Toolebuc Formation Vanadium - Julia Creek, Richmond, Saint Elmo (St Elmo), Linfield, Burwood, Manfred, Allura, Debella, Rothbury, Lilyvale, Cambridge
Queensland, Qld, Australia
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Extensive stratabound vanadium mineralisation is hosted within the oil shale and interbedded oil shale and coquina of the Toolebuc Formation which occurs in the northern part of the Jurassic to Cretaceous Eromanga Basin in the Julia Creek-Richmond district of northwest Queensland, Australia. A string of deposits/prospects have been outlined in two linear trends with a combined total strike length of >200 km (Fig. 2). These include the Saint Elmo deposit, ~25 km east of Julia Creek and ~155 km east of Cloncurry; the Julia Creek deposit, to the SE; Burwood to the NNW of St Elmo; Manfred further to the NNW, and the smaller Linfield to the NE of St Elmo. Together these deposits define a NNW-SSE trend. The Allaru (previously Arizona) prospect is located ~60 km NW of Saint Elmo, west of the main western corridor. The Cambridge and Lilyvale deposits that are ~100 km to the ENE of Saint Elmo, and Rothbury and Debella are located progressively to the NW, forming a NW-SE corridor to the east that converges with the western trend to the north. See the main map below (#Location: St Elmo - 20° 37' 25"S, 141° 54' 25"E).
Geotectonic and Geological Setting
The Eromanga Basin covers an area of ~1.5 million km2, predominantly in the state of Queensland and neighbouring Northern Territory, South Australia and New South Wales. It is the youngest of a series of partially to fully overlapping nested basins spanning the time interval from the Cambrian to Cretaceous, including the Cambrian to Devonian Warburton Basin, the Early Devonian to Early Carboniferous Adavale and Drummond basins, the Carboniferous to Triassic Bowen, Cooper, Galilee and Arckaringa basins, and the Permian to Triassic Pedirka Basin.
These older basins underlie much of the Eromanga Basin, except the northern and narrower section, which directly overlies Proterozoic to Palaeozoic basement and the Carpentaria Basin to the north. Particularly where separated by unconformities, these nested basins are hydrologically connected resulting in transfer of fluids, including water, brines and petroleum/gas. In the north, the Eromanga Basin passes across the ENE-WSW Euroka Arch into the Carpentaria Basin and the connected Laura Basin, and to the SE over the NNE-SSW Nebine-Eulo Ridge into the Surat and satellite basins in southern Queensland and northern New South Wales. To the SW, the generally north-south Birdsville Track Ridge and NW-SE Toomba Fault divide the Eromanga Basin into Central and Western sub-basins. The major subsidence-induced basin of the latter is the Poolawanna Trough. These three connected equivalent basins, the Carpentaria, Eromanga and Surat, together comprise the Great Australian (or Great Artesian) Basin.
The combined Eromanga and Carpentaria basins (excluding the Surat Basin) contain a sequence that is up to 3000 m thick and comprises an extensive, but relatively shallow, arcuate, southward widening structural depression within continental eastern Australia over a north-south to NE-SW length of >1500 km and width that ranges from 200 to 700 km. It was developed as a major downwarp on a basement of Proterozoic to Palaeozoic metamorphic and igneous rocks. The closest exposed basement to the Julia Creek-Richmond district are the Palaeo- to Mesoproterozoic Eastern Succession of the Mount Isa Inlier, ~140 km to the west, and the dominantly Palaeo- to Mesoproterozoic basement rocks and Palaeozoic granitoids of the Georgetown Inlier ~220 km to the NE.
Basement below the Eromanga Basin in the Julia Creek region overlies the older Archaean and/or Palaeoproterozoic Numil Seismic Province that is separated from the Eastern Succession of the Mount Isa Province to the west by the postulated west dipping Gidyea Suture Zone. That suture, which is curvilinear, concave to the east, passes ~10 km to the east of the ~1730 Ma Ernest Henry IOCG deposit and ~80 km west of Julia Creek. Subduction that culminated in this suture is interpreted to be related to the 1900 to 1870 Ma Barramundi Orogeny that is widely represented in the North Australian Craton (e.g., Etheridge et al., 1987). The Kalkadoon-Leichhardt Volcanics, ~100 km to its west of the suture, separating the Western and Eastern succession of the Mount Isa Province, represent the Barramundi Orogeny in the Mount Isa Inlier. The older, inferred Archaean to Palaeoproterozoic basement of the Mount Isa and Numil Seismic provinces are therefore interpreted to have been cratonised by 1800 Ma. The Eastern Succession of the Mount Isa Province, overlying this older basement, is composed of three cover sequences, exposed progressively to the east. The first of these comprises the Kalkadoon-Leichhardt Volcanics, followed by the second composed of 1790 and 1690 Ma rift clastic, carbonate and volcanic rocks immediately to the east. The third, further to the east, represented by the 1680 to 1610 Ma Soldiers Cap Group. On the eastern margin of the Mount Isa Province, adjacent to the by then largely dormant Gidyea Suture Zone, the Soldiers Cap Group commences with arenites and pelites, minor carbonates, volcanic rocks and ironstones, followed by more quartzites, conglomerates and ironstones, overlain, in turn, by basaltic volcanic rocks which also include calc-silicates and further ironstones. To the east of the Gidyea Suture Zone, the basement Numil Seismic Province is overlain by the unexposed Kowanyama Sequence, largely interpreted from deep seismic traverses, but which has been correlated with the Soldiers Cap Group to the west, and broadly, but not in detail with the slightly younger temporally overlapping Etheridge Province of the Georgetown Block to the east. The Etheridge Province overlies the Numil Seismic Province, which in turn overlies the Abington Seismic Province across the west dipping Rowe Suture formed during the ~1700 Ma collision between the two provinces. This collision predates deposition of the Etheridge Group. The Abington Seismic Province underlies the heart of the Georgetown Block (Korsch et al., 2012). However, Olierook et al. (2021) interpret a major, west dipping transcrustal feature between the Rowe and Gidyea sutures to reflect a 1560 to 1550 Ma suture between the Laurentian affinity Georgtown Inlier and the Mount Isa Inlier of the North Australia Craton. This structure, the Empress Suture Zone, which post-dates the Etheridge Group, is evident on the same regional deep seismic data used to construct the model above of Korsch et al. (2012) and would mean the Numil Seismic Province represents two juxtaposed separate geologically distinct domains. This Empress Suture Zone coincides with the western edge of the Croydon Province, on the eastern margin of the Eromanga Basin, while the Rowe Suture is further to the east. The major thrusts to the west of the postulated Empress Suture are predominantly antithetic, dipping east, while those to the east, dip west, parallell to the Empress and Rowe structures.
In the Julia Creek-Richmond district, the basement is represented by (as interpreted by the Queensland Department of Natural Resources, Mines and Energy, 2018):
• Soldiers Cap Group equivalents - composed of gneiss and schist, ranging from local migmatite to low grade sedimentary rocks comprising quartzite to psammitic schist, as well as amphibolite, grading to meta-basalt, meta-dolerite and meta-gabbro with minor ironstone.
• Schistose amphibolite, metabasalt and metadolerite, mainly occurring as sills within the Soldiers Cap Group, that are sufficiently thick (up to 2 km wide) to be differentiated from the background mafic rocks within that group. These belong to the ~1680 Ma Woman in White mafic magmatic event.
• Williams Super-suite granitoids, interpreted from magnetic data, and assumed to be equivalent to the 1540 to 1500 Ma Williams Supersuite exposed in the Mount Isa Inlier, Eastern Succession;
• Millungera Basin succession - unconformably overlying the Soldiers Cap Group equivalents, entirely covered by the Eromanga Basin, and interpreted from geophysical data and sparse drill holes. These drill holes have intersected predominantly pink to red, quartzose sandstones to quartzites with minor micaceous siltstones, and clay bands (Korsch, Struckmeyer, et al., 2011). Detrital zircons have been dated at 1593 Ma to 1560 Ma (Neumann and Kositcin, 2011), while fault gauge cutting these rocks has been dated at ~1115±26, to 905±21 Ma (Uysal, et al., 2020). The sequence is inferred from seismic data to have a maximum thickness of 4000 m and covers a generally north-south area of ~ 250 x 50 km from 20 to 50 km east of the Mount Isa Inlier.
