites and angular quartz chips occur (draining into Myers Creek), discharging 2867 m3 of within this unit, with deposits around Bendigo being sludge daily, (573 450 m3 annually), and 1500 coarser grained, and with lenses of coarse grained puddling machines whose waste drained into quartz cobbles and pebbles and ferricreted bedrock Bendigo Creek and its tributaries, discharging clasts common. Mining residue further away from 1 720 350 m3 of ‘sludge’ annually (Peterson, 1995). Bendigo is much finer grained, concrete-like (but not always), and apedal. It usually overlies soils with a well-developed pedal horizon or directly overlies 4.2 Volcanic units fluvial sands and gravels. The presence of pisolitic ferricrete within these deposits suggests that the Regolith derived from volcanic material is present puddlers also worked the regolith between and above around Bald Hill near Woodstock and in the gullies (Peterson, 1995). It has been observed up to southeast corner of BENDIGO near Myrtle Creek 64 km (45 miles) from the township of Bendigo along the Coliban River. Most of the units consist of (Victoria Parliamentary Papers 1859–60). basaltic stony rises lava flows. Red-brown gradational soils occur over the Bald Hill volcanic The unit is exposed along creek banks and dams complex, while very little soil is developed on the along Myers, Bendigo and Axe creeks, and along the Coliban River flows—although the latter is the older broad valley between Raywood and Neilborough East of the two (Fig. 14). The Coliban River flow is dated (including the Elysian Flat Deep Lead). Radiometric at 2.62 Ma (Wallace & Ollier, 1990), whereas the Bald imagery shows that areas containing mining residue Hill volcanic complex is dated at 1.64 Ma (Webb, have a high radiometric response and are associated 1989). This age difference, while the reverse of that with gold producing regions, contrasting with many expected based on soil development, is reflected in gullies and creeks draining bedrock rises that have a the landforms associated with each flow. The Coliban low total radioelement response. River flow forms flat-lying residuals, as significant Puddling lateral and soil erosion has occurred, exposing the The mining methods around Bendigo directly sub-basaltic sediments, whereas minimal erosion has contributed to significant modification of large areas occurred on the low rises of the Bald Hill volcanic of the land surface. In the early days of Bendigo, complex. most of the gold was recovered from washing the VFep alluvial deposits along creek and gully floors. Lava flows on erosional plains Initially, the gold was recovered from the sands and Small mesas of vesicular basalt are located along the gravels below the topsoil (‘first bottoming’ or ‘shallow Coliban River and Myrtle Creek. The streams have sinking’; Anderson, 1978), but there was a reluctance incised though the sub-basaltic sediments and into to mine the clay (alluvium and regolith), as the underlying bedrock. Two lava flows have been extracting the gold was far more difficult. When the identified around Myrtle Creek (Coceani, 1999). The clay was wet it was sticky—fine gold would stick to it thicknesses of the flows vary depending on and was difficult to extract without washing with preservation, but they can be over 40 m thick. No significant amounts of water. However, when dry it streams are developed over the flows around the became extremely hard, and was frequently referred Coliban River. to as ‘cement’, sometimes requiring the use of a sledge hammer or even explosives to break up The upper surface of the unit consists of stony rises (Brough Smyth, 1869). Puddling machines of blocky sub-angular to rounded vesicular basalt dramatically increased the amount of material that boulders. Spheroidal weathering is uncommon, and could be worked and in addition they could only occurs near springs. No complete soil profile successfully work the clayey alluvium and regolith. BENDIGO REGOLITH 27

A B

profile. The only significant exposure occurs at the All Stone Quarry (AMG 233800 5929400) where 6–8 m of columnar basalt is exposed. Figure 14 VFep, VFvl. Comparision of soil profiles. A: old flow with little soil. West bank of Coliban River, AMG 276400 5905200. B: young Drainage over this unit is poorly developed, with flow with thicker soil. All Stone Quarry, AMG 233800 5929400. The rate swamps and shallow streams with an irregular of erosion is greater than the rate of soil formation in the area of the drainage pattern common. These thin and older Coliban River flows, whereas the rate of erosion around the discontinuous sediments overlying the lava plain are younger Bald Hill volcano is much less, preserving the soil. equivalent to the alluvial sediments of the Riverine Plain (Shepparton Formation). The eruption of the was seen, although a thin residual layer of red-brown Bald Hill volcano resulted in a disruption of drainage clay is sometimes present. patterns in the Little Creek valley. The elevation of the sub-basaltic sediments across The surface of the flows around Bald Hill is stony the Coliban palaeovalley is uniform, and mapping by rises with clayey red-brown gradational soil (Gn). Coceani (1999) revealed that the pre-basaltic Coliban Pisolitic ferricrete is sometimes found in the upper palaeovalley was wide and shallow compared to the parts of the soil profile. Cobbles and boulders of sub- modern Coliban River valley. The sub-basaltic rounded basalt, showing spheroidal weathering and sediments under the lava flows consist of granite- coated with iron oxides and clay, are common derived quartz sands and gravels with only minor throughout the soil profile. With depth, the basalt iron oxide cementing and staining. Lenses of angular boulders become more closely spaced and begin to sub-angular reef quartz and ferruginised bedrock following joint patterns, which in turn become pebbles also occur throughout. boundaries between basalt columns in the fresh basalt. Vesicles in basalt boulders in the lower parts This unit has a low total radioelement response, of the soil profile are sometimes infilled with calcium imparting dark tones to the RGB image (Fig. 7) that carbonate, but no carbonate was found within the contrast with the generally brighter signature of the clayey soil matrix. surrounding units. The flows are generally remanently magnetised, which also contrasts sharply This unit has a low total radioelement response, with the surrounding bedrock units. imparting dark tones to the RGB image (Fig. 7) that contrast with the generally brighter signature of the VFvl surrounding units. The flows have a high frequency Lava flows on lava plains magnetic response, which also contrasts sharply with This unit surrounds, and is derived from, the Bald the surrounding bedrock units. Hill volcano. Exposure is mostly limited to dams and road cuttings that show the upper parts of the soil 28 BENDIGO REGOLITH

VFv present in the saprolite will reflect chemical Lava flows and scoria on a composite volcano dispersion patterns, possibly forming a dispersion This unit is limited to the area around the Bald Hill halo of some size. volcano (AMG 236600 5926500). Bald Hill is a The extent and preservation of fossil soils developed composite volcano (scoria vent and lava dome) that on the turbidites and associated with in situ rises 30–40 m above the stony rises lava field. The weathering is unclear, but their significance for Bald Hill volcano lies within a gently sloping alluvial exploration is important, particularly where valley of the Riverine Plain and to the west of a exploring for concealed deposits. A buried fossil soil north–south trending ridge of sedimentary bedrock. on the eastern slope of the Myers Creek valley This has resulted in lava flows directed to the west between Sebastian and Neilborough has been and northwest of this bedrock ridge towards identified that consists of isolated remnants of DUNOLLY. One small lava flow to the north of Bald ferruginous duricrust developed over mineralised Hill (AMG 237300 5928200) has flowed through a bedrock which shows elevated As and slight Au breach across this bedrock divide towards Spring enrichment (Hughes et al., 1998; Kotsonis et al., Creek. The regolith materials over the volcano are 2000). The extent of this ferricrete is unknown, but similar to those over the lava plain. drilling throughout Raywood, Neilborough and The unit has an identical radiometric response to the Neilborough East has revealed sub-surface ferricrete surrounding lava plain (Fig. 7). (termed “cemented wash”) overlying weathered bedrock that may be equivalent to this soil 4.3 In situ units (Patterson, 1982). Similar fossil soils may be encountered fringing the upland ranges and buried beneath younger transported regolith throughout The in situ regolith–landform units in BENDIGO are BENDIGO, and may form a significant geochemical developed over three main geological units, which marker for mineralisation. each have characteristic regolith materials:

l sandstone, siltstone and mudstone (turbidites) of Deep marine turbidites (Castlemaine the Castlemaine Group that have been regionally Group) metamorphosed up to and including greenschist facies; Regolith–landform units developed over the Castlemaine Group form low hills, with strike ridges Castlemaine Group turbidites that have been l that trend in a northerly direction. Drainage is fixed contact metamorphosed; and, within creek and stream channels that form an l granite of the Harcourt Batholith. integrated tributary network that drains northwards into the Riverine Plain. In the central parts of The present landforms developed on all of these units BENDIGO, the bedrock ridges formed interfluves in are erosional, that is, the rate of erosion is currently the early Cainozoic landscape. outstripping the rate of deposition. The soils, therefore, mostly reflect the present equilibrium The degree of weathering and thickness of the in situ between weathering and erosion and are probably regolith varies and is dependent on geological quite young in the landscape, and as such they do not structure, position in the landscape (and reflect the period of weathering that produced the palaeolandscape), and proximity to gold underlying thick saprolite. This has resulted in a mineralisation. The turbidites range from variable soil cover that instead reflects the antiquity moderately to very highly weathered; fresh bedrock of landforms preserved at the surface. is only exposed in the mullock from old mines. The average thickness of in situ regolith in BENDIGO is The understanding of the relationship between soil 35–50 m. This varies depending on proximity to gold cover and landform antiquity is most relevant where mineralisation or presence of significant bedrock the variable soil cover may hinder exploration for fracturing—thicker weathering profiles are seen in gold mineralisation. Bedrock gold mineralisation in these areas. BENDIGO is confined to the Castlemaine Group, including the contact aureole of the Harcourt Due to the extensive gold mining history of Batholith. Erosion has liberated gold into the BENDIGO, soils developed on the turbidites are pedolith and further recycled gold into the younger poorly preserved, particularly around the city of transported units. The current erosional landforms Bendigo and other goldfields. Puddling machines have a soil cover that is not connected in time with were brought to many of the goldfields after the the deep weathering of the underlying saprolite. initial “rushes” and were used to extract gold from Anomalies associated with gold mineralisation in the the alluvium and the regolith. This was particularly soil reflect predominantly physical weathering the case for soils developed over mineralised bedrock, processes—the extent of chemical weathering and as the gold in the soil could be easily extracted and dispersion within the soil will increase with the age. processed. However, the underlying saprolite has undergone Soils on these units are very variable, with some moderate to very high chemical weathering, and any areas having no soil preserved at all. These anomalies associated with gold mineralisation BENDIGO REGOLITH 29

