Australian Iron Ore Deposits - Overview
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The first significant iron ore mining in Australia was from 1915, when the Broken Hill Proprietry Company (BHP) sourced ore from the Iron Knob and Iron Monarch deposits in the Middleback Ranges of South Australia to feed their newly established blast furnaces in NSW. BHP had previously been mining from these deposits since 1899 to provide flux for their part owned lead smelter at Port Pirie, also in SA. Mining at the Yampi Sound deposits in northern Western Australia commenced in 1950 to supplement feed from the Middleback Ranges.
Following the lifting of the Australian Government's iron export embargo in 1960, exploration quickly led to the discovery of the major deposits of the Hamersley Province, most importantly, those of the late Neoarchaean to early Palaeoproterozoic Hamersley Basin (e.g., Mount Whaleback and Mount Tom Price), predominantly high grade (>62% Fe) microplaty hematite deposits. Significant deposits were also discovered and exploited in the Mesoarchaean greenstone belt iron formations in the northern Pilbara craton (e.g., Mount Goldsworthy), and in the Meso- to Neoarchaean greenstone belt BIFs of the Yilgarn craton (e.g., Koolyanobbing)
Mining at Robe River (Mesa J), the first major Channel Iron Deposit (CID) in the Hamersley province, commenced in 1972. CID ore now accounts for ~40% of Australia's iron ore production. The first pellets from the Savage River magnetite deposit in Tasmania were shipped in 1968. During the late 1990s and early 2000s, a number of lower grade (60 to 62% Fe) Hamersley Group Marra Mamba martite-goethite deposits were brought into production (e.g., West Angelas and the nearby Area C), while in 2005, microplaty hematite was recognised within the martite-goethite Chichester Range Marra Mamba deposits (e.g., Christmas Creek) north of the main Hamersley Range belt. Increased demand from China over the last 10 years has led to the discovery of new, and/or development of known deposits (e.g., Hope Downs) in the Pilbara craton, as well as new and proposed developments of lower grade hematite (e.g., Roy Hill) and magnetite (e.g., Karara) deposits in W.A., S.A. and NSW (e.g., Razorback) and in Queensland and Northern Territory (e.g., Constance Range).
Until recently, over 95% of Australia's exported iron ore has been high-grade (>62%, but more recently >56% Fe), direct shipping ore (DSO), composed of hematite(-goethite). This DSO, once mined, only requires crushing and screening before sale. Lump ore (>12 mm) can be fed direct into a blast furnace and commands a higher price, whilst fines (i.e., <12 mm), which would be blown straight through a blast furnace, must first be aggregated by sintering before smelting, and hence attracts a lower price than lump ore.
Hematite DSO has been exported from Australia, Brazil and South Africa to destinations without a domestic supply that rely on sea-borne ore, and have built smelters to accommodate this type of ore (e.g., Japan and South Korea), or those that need to supplement their own hematite ore (e.g., India).
However, ~50% of global iron ore production (e.g., China, USA, Canada, Ukraine, Russia, Kazakhstan, Sweden, Chile, Peru and Mauritania) is from lower grade (15 to 50% Fe) magnetite dominant ores, which are beneficiated to 67 to 69% Fe concentrates and pelletised before sale and smelting.
Steel mills that have traditionally sourced magnetite in or from these countries, are direct reduction steel-making plants (e.g., most in China). To accept DSO hematite with a fines component, they must install sinter facilities, which require additional capital and a greater energy input, and hence higher cost of steel making. Consequently, magnetite pellets are preferred. The beneficiation of magnetite ore, results in increased capital, operating and energy costs at the mine, but because of its higher feed grade (compared to the lower grade DSO Marra Mamba and CID hematite-goethite ores) and lower cost of smelting, commands a premium price from direct reduction steel-making plants. This premium price generally offsets the greater production costs at the mine. A number of mines, backed by Chinese steel producers (e.g., Karara, Extension Hill, Cape Lambert and Cape Preston), are being developed to take advantage of this market.
NOTE: Links above go to summaries of regions below, where there are links to individual deposit descriptions.
Palaeo- to Mesoarchaean Iron Formations - Northern Pilbara Craton, W.A.
The northern Pilbara craton is occupied by a Palaeo- to Mesoarchaean, largely granite-greenstone terrane, that forms the basement to the major late Neoarchaean to lower Palaeoproterozoic Hamersley iron province. The greenstone belts include numerous banded iron formations, are among the oldest to have produced economically exploited iron ores in Australia.