• Siluro-Devonian granitoids - which are almost entirely restricted to the area to the east of the major, WSW vergent Savannah Downs Thrust which post-dates the intrusives. These granitoids have been subdivided into strongly and weakly magnetic populations.
These basement sequences have been deformed during the Early Mesoproterozoic Isan Orogeny, resulting in the interpreted angular unconformity between the Soldiers Cap Group and Millungera Basin succession and intrusion of the Williams Supersuite. Further deformation occurred during the Late Meso- to Early Neoproterozoic, subsequent to deposition of the Millungera Basin succession, as detailed above. A series of major east-dipping reverse to thrust faults post-dates the Millungera Basin and thrust the Siluro-Devonian granitoids over the Soldiers Cap Group (e.g., the Savannah Downs Thrust), and that group, in turn, over the Millungera Basin sequence, the result of tectonism to the east of the Georgetown Block. In the process, this compressive event generated a NW-SE to NNW-SSE trending basement high, largely occupied by Soldiers Cap Group equivalent rocks that persisted into the Mesozoic to influence the facies of the Eromanga Basin. This basement high, known as the Saint Elmo Structure (Fig. 2), was activated again following deposition of the Eromanga Basin sequence to form an antiformal structure in the Eromanga Basin sedimentary hosts, the crest of which is occupied by the vanadium mineralised Toolebuc Formation in the western trend of deposits. No similar uplift is evident below the eastern trend, other than it represents the eastern, up-dip margin of Toolebuc Formation exposure.
The Eromanga Basin sequence is as follows, from the base:
► Basement - as described above.
► Jurassic to Lower Cretaceous Sequence, which further to the south commenced with the Early to Middle Jurassic Poolowanna Formation that is restricted to the subsurface in the south-western Central Eromanga Depocentre and across the Birdsville Track Ridge into the Poolowanna Trough. It comprises 50 to 205 m of interbedded grey to brown carbonaceous siltstone, grey to buff very fine- to medium-grained sandstone and rare coal seams. The overlying Hutton Sandstone is a succession of poorly sorted, mainly non-marine and fluviatile rocks, comprising coarse to medium-grained, feldspathic, sub-labile sandstone at the base, overlain by fine-grained, well-sorted quartzose sandstone; with minor carbonaceous siltstone, mudstone, coal and rare pebble conglomerate. The non-marine Jurassic sandstones of this sequence are the main aquifers of the Great Artesian Basin. Where these sandstones unconformably overlie aquifers of older basins, they may be recharged from these older sequences. The Hutton Sandstone suite is overlain by an aquitard in the form of the Birkhead Formation shale, siltstone and coal. Fluviatile, lacustrine, and possibly deltaic sedimentation, continued through the close of the Late Jurassic with deposition of the Adori Sandstone, a fine- to medium-grained clayey sandstone and minor pebbly sandstone and siltstone. This was followed by the Westbourne Formation, composed of fluvial to lacustrine sedimentary rocks, mainly fine-grained sandstone interbedded with siltstone, claystone and minor coal.
Fluviatile, lacustrine, and possibly deltaic sedimentation, continued through the close of the Jurassic into the Lower Cretaceous. During this period, predominantly sandstone units were deposited with variable clay and carbonate matrices and lesser conglomerate, siltstone, mudstone and carbonaceous interbeds, grading to lignite and coal. These included an upward to equivalent succession in various parts of the basin, comprising from oldest to youngest, the Blantyre Sandstone, Ronlow Beds, Hooray Sandstone, Guilbert River Formation and Cadna-owie Formation. Of these, the Hooray Sandstone is the most significant and is a major aquifer. It is known to overlie the Westbourne Formation, is equivalent to many of the units listed in this association, and is conformably overlain by the Cadna-owie Formation. The latter is disconformably overlain by the Wallumbilla Formation, which represents the onset of a global marine transgression during the Cretaceous that resulted in the deposition of largely shallow marine and paralic sediments which represent an aquitard capping the sandstone sequence.
In the southern Eromanga Basin, particularly above the Cooper Basin, the Jurassic to Lower Cretaceous sequence of the Eromanga Basin, from the Poolowanna Formation to the Murta Formation/Hooray Sandstone, contain free-flowing oil reservoirs, with the exception of the Adori Sandstone. Commercially producible oil has also been discovered in the Wyandra Sandstone Member of the Cadna-owie Formation. These reservoir rocks host hydrocarbons derived from both the underlying Permian sequence of the Cooper Basin, and from the Eromanga Basin, probably the Birkhead Formation (e.g., Kramer, et al., 2004). Similarly, generally equivalent sandstone facies of the Lower Jurassic Evergreen Formation and Precipice Sandstone in the basal section of the Surat Basin host hydrocarbons. The presence of hydrocarbons could be of significance in the provision of reductants to trap metals in these units.
In the Julia Creek-Richmond area, the lowest members of the Jurassic to Lower Cretaceous sequence belong to the Eulo Queen Group which straddles the Euroka Arch in the northern Eromanga and southern Carpentaria basins. This group commences with the:
- Hampstead Sandstone that ranges in thickness from 6 to 115 m, averaging ~45 m (Smart et al., 1980), thinning to the east and north. It is exposed to the north of Richmond and is an equivalent of the Birkhead Formation and Adori Sandstone section of the main Eromanga Basin. It predominantly comprises a sequence of fine-, medium- and coarse-grained quartzose sandstone with some pebbly beds and conglomerate, and is strongly cross-bedded with interbedded micaceous siltstone, mudstone and very fine-grained sandstone (Smart and Senior, 1980).
- Loth Formation, which is Late Jurassic and forms an overlying, 50 to 90 m thick 'leaky aquitard' composed of clayey quartzose sandstone, fine- to very fine-grained micaceous, clayey quartzose to feldspathic sandstone grading to coarse-grained siltstone and mudstone. It is thin to very thin-bedded and has a middle 30 m section of micaceous siltstone and fine-grained sandstone, and cross-bedded fine-grained clayey quartzose sandstone. This middle section separates ~30 m thick upper and lower layers of interbedded medium- to coarse-grained quartzose sandstone, siltstone with fine-grained sandstone, and white porcellaneous mudstone (Smart et al., 1971). It is broadly equivalent to the Westbourne Formation (CSIRO, 2012).
The Eulo Queen Group is unconformably overlain by the Lower Cretaceous (Lower Aptian), Gilbert River Formation in the northernmost part of the Eromanga Basin where it occurs as a thin erosional unit that thickens substantially north of the Euroka Arch in the Carpentaria Basin, but thins to the south. It is ~60 m thick in the immediate Julia Creek area where it occurs at a depth of ~250 m below the surface (Breitfuss, 2018). Where exposed to the north of Richmond, it comprises a clayey quartz sandstone, with some sub-labile and glauconitic sandstone, and minor ferruginised shale. It is a condensed equivalent to the Hooray Sandstone and Cadna-owie Formation, and represents the Hooray Aquifer in the Julia Creek-Richmond area. It is also known as the Longsight Sandstone where it is adjacent to the Mount Isa Inlier (Radke et al., 2012).
► Early to Late Cretaceous Sequence, which coincided with a global marine transgression that resulted in the deposition of largely shallow marine and paralic sediments, including the Toolebuc Formation. This transgressive event is represented by the 1200 m thick Rolling Downs Group and the Wilgunya Subgroup over much of the Eromanga Basin. Through much of the central and eastern section of the Eromanga and Surat basins, the lowermost subdivision of the latter is the Wallumbilla Formation, which is further subdivided into the Doncaster Member, described below, and the overlying Coreena Member. This second member comprises an ~100 m, locally up to 155 m, thick sequence of grey and blue-grey interbedded siltstone and mudstone. The siltstone is coarse-grained and gradational to very fine- and fine-grained labile sandstone, that is in part calcareous, grading to silty limestone, thin to thick-bedded, commonly laminated, locally cross-laminated or thinly cross-bedded. It approximates a partial aquifer and directly underlies the Toolebuc Formation. Further south in northeastern South Australia, the Wallumbilla Formation, along with the Toolebuc Formation and Allaru Mudstone grades laterally into the 300 m thick Coorikiana Sandstone composed of laminated and thin-bedded claystone and siltstone with inter-beds of fine-grained sandstone, calcareous and ferruginous concretions and a thin unit of calcareous siltstone.