variations can occur on a local scale reflecting variable thickness mantles highly weathered differences in position in the landscape (ie. ridge saprolite. crest and ridge slope), but there also appears to be a SHel1 regional influence to the distribution and extent of Highly weathered bedrock on low hills soil profiles. Between the Sebastian and Whitelaw Highly weathered bedrock occurs on the slopes of faults soils are typically absent, whereas east of the ridges and on low hills; these tend to be more Whitelaw Fault and west of the Sebastian, relatively weathered than the higher ridge crests, which often thick and well developed gradational and duplex soils consist of moderately weathered bedrock. The highly are common (Chapter 7). weathered bedrock is characterised by a moderate K, SMel1 variable U and Th radiometric response. Moderately weathered bedrock on low hills In the central and southern parts of BENDIGO Moderately weathered bedrock occurs on strike highly weathered bedrock occurs on the lower slopes ridges and on the crests of hills and rises throughout of bedrock ridges. East of the Whitelaw Fault and the central and southern parts of BENDIGO. To the north of Axe Creek, most of the exposed bedrock is east of the Whitelaw Fault and north of Bendigo highly weathered, whereas north of Bendigo Creek Creek, only the highest ridge crests along the highly weathered bedrock forms the ridge crests. To drainage divide expose moderately weathered the east of the Sebastian Fault, some ridge crests and bedrock. West of the Leichardt Fault it is limited to most slopes are highly weathered bedrock. the higher ridge crests. Moderately weathered bedrock is characterised by high K, and moderate to The highly weathered bedrock consists of saprolite low U and Th. exposed at the surface, mantled in places with a clayey gradational soil (Gn) or a duplex soil (Dy). The The typical regolith profile consists of saprolite at the presence or absence of soil cover is related to position surface with no soil, or a thin residual lag of bedrock in the landscape, with areas of active erosion such as float and angular fragments of quartz, with gullies or rises with steep slopes usually lacking soil. uncommon ferruginous bedrock clasts. The saprolite The underlying geology also plays a significant role consists of yellow-brown and red-brown interbedded in soil development, with sandstone units forming sandstone, siltstone and mudstone, with original thin lithic soils, whereas mudstone and siltstone bedrock features such as bedding and quartz veining units form relatively thick clayey gradational or readily identifiable. No significant weathering duplex soils. The latter typically have a bleached textures such as mottling, ferricrete, or destruction of silty and clayey A horizon, with poorly sorted angular bedrock sedimentary fabrics was seen. bedrock and reef quartz float, grading to a weakly In areas of primary gold mineralisation, the mottled red-brown and yellow-brown clayey and silty moderately weathered bedrock may be highly to very B horizon. highly weathered due to chemical weathering The saprolite is poorly exposed and the only associated with the oxidation of accessory sulphide significant outcrop occurs in areas near historic gold minerals. This can result in a significant thickness of workings (ie. sluicing at White Hills). Where saprolite near mineralised gold veins, the presence of exposed, the highly weathered bedrock consists of ferruginous mottling and ferricrete, the destruction weakly mottled red-brown and yellow-brown of bedrock textures and the alteration of bedrock kaolinitic clays with original bedrock features are minerals to kaolinite. still preserved. It also tends to be soft and friable, The influence of the bedrock geology on the and breaks up easily in the hand or with a shovel. In development of the regolith is most obvious in the most areas, the mottling is weak, but in some areas Sugarloaf Range. It consists of quartz sandstones that form a long, narrow range on the eastern margin of BENDIGO (compared to the interbedded sandstone, siltstone and mudstone of the rest of the Castlemaine Group). The orientation and geomorphology of the Sugarloaf Range is strongly controlled by the bedrock structure, with the sandstones deformed into a northerly plunging anticline trending NNW and bound to the east by the Sugarloaf Fault. The range consists of moderately weathered sandstone outcrop with variable soil cover. On the upper slopes, which tend to be steep, soil cover is generally absent, and sandstone boulders and cobbles are exposed (Fig. 15). However, towards the lower slopes, a mixture of poorly sorted colluvium and red-brown gradational or duplex soil cover of Figure 15 SMel1. Moderately weathered bedrock exposed in the Sugarloaf Range. Sugarloaf Road, AMG 276080 5928350. 30 BENDIGO REGOLITH

there is significant mottling, with ferricrete present in the saprolite. SVer1 Very highly weathered bedrock on low hills Very highly weathered bedrock crops out on the lower slopes of bedrock ridges and low hills, and is restricted to areas near Bendigo Creek, east of the Whitelaw Fault and west of the Sebastian Fault. Gullies incised into very highly weathered bedrock on hills and rises have exposed highly weathered bedrock in the creek banks, which can be easily identified in the radiometric imagery. The very highly weathered bedrock is characterised by a high Th, low K and U radiometric response. The typical profile consists of mottled red-brown and yellow-brown saprolite mantled with a clayey gradational (Gn) or duplex soil (Dy), with the underlying weathered bedrock poorly exposed. It is mostly weathered to soft kaolinitic clay with bedrock features poorly preserved, although in places it contains ferricrete. The soils are similar to those developed on the highly weathered bedrock (see above), and consist of a compact bleached silty and clayey A horizon with poorly sorted ferricrete grading to mottled red-brown and yellow-brown clayey and silty B horizon. Most of the ferricrete at surface consists of ferruginised soil material with minor ferruginised bedrock clasts and iron stained reef Figure 16 SSeh3. Typical profile of slightly weathered saprock and quartz. thin lithic soil profile. Fogartys Gap, AMG 253300 5905900. Contact metamorphosed turbidites whereas the lower slopes have a thin horizon of (Castlemaine Group) lithics with a clayey subsoil. SSeh3 This unit has a distinctive high K signature (Fig. 7) Slightly weathered bedrock on hills and a relatively uniform thickness. It is slightly The contact metamorphic aureole surrounding the magnetic, contrasting with the nonmagnetic Harcourt Batholith forms prominent arcuate ridges Harcourt Batholith and the sedimentary rocks around either side of the granite. Exposures of the outside the aureole. regolith can be found in road cuttings, particularly at Fogartys Gap (AMG 253300 5905900; Fig. 16) and at Granite (Harcourt Batholith) Big Hill (AMG 252800 5918000). The Harcourt Batholith contains two granite plutons The regolith developed is in situ, consisting of deeply in BENDIGO, the Harcourt and Baringhup weathered contact metamorphosed turbidites granodiorites (Cherry & Wilkinson, 1994). These (saprock). The maximum exposed thickness of this plutons can be readily identified in the magnetic and unit is 15 m, at Big Hill, where the rocks are radiometric images; however, the regolith cover does weathered to below the base of the road cutting. The not clearly distinguish them. The batholith is saprock is red-brown to pale brown, with colour differentiated into fresh granite outcrop with thin variations controlled by lithology, and is quite hard. and minor regolith cover, and highly weathered Bedding and quartz veining are easily recognisable. granite saprolite of variable thickness with minor Duplex soils (Dy) are poorly developed and tors. The unweathered granite is limited to the immature, and are dominated by rock fragments and central part of the Harcourt Batholith in BENDIGO reef quartz that are scattered throughout the profile. and is bounded to the east and west by highly The upper surface consists of a thin (10–30 cm) A weathered granite, the contact metamorphic aureole horizon of eluvial rock fragments, reef quartz and to the north, and mantled by transported regolith clayey silt, grading to a B horizon (10–60 cm) cover to the south. dominated by rock fragments, reef quartz and mottled red-brown and grey sandy clay. The soil The differences in regolith materials over the profile varies along the length of the exposure, with Harcourt Batholith are poorly defined in both the ridge crests and upper slopes dominated by lithic radiometric and magnetic data. The boundary with rock fragments and minimal soil development, the contact metamorphic aureole is well defined by a change in the K signature (Fig. 7), but internal BENDIGO REGOLITH 31

variation is due more to compositional variations in areas the highly weathered granite is mantled by the batholith. Dark patches in the radiometric image younger transported regolith. on the Harcourt Batholith reflect the presence of The landforms consist of low hills and rises that are transported regolith cover, but it is not extensive or topographically lower in the landscape than the fresh persistent enough to map as a separate unit. The granite (220–300 m a.s.l). They generally have north-trending bright pink patch in the RGB image gentle to steep slopes and widely spaced shallow 5 km east of Bradford (AMG 244000 5912000) streams with a dendritic pattern. Most rises and coincides with shearing in the granite associated ridge slopes have tors exposed, with fresh granite with movement along the Muckleford Fault, but near or at the surface mantled by a thin layer of there is no discernible difference in the regolith quartz sand and clay, but many of the lower hills and materials. rises have no outcrop of granite. BUeh2 The highly weathered granite is characterised by the Fresh bedrock on hills presence of saprolite consisting of granitic quartz Fresh granite outcrop with thin or minor regolith sand, feldspars and clay. The saprolite preserves the cover and very little or no saprolite preserved, forms original granitic textures and typically has hills and mountains (340–742 m a.s.l.) that lie interlocking quartz, slightly weathered feldspar topographically higher than the highly weathered crystals and kaolinitic clay pseudomorphing feldspar. granite. It forms a range of mountains with the Weathering is predominantly chemical alteration of highest elevation in the map area (Mount Prospect, feldspar to clay and granular disintegration between Mount Barker and Mount Alexander). This region grains. Aplite and quartz–feldspar veins preserved has extensive jointing oriented NNW–SSE and a in the saprolite indicate in situ weathering. weaker perpendicular series oriented E–W, which controls the form of the hills. It is bounded to the The thickness of the saprolite varies and corestones west and east by topographically lower weathered of fresh granite sitting in saprolite are common. granite (SHel2) that does not show any jointing. Corestones tend to be rounded and floating within Drainage is fixed within shallow widely spaced structureless saprolite. The surface of the erosional channels. underlying fresh granite is generally smooth and uneven, with interlocked angular corestones. Ridge slopes and crests have fresh granite and tors exposed. Soils are thin and poorly preserved, Determining the boundary with the overlying consisting of uniform grey-brown and red-brown pedolith is often difficult, but the saprolite typically clayey quartz sand (Um). Saprolite is typically has the original igneous texture preserved. The absent, and the soil material is derived pedolith consists of red-brown to grey-brown uniform predominantly from creep of granitic quartz and clay (Um) soils of angular quartz, feldspars and clay. To down slope under the influence of gravity. the north of Maldon ferruginous mottling and pisolites on weathered granite have been noted SHel2 (Jason Fothergill pers. comm.) Highly weathered bedrock on low hills Highly weathered granite forms the western and The radiometric signature of the highly weathered eastern part of the Harcourt Batholith in BENDIGO Harcourt Batholith does not clearly distinguish and is dominated by saprolite of variable thickness between areas of granite outcrop and saprolite. The and minor outcrop of fresh granite (Fig. 17). In many differences in the radiometric signature either reflect the presence of transported regolith cover, or variations in the composition of the granite and associated regolith. This is clearly demonstrated northeast of Newry Meadows (AMG 244200 5910700), where quartz and feldpar granite is foliated and sheared, and intruded with quartz veins, in a NNE direction. The outcrop of this foliated granite is limited and only occurs along ridge crests, with the ridge slopes dominated by a uniform grey- brown granitic quartz and feldspar sand and clay soil. The radiometric signature of this foliated and sheared granite is darker than the surrounding Harcourt Batholith and dominated by high K, with the surrounding area of soil cover having a similar radiometric signature.