The oldest rocks within the Pilbara Craton represent 3.80 to 3.53 Ga crust (seen in rare exposures of gneissic granite and gabbroic anorthosite), which was widely exposed throughout the evolution of the craton. These rocks are intruded and overlain by a granite-greenstone terrane, characterised by a regional outcrop pattern of ovoid granitic domes separated by arcuate belts of volcanosedimentary rocks that define the greenstone belts, representing at least eight successive volcanic cycles. The oldest sequence in the greenstone belt stratigraphy is the 15 to 20 km thick Pilbara Supergroup, which has been subdivided into the lower, dominantly volcanic, 3.53 to 3.42 Ga Warrawoona Group, intruded by 3.53 to 3.46 and 3.45 to 3.42 Ga granitoid supersuites. The Warrawoona Group is overlain by the 3.35 to 3.31 Ga Kelly and 3.25 to 3.24 Ga Sulphur Springs Groups, represented in the area by intermediate to felsic volcanic and sedimentary rocks. Each is separated by unconformities that were preceded by deformation and metamorphism, and accompanied by subaerial erosion and deposition of shallow water sediments. The Kelly and Sulphur Springs groups were cut by 3.32 to 3.29 and 3.27 to 3.23 Ga granitoid supersuites (Hickman and Van Kranendonh, 2012).
These rocks are unconformably overlain to the north and west, by the De Grey Supergroup, composed of a thick sequence of shale, wackes, feldspathic sandstone, arkose, banded iron formation and conglomerate, with interspersed significant basalt, high-Mg basalt, siltstone, chert and lesser felsic tuffs and volcaniclastic rocks. The lower section of the supergroup includes the widespread iron formation and clastic meta-sediments of the 3.05 to 3.02 Ga Gorge Creek Group which in most areas consists of basal conglomerate and sandstone overlain by a 1000 m thick unit of BIF, chert and black shale.
The Sulphur Springs and Kelly groups thin and pinch-out northward, where the Gorge Creek Group unconformaby rests on the Warawoona Group, following an interval of deformation at 3.15 Ga.
All of these rocks suffered their most intense tectonic imprint together as a result of subsequent granitic diapirism which produced batholiths between 3.0 and 2.8 Ga. These intrusions dominate the structural regime and separate the sequence into isolated greenstone belts (Hickman and Van Kranendonh, 2012).
The most significant iron ore deposits are developed within the Pincunah Banded-iron Member at the top of the 3.25 to 3.24 Ga Sulphur Springs Group (e.g., the primary magnetite North Star and Glacier Valley deposits of the Iron Bridge Project - 5.205 Gt @ 30.4% Fe) and the extensive Nimingarra iron formation near the base of the 3.05 to 3.02 Ga Gorge Creek Group, following an ~100 m.y. period of relative quiescence. Several hundred km strike length of Nimingarra iron formation have been mapped. Iron ores associated with this unit include: i). large primary magnetite deposits (e.g., Ridley - 2 Gt @ 36.5% Fe; Cape Lambert - 1.56 Gt @ 31.2% Fe); ii). conformable, steeply dipping hematite lenses within the host BIF over vertical intervals of generally 50 to 150 m (but locally up to 320 m) and widths of 50 to 100 m. The latter ore is commonly massive, structureless and microplaty hematite with some relict banding from the original BIF, and is the result of metasomatic replacement of the original cherty BIF, predating, and/or partly contemporaneous with, Proterozoic dolerite dykes which intrude it (e.g., Mt Goldsworthy, Yarrie, Pardoo and Wodgina - that individually contain <10 to >100 Mt @ >60% Fe); iii). Proterozoic conglomerate ore, which occurs within Neoproterozoic (~820 Ma) conglomerates at Yarrie 10, where moderately hard, rounded to ellipsoidal hematitic pebbles and cobbles with an average 63% Fe content are cemented by fine grained hematite-sand matrix, with thin shale interbeds, lapping onto Nimingarra BIF, and varying from 1.5 to 12 m in thickness; iv). Mesozoic or Tertiary supergene crust, comprising irregularly shaped masses of platy, fissile hematite that form tabular deposits underlying the weathered laterite zone, with thicknesses that vary from a few up to 25 m, with irregular floors.
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Archaean Greenstone Belt Hosted