In the Julia Creek-Richmond district the Wallumbilla Formation is subdivided into the:
• Doncaster Member, which conformably overlies the Gilbert River Formation and comprises a <59 to 170 m Aptian sequence of mainly blue mudstone with subsidiary glauconitic mudstone and glauconitic siltstone. Some siltstones are calcareous, and some have a grain size gradational with very fine-grained sandstone. Limestone may be present, and gypsum is locally abundant (Radke et al., 2012).
• Jones Valley Member, which is a thin, ~8 m thick unit only found to the north of the Hughenden-Richmond area. It is of Late Aptian age and conformably overlies the Doncaster Member. It is a pale green coarse siltstone grading to very fine labile sandstone and siltstone, commonly cross-stratified and micaceous, with some calcareous beds grading to silty limestone. Locally it is glauconitic, with minor interbedded mudstone. The unit has sufficient porosity and permeability to be a thin aquifer in the middle of the Wallumbilla Formation to the SE near Hughenden (Radke et al., 2012).
• Ranmoor Member, which is of Early Albian age, and is restricted to the north of the Eromanga Basin, around Richmond, where it is up to 12 to 60 m thick and conformably and gradationally overlies the Jones Valley Member. It is also overlain conformably, or possibly locally interfingers with, the Toolebuc Formation. The Ranmoor Member is predominantly made up of blue-grey to black cleaved and silty claystone, and is locally carbonaceous, being described as 'oily shale' in drill logs. Lighter-coloured calcareous shales and siltstones with thin coquinite of flattened Inoceramus plates and fragments occur near the top of the unit and grade into the overlying Toolebuc Limestone. Pellet rich claystone, carbonaceous shale, immature detrital minerals and glauconite are present (Radke et al., 2012).
• Toolebuc Formation is also within the Rolling Downs Group and Wilgunya Subgroup. It conformably and gradationally overlies the uppermost unit of the Wallumbilla Formation, the Ranmoor Member, and is late Early Cretaceous (Albian, at ~105 Ma) in age. It can be readily identified in downhole geophysical logs of water bores by its distinctive gamma response (Moore et al., 1986; Patterson et al., 1986). It is a relatively thin unit, generally 20 to 45 m thick, to a maximum of 65 m in the Eromanga Basin and between 6 and 21 m in the Carpentaria Basin (Smart et al., 1980). It is the principal host of the vanadium mineralisation of the Eromanga Basin, and occurs extensively across ~500 000 km2 of the northern section of that Basin and the Carpentaria Basin. However, it is not encountered south of 27°50'S (close to the latitude of Brisbane). Within the Surat Basin, the Surat Siltstone, an up to 300 m thick siltstone to carbonaceous and pyritic mudstone, with some fine glauconitic sandstone is the stratigraphic equivalent, conformably overlying the Coreena Member. On the western margin of the Eromanga-Carpentaria basin it has been traced from Bedourie (~175 km south of Boulia) in the south, following the western margins of the combined basins for ~800 km to the shores of the Gulf of Carpentaria. To the south of Bedourie, the stratigraphic position is masked by Simpson Desert sand cover. To the east, it is exposed over a similar interval of ~800 km, from Barcaldine (east of Longreach) in the south, and extends northward, through Richmond, to ~17°S in the Carpentaria Basin, ~200 km NE of Normanton (Habermehl and Lau, 1997) where its distinctive gamma signature disappears. It was deposited within an epeiric sea (Frakes et al., 1987; Henderson et al., 2000; Henderson and Kennedy 2002) and reflects the period of maximum marine flooding, when deeper parts of the water column and seafloor frequently became oxygen-deficient (Henderson 1998). In combination with high levels of primary faunal productivity in the surface waters, these conditions led to the accumulation of organic-rich shale. The absence of benthic fauna implies strong oxygen depletion at and below the water-sediment interface (Moore et al., 1986), although the presence of coquinite layers suggests a zone of oxygenated waters close to shore, and/or areas oxygenated by wave action (Gray et al., 2002). However, during some intervals of Toolebuc deposition, particularly those characterised by interlayering of coquina and oil shale, there was a fluctuation in dissolved oxygen levels in bottom waters, allowing widespread growth of the benthic mollusc Inoceramus (Henderson 2004).
The Toolebuc Formation predominantly comprises black carbonaceous and bituminous shale and minor siltstone, with limestone lenses and coquinites (mixed shelly limestone and clays). It is composed of three main lithofacies (Radke et al., 2012): i). black calcareous and carbonaceous mudstone with abundant fish remains; ii). dark grey fossiliferous mudstone with coquinite composed of abundant large bivalve Inoceramus shells; iii). dark grey mudstone (Moore et al., 1986), which in the type section to the SE (between Boulia and Winton) comprise bituminous shales (Senior et al., 1978). This facies includes oil shale that was largely derived from planktonic algae and cyanobacterial mats (Glikson and Taylor, 1986; Sherwood and Cook, 1986).
In the northern Eromanga basin, it has been divided into two distinct units based on lithofacies abundance: i). an upper coarse limestone and clay-rich oil shale unit (coquina) and ii). a lower fine grained carbonate-clay oil shale unit. These will be described in more detail below in the different deposit areas.
In most areas, the Toolebuc Formation lies >200 m below land surface (Ozimic 1986).
• Allaru Mudstone, which is also within the Rolling Downs Group and is similarly very widespread. It is bounded by the Eulo and Nebine ridges to the east and is not found in the Surat Basin, but extends northward from northern South Australia and NW New South Wales, through the central Eromanga Basin in Queensland, and across the Euroka Arch into the Carpentaria Basin. It is of Mid Cretaceous age, from Late Albian to Early Cenomanian in the Eromanga Basin, although only Late Albian facies are found in the Carpentaria Basin. In the Eromanga Basin, the Allaru Mudstone conformably overlies the Toolebuc Formation or the Wallumbilla Formation where the latter is absent, and is conformably followed by the Mackunda Formation. It is generally from 200 to >300 m thick, but reaches 350 to 400 m in the central Eromanga Basin depocentre, thinning to 100 to 150 m in the NW and SE regions (Gray et al., 2002). In the Carpentaria Basin, it varies from 160 to 215 m, thickening southward (Smart et al., 1980). It primarily comprises a blue-grey mudstone, in part pyritic, with interbedded calcareous siltstone, cone-in-cone limestone and lesser sandstone. Sandstone, that is interbedded in the uppermost part of the formation, is grey, very fine-grained, laminated to thinly bedded, labile, lithic, and in part calcareous, with carbonaceous partings (Gray et al., 2002).
• Mackunda Formation, also within the Rolling Downs Group, covers the entire Eromanga Basin, but does not extend into the Carpentaria Basin. It contains fossils indicating a mid-Cretaceous, Late Albian to Early Cenomanian age, and conformably overlies the Allaru Mudstone. It is generally 75 to >100 m thick, ranging up to 120 to >150 m within the Central Eromanga depocentre. It represents a late Early to Mid Cretaceous regression and comprises interbedded sandstone, siltstone and mudstone with lesser mud-clast intraformational conglomerate, whilst bioclast and cone-in-cone limestone occur throughout. The sandstone is light green-grey, very fine- to locally fine-grained, well sorted, laminated and thinly bedded. It is labile lithic with accessory mica and glauconite, with an argillaceous and calcareous matrix. Carbonaceous partings are evident. Siltstone and mudstone are grey to light green, laminated and thinly bedded, contain numerous plant remains, and are calcite-cemented in part. The Mackunda Formation is a regional aquifer.