Figure 17 SHel2. Typical profile showing highly weathered granite saprolite. Road cutting on western side of , north of Harcourt, AMG254700 5904900. 32 BENDIGO REGOLITH

5 Regolith resources that the oxide zone has undergone depletion rather than enrichment. This does not necessarily imply Weathering and regolith development can result in that removal of gold from the oxide zone was the only economically significant accumulations of many process operating during weathering, but that only different commodities, both metallic and non- depleted oxide ore is preserved at Fosterville. In metallic. There is increasing evidence for supergene other areas, for example Western Australia (Butt, gold enrichment in the weathering zone in Victoria, 1989), an upper enriched oxide zone is often including BENDIGO. Local councils and private preserved; a similar profile may once have been industries currently exploit a number of non-metallic present at Fosterville, but has since been removed by surficial and sub-surface deposits. The following erosion. provides a brief description of current economic Secondary gold does occur within oxidised deposits and potential future regolith resources quartz–gold-stibnite veins in the oxide zone of within BENDIGO. mineralisation at Robbins Hill pit, immediately east of BENDIGO (Kotsonis et al., 1998, 2000; McKnight 5.1 Gold et al., 2001). The veins host primary crystalline nuggetty gold that has undergone refinement and Supergene gold enrichment associated with deep remobilisation, with precipitation of colloform and weathering is not considered a traditional feature of small cauliflower encrustations of extreme fineness the Victorian gold province, but there is increasing (Fig. 18). The remobilised gold is limited to the evidence for the widespread occurrence of secondary colloform iron oxides precipitated within the oxidised gold in the weathered zone (Hughes & Carey, 1998; veins and does not occur in the surrounding host Hughes et al., 1998; Jackson, 1998; Kotsonis et al., rock. The primary crystalline nuggetty gold tends to 1998, 2000; McKnight et al., 2001). Textures common have uniform silver content of 2.6 to 2.8 %wt Ag, with secondary gold, such as colloform, arborescent whereas the refined gold has variable silver contents and botryoidal gold, fine grained “flour” gold, from <1 to 35 %wt Ag, and the remobilised gold is nuggetty and crystalline gold have been identified extremely fine (<0.1%wt Ag). Other occurrences of from the Victorian gold province, particularly in gold of possible supergene origin have been recorded association with iron and manganese oxides (Hughes from the Confidence Reef at the Bendigo gold field et al., 1998). Secondary gold is widespread at where fine flour, scaly and hackly gold occurs within Nagambie (Gillies, 1990), Fosterville (Zurkic, 1998) manganese and iron oxides (Jackson, 1998). and Tallangalook (Hughes et al., 1998), but its Although historical records provide evidence for the economic importance is difficult to determine. In widespread occurrence of gold, including nuggets, in other areas, such as at Dunolly, , Rheola, the regolith, it does not necessarily imply that any of Wedderburn, Inglewood and the Pyrenees Ranges, this surficial gold was of supergene origin. Puddling the majority of the gold reefs became poor grade and machines were extensively used in BENDIGO for the uneconomic below the base of weathering (Junner, extraction of gold from the regolith, particularly from 1921; Hughes et al., 1998). clay-rich regolith and soils overlying mineralised The secondary gold described at Fosterville by Zurkic bedrock. Most of the gold extracted in this manner (1998) forms the oxide zone of mineralisation, where would have been eluvial and detrital gold released the oxidation of sulphides from weathering has from the bedrock, although it is probable that much liberated gold trapped within the sulphides. of the gold would have undergone refinement similar However, the gold is rarely observed in either the to that described by Jackson (1998), with some oxide or primary zone of mineralisation. It is most nuggets possibly of supergene origin. Gold-rich rims likely present within the lattice of the primary on alluvial grains with low silver content are present sulphides, either in solid solution or as sub- in BENDIGO and throughout central Victoria, nanometre inclusions, suggesting weathering has suggesting refinement of gold is a common feature in only liberated the gold from the sulphides and has the surficial environment (Jackson, 1998). not resulted in secondary or supergene enrichment (McKnight et al., 2001). 5.2 Clay However, supergene enrichment of gold in the Fosterville goldfield, or in BENDIGO, should not be Weathered shale and mudstone (SHel1, SVer1) east discounted. Only limited work has been conducted to of the Whitelaw Fault have provided a source of clay confirm the presence and extent of secondary gold in for brick and pipe manufacture and pottery clay since the regolith, and the focus of gold exploration has the 1850s (Willman & Wilkinson, 1992; Cherry & been directed towards to the discovery of Bendigo- Wilkinson, 1994). East of the Whitelaw Fault, where style narrow, low tonnage, high grade quartz vein the turbidites are very highly weathered, clays mineralisation, or high tonnage, low grade derived from grey and coloured shale that is usually mineralisation amenable to bulk mining. At free of quartz and sandstone is blended with plastic Fosterville, gold grades in the oxide zone tend to be clay from other sources to produce bricks (Willman & significantly lower than the underlying primary Wilkinson, 1992). Clay for local brickworks is disseminated pyrite–arsenopyrite ore, suggesting predominantly sourced from areas around White BENDIGO REGOLITH 33

Figure 18 Secondary gold. Scanning electron microscope images of gold that has undergone refinement and remobilisation from oxidised quartz- gold-stibnite veins. A: transect across a gold grain showing zone refinement and changes in silver content. B: colloform gold within colloform iron oxides. C: small cauliflower encrustations of gold of high fineness within colloform iron oxides. Robbins Hill pit, AMG 276700 5938300 (in HEATHCOTE).

Hills ( Economic longer quarried from McKenzies pit, but was used in Development Unit, 2001). Darker coloured sanitary and table ceramics, tiles, bricks, pipes and weathered mudstone and shale with a higher content insulators (Cooney, 1989). of sand and vein quartz are also used for the Extensions of these possible lacustrine sediments manufacture of bricks (Chambers, 1959). The may occur along Axe Creek and the Campaspe River. uplifted region between the Sebastian and Whitelaw The bedrock underlying these deposits is also highly faults is less likely to produce extensive areas weathered in places (e.g. Osterfields pit northeast of prospective for moderate quality clay due to the Axedale in HEATHCOTE) and may represent a greater erosion of the in situ regolith. Areas of deep future resource for kaolinitic ball clay in the region. weathering on the turbidites to the northeast of the However, this weathered bedrock may contain and areas to the west of the Sebastian significant reef quartz, which would require Fault are prospective for clay. extraction before it can be used for ceramics. Kaolinitic ball clay used in white ceramics and the brick industry, of possible lacustrine origin, occur in 5.3 Sand and gravel the Axedale area. This clay is believed to have formed from in situ kaolinisation of transported clay Battery tailings from historic gold mines and hills derived originally from weathered metasedimentary capped with alluvial gravel provide low quality but bedrock (Cherry & Wilkinson, 1994). Similar readily accessible resources for use on roads and kaolinitic clay of fluvial origin occurs at Fosterville railways. Surrounding the city of Bendigo are (Sharkeys pit). These deposits form a large resource several hills capped with channel sediments (ACer) to the east of the map area (east of the Campaspe that provide high quality washed sand and gravel as River) in HEATHCOTE. In BENDIGO, the largest well as aggregate. Deposits at White Hills and deposit occurs at McKenzies pit on Axe Creek, Axedale currently provide material to the concrete approximately 4 km northwest of Axedale. Clay is no 34 BENDIGO REGOLITH

Figure 20 Crushed rock resources. The thin regolith cover on the lava flows around Bald Hill facilitates fresh rock quarrying. All Stone Quarry, AMG 233800 5929400.

of the Riverine Plain. More extensive channel sands and gravels can be identified in the magnetic intensity data (Fig. 19). Within the Upland valleys, channel deposits form extensive sources of low quality sand and gravel consisting of predominantly metasedimentary bedrock clasts and quartz.

Figure 19 Sand and gravel resources. Total magnetic intensity (TMI) 5.4 Other resources image of part of BENDIGO showing high frequency dendritic response of subsurface channels. These channels may represent a potential Fresh rock suitable for crushed aggregate and subsurface sand and gravel resource. dimension stone are found close to the surface due to the poor development, or preservation, of regolith industry. Other early Cainozoic deposits have also materials. In the case of dimension stone sourced been quarried for sand. from the Harcourt Batholith, a combination of neotectonics and erosion have exposed essentially The regolith developed on the highly weathered fresh rock at the surface in otherwise highly Harcourt Batholith (both in situ and transported) weathered granite. offers the possibility for well-sorted quartz sand and gravel. Opportunities would be dependent on the Crushed rock thickness and extent of the regolith; the most prospective areas are on the lower slopes of hills or High quality crushed aggregate for the Bendigo along streams away from the metamorphic aureole. region is sourced from the basalt flows of the Bald Small outcrops of marine sand (OMep) throughout Hill volcanic complex (VFvl), which form an BENDIGO provide a source of fine sand and gravel, extensive resource. Fresh rock with interlocking and have been quarried from council pits east and corestones is encountered at only 2 m depth northeast of Bendigo (e.g. AMG 259200 5943200). (Appendix 3). Quarrying is currently conducted at This unit is mostly surficial and can be readily All Stone Quarry (AMG 233800 5929400; Fig. 20). identified by its low radiometric response (Fig. 7). Other sources for crushed aggregate include basalt Underneath the ferruginous duricrust that mantles flows along the Campaspe River south of Axedale, this unit, well sorted and clean fine quartz sand can outside BENDIGO. be extracted. However, as the sands have been The rocks in the contact metamorphic aureole around greatly eroded, these deposits may be limited in area the Harcaourt Batholith offer low quality crushed and thickness. aggregate that is currently quarried at Neivandt Hill Alluvium on floodplains (Aap) provides limited Quarry, Shelbourne (AMG 234500 5919100). Other sources of sand and gravel in the Riverine Plain and possible sources for aggregate would be to the west of within the Upland valleys. Lenses of clean and well- the Leichardt Fault where the relief of the sorted fluvial sand from prior streams occur as metamorphic aureole is low. shallow subsurface shoe-string sand bodies along abandoned fluvial channels, and can be identified by the traces of prior streams preserved on the surface BENDIGO REGOLITH 35

Dimension stone Dimension stone is only produced at Mount Alexander where grey granite of the Harcourt Batholith is extracted for use in monumental work, facings for buildings, floor pavings and crushed rock for terrazzo (City of Greater Bendigo Economic Development Unit, 2001). The unweathered region of the Harcourt Batholith, BUeh2, where little or no regolith is preserved at surface, is prospective for dimension stone. 36 BENDIGO REGOLITH

6 Synthesis strong influence on the distribution and preservation of regolith materials in this area.

6.1 Discussion Transported units The age of weathering of the transported units can be The regolith of BENDIGO, in combination with broadly constrained by the age of deposition of the drainage patterns and geomorphology, suggests a sediments and topographic relationships. These can complex history of weathering and tectonic then be used to interpret the evolution of the instability in the late Cainozoic (Kotsonis & Joyce, landscape and drainage systems in the area. 2002). Thick weathering profiles and duricrusts are discontinuous and poorly preserved. However, The White Hills Gravel reflects the oldest known remnant pallid zones developed on Ordovician drainage system in the region. It is elevated in the metasediments and Devonian , and isolated landscape and overlies deeply weathered bedrock. outcrops of ferruginous and clay duricrusts indicate The top of the profile has no soil, but is capped and three thick chemical weathering profiles of different strongly indurated with silcrete and clay. Any ages: ferricrete observed in the White Hills Gravel is ferruginised sediment (Bourman, 1993) rather than l an earlier (Paleocene–Eocene) weathering profile ferricrete associated with a lateritic profile. preserved on bedrock units and the earliest fluvial Similarly, the silcrete cappings, although associated sediments (White Hills Gravel); with weathering, probably do not represent a soil l bleached kaolinitic clays developed on incised profile, but rather the sub-surface expression of deep lead deposits (Mologa Surface); and, weathering, similar to the groundwater or pedogenic silcrete of Thiry and Milnes (1991). Many workers l a younger ferruginous pisolitic soil on Pliocene have recognised ferricrete in the upper 1–2 m of the sediments (Karoonda Regolith). White Hills Gravel throughout central and western These weathering profiles do not represent the only Victoria (Cayley & McDonald, 1995) and the presence periods of intense weathering, but rather are the only of a pallid zone 6–9 m deep in the underlying bedrock three that can be clearly recognised and (Williams, 1983; King, 1985). Very highly weathered differentiated using a combination of landscape bedrock clasts within the gravel near Ararat and position, drainage analysis and regolith material. Ballarat (Hughes & Carey, 1998; Taylor & Joyce, 1996), indicate weathering after deposition, as these In situ units soft clasts would not have survived transport. The Palaeozoic bedrock is weathered to depths of In BENDIGO the regolith profile developed over the 35–50 m. The variations in the in situ regolith White Hills Gravel (ACer) is preserved on the developed on the bedrock appear to be largely flanking ranges along the present drainage of Myers controlled and influenced by the major bedrock faults Creek, Bendigo Creek, and Axe Creek, showing that in BENDIGO, which is well illustrated in the in many areas the modern drainage system occupies, radiometric imagery (Fig. 7). The radiometric and has been inherited from, this earlier fluvial response of the bedrock does not correlate to gross system. This suggests that the present drainage lithological variations defined by biostratigraphic pattern had developed by at least the early Cainozoic. zonation (Cas & VandenBerg, 1988; Cherry & However, east of the Whitelaw Fault the older stream Wilkinson, 1994), but rather with the nature and flowed north-northwest along the Heathcote Fault in type of the surficial material and the degree of its headwaters, then west to White Hills where it was weathering. deflected by the Whitelaw Fault (Williams, 1983) before turning east-northeast to follow the Bendigo The region bounded by the Whitelaw and Sebastian Creek valley (Hughes & Carey, 2002). faults is characterised by less-weathered bedrock and the general absence of soil cover. This contrasts with These mature quartz gravels have been interpreted the very highly weathered bedrock east of the as the products of erosion and reworking of the deep Whitelaw Fault to the north of Bendigo Creek, which regolith of the Mesozoic palaeoplain (Ollier, 1988) is mantled with a clayey soil profile. This apparently after dissection to depths of 430–700 m (Cayley & tectonic control on regolith preservation and McDonald, 1995; Taylor et al., 1996; Hughes et al., distribution is most obvious in the Harcourt 1998; Hughes & Carey, 2002). Batholith. The high area of fresh granite outcrop in The next oldest group of transported units occupies a which Mount Alexander (742 m), Mount Prospect broad time range in which fluvial and fluvio- (560 m) and Mount Barker (550 m) are situated is lacustrine sediments were deposited. Informally bounded to the west and east by the southern known as ‘deep leads’, the age constraints for these extensions of the Sebastian and Whitelaw faults often auriferous deposits are unclear but they do respectively. Cainozoic uplift and erosion of the postdate the White Hills Gravel. The close spatial regolith in the uplifted block best explain the association of fluvial sediments of various ages differences in the soil preservation and intensity of in within confined valleys over long depositional situ weathering. Therefore, neotectonism has had a periods, and the similarity in sediment type of BENDIGO REGOLITH 37

mature recycled material means there has been some l the steeply sloping valley sides at Sharkeys pit confusion in the literature on the differentiation and indicate deposition in a narrow confined valley, naming of these units. whereas the White Hills Gravel was deposited in broad valleys. The age of the auriferous deep lead deposits in BENDIGO is unknown, but they can be correlated These deposits therefore represent a fluvial system with the clay rich deposits exposed at Axedale and at younger than that of the White Hills Gravel, but Sharkeys pit, Fosterville. The intense chemical older than the Shepparton Formation, which is weathering on the deposits at Axedale and topographically lower in the landscape and mantles Fosterville and the underlying bedrock indicates the surface of the Riverine Plain. weathering post-dated deposition of the stratified The youngest of the recognised weathering profile clays; the absence of ferricrete is a characteristic of preserved in BENDIGO is developed on the Mologa Surface of Macumber (1991). The quartz Pliocene–Pleistocene sediments (Parilla Sand and and clay fluvial sediments at Fosterville lie in narrow Shepparton Formation), and the Bald Hill volcanic confined valleys, indicating that they belong to the complex. It consists of a ferruginous pisolitic soil lower Loddon River Group (Hughes et al., 1998, 1999; overlying mottled saprolite. The fluvial Shepparton Hughes & Carey, 2002) and implies that they are Formation is a time-equivalent to, and partly onlaps, partly time equivalent to the Renmark Group of the the shoreline and marginal marine Parilla Sand of Murray Basin (Brown & Stephenson, 1991). There is the western Murray Basin (Brown & Stephenson, no evidence in BENDIGO for the presence of Calivil 1991). Both formations are capped by a pisolitic iron Formation as defined by Macumber (1991). The deep duricrust overlying mottled clays called the leads in BENDIGO were backfilled and buried by the Karoonda Surface, or Karoonda Regolith (Coaldrake, Parilla Sand due to rising sea levels in the late 1951; Blackburn et al., 1967; Firman, 1966, 1973; Miocene–early Pliocene in the Murray Basin Kotsonis, 1995). Lateral equivalents of the Karoonda (Bagshot Formation of Cherry & Wilkinson, 1994). Regolith can be found in the sediments of the The stratigraphic relationships of the Axedale clay Shepparton Formation underlying the surficial deposits are ambiguous (Edwards et al., 1998). calcareous soils and sediments, and can be used as a Previously, Cherry and Wilkinson (1994) interpreted chronostratigraphic marker in landscape evolution. the clay and gravel deposits at Axedale as White Similar ferruginisation of the Shepparton Formation Hills Gravel, whereas others have named these encountered under the Loddon Plain (basal Yando deposits the Torrumbarry Clay and correlated them Member) has also been correlated with Karoonda with the Calivil Formation (Lawrence, 1975; Brown Regolith (Macumber, 1991). The presence of a & Stephenson, 1991). These deposits are believed to similar ferruginous pisolitic weathering profile have formed from clay of probable lacustrine origin developed on the Bald Hill volcanic complex with a (Cherry & Wilkinson, 1994) transported from eroded lower age limit of 1.64 Ma (Webb, 1989) indicates kaolinised bedrock in adjacent Highland areas that weathering of the Karoonda Regolith continued (Lawrence, 1975) and developed during the period of into the Pleistocene. The presence of the Karoonda weathering of the Mologa Surface in the middle- to Regolith throughout BENDIGO suggests regional late Miocene (Brown & Stephenson, 1991). In places landscape stability in the Pliocene–Pleistocene and is the clay contains intercalated sand and silt and interpreted as following Late Pliocene uplift that lesser gravel of granitic origin (Edwards et al., 1998). initiated Shepparton Formation deposition (Cherry An attempt to date the Axedale clays using & Wilkinson, 1994). Ferruginous weathering palynology produced an anomalous age of Pleistocene associated with the Karoonda Regolith is believed to to Recent when a much older age was expected have terminated approximately 1 Ma with the onset (Morgan, 1992), probably due to contamination from of arid climates in southeastern Australia (Kotsonis, the Pliocene to Recent Shepparton and 1995, 1998). Coonambidgal formations in adjacent Axe Creek The marine incursion that ultimately deposited the (Cherry & Wilkinson, 1994). Parilla Sand was associated with deglaciation and The Axedale deposits differ from the White Hills retreat of the polar ice caps, resulting in a sea level Gravel in several ways: rise of 65 m above present sea level (Kotsonis, 1995, 1999). However, the Parilla Sand in BENDIGO they have a significant kaolinitic clay content, l attains elevations of over 180 m a.s.l., indicating that which is not a characteristic of any of the other the Western Uplands have been uplifted over 115 m White Hills Gravel deposits in the Bendigo region since marine regression approximately 3.5 Ma or the Highlands, (Kotsonis, 1995; 1998). This is consistent with l the high clay content is also inconsistent with the evidence of uplift of the Western Uplands in other high-energy braided river system interpreted for areas such as Ballarat (Taylor & Joyce, 1996), and the White Hills Gravel; the Dundas Tablelands (Quinn, 1997) and significant neotectonism in the Murray Basin (Kotsonis, 1995, they have a different weathering profile to other l 1998). White Hills Gravel deposits; and, 38 BENDIGO REGOLITH

By the late Pliocene to early Pleistocene, the modern MESOZOIC: deep weathering and erosion during a landscape had essentially developed, and there is period of tectonic stability resulted in the formation little evidence for significant geological or tectonic of a deeply weathered palaeosurface (Hills, 1975), activity either in the Western Uplands or on the which is not preserved in BENDIGO. BENDIGO lies Riverine Plain after this time. The only evidence for several hundreds of metres below inferred remnants a period of landscape instability in the of this Mesozoic landsurface, which lies nearby at Pliocene–Pleistocene is found along the Coliban and about 1000 m a.s.l. (e.g. Mount Cole, Mount Lonarch Campaspe rivers, where twin lateral streams have and Mount Avoca; Hills, 1975; Cayley & McDonald, developed along the margins of the basalt flows 1995). (4.49–5.57 Ma). However, since the time of eruption CRETACEOUS TO PALAEOGENE: Gondwana of the Bald Hill volcanic complex at 1.64 Ma, the began to break up in the late Mesozoic and by the modern landscape has only undergone minor erosion Cretaceous an east–west trending ridge, the Victoria and deposition. Divide, had developed. Erosion occurred throughout Within the Upland ranges, minor incision and this period, with the development of the gently deposition of fluvial Shepparton Formation sloping palaeoplain and earliest recognisable continued throughout the Quaternary, whereas flat- coordinated drainage system developed (White Hills lying fluvio-lacustrine and aeolian sediments were Gravel). Weathering of these sediments resulted in a deposited on the Riverine Plain, with also the ferricrete, silcrete and argillan profile (White Hills incision of streams (Coonambidgal Formation) and profile of Hills, 1975; Norval Regolith of Hughes & deposition of prior streams with levee banks. These Carey, 1998). Sometime around the Mesozic– Quaternary sediments are characterised by the Cainozoic boundary, the Murray Basin began to presence of calcareous soils, which are typical for arid subside, and was filled with fluvio-lacustrine landforms such as the Woorinen Formation in the sediments derived from the erosion of Palaeozoic (Lawrence, 1966) and parna in the Riverine bedrock. Plain (Butler, 1956). These soils were sourced from EOCENE TO MIOCENE: Eocene uplift resulted in wind-blown dust and herald the onset of arid incision of rivers and deposition of gold bearing deep climates in the Quaternary of southeastern Australia leads from the erosion of both Palaeozoic bedrock and (Bowler, 1982). earlier fluvial deposits. These sediments were Neotectonics has influenced the character and deposited within pre-existing valleys that were distribution of in situ regolith developed on bedrock incised and backfilled. Weathering associated with units and the preservation of transported regolith the Mologa Surface of both Palaeozoic bedrock and units. Evidence exists for late Cainozoic movement the younger fluvial sediments occurred following the long all the major bedrock structures within retreat of the sea from the Murray Basin in the BENDIGO. Movement along these structures has middle Miocene. affected weathered profiles and soils preserved on PLIOCENE TO PLEISTOCENE: fluvio-lacustrine bedrock units, displaced buried auriferous leads, and deposition continued throughout the Neogene, affected modern drainage systems. resulting in the deposition of gravel, sand and clay within highland valleys and out in the Murray Basin 6.2 Landscape evolution (Shepparton Formation). In the Pliocene, a marine incursion into the Murray Basin deposited marginal The evolution of the landscape in BENDIGO is and near-shore marine quartz sand (Parilla Sand). summarised below (Fig. 21): Weathering formed the Karoonda Regolith, a ferricrete +/- silcrete profile on the Parilla Sand and PRE-PERMIAN: the geological record shows that a the Shepparton Formation. Within the highland major mountain-building event, the Benambran valleys gold was eroded from the Palaeozoic bedrock , occurred in the Silurian and that the and fluvial processes concentrated alluvial gold Harcourt Batholith intruded in the Devonian within gully deposits and shallow leads exiting (VandenBerg et al., 2000). However, no record of the highland valleys. Erosion of Palaeozoic bedrock also landscape prior to the Permian is preserved in resulted in the deposition of colluvium flanking BENDIGO. bedrock rises and within gullies. PERMIAN: glaciation radically altered the Volcanic activity (Newer Volcanic Group) within landscape, removing any existing regolith and BENDIGO occurred at and around the Bald Hill leaving behind till deposits. Only minor sub-surface volcano and along the Coliban River. Fluvio- occurrences of tillite are found within BENDIGO. lacustrine deposition occurred throughout the Large areas of Permian tillite are exposed to the Quaternary. Fluvial sediments (Coonambidgal south in CASTLEMAINE. Where valleys expose the Formation) were deposited in valleys incised into the lower contact of the Permian glacial deposits, the older fluvial deposits of the Shepparton Formation, Castlemaine Group immediately below the base of forming narrow floodplain terraces: these represent the Permian is essentially fresh rock (Willman et al., the present drainage system. Minor aeolian and 2002), indicating that the glaciation removed any swamp deposits also formed at this time. regolith that was in the landscape. BENDIGO REGOLITH 39