• Winton Formation, also within the Rolling Downs Group and widely distributed across the Eromanga Basin. It conformably overlies the Mackunda Formation and is composed of 400 to 1000 m of interbedded fine- to coarse-grained green-grey sandstone, carbonaceous and pyritic shale, siltstone and brown to black coal seams interbedded with carbonaceous mudstone and intraclast conglomerates. Sandstone beds contain abundant volcanogenic debris, lithic feldspar, traces of apatite, ferromagnesian minerals and mica (Krieg, 1985; Senior et al., 1978). The upper boundary of the formation is unconformable with Cainozoic sediments (Glendower Formation) of the Lake Eyre Basin.
Geology and Mineralisation
The Julia Creek - Richmond section of the Eromanga Basin lies toward its northern margin, straddling and up to ~100 km south of the Euroka Arch that separates it from the Carpentaria Basin to the north. In this section of the basin, the Toolebuc Formation is exposed and mineralised within two corridors:
i). on the northeastern margin of the basin, where it occurs as an almost flat lying, very shallowly SW dipping, NW-SE striking sheet, and includes, from SE to NW, the Cambridge-Lilyvale, Rothbury and Debella deposits; and
ii). the exposed crest of an antiform where the formation is draped over the syn-depositional Saint Elmo Structure (Fig. 2) basement high that has since been structurally reactivated and brought the mineralised section of the formation to the surface. As such these two corridors represent the limbs of a gently SSE plunging synform. This corridor includes the Julia Creek, Saint Elmo, Burwood, Manfred and Linfield deposits/prospects.
Although the Saint Elmo Structure below the western corridor was a basement high during deposition of the Eromanga Basin sequence, it was not apparently emergent. The Jurassic Eulo Queen Group may have thinned over the structure, but the Hooray Aquifer, represented by the Gilbert River Formation and Longsight Sandstone, is ~60 m in thickness, and is separated from the Toolebuc Formation by ~120 to 220 m of the aquitard Wallumbilla Formation (Douglas Partners, 2019).
Where exposed, due to its shallow dip, the Toolebuc Formation outcrops over a broad area as low, rubbly, subtle topographic highs that are elongated parallel to the Saint Elmo Structure, and have been the source of road building materials in many areas. Over the Saint Elmo Structure, the Toolebuc Formation outcrops along the gently dipping limbs and crest of the antiform and is composed of two distinct units representing two main faunal assemblages: i). an upper coarse limestone-rich clay and oil-shale unit (coquina) containing abundant shelly limestone in a clay matrix; and ii). a lower fine grained carbonate-clay-oil shale unit. Both have undergone strong oxidation to depths of 12 to 19 m, averaging ~15 m, below the current surface (Coxhell and Fehlberg 2000).
The upper Coquina Unit averages 5 to 6 m in thickness and comprises alternating 1 to 10 cm thick layers of coarse shelly limestone and oxidised (where weathered) fine grained black oil shale, which where unweathered, is identical to the fresh lower oil shale unit. The interlayered limestone and organic-rich shale impart a distinctive black and white colouration in fresh exposures and in core cutting the unit. The shelly limestone layers are composed of single and multiple laminae of crystalline calcite, dominantly derived from abundant Inoceramus and Aucellina shells within a matrix of black oil shale. Less common fossils within the same unit include fish debris (scales, bones and teeth), reptilian bone fragments and belemnites (Henderson 2004) that, with the associated phosphate component, are interpreted to contribute to its distinctive gamma ray response (Moore et al., 1986; Patterson et al., 1986). The average grain size of the coquina ranges from 200 mm plates of calcite, to fine clays and coccoliths between 0.5 to 10 µm. The clay rich layers increase in abundance and thickness towards the base, reflecting alternating and changing environmental conditions during deposition.
The lower Black Oil Shale Unit averages 7 to 8 m in thickness, but varies considerably outside of this range. It is predominantly composed of calcite, clays and kerogen/organic matter. The latter is predominately bituminite and micrinite from planktonic or benthonic algal sources, with lesser liptodetrinite, lamalginite (both from dinoflagellate and cyst sources), telalginite (tasmanitid cysts) and inertodetrinite (higher plant matter; Sherwood and Cook 1986). The organic matter has been described as a 'vitrinite-like' component that formed from cyanobacteria mats with disseminated specks of pyrite found throughout, together with humic acids (Glikson and Taylor, 1986).
Approximately 5% of the rock mass in both units of the Toolebuc Formation, including the upper Coquina Unit is composed of 1 to 2 cm thick goethite bands representing oxidation after pyrite rich sediments in the fresh rock.
Oil grade within the fresh rock varies from 55 to 100 litres per tonne, averaging between 65 and 75 litres per tonne. The oil is contained within kerogen, which comprises approximately 18 wt.% of the fresh oil shale. The composition of the kerogen is about 75% carbon, 8% hydrogen, 5% sulphur, 2% nitrogen and 10% oxygen (Tolmie, 1987). Within the fresh shale, the organic matter is predominantly lamellar and referred to as ‘lamosite’ (lamellar oil shale; Hutton et al. 1980), with organic compounds described as Alginite B. Alginite B is composed of elongate anastomosing films derived from benthonic algae that belong to the Cyanophyceae genera of blue-green algae (Ozimic, 1986). As seen under high magnification scanning electron microscopy, the oil shale contains abundant micro fossils, dominantly small planktonic foraminifera and coccoliths (algal plates) believed to be derived from Cyanophyta/blue-green algae. The average grain size of the lower oil shale calcareous nanofossils and clays are <5 to 7 µm. Blue-green algae are interpreted to have formed extensive algal mats on the sea floor, with the preservation of dead algal matter being related to an oxidation-reduction boundary probably located immediately below the base of the living algal mat layer and keeping pace with its upward growth. The clear water calcareous sedimentation of the Toolebuc Formation ended when muddy conditions returned, preventing further growth of the benthonic fauna and leading to widespread deposition of the argillaceous sediments of the overlying Allaru Mudstone (Ramsden, 1983).
The post-Cretaceous history of the basin has involved weathering, which can include both oxidation and carbonate cementation, erosion and some tilting. Weathering and cementation changes the colour of the Toolebuc shales from black to light grey. Narrow northwest trending subvertical faults are evident in the road quarries east of Julia Creek, paralleling the broad trend of the Toolebuc outcrop and St Elmo Structure. Deep weathering during the Tertiary resulted in oxidation to greater than 30 m locally, and averaging 15 m in the vicinity of Julia Creek.
The fresh oil shale is predominantly composed of calcite, kerogen, quartz, kaolinite, smectite and pyrite with minor mixed layered clays and gypsum, and trace sphalerite, chalcopyrite and galena. Where weathered, the kerogen and pyrite are completely oxidised, with the former apparently breaking down into amorphous oxide wad, while the pyrite forms goethite and hematite. Tyayamunite, a calcium-uranium-vanadium oxide mineral has been found, in a rare occurrence in a road building gravel quarry near Julia Creek. The Toolebuc formation contains anomalous levels of a wide range of elements including copper, zinc, nickel and
molybdenum. Typical values in the oxidised upper Coquina and lower Oil Shale units respectively are quoted by Coxhell and Fehlberg (2000) as follows: CaCO3 - 85 and 40%; SiO2 - 10 and 35%; Al2O3 - 1 and 7%; Fe - 0.75 and 3%; S - 0.30 and 2%; TiO2 - 0.6 and 0.3%; V - 1400 and 2250 ppm; Mo - 100 and 300 ppm; Zn - 400 and 1100 ppm; Cu - 100 and 200 ppm; Ni - 100 and 300 ppm; U - 20 and 35 ppm; Ag - 1 and 2 ppm; Au - 10 and 15 ppb; Pt - 2 and 4 ppb; Pd - 2 and 4 ppb. It is noted that the levels of many elements is quite substantial.
A number of mineralogical studies have been undertaken, with Norrish and Patterson (1976) concluding that the vanadium in the Toolebuc Formation oil shale facies at Julia Creek is associated with mixed layered clays which contains ~60% of the vanadium present in the fresh oil shale. The other 40% is held within silicates, pyrite and organic compounds. The mixed layer clays isolated from weathered and unweathered oil shale contain 5 to 10% V2O5. Vanadium is understood to substitute in the octahedral positions of the clay structures to give an idealised formula of K(Al,V,Mg)4Si7Al2O20(OH)4 (Patterson, 1994). High levels of organically bound vanadium are evident at Julia Creek, with one example of unweathered oil shale containing ~50% of its vanadium chemically bound within the kerogen as vanadyl porphyrins (Riley and Saxby, 1982). The remainder occurs either within the mixed layered clays (illite-smectite), or associated with pyrite or goethite within the fresh or oxidised material respectively.
Vanadium occurs in a variety of forms, based on acid solubility (Riley and Saxby, 1982), as follows:
• soluble in hydrochloric acid, probably hydrated oxides and vanadates adsorbed on clays or precipitated in limestone;
• soluble in hydrofluoric acid, probably vanadium silicates within clays or micas; and
• organically bound vanadium.
Weathering destroyed the vanadyl porphyrin structures in the kerogen, releasing vanadium from the organic matter, interpreted to have resulted in the transfer of hydrated oxides of vanadium into clay structures (Riley and Saxby, 1982). Similarly, weathering of the laterally continuous pyritic bands has oxidised the sulphides, resulting in higher grade goethite bands which, in the coquina, can contain grades of up to 0.5% V2O5. It is further suggested that oxidation of the sulphides lowered the pH, enhancing the release of vanadium from the various mineral species, particularly from the kerogen and pyritic zones, resulting in some mobilisation and enrichment of grades. The vanadium within the soft oxide coquina and the underlying oxidised oil shale has been found to be associated with hydrated iron or iron/titanium oxides and mixed clays, with the grade in particles of hydrated iron oxides about three times those of the clays. However, the clay-like phase is considerably more voluminous (Burger et al., 1999). Vanadium was also found in wad, an amorphous mixture of various oxides, mainly of manganese, cobalt, iron and copper, with 10 to 20% water, and grades approximately equivalent to that in hydrated Fe/Ti oxides.
The bulk of the information above refers to the Saint Elmo deposit, which is the most advanced of the projects. This deposit covers an area of ~4232 ha, with a ~14 km length in a NNW-SSE direction and width of 2 to 7 km.
Little additional information is available for the Manfred, Burwood and Linfield resources, which re assumed to have a similar geology and mineralisation style to St Elmo.
The Allaru (previously Arizona) resource is located 60 km north-west to NNW of the town of Julia Creek, within the Carpentaria Basin. It is ~35 km to the west of the western corridor, over the northern slope of the Euroka Arch. As such, it is between the Saint Elmo Structure and the western (or Mount Isa Inlier) margin of the Eromanga Basin. It is hosted within the Toolebuc Formation and has a NNW-SSE trending strike length of more than 25 km. The bulk of the mineralisation is contained within the shallow weathered zone, with primary enrichment of vanadium in the shale facies. In addition to the resource quoted below, the resource remains open in all directions, progressively shallowing to the east where it it is exposed. The upper Toolebuc varies from 0.3 to 3.0 m in thickness, averaging 2.8 m, whilst the lower unit ranges from 1.3 to 4.1 m, also averaging 2.8 m.
The Julia Creek resource to the south of St Elmo is predominantly in unoxidised Toolebuc Formation, the top of which is at a minimum depth of 37.75 m below the surface, although there are some outcropping and weathered areas. The resources quoted below cover an area of ~23 km east-west and 4 to 8 km north-south. In this prospect, the Toolebuc Formation is reported to have a thickness of generally between 5 and 15 m, and comprises four separate units, from base:
• Arrollo Siltstone, the base of which is at a maximum depth of 104.42 m, where it is generally in sharp contact with the underlying Wallumbilla Formation. It is an oil shale unit composed of dark grey, finely laminated, pyritic and kerogenous shales. The unit is divided into an Upper (OSU) and Lower (OSL) Oil Shale. There is a marked decrease in clay and a corresponding increase in oil yield and organic matter across the contact between the OSL and OSU. The OSL averages 1.56 m, ranging from 0.90 to 2.04 m, whilst the OSU ranges from 0.89 to 2.16 m, averaging ~1.40 m in thickness.
• Manfred Coquina, which appears to be lithologically similar to the Saint Elmo Coquina higher in the sequence, although it is not as areally extensive. It has an average thickness of 3.14 m, ranging from 1.29 to 5.41 m, and has a noticeably lower vanadium content but a spike in phosphorous, due to a distinctive phosphatic band at the base, an accepted marker with the Toolebuc Formation.
• Willats Crossing Siltstone, that is lithologically similar to, and gradational into, the overlying Saint Elmo Cocqina, but differentiated by having >50% oil shale bands.
• Saint Elmo Coquina, composed of interbedded shelly limestone and kerogenous siltstone, with an average thickness of 4.05 m, ranging from 2.59 to 5.02 m. The contact with the overlying Allaru Mudstone is gradational.
NOTE: No Toolebuc Formation is shown at the Julia Creek deposit on Fig. 2 because it does not outcrop, bring covered by Allaru Formation, and as such has not been mapped.
At the Lilyvale deposit, which is located 45 km NW of the township of Richmond, the deposit is 5 to 10 m thick, up to 4 km wide, over 5 km long and is open along strike. Intersections range from 5 m @ 0.59% to 14 m @ 0.53% V2O5, with depths to the top ranging from ~2 to 16 m below surface. The mineralisation, as at the deposits/prospects described above, occurs in two different facies: i).> An oxidised coarse limestone rich clay unit that extends from near the surface to a depth of ~15 m, over which interval the oil/carbonaceous material has been leached and the vanadium and other metals enriched. Test work has shown that >90% of the contained metal lies within the -38 µm size fraction; ii).> An unoxidised, fine grained carbonate-clay-oil shale unit containing vanadium, molybdenum, nickel, copper and 65 to 75 litres/tonne of oil (Horizon Minerals website, viewed Oct., 2021.
The Cambridge deposit constitutes the eastern extension of the Lilyvale mineralisation into a neighbouring property. The host Toolebuc Formation is flat-lying, predominantly composed of black carbonaceous and bituminous shale and minor siltstone containing limestone lenses and coquinites. Mineralisation extends from 1 to 22 m below surface, averaging 10 m, and ranges from 2 to 17 m in thickness, averaging 9.7 m. The resource outlined to 2018 was 5 km long and up to 3 km wide (Liontown Resources Limited, 2020).
The Debella deposit is located towards the northern intersection of the western and eastern corridors, above the Euroka Arch. Only scant information is available (October, 2021). The host sequence in this part of the Carpentaria Basin is lithologically similar to that described above and comprises 150 to 180 m of the Wallumbilla Formation, overlain by the Toolebuc Formation that is 8 to 15 m thick. This is, in turn, followed by 10 to 100 m of the Allaru Formation, which is unconformably overlain by 5 to 10 m of unconsolidated sands, clays and gravels of the Quaternary Wondoola Beds of the Karumba Basin. All of these are overlain by 0 to 2 m of Quaternary alluvium. Mineralisation is hosted by the Toolebuc Formation, which at Debella is reported as comprising banded shelly limestone and shales, with primary vanadium enrichment in the shale portion of the formation. The formation occurs over a depth interval range of from 16 to 35 m, with a thickness that typically varies from 4.5 to 7 m. It is said to be a shallow resource from a depth of 16.4 m with a flat dip and free-dig overburden. The bulk of the deposit is contained within the shallow weathered zone. It is to produce a high purity vanadium pentoxide product, vanadium electrolyte and high purity alumina from ore treated by atmospheric leaching of the vanadium followed by a standard vanadium recovery process (Vecco Group website viewed October, 2021; Northcott, Vecco Group, 2020).