Figure 21 Landscape evolution diagram for BENDIGO. 40 BENDIGO REGOLITH

7 Conclusions

The distribution of regolith materials in BENDIGO is complex and has been largely controlled by the landscape evolution and an extensive gold mining history. The nature of the regolith now preserved on the bedrock RLUs has been controlled by Cainozoic erosion and landscape evolution, with deep weathering interpreted to have begun in the Cretaceous to early Palaeogene. Transported RLUs are poorly preserved in the Western Uplands, but form a flat-lying composite fluvio-lacustrine plain to the north, the Riverine Plain. Residue produced by puddling machines and mine tailings, associated with historic gold mining blankets the present floodplains along creeks draining the historic gold fields of BENDIGO. Regolith profiles over the basaltic lava and scoria of the Newer Volcanic Group are a minor feature of the area, but they provide information on the recent landscape evolution. Older flows now in highstanding landscape positions have less soil on them than younger flows that have not experienced the same degree of dissection. Early Cainozoic weathering, postdating late Eocene uplift of the Western Uplands, has influenced much of the present landscape. The deep lead deposits were formed at this time, and were weathered in the Miocene. Rising sea levels in the Late Miocene–early Pliocene in the Murray Basin led to backfilling of fringing valleys. Chemical weathering associated with pisolitic ferricrete (Karoonda Regolith) is characteristic of the Plio–Pleistocene, and contrasts with the calcareous soils of the Quaternary. The information gained during this work provides a context for designing and interpreting exploration geochemical surveys. In particular, the major division between in situ and transported materials allows for meaningful differentiation of sample populations, as sampling can be placed in the context of the landscape evolution. Large floodplains exiting the main goldfields in the area have been contaminated with respect to gold by the mining residue of the 19th and early 20th centuries, which may significantly influence sampling results. Secondary gold is probably widespread in BENDIGO, and shows a variety of textures, with refinement of primary gold and deposition of supergene colloform gold common. However, the timing and extent of secondary gold precipitation is unclear, but there is evidence for localised gold movement within in situ regolith developed on mineralised Palaeozoic bedrock. Secondary gold provides another possible exploration target in the area. BENDIGO REGOLITH 41

References CHERRY, D.P. & WILKINSON, H.E., 1994. Bendigo, and part of Mitiamo 1:100 000 map geological report. Geological Survey of Victoria Report 99, 80 pp. ANAND, R.R., 2001. Regolith landform mapping for mineral exploration. In Paine, M. (ed.), Regolith CITY OF GREATER BENDIGO ECONOMIC DEVELOPMENT geology and its application to exploration and UNIT, 2001. City of Greater Bendigo—Economic environmental issues. Course Notes, University of Profile. TBA Planners, 36 Wattle Street, Bendigo Vic Ballarat, 21–25 April 2001. CRC LEME Report 159. 3550. 107 pp.

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Appendix 1

Full list of RTMAP codes for regolith–landform units (after Pain et al., 2001)

The regolith–landform map codes on the accompanying map follow the RTMAP system devised by Geoscience Australia (see Pain et al., 2001). Each regolith–landform map code is made up of three components, a regolith description code, a landform code and a number representing the gross lithology of the bedrock (in situ regolith–landform units only). 46 BENDIGO REGOLITH

Regolith Description Map Code Landform Description Map Code Landform Description Map Code unweathered bedrock BU alluvial landforms a etchplain ee evaporite E alluvial plain ap rises er halite EH flood plain af residual rise eu gypsum EG anastomatic plain aa low hills el calcrete EC bar plain ab residual low hill es alluvial sediments A covered plain ac hills eh channel deposits AC meander plain am mountains em overbank deposits AO floodout ao escarpment ec colluvial sediments C alluvial terrace at badlands eb scree CS stagnant alluvial plain as drainage depression ed landslide deposit CL terraced land al fan f mudflow deposit CM alluvial swamp aw alluvial fan fa creep deposit CC coastal lands c colluvial fan fc sheet flow deposit CH beach ridge cb sheet-flood fan fs fanglomerate CF chenier plain cc glacial features g aeolian sediments I coral reef cr depositional glacial features gd aeolian sand IS marine plain cm erosional glacial features ge loess IL tidal flat ct karst k parna IP coastal dunes cd made land m fill F coastal plain cp meteor crater t glacial sediments G beach cc plain p lacustrine sediments L delta d depositional plain pd marine sediments OM aeolian landforms u lacustrine plain pl swamp (paludal) sediments P aeolian dunes ud playa plain pp peat PP longitudinal dunefield ul sand plain ps coastal sediments O transverse dunefield ut plateau l beach sediments OB irregular dunefield ui plateau edge le estuarine sediments OE source bordering dune ub plateau surface ls coral OC lunette uu volcano v terrestrial sediments T aeolian sheet us caldera vc clay (unknown origin) UC climbing sheet uc cone (volcanic) vv weathered material UW erosional landforms e lava plain vl (unknown origin) sand (unknown origin) US erosional plain ep ash plain va volcanic sediments V pediment ei lava flow vf lava flow VF pediplain ea lava plateau vp tephra VT peneplain en saprolith S saprock SS Bedrock lithology Map Code Bedrock lithology Map Code moderately weathered SM Deep marine sedimentary 1 Felsic volcanic rocks 6 bedrock rocks highly weathered bedrock SH Felsic plutonic rocks 2 Intermediate volcanic rocks 7 very highly weathered SV Metamorphosed deep 3 Shallow marine 8 bedrock marine sedimentary rocks sedimentary rocks (above chlorite grade) completely weathered SC Mafic volcanic rocks 4 Terrestrial sediments and 9 bedrock sedimentary rocks mottled zone SV Metamorphosed mafic 5 Ultramafic rocks 10 volcanic rocks pallid zone SV saprolite SP residual material R lag RL residual sand RS residual clay RC soil on bedrock RB BENDIGO REGOLITH 47

Appendix 2

Regolith–landform unit summary data

Transported units

Figure 22 Simplified relationships between the transported regolith units in BENDIGO.

Aam Alluvial sediments on meander plains Tectonic province: Murray Basin Geomorphic province: Riverine Plain Elevation: 110–300 m Regolith characteristics Type: channel and overbank deposits Maximum observed thickness: 2m Boundaries: follow contours Induration: none Soil type: uniform grey to grey-brown sand and clay (Um) Description: slightly weathered, poorly sorted angular to sub-rounded lithic and mineral fragments in sandy to clayey matrix (Figs 23, 24) Figure 23 Aam. Typical profile. Bullock Creek, Lockwood South, AMG 246100 5919800. Landform characteristics Type: depositional Geomorphic processes: channelled and overbank stream flow Classification: incised meander plain Relief: 3 m (maximum) Drainage: dendritic, anabranching; moderate density Vegetation: cleared, native Weathering Degree: slight Processes: physical weathering Informal age: Recent Bedrock geology Type: channel and overbank deposits Stratigraphic unit: Coonambidgal Formation Geophysical response Figure 24 Aam. Aerial photograph showing Spring and Bullock creeks, Radiometrics: low response which have cut down into the existing alluvial plain sediments (Aap). Magnetics: no distinctive response 48 BENDIGO REGOLITH

Aap Aep Alluvial sediments on alluvial plains Alluvial sediments on erosional plains Tectonic province: Murray Basin Tectonic province: Lachlan Fold Belt Geomorphic province: Riverine Plain Geomorphic province: Western Uplands Elevation: 110–220 m Elevation: 140–190 m Regolith characteristics Regolith characteristics Type: alluvial sediments, overbank deposits; minor lacustrine and Type: alluvial sediments aeolian deposits Maximum observed thickness: 20 m Maximum observed thickness: 6m Boundaries: overlies saprolite; gravels mostly buried beneath Boundaries: follow contours younger units Induration: ferruginisation (relict) Induration: none Soil type: red-brown gradational or duplex Soil type: gradational grey-brown clay (Gn) Description: variably ferruginised clay, sand and gravel with angular Description: pallid quartz pebble and cobble gravel with kaolinitic sedimentary bedrock and reef quartz clasts; sandy clay (Fig. 25) clay and quartz sand matrix overlain by finer grained clay and silty Landform characteristics clay; auriferous (Figs 26, 27) Type: depositional Geomorphic processes: channelled and overbank stream flow Classification: alluvial plain Relief: 5 m (maximum) Drainage: dendritic, anabranching Weathering Degree: moderate Processes: physical weathering, induration Informal age: Pliocene–Pleistocene Bedrock geology Type: channel and overbank deposits Stratigraphic unit: Shepparton Formation Geophysical response Radiometrics: low response Figure 26 Aep. Typical profile. Sharkeys pit, AMG 276100 5935200. Magnetics: no distinctive response See also Figure 10. Comments: this unit is dominated by cobbles/pebbles of ferruginised bedrock clasts, whereas the older alluvial regolith types, e.g. ACer, are dominated by sub-rounded to rounded quartz cobbles and pebbles Landform characteristics Type: erosional Geomorphic processes: creep Classification: palaeo-alluvial plain; deposits now on valley sides or buried beneath younger alluvium Relief: 10 m (maximum) Drainage: generally absent Vegetation: cleared, scrub Weathering Degree: very high Processes: physical weathering Informal age: late Eocene–Miocene Bedrock geology Type: alluvial deposits Stratigraphic unit: Loddon River Group Geophysical response Radiometrics: no distinctive response Magnetics: no distinctive response Comments: this unit is characterised by kaolinitic clay and rounded Figure 25 Aap. Typical profile. Myers Flat, AMG 251200 5933800. quartz and a lack of induration; limited outcrop along margins of present See also Figure 9. drainage BENDIGO REGOLITH 49

Figure 27 Aep. Regolith profile at Mackenzies pit, AMG 274200 5928400.