NOTE: No Toolebuc Formation is shown at Debella on Fig. 2 because it does not outcrop, bring covered by a thin carapace of Allaru Formation, and as such has not been mapped.
Southwest Eromanga Margin
Hardey Resources (2018) reported relatively sparse sampling distributed over ~150 km of the Toolebuc Formation on the western margin of the Eromanga Basin, ~100 km east of Boulia and ~240 to 400 km SSW of Julia Creek. This sampling reported returned assays ranging from 0.3 to >0.5% V2O5 on their Spike, Cera and Petrie projects (Hardey Resources Limited, Annual Report, June 2018).
The Toolebuc Formation vanadium mineralisation has been interpreted to have been extracted from sea water and concentrated by marine organisms in an anaerobic environment over an extended period. The vanadium occurs as a variety of both organic and inorganic species, suggesting a combination of physical and chemical conditions was involved in the accumulation of the extensive resources that have been outlined and inferred.
The two main facies based units of mineralised Toolebuc Formation differ in their mineralogy, fossil assemblage and conditions of deposition. The lower fine grained oil shale was deposited in a reducing environment, while the upper laminated coquina represents fluctuating and progressively increased levels of oxygen in the sea suitable for the establishment of specialised low oxygen tolerant large benthonic shelly fauna. However, in the case of the latter, these conditions may have prevailed in an upper oxidised layer, whilst the sea floor was still reduced. Never-the-less, conditions necessary for deposition of alternating shelly and oil-shale only beds in the upper unit suggests fluctuations in the sea level and/or other physio-chemical conditions from time to time, favoured one facies over the other (Ramsden, 1986). The fine grained oil shale is interpreted to have been deposited in a quiet anaerobic deep water environment at ~200 m, well below the depth where wave action and currents could stir up the alternating fine sedimentary layers of clay and fine mats of algal plates (coccoliths), foraminifera and associated organic debris (Ozimic, 1986). However, the abundance of planktonic foraminifera and coccolith remains in the oil shales suggests a productive oxygenated upper water layer in the environment of deposition (Glikson and Taylor, 1986).
Pyrite, which occurs as both framboidal and massive bands throughout the organic-calcareous suite, and within foraminifera shells, is consistent with anoxic conditions at the water-sediment interface and possibly above. It also points to the presence of sulphate reduction processes. Such an anaerobic setting would have enhanced growth of a cyanobacterial community as well as preserving organic matter after the organisms die (Sherwood and Cook, 1986). It is also known that strongly reducing conditions facilitate the chelation of heavy metals with organic matter. Consequently, sediments deposited in anoxic marine waters usually contain anomalously high levels of uranium, copper, molybdenum, nickel, phosphorous and sulphur, which generally correlate with organic carbon concentrations (Schlanger and Jenkyns, 1986; Damison and Moore, 1986). A close association has also been observed between calcite and organic matter at Julia Creek, where calcareous outlines or casts of microorganisms closely resembling Oscillatoria cyanobacteria have been observed (Sherwood and Cook, 1986). This has been attributed to calcite precipitation upon the death of cyanobacteria caused by the production of amino acids during their decomposition. Such decomposition of amino acids under anaerobic conditions in sediments can result in an accumulation of ammonia, raising the pH, and causing the precipitation of calcium carbonate (Glikson and Taylor, 1986).
The close association between vanadium mineralisation and both organic and inorganic mineral species has been interpreted to imply the fixing of vanadium during these periodic pH and chemical changes at the seafloor. The interpreted depositional environment for the formation and preservation of the Toolebuc Formation involved a 'positive water balance basin' (Damison and Moore, 1980), whereby saline water entered from the north and circulated, while fresh water from the hinterland flowed northwards out of the region. This would result a stratified water column with a halocline comprising a permanent lower saline and an upper fresh water layer (Damison and Moore, 1980). The environment favourable to oil-shale deposition appear to have been terminated during the late Cretaceous with a return to normal marine conditions, possibly due to an increase in saltwater inflow, the result of a rising sea level during deposition of the thicker Allaru Mudstone, and possible variations in conditions in the euphotic zone, limiting the productivity (Ozimic, 1992).
The uranium of the Toolebuc Formation has been interpreted to have been transported into the depositional area in a soluble hexavalent state by run-off waters from the adjacent hinterland, and reduced at the sea floor by organic matter to the insoluble tetravalent precipitate (Ozimic,1986). A similar mechanism for the transport and reduction of vanadium has been proposed (Coxhell and Fehlberg, 2000).
If the vanadium has been sourced from weathering and erosion of the hinterland adjacent to the Eromanga Basin, consideration needs to be given to what potential vanadium bearing rocks that were available to erode and contribute to the basin. To the SW, in southeastern Northern Territory, a possible source are the widespread and numerous dykes, sills and intrusions of the Kalkarindji Event large igneous province (LIP), most densely distributed in the Irindina Province, to the ENE of Alice Springs. This concentration is interpreted to have been one of the major foci of magma passage feeding the Kalkarindji LIP that extended across large areas of the Western and Northern Australian cratons (as illustrated on Fig. 1), as far west as the Antrim Plateau Basalts in Western Australia. These rocks were intruded at ~510 Ma, and were subsequently deformed and metamorphosed at deep-crustal levels during the Ordovician (Maidment, 2005). They were subsequently exposed and fringe and unconformably underlie the Eromanga Basin (Scrimgeour, 2013). One of the Kalkarindji intrusions to the NNW of Alice Springs, a gabbro complex, hosts the significant Mount Peake V-Ti-Fe deposit. The Kalkarindji intrusions cut both Palaeo- to Mesoproterozoic basement and relict terranes of the Centralian Superbasin. If sufficient dykes and sills of Kalkarindji Event mafic rocks are present they are a possible source of elevated vanadium levels in water flowing into the southwestern Eromanga Basin. Similarly widespread mafic intrusions, mostly sills, and mafic volcanic units are found within the Mount Isa Inlier and Croydon Province (Fig. 1) that are to the west and east respectively of the main areas of vanadium mineralised Toolebuc Formation. These mafic rocks represent multipulse LIPS that were intermittently active over a period that extended from 1720 to 1590. They included the 1780 Ma Hart Event that saw the intrusion and extrusion of mafic and/or ultramafic rocks over much of the Western Fold Belt of the Mount Isa Inlier, including the extensive, up to 8 km thick Eastern Creek Volcanics. These volcanics occur immediately adjacent to und pass beneath the Eromanga Basin, and host the significant Valhalla U-V deposit. Hart Event magmatism is also present in the Irindina Province. This was followed by the 1680 Woman-in White Event, which had migrated east into the Eastern Fold Belt, now partly lying below the Eromanga Basin in the Saint Elmo Structure, and in the Croydon Province. The next was the 1655 Ma Lane Creek Event, within and to the east of the Croydon Province (Hoatson et al., 2008; Thorne et al., 2014). Fe-Ti-V mineralisation and deposits are commonly found in association with mafic large igneous provinces (e.g., Panzhihua in the Emeishan LIP in China). Maughan 2016 studied and analysed mafic dykes and sills (n=23), mainly dolerites, associated with Cu-Co deposits and occurrences in the Eastern Succession of the Mount Isa Inlier and found they contained background levels of vanadium that ranged from ~200 to 450 ppm, with outliers as high as 1080 ppm.
The close coincidence of a basement high containing abundant mafic sills, an overlaying antiform updoming a basal aquifer and a capping sulphidic, hydrocarbon saturated aquitard hosting upward decreasing vanadium resource might at first sight suggest an alternative mode of formation. This relationship is evident along the western mineralised corridor at Julia Creek. This option would involve leaching of metal from the basement Soldiers Cap and abundant mafic sills, upward transfer of pregnant fluids via the Hooray Aquifer and precipitation in the strongly reduced Toolebuc Formation cap. However, a number of considerations render this interpretation less likely, specifically: i). no similar antiform and mafic sill source is evident below the eastern mineralised corridor, although it is an up-dip location on the eastern margin of Toolebuc Formation exposure; ii). the Hooray Aquifer and Toolebuc Formation are separated by ~120 to 220 m of the Wallumbilla Formation which acts as an aquitard, if somewhat 'leaky' (Douglas Partners, 2019), and no aquifer has been reported at the base of the host unit; iii). anomalous vanadium is sporadically noted over a strike length of hundreds of kilometres, suggesting it is a regional characteristic of the Toolebuc Formation (e.g., the occurrences east of Boulia). However, further south beyond the known vanadium occurrences the Toolebuc Formation is underlain by or interfingers with limited aquifers (see the stratigraphic description section above).
Exploration and Development History
Exploration tenements were originally granted to Australian Aquitaine Petroleum Ltd in 1968 in the general Julia Creek area, and were the focus of an unsuccessful sedimentary uranium program directed at the Toolebuc Formation. The focus changed to oil-shale and vanadium in 1969, with Aquitane taking on The Oil Shale Corporation of America, through TOSCO (Australia) as a partner. A drilling program involving 55 holes on a roughly a 6 km centres grid outlined a very consistent mineralised horizon. Preliminary mining and processing studies for a proposed oil shale and vanadium project were undertaken between 1970 and 1973, principally focussed on vanadium extraction (Whitcher, 1992). By 1973, TOSCO had exited the joint venture and CSR Limited, through Pacminex Pty Ltd had joined. A rise in the petroleum price in 1973 shifted the emphasis and resulted in a more extensive program of drilling to delineate an oil shale resource. This work outlined a large oil shale resource with a reasonably uniform grade of 65 to 75 litres per tonne along the west flank of the St Elmo Structure, adjacent to the St Elmo Homestead. Aquitaine withdrew from the joint venture in 1975, leaving CSR as the sole owner. Another, more substantial price rise in 1979 reinvigorated interest, and by 1982 detailed drilling had defined a shallow open-pitable oil shale resource of 1.798 Gt of unoxidised oil shale @ 63.5 litres per tonne of oil and 0.35% V2O5 (Whitcher, 1992). Additional test work was initiated as well as pilot plant studies to investigate oil shale extraction technologies, largely by the CSIRO (the Australian Commonwealth Scientific and Industrial Research Organisation) and CSR. However, whilst CSR's continued to advance technological research into aspects of oil shale processing between 1983 and 1988, they withdrew from the oil shale project in 1988 and the Canadian company Placer acquired the ground in 1988 and completed a review of the data, before withdrawing in 1991. CRA Exploration Pty Limited acquired the tenements in 1991 and focused on the extraction of oil from the oil shale. A number of holes were drilled and some metallurgical work was completed. Again, after an extensive review of previous work and their own results, CRAE relinquished their titles in 1994 after concluding that the production of oil from the Julia Creek deposit was uneconomic at the oil price of the day. New mineral tenements applications were submitted by prospector, Wayne Jones, in July 1996, and he entered into an agreement with a junior, Fimiston Mining NL whose aim was to develop a large oxide vanadium project in the upper oxide zone where the oil shale has been leached of kerogen. Drilling and assaying work completed subsequently, according to Fimiston, established one of the world’s largest vanadium resources (Coxhell and Fehlberg, 2000). Fimiston Mining undertook metallurgical testwork, including the potential to upgrade the coquina to 1.4% V2O5 via wet scrubbing, trommelling and cycloning. However, due to the very fine grained nature of the fine calcareous microfossils in the underlying oil shale this material cannot be beneficiated using conventional cyclone technology, and the dilutant microfossils, which contain negligible vanadium, cannot be readily separated from the fine clays and iron oxides thus impeding upgrading.
Test work has shown that both alkaline and acid leaching can be used to dissolve the vanadium from the clays and iron oxides within the concentrate. Acid is more effective than alkali leach methods at lower temperatures. However the excessive acid consumption due to the high levels of calcite in the concentrate renders the process uneconomic. In the case of alkali leaching, high consumption of the principal reagent, sodium carbonate has a significant affect on the financially viability of any development. Stoichiometrically, the vanadium in the concentrate requires only one tenth of the sodium carbonate consumed, but the formation of a sodium rich zeolite (analcime) in the autoclave is consuming any free sodium. This results in excessive reagent consumption.
Work has continued on a detailed program of metallurgical testing to establish a method for the economic beneficiation, leaching and purification of vanadium products from the oxidised oil shale.
Work on the unoxidised Julia Creek deposit at the southern extremity of the western corridor has investigated the use of a solvent based oil extraction technology to extract hydrocarbons and to upgrade and treat the vanadium mineralisation with some apparent encouraging results. This approach uses a closed loop, solvent based process with 99% recycling of the solvents. Tests have shown 90 to 92% vanadium extraction from shale ash produced at temperatures of 900°C in the Upper and Lower Arrollo Siltstone (i.e., OSL and OSU) respectively, corresponding to 71.3 and 74.4 recovery from the preprocessed shale (QEM Limited ASX Announcement August 2101).
Mineralisation from deposits on the eastern corridor has undergone extensive metallurgical test work initially focussed on upgrading the run of mine ore prior to downstream processing of the concentrate. Results from concentration tests on weathered Lilyvale mineralisation using simple screening, gravity and flotation mineral dressing techniques produced encouraging results with the concentrate comprising 21% of the original mass at an improved grade of 1.6% V2O5 and a 73% recovery. The concentrate produced also has a greatly reduced calcium content enabling a number of downstream processing options to be pursued.
Metallurgical testing of ore from the Saint Elmo Project has concluded that oxidised ore from a shallow, low strip ratio, open-cut mine can be economically processed on site via a roast, leach and solvent extraction process to produce a >98% purity V2O5 product.
At Debella, metallurgical testing suggests recoveries of 87% utilising a low-cost atmospheric leaching plant and vanadium recovery processes. Aluminium will also be produced with the vanadium.
Mineral Resource Estimates
Julia Creek-Richmond District
Unoxidised oil shale resource - 1.798 Gt @ 63.5 litres per tonne of oil and 0.35% V2O5 (Whitcher, 1992; quoted by Coxhell and Fehlberg, 2000).
Oxidised Mineral Resource - 2 Gt @ 0.39 wt.% V2O5 and 340 g/t MoO3 (Intermin Resources Ltd. 2007; quoted by Lewis et al., 2010).
Oxidised Mineral Resource quoted by Multicom Resources Pty Ltd (2018) in report by Breitfuss (2018) at a 0.2% V2O5 cut-off.
• Oxide oil shale - 5 Mt @ 0.35% V2O5, averaging 2.63 m thickness;
• Oxide Coquina - 6 Mt @ 0.26% V2O5, averaging 2.22 m thickness;
• Fresh Coquina - 4 Mt @ 0.28% V2O5, averaging 2.65 m thickness;
TOTAL Indicated Resource - 15 Mt @ 0.30% V2O5.
• Oxide oil shale - 135 Mt @ 0.35% V2O5, averaging 4.29 m thickness;
• Oxide Coquina - 48 Mt @ 0.25% V2O5, averaging 1.31 m thickness;
• Fresh Coquina - 35 Mt @ 0.25% V2O5, averaging 2.05 m thickness;
TOTAL Indicated Resource - 219 Mt @ 0.31% V2O5.
• Oxide oil shale - 63 Mt @ 0.36% V2O5, averaging 3.86 m thickness;
• Oxide Coquina - 30 Mt @ 0.25% V2O5, averaging 1.42 m thickness;
• Fresh Coquina - 220 Mt @ 0.25% V2O5, averaging 2.03 m thickness;
TOTAL Inferred Resource - 313 Mt @ 0.27% V2O5.
TOTAL Mineral Resource - 546 Mt @ 0.29% V2O5.
Oxidised Mineral Resource, JORC compliant, quoted by Horizon Minerals Limited at June, 2020 (ASX Announcement, 16 June, 2018) at a 0.30% V2O5 cut-off.