ACer Channel sediments on erosional rises Tectonic province: Lachlan Fold Belt Geomorphic province: Western Uplands Elevation: 160–220 m Regolith characteristics Type: alluvial sediments Maximum observed thickness: 10 m Boundaries: unconformably overlies saprolite Induration: silcrete, ferricrete, clay Soil type: none seen Description: sandy coarse quartz pebble and cobble conglomerate, cemented with iron oxides and silica; duricrust on upper surface of Figure 28 ACer. Typical profile. Council quarry, White Hills, AMG silcrete, argillans and sometimes ferricrete (Figs 28, 29) 230700 5959800. Landform characteristics Type: erosional Geomorphic processes: creep Classification: palaeo-alluvial channels; deposits now on valley sides or small hilltops Relief: 25 m (maximum) Drainage: generally absent Vegetation: cleared, scrub Weathering Degree: very high Processes: induration (relict); physical weathering Informal age: ?Cretaceous to Paleocene–Eocene Bedrock geology Type: alluvial deposits Stratigraphic unit: White Hills Gravel Geophysical response Radiometrics: low response Magnetics: no distinctive response Comments: upper surface may vary depending on degree of preservation, from ferruginsed conglomerate to silicified +/- clay duricrust; clasts mostly rounded reef quartz, whereas younger units Figure 29 ACer. Duricrust developed in quartz conglomerate. Council have mostly ferruginised bedrock clasts quarry, White Hills, AMG 230700 5959800. See also Figure 11. 50 BENDIGO REGOLITH

Cfc Colluvial sediments in colluvial fans and fan systems Tectonic province: Lachlan Fold Belt Geomorphic province: Western Uplands Elevation: 110–380 m Regolith characteristics Type: colluvial sediments Maximum observed thickness: 6m Boundaries: unconformably overlies saprolite; interfingers with alluvial sediments (Aap) Induration: ferruginisation (relict) Soil type: uniform coarse textured (Uc) and fine textured non- cracking (Uf) Description: poorly sorted angular to sub-rounded lithic and mineral fragments in sand and clay (Figs 30, 31) Landform characteristics Type: depositional Figure 30 Cfc. Typical profile. Nuggetty mine, Maldon, AMG 205300 Geomorphic processes: creep 5938800. Classification: low relief hills and flanks Relief: 15 m (maximum) Drainage: widely spaced, low density Vegetation: cleared Weathering Degree: slight Processes: induration (relict) Informal age: Pliocene–Pleistocene Bedrock geology Type: colluvial deposits Stratigraphic unit: unnamed Geophysical response Radiometrics: low response Magnetics: no distinctive response Figure 31 Cfc. Colluvium exposed near Nuggetty mine, Maldon, AMG 205300 5938800. BENDIGO REGOLITH 51

OMep Marine sediments on erosional plains Tectonic province: Murray Basin Geomorphic province: Riverine Plain Elevation: 150–190 m Regolith characteristics Type: marine quartz sands Maximum observed thickness: 3.5 m Boundaries: follows contours Induration: ferruginisation (relict) Soil type: pisolitic red-brown duplex Description: pisolitic duricrust overlying mottled clayey B horizon, grading to mottled red-brown and grey clayey fine sand; pallid at depth (Fig. 32) Landform characteristics Type: erosional Geomorphic processes: channeled stream flow Figure 32 OMep. Typical profile. East of Epsom, AMG 236700 Classification: low relief hills and flanks 5963000. See also Figure 12. Relief: 10 m (maximum) Drainage: widely spaced, low density Weathering Geophysical response Radiometrics: low response Degree: moderate to high Magnetics: no distinctive response Processes: induration (relict), physical weathering Comments: typical exposure is residual clasts of ferruginised sand or Informal age: Pliocene pebbles/cobbles of ferricrete on flanks or rises of bedrock Bedrock geology Type: fine to medium grained marine quartz sands Stratigraphic unit: Parilla Sand

Faf Mining residue on floodplains Tectonic province: Murray Basin Geomorphic province: Riverine Plain Elevation: 160–260 m Regolith characteristics Type: gold mining residue Maximum observed thickness: 3m Induration: none (compaction) Soil type: none Description: hard setting fine silty clay with interbedded lenses of quartz and ferruginised bedrock pebbles and cobbles (Fig. 33) Landform characteristics Figure 33 Faf. Typical profile. Mining residue overlies alluvial Type: depositional sediments in alluvial plains (Aap) or meander plains (Aam), which can Geomorphic processes: minor river incision be recognised by the presence of an old soil profile. North of Myers Classification: floodplain Flat, AMG 248800 5937600. See also Figure 13. Relief: less than 1 m Drainage: not developed Bedrock geology Type: fine grained floodplain sediments Vegetation: cleared Stratigraphic unit: unnamed Weathering Geophysical response Degree: unweathered Radiometrics: high response, variable K and Th Processes: physical weathering (compaction, agricultural disturbance) Magnetics: no distinctive response Informal age: Recent Comments: sometimes referred to as ‘sludge’ or ‘slimes’; this unit forms a thin flat layer over floodplains exiting the Bendigo goldfield; exposed along creek beds, channels and dams 52 BENDIGO REGOLITH

Volcanic units

VFep Lava flows on erosional plains Tectonic province: Lachlan Fold Belt Geomorphic province: Western Uplands Elevation: 240–270 m Regolith characteristics Type: lava flows Maximum observed thickness: 12 m Boundaries: follow contours Induration: Clay, minor ferricrete Soil type: none Description: rounded basalt boulders with spheroidal weathering; soil mostly absent (Figs 34, 35, 36) Landform characteristics Type: erosional Geomorphic processes: particle fall, creep Classification: erosional plain Figure 35 VFep. Typical profile. The Pines, AMG 276400 5905200. Relief: less than 10 m Drainage: radial, low density Vegetation: cleared Weathering Degree: slight Processes: induration (relict), physical weathering, solution Informal age: Pliocene Bedrock geology Type: massive to vesicular basalt Stratigraphic unit: Newer Volcanic Group Geophysical response Radiometrics: low response Magnetics: high frequency, high magnetic intensity Comments: weathered stony rises with multiple flows Figure 36 VFep. Boundary between a flat-topped lava residual and the slope down to the lateral stream. The Pines, AMG 276400 5905200. See also Figure 14A.

Figure 34 VFep. Idealised cross section of the area around the Coliban River showing regolith relationships. BENDIGO REGOLITH 53

VFvl, VFv Lava flows on lava plains and a volcano Tectonic province: Lachlan Fold Belt Geomorphic province: Western Uplands Elevation: 110–220 m Regolith characteristics Type: lava flows Maximum observed thickness: 7m Boundaries: follow contours Induration: Clay, minor ferricrete Soil type: red-brown gradational soil Description: clayey red-brown gradational soil with occasional pisolitic ferricrete overlying weathered basalt with speroidal weathering and minor carbonate (Figs 37, 38) Landform characteristics Type: volcanic Geomorphic processes: creep Classification: lava plain and volcano Relief: lava plain less than 5 m; volcano 40 m Drainage: radial to non-directional and tributary, moderate density Figure 38 VFvl. Typical profile. All Stone quarry, AMG 233800 5929400. See also Figures 14B and 20. Vegetation: cleared

Weathering Geophysical response Degree: moderate Radiometrics: low response Processes: induration (relict) Magnetics: high frequency, high magnetic intensity Informal age: Pliocene–Pleistocene Comments: weathered stony rises and eroded volcanic hill Bedrock geology Type: massive to vesicular basalt Stratigraphic unit: Newer Volcanic Group

Figure 37 Idealised cross section for the Bald Hill volcano and surrounds, showing regolith relationships. 54 BENDIGO REGOLITH

In situ units

Deep marine turbidites (Castlemaine Group)

SMel1, SHel1, SVer1 Weathered sedimentary bedrock on low hills and rises Tectonic province: Lachlan Fold Belt Geomorphic province: Western Uplands Elevation: 140–380 m Regolith characteristics Type: deep weathered bedrock Maximum observed thickness: 5m Boundaries: gradational boundary with units over turbidites in the metamorphic aureole Induration: minor ferricrete Soil type: red-brown clayey gradational or duplex; also lithic soils Description: soft to hard, moderately to very highly weathered turbidites with variable soil cover; some iron staining (Figs 39, 40) Landform characteristics Type: erosional Figure 40 SMel1, SHel1, SVer1. The typical profile over the bedrock Geomorphic processes: creep, rill/gully erosion units developed in the Castlemaine Group is essentially the same; most Classification: low hills and rises profiles differ only in the degree of weathering of the saprolite. See also Relief: 10–100 m Figure 15. Drainage: dendritic, high density Vegetation: cleared and/or box ironbark Bedrock geology Type: turbidites Weathering Stratigraphic unit: Castlemaine Group Degree: moderate to very high Processes: physical weathering, chemical weathering Geophysical response Informal age: ?Cretaceous to Paleocene–Eocene Radiometrics: moderate to high response Magnetics: very low response

Figure 39 Idealised cross section for BENDIGO highlighting the relationship between different degrees of weathering in the Castlemaine Group and major faults. BENDIGO REGOLITH 55

Contact metamorphosed turbidites (Castlemaine Group)

SSeh3 Slightly weathered bedrock on hills Tectonic province: Lachlan Fold Belt Geomorphic province: Western Uplands Elevation: 260–530 m Regolith characteristics Type: deep weathered bedrock Maximum observed thickness: 15 m Boundaries: sharp with units developed over granite, gradational boundary with units over turbidites outside the metamorphic aureole Induration: ferricrete along jointing Soil type: red-brown duplex; lithic silty clay over clayey subsoil Description: hard, slightly to moderately weathered contact metamorphosed turbidites; iron staining and cementing common (Figs 41, 42) Landform characteristics Figure 41 SSeh3. Typical profile. Fogartys Gap, AMG 253300 Type: erosional 5905900. Geomorphic processes: creep Classification: low hills and hills Relief: 80–140 m Drainage: radial, high density; perennial Vegetation: cleared and/or sparse eucalypts Weathering Degree: slight to moderate Processes: chemical weathering, physical weathering Informal age: ?Cretaceous to Palaeogene Bedrock geology Type: contact metamorphosed turbidites Stratigraphic unit: Castlemaine Group Geophysical response Figure 42 SSeh3. Soil profile over slightly weathered, contact Radiometrics: high K metamorphosed Castlemaine Group. Fogartys Gap, AMG 253300 Magnetics: low response, surrounded by nonmagnetic granite and 5905900. See also Figure 16. turbidites

Figure 43 Idealised cross section through the Harcourt Batholith and its contact aureole, showing the distribution of regolith materials. 56 BENDIGO REGOLITH

Granite (Harcourt Batholith)

BUeh2, SHel2 Fresh bedrock on hills and highly weathered bedrock on low hills Tectonic province: Lachlan Fold Belt Geomorphic province: Western Uplands Elevation: 220–742 m Regolith characteristics Type: deep weathered bedrock Maximum observed thickness: 8m Boundaries: sharp contact with units over turbidites in the metamorphic aureole Induration: minor clay in highly weathered unit Soil type: red-brown and grey-brown uniform; clay and granitic quartz sand Description: saprolite of variable thickness overlying fresh granite or fresh granite outcrop with thin soil; fresh tors crop out on hillcrests (Figs 43, 44) Landform characteristics Figure 44 SHel2. Typical profile. Truck stop on Calder Highway, Type: erosional Harcourt, AMG 254700 5904900. See also Figure 17. Geomorphic processes: creep, gully erosion Classification: low hills and mountains Relief: 100–250 m Bedrock geology Drainage: dendritic, moderate density Type: granite Stratigraphic units: Harcourt Granodiorite, Baringhup Granodiorite Vegetation: cleared and/or sparse eucalypts Geophysical response Weathering Radiometrics: high response Degree: high or unweathered Magnetics: very low response or very high; differences related to Processes: abrasion, sheeting, chemical weathering parent rocks and not reflected in the regolith materials Informal age: ?Cretaceous to Palaeogene BENDIGO REGOLITH 57

Appendix 3 sedimentary rocks. The soil profile varies throughout the length of the road cutting. The crest of the hill lacks a soil profile, with metamorphosed Regolith excursion guide lithic fragments scattered across the surface, whereas the flanks of the hill have a gradational soil The excursion begins to the north of Harcourt and profile dominated by lithic fragments with clayey concludes at one of the Fosterville mine pits. Typical subsoil. exposures of most of the regolith–landform units Similar exposures occur at Big Hill on the Calder described in the text are included. The full excursion Highway to the south of Bendigo (AMG will take about two days to complete; many of the 252800 5918000), where over 10 m of the profile is sites in the middle of the excursion are around exposed. Big Hill marks the northern boundary of Bendigo, a convenient overnight stop. contact metamorphism associated with emplacement 1 Truck stop north of Harcourt, Calder of the Harcourt Batholith. Highway: highly weathered granite on low hills 3 Nuggetty Road: colluvial fan sediments (SHel2) overlying in situ granitic regolith (Cfc) AMG 254700 5904900 AMG 238800 5905300 Approximately 3.5 km north of the township of Continue east along this road towards Maldon. The Harcourt there is a truck stop on the left side of the surrounding countryside becomes subdued, with low road where in situ regolith over the Harcourt hills and rises characteristic of the landscape over the Batholith is exposed. There are similar outcrops on turbidites in BENDIGO. To the right, the contact the eastern side of the road. metamorphic aureole forms a prominent ridge, with The road cutting exposes approximately 6–8 m of colluvial and alluvial deposits near the road and variably weathered granite. The basal parts of the along the creek. exposure consist of in situ regolith over fresh granite, Near Maldon the extent of both current and historic with the upper parts composed of transported gold mining becomes evident. Alluvial gold was regolith and soil. The granite is slightly to highly discovered in 1853, but quartz reef mining became weathered and shows characteristic granitic dominant shortly thereafter and continued until textures, with fresh granite cropping out along the 1926. An estimated 9.3 tonnes of gold was produced base of the exposure. Quartz veins in the granite from alluvial mining and 55.6 tonnes from reef show that is largely in situ. The upper parts of the quartz (Cherry & Wilkinson, 1994). saprolite have begun to break up along joints, with corners being rounded at the contact with the Travel through Maldon, then turn left on the main overlying soil. This upper part of the saprolite show road and head north east towards sub-horizontal layering and hard banding caused by Laanecoorie–Bridgewater (Bridgewater–Maldon weathering, but igneous fabrics are still visible. Road). After approximately 1.5 km, turn right on There is a sharp contact between the saprolite and a Nuggetty Road and head east towards the Nuggetty uniform red-brown soil (Um) that consists of a friable mine. Within the first kilometre on this road, two mix of quartz, feldspar and clay. small creeks have cut through several metres of colluvium derived from the contact metamorphic 2 Fogartys Gap: slightly weathered contact aureole. The sediments are well exposed but difficult metamorphosed sedimentary rocks on hills to access due to the steep creek banks, but are worth (SSeh3) observing from the road. Although both creeks drain AMG 253300 5905900 northwards into the Harcourt Batholith, the colluvium is dominated by sub-angular to angular Continue driving north on the Calder Highway, and cobbles and pebbles of contact metamorphic bedrock. take the road left prominently signposted to Maldon. A deep road cutting through a hill exposes over 10 m Continue along Nuggetty Road for about 2 km. The of slighltly weathered metamorphosed sedimentary contact aureole forms the prominent ridge on the rocks (Castlemaine Group). Park at the end of the right. However, the north facing slope of the ridge road cutting. consists of fresh granite, with contact metamorphosed bedrock only cropping out on the ridge crest. Tors and The aureole forms a prominent ridge that is boulders of rounded granite are common along the generally higher than the adjacent Harcourt ridge, and contrast with the absence of fresh granite Batholith and lower grade Castlemaine Group. outcrop to the left on the topographically lower Looking northwest from Fogartys Gap, the Harcourt granite basin. Batholith is seen to form a topographic basin, with the granite uplands of Mount Barker, Mount Park at the first intersection to the left (dirt track) Prospect and Mount Alexander visible in the along Nuggetty Road. Walk northwest approximately distance. 100 m towards the shallow creek draining to the north and northwest. Bedding and jointing patterns are preserved throughout the road cutting, reflecting the original 58 BENDIGO REGOLITH

Figure 45 Simplified regolith-landform map of BENDIGO showing excursion sites.

The creek has its headwaters at the Nuggetty mine cobbles of contact metamorphosed bedrock, overlain and has incised through an alluvial–colluvial plain by predominantly angular granitic quartz sand and that gently slopes to the northwest. In the creek bed clay. There are no granitic clasts in the alluvium and colluvium derived from the Harcourt alluvial/colluvial sediments; however numerous Batholith and the contact metamorphic aureole cobbles and boulders of rounded fresh granite can be overlie in situ weathered granite of the Harcourt found further upslope near the road. Batholith. Walk along the creek for approximately 50 m to the In situ granitic saprolite crops out in the creek bed. northwest of this initial location to the intersection It consists of quartz and slightly weathered feldspar. with another shallow creek. An organic-rich red- The overlying alluvium and colluvium contains a brown gradational soil is preserved underneath basal unit of angular granitic quartz sand and sub- about 1 m of alluvium. This is in turn overlain by angular ferruginised or iron-stained pebbles and BENDIGO REGOLITH 59

another alluvial sequence with a poorly developed 5 Bradford Creek: channel sediments soil profile. overlying highly weathered granite (ACer) AMG 238200 5909400 Towards the south is a ridge of hills that defines the boundary between the Harcourt Batholith and the Take Almond Tree Road and travel southwest. After contact metamorphic aureole. Fresh granite tors and approximately 1.5 km, turn right onto Bradford Hills boulders are common on the lower slopes of this Road and travel north west and west for about 4 km. ridge, but the upper slopes consist of contact Cross Bradford Creek and continue through the metamorphic rocks. The Nuggetty Mine is located intersection and follow Bradford Road directly ahead towards the upper parts of the hills and at the head in a south-west direction for approximately 800 m. of the creek. Park at the disused railway cutting. This area was extensively worked for both alluvial Throughout the length of the railway cutting and reef gold. The large mullock heaps at the silicified fluvial quartz conglomerate is exposed, and Nuggetty mine attest to the bedrock mining history crop out along the upper slopes of Bradford Creek, of this area, but the plain now shows very little approximately 20–40 m above the present creek bed. evidence of alluvial mining. This is largely due to The conglomerate is silicified and moderately sorted infilling of the shallow shafts on the plain by the local and consists of pebbles and cobbles with a sandy farmers. This area is not recorded on the geological matrix. The quartz pebbles and cobbles are of reef maps as auriferous alluvium. However, about half a quartz, but in some areas (i.e. south of the road), the kilometre to the northeast (AMG 239800 5905800) is outcrop consists entirely of bleached well sorted fine a small wooded hill topped with vein quartz to medium grained clayey quartz sand of granitic conglomerate (ACer) where numerous shallow shafts origin. In this section occasional mega-mottles are are still preserved. visible. Weak cross-bedding is preserved in some 4 Newry Meadows: highly weathered areas. granite on low hills (SHel2) These conglomerate outcrops follow the drainage AMG 244200 5910700 pattern of Bradford Creek, and represent an earlier drainage system. They are similar to the White Hills Continue east along Nuggetty Road. Near the end of Gravel observed elsewhere in BENDIGO and show a Nuggetty Road, a disused railway cutting exposes similar weathering pattern. weathered Harcourt Batholith mantled with soil, similar to that exposed at Stop 1. The best exposures 6 All Stone quarry: lava flow of the Bald Hill occur to the south of the road. Fresh granite outcrops volcanic complex (VFvl) at the base of the cutting overlain by in situ granitic AMG 233800 5929400 regolith. The granite is jointed and shows an irregular upper surface. The in situ granitic regolith Return along Bradford Road and turn left onto is variably weathered, and in some areas it is difficult Shelbourne Road. Travel northwest for to determine the contact with the overlying soil, approximately 7.5 km. Turn right onto Ponton Road particularly on the eastern face. Although granitic and travel north to Shelbourne for about 4.5 km. textures are difficult to identify, in situ quartz veins After crossing the Bendigo–Maryborough Road the occur throughout the length of the profile, indicating track (Neivandt Road) begins to climb the contact in situ regolith. Only the upper 20–30 cm of the metamorphosed aureole, and the Neivandt Hill profile, which is a more uniform red-brown colour, Quarry is located just behind the ridge crest (AMG represents the soil profile. 234500 5919100) and provides low quality crushed aggregate (optional visit). At the end of Nuggetty Road turn left and travel north on the Bendigo–Maldon Road for If not visiting the Neivandt Hill Quarry, turn right at approximately 6 km. Turn right at Hokins Road and the Bendigo–Maryborough Road and travel east to park near the intersection. Cross the fence and walk Lockwood, where Bullock Creek exits the Harcourt south to the crest of the hill where there are Batholith. Turn left onto the Calder Alternative numerous old trees. Highway to Marong. Bullock Creek forms a shallow but sinuous stream incised within floodplain On the eastern slope of this hill foliated and sheared sediments of the Shepparton Formation, and the granite intruded by quartz veins is exposed. The alluvium consists of granitic quartz and mica. There foliation is oriented in a NNE–SSW direction parallel are many opportunities to examine the sediments to and continuous with the Muckleford Fault to the along the road. Approaching Marong, turn left (west) south and the Leichardt Fault to the north, on the Highway towards Newbridge. indicating post-Devonian movement. The outcrop of this foliated granite is limited and only occurs along The Wilson Reef township to the west of Marong ridge crests, with the ridge slopes dominated by a represents the remains of the historic gold workings at uniform grey-brown granitic quartz and feldspar Wilson’s Hill (or the Marong) gold field. The area was sand and clay soil. The foliated granite has a darker initially an alluvial field, but rich quartz reefs were radiometric signature than the surrounding later discovered, some of which were worked until Harcourt Batholith (Fig. 7). about 1900. Mine tailings from both alluvial/deep lead and reef quartz are visible from the road. 60 BENDIGO REGOLITH