Inferred Resource - 76 Mt @ 0.345% V2O5, 369 ppm Mo, 249 ppm Ni;
Oxidised Mineral Resource, JORC compliant, quoted by Intermin Resources Limited at March, 2018 (ASX Announcement, 20 March, 2018) at a 0.29% V2O5 cut-off.
Inferred Resource - 96 Mt @ 0.33% V2O5, 335 ppm MoO3.
Oxidised Mineral Resource, JORC compliant, quoted by Intermin Resources Limited at March, 2018 (ASX Announcement, 20 March, 2018) at a 0.29% V2O5 cut-off.
Inferred Resource - 48 Mt @ 0.31% V2O5, 264 ppm MoO3.
Inferred oxide resource quoted by Cranley, 2010 as Intermin Resources Limited Statutory Annual Report to the Queensland Department of Natural Resources, Mines and Energy on EPM 14800, August, 2010:
170 Mt @ 0.46% V2O5
Mineral Resources, JORC compliant, quoted on Vecco Group website (viewed October, 2021):
Indicated Resource - 45.1 Mt @ 0.47% V2O5;
Inferred Resource - 130.1 Mt @ 0.43% V2O5
Mineral Resources, JORC compliant, quoted on Ausvan Battery Minerals website (viewed October, 2021):
Inferred Resource - 618 Mt @ 0.45% V2O5, plus,
Exploration Target - 850 to 1100 Mt @ 0.45% V2O5.
Unoxidised Mineral Resource quoted by QEM Limited (QEM website, viewed Oct. 2021) at a 0.2% and 0.15% V2O5 cut-off in oil shales and coquina respectively.
• Willats Crossing Siltstone (CQLA) - 73 Mt @ 0.25% V2O5, 155 ppm Cu, 138 ppm Mo, 123 ppm Ni, 780 ppm Zn, 0.475% Al, averaging 3.16 m thickness;
• Manfred Coquina (CQLB) - 67 Mt @ 0.28% V2O5, 182 ppm Cu, 168 ppm Mo, 142 ppm Ni, 890 ppm Zn, 0.571% Al, averaging 2.97 m thickness;
• Arrollo Siltstone Upper (OSU) - 40 Mt @ 0.33% V2O5, 223 ppm Cu, 153 ppm Mo, 191 ppm Ni, 1087 ppm Zn, 5.53% Al, averaging 1.94 m thickness;
• Arrollo Siltstone Lower (OSL) - 38 Mt @ 0.32% V2O5, 199 ppm Cu, 149 ppm Mo, 184 ppm Ni, 1015 ppm Zn, 5.50% Al, averaging 1.87 m thickness;
TOTAL Indicated Resource - 220 Mt.
• Willats Crossing Siltstone (CQLA) - 687 Mt @ 0.23% V2O5, 154 ppm Cu, 139 ppm Mo, 121 ppm Ni, 819 ppm Zn, 0.285% Al, av. 2.57 m thickness;
• Manfred Coquina (CQLB) - 874 Mt @ 0.38% V2O5, 220 ppm Cu, 221 ppm Mo, 201 ppm Ni, 1184 ppm Zn, 0.532% Al, averaging 2.97 m thickness;
• Arrollo Siltstone Upper (OSU) - 504 Mt @ 0.30% V2O5, 232 ppm Cu, 147 ppm Mo, 188 ppm Ni, 1148 ppm Zn, 6.25% Al, averaging 2.01 m thickness;
• Arrollo Siltstone Lower (OSL) - 481 Mt @ 0.29% V2O5, 212 ppm Cu, 134 ppm Mo, 171 ppm Ni, 1058 ppm Zn, 6.03% Al, averaging 1.98 m thickness;
TOTAL Indicated Resource - 2540 Mt.
TOTAL Mineral Resource - 2.760 Gt @ 0.30% V2O5, 201 ppm Cu, 166 ppm Mo, 170 ppm Ni, 1043 ppm Zn, 2.61% Al.
SPE-PRMS Contingent Oil Resource
• Willats Crossing Siltstone + Manfred Coquina (CQL) - 1701 Mt @ 44 L/tonne, averaging 5.93 m thickness;
• Arrollo Siltstone Upper (OSU) - 544 Mt @ 72 L/tonne, averaging 2.01 m thickness;
• Arrollo Siltstone Lower (OSL) - 518 Mt @ 63 L/tonne, averaging 1.97 m thickness;
TOTAL Mineral Resource - 2.760 Gt @ 533 L/tonne = 783 million barrels of Oil in the 3C category.
Oxidised Mineral Resource, JORC compliant, quoted by Liontown Resources Limited at July, 2018 (ASX Announcement, 30 July, 2018) at a 0.25% V2O5 cut-off.
Inferred Resource - 83.7 Mt @ 0.30% V2O5, 188 ppm MoO3, at < 22 m depth; plus an additional
Exploration Target - 100 to 110 Mt @ 0.28 to 0.32% V2O5.
Oxidised Mineral Resource, JORC compliant, quoted by Horizon Minerals Limited at 2021 (Horizon Minerals website, viewed Oct, 2021) at a 0.30% V2O5 cut-off.
Indicated Resource - 430 Mt @ 0.50% V2O5, 240 ppm Mo, 291 ppm Ni;
Inferred Resource - 130 Mt @ 0.41% V2O5, 213 ppm Mo, 231 ppm Ni;
TOTAL Mineral Resource - 560 Mt @ 0.48% V2O5, 234 ppm Mo, 277 ppm Ni.
Oxidised Mineral Resource, JORC compliant, quoted by Intermin Resources Limited at March, 2018 (ASX Announcement, 20 March, 2018) at a 0.29% V2O5 cut-off.
Inferred Resource - 1.764 Gt @ 0.31% V2O5, 253 ppm MoO3. Note
Oxidised Mineral Resource, JORC compliant, quoted by Horizon Minerals Limited at June, 2020 (ASX Announcement, 16 June, 2018) at a 0.30% V2O5 cut-off.
Inferred Resource - 1.202 Gt @ 0.312% V2O5, 259 ppm Mo, 151 ppm Ni.
Sources quoted include:
Breitfuss, M., 2018 - Saint Elmo Vanadium Project Initial Advice Statement, a report prepared for Multicom Resources Pty Ltd by Epic Environmental Pty Ltd., 50p.
Coxhell, S., 2004 - Partial Relinquishment Report, EPM 12863, Period 22 Feb 2000 - 6 Jan 2004; A report for Visiomed/Fiva Resource Corporation, 20p.
Cranley, N., 2010 - Julia Creek Vanadium and Molybdenum Project, Annual Report, EPM 14800, Period 8 August 2009 - 7 August 2010; A report for Intermin Resources Limited, 23p.
Independent Investment Research, 2018 - QEM Limited ASX:QEM, An investment and project report o the Julia Creek Project, Queensland; 25p.
Radke, B.M., Kellett, J.R., Ransley, T.R. and Bell, J.G., 2012 - Lexicon of the lithostratigraphic and hydrogeological units of the Great Artesian Basin and its Cenozoic cover; A technical report to the Australian Government from the CSIRO Great Artesian Basin Water Resource Assessment, 175p.
Senior, B.R., Harrison, P.L. and Mond, A., 1978 - Geology of the Eromanga Basin, BMR Bulletin 167, 134p.
Stadter, M. and Hair, I., 2019 - Groundwater Technical Report, St Elmo Station, via Julia Creek, Northwest Queensland; a report prepared by Douglas Partners for Epic Environment Pty Ltd, and Multicom Resources, 293p.
The most recent source geological information used to prepare this summary was dated: 2020.
This description is a summary from published sources, the chief of which are listed below.
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Coxhell, S. and Fehlberg, B., 2000 - Julia Creek vanadium and oil shale deposit: in AIG Journal, Applied geoscientific research and practice in Australia, Paper 2000-11 14p.|
Lewis, S.E., Henderson, R.A., Dickens, G.R., Shields G.A. and Coxhell, S., 2010 - The geochemistry of primary and weathered oil shale and coquina across the Julia Creek vanadium deposit (Queensland, Australia): in Mineralium Deposita v.45, pp. 599-620.|
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