The All Stone Quarry is located on the Wimmera discontinuous lenses that probably represent Highway (AMG 233800 5929400). Along the road, disturbed soil and alluvium sourced from alluvial the stony rises is the typical landform seen on this gold mining. unit. To the south of the road and in the distance, the 8 Myers Creek: mining residue (Faf) Bald Hill volcano is visible (AMG 236600 5926500), a AMG 248800 5937600 composite volcano with a scoria vent and lava dome that rises 30–40 m above the stony rises lava field. Return to the and turn left onto Allies Road. Travel for approximately 5 km Typical outcrop consists of stony rises with clayey northwards and turn left on Myers Flat Road and red-brown gradational soil. Road cuttings near the travel west for approximately 1 km towards Myers quarry expose sub-rounded cobbles and boulders of Creek. Stop at the bridge crossing Myers Creek. Good basalt, which show spheroidal weathering and are exposures of mining residue occur to the north of the coated with iron oxides and clay. At the All Stone bridge along the banks of Myers Creek. Quarry, the basalt boulders become more closely spaced and begin following joint patterns, which in Mining residue is well exposed along the banks of turn become boundaries between basalt columns in Myers Creek. It consists of laminated uniform silty the fresh basalt. Vesicles in these basalt boulders in clay, with occasional lenses of quartz and the lower parts of the soil profile are sometimes ferruginised bedrock gravel. These gravel lenses can infilled with calcium carbonate, but no carbonate was occur at the base, within the unit, and at the top of found in the clayey soil matrix. the unit. There is no discernible soil development, 7 Laugoons quarry, Myers Flat: alluvial and the top parts of the unit are now disturbed by agricultural activity. Underlying the mining residue sediments (Aap) are fluvial sediments with a mottled gradational soil AMG 251200 5933800 profile of either the Shepparton Formation or the Return to Marong, turn left and follow the Calder Coonambidgal Formation. Further northwards Highway to the city of Bendigo. After 7 km turn left (approximately 100–150 m) along the banks of Myers at Maiden Gully and travel to the Loddon Valley Creek, a calcareous soil with rhizomorphs occurs Highway. Turn left and follow the Loddon Valley below the mottled soil at a depth of 1.2 m. Highway through Eaglehawk and past Myers Flat for This area was extensively mined for alluvial gold. approximately 5 km. The area further upstream was also worked for Laugoons quarry is located at Myers Flat behind the alluvial gold, and later, a floating dredge was erected hotel on the corner on the left. Turn left and cross the to extract gold from the shallow alluvium. Puddling railway line. Just past the railway line is the machines were also located to the west of Myers Flat. entrance to Laugoons quarry at Myers Flat (AMG Note that Myers Creek is incised through fluvial 512338). This quarry is on private land and entry sediments (Shepparton Formation) similar to those requires permission from the landholder. Laugoons exposed at Laugoons quarry further upstream. quarry is an alluvial gold mine that exposes several However, the lead of alluvial workings to the west of metres of alluvium (Aap) overlying bleached the Myers Creek that cross Myers Flat Road consists metasedimentary bedrock (saprolite). This site also of sub-surface White Hills Gravel that only outcrops shows the legacy of historic shallow lead gold mining, along the banks of the dam on Myers Creek (AMG and is one of the few sites in BENDIGO where a cross 247800 5937300). The outcrop at Myers Creek and section of auriferous shallow lead deposits is exposed. the mullock from the alluvial workings are The base of the alluvium is characteristically dominated by sub-rounded to rounded quartz cobbles irregular and contains a generally flat-lying layer of and pebbles, whereas the deposits of the Shepparton pebble and cobble conglomerate dominated by sub- Formation are predominantly sub-rounded to sub- angular clasts of iron stained and ferruginised angular lithic fragments. bedrock, and reef quartz. Although the bedrock It is interesting to note that the trees growing on the clasts are iron stained and cemented, the underlying banks of Myers Creek have been undercut by bedrock is bleached and weakly mottled. The basal gullying. The trees and tree roots appear to be conglomerate layer is overlain by finer sand and clay concentrated at the contact between the mining and in turn by a gradational red-brown soil. residue and the underlying alluvium, and show Myers Flat was an area of extensive historic gold multiple shoots, suggesting that many of the original mining in the shallow alluvium, and shafts and trees were felled for use during the period of mining mining residue (Faf) are preserved on the quarry activity and have since regenerated, producing walls. The mining residue deposits are bleached multiple new trunks. It therefore appears that laminated clays and silts, sourced from puddling Myers Creek prior to extensive mining activity was machines that were located to the west of Myers Flat, originally a shallow (approximately 1–2 m deep) and also from a floating dredge which was later stream, similar to the small channel to the east of the erected. Overlying the buried soil is red-brown and creek that drains into Myers Creek just north of the grey-brown sandy clay with poorly sorted coarse sub- bridge. angular to sub-rounded bedrock pebbles forming BENDIGO REGOLITH 61

9 Council quarry, White Hills: channel 11 Marine sand on erosional plain, disused sediments on erosional rises (ACer) quarry, Epsom (OMep) AMG 259800 5930700 AMG 263000 5936700 Return to the Loddon Valley Highway and the city of Access to this site requires travel on an unsealed dirt Bendigo. Approximately 3 km northeast of the city of track and it may not be accessible under some weather Bendigo and to the east of the Midland Highway is conditions. the White Hills area (the original place for which the Travel north through the city of Bendigo to White Hills Gravel is named) where extensive outcrop approximately 2 km north of White Hills and take of the White Hills Gravel occurs. There are numerous Taylor Street on the right to . Cross the exposures of the White Hills Gravel and overlying railway line and travel northeast for about 3.5 km, cemented duricrust, and the underlying weathered then take the dirt road to the left and travel west for bedrock. The numerous shafts and extensive sluiced approximately 600 m. Take the first dirt track areas at White Hills area attest to the extent to which heading north for several hundred metres, and then gold was historically explored in this region. take the next track heading east. Travel for Similarly, the numerous areas where the surficial approximately 100 m and park at the top of the material has been bulldozed for metal detecting disused quarry. indicates the area is still regarded as rich in gold. The White Hills area is quarried for gravel and sand, Iron indurated clasts of sandstone of marine origin and nuggets have been recovered during processing. (Parilla Sand) can be found scattered throughout the area overlying very highly weathered bedrock (e.g. At the council quarry at White Hills, the surface of along the dirt track). Most of the outcrop of this sand the White Hills Gravel is strongly cemented with consists of only residual iron indurated sandstone silcrete, clay and minor ferricrete, and forms a clasts scattered at the surface, and forms duricrust and resistant cap several metres thick topographically subdued and isolated outcrops on the overlying weathered quartz cobble conglomerate. lower slopes of bedrock hills and hill margins. At the The duricrust consists of cemented sandy quartz disused quarry, the unit consists of bleached and pebble and cobble conglomerate. This layer grades in well-sorted and predominantly fine quartz sand and depth to compacted and generally uncemented sandy silt with a ferruginous pisolitic soil overlying very quartz pebble and cobble conglomerate, with patchy highly weathered bedrock. The sand is generally silicification, ferruginisation, and argillan cement uniform, but weak bedding structures are sometimes resulting from groundwater precipitation. Sub- visible, and strongly bioturbated in some areas with parallel joints in the White Hills Gravel are silicified well-defined vertical burrows, similar to Skolithos and cemented with clay. ichnofacies, suggesting shallow water and tidal flat Due to the extensive mining history in the White environment (AMG 259200 5943200; Cherry & Hills area, the upper surface has been considerably Wilkinson 1994). disturbed and soil profiles are absent. In the eastern face of the quarry, a ferruginous 10 Very highly weathered metasedimentary pisolitic soil is well preserved and is equivalent to the bedrock, White Hills (SVer1) pisolitic Karoonda Regolith described for the marine AMG 260300 5930400 Parilla Sand in the Murray Basin. The soil consists of a detrital pisolitic ferricrete lag at the surface Return to the main road and head to the east side of overlying mottled red and yellow clayey and sandy B the White Hills area. Turn on Rowina Street and horizon that grades with depth to mottled clayey continue to the south-eastern end. Park at a small friable sandstone. The pisolites at the surface tend to dirt track leading into the White Hills area. be rounded to sub-rounded with polished outer This area exposes weathered and iron indurated surfaces. Mottling in the B horizon decreases with metasedimentary bedrock (Castlemaine Group) with depth, and the mottles near the surface tend to be strong mottling. It is one of the few areas where very more strongly cemented with iron oxides, suggesting highly weathered bedrock is exposed, and is located that the pisolites have formed from iron cemented to the east of the Whitelaw Fault. Although the mottles. The underlying Parilla Sand is often weakly degree of weathering is significant, bedrock textures to moderately cemented with argillans (cutans), and are obvious throughout the exposure. This contrasts sometimes cemented with iron oxides. with the weathering developed on the bedrock Note that on the northern face of the disused quarry, observed at base of the council quarry at White Hills very highly weathered metasedimentary bedrock is located to the west of the Whitelaw Fault, which is capped with a clayey soil, whereas the outcrop of highly weathered. Soil profiles on the bedrock are surrounding bedrock has very little soil preserved at not preserved at this site. In the surrounding area the surface. the weathered bedrock is quarried for brick clay. 62 BENDIGO REGOLITH

12 Alluvial sediments on erosional plains, McKenzies pit (Aep) AMG 274200 5928400 Return to the city of Bendigo and take the McIvor Highway to Axedale. Travel about 14 km east and after crossing Axe Creek turn left on the first road, O’Briens Road. Travel northeast for about 4 km and turn right at the first intersection and park at the gate of McKenzies pit. At McKenzie’s pit bleached grey-white kaolinitic clay was quarried for use in ceramics. The clay shows negligible texture or structure, and is very highly weathered. The northeastern face of the pit shows some mottling and weak soil development, but the upper surface is mantled with younger alluvial sand and sandy clay (Aap). Similar clay pits around Axedale (e.g. Osterfields pit) also have young soil profiles. The clay deposits around Axedale have been interpreted as equivalent to the White Hills Gravel, whereas others have correlated them with the Calivil Formation. Although stratigraphic relationships are not clear at this site or with other clay deposits around Axedale, they are both lithologically distinct and have different weathering profiles to those developed on the White Hills Gravel (ACer), suggesting that they may represent a different fluvial system.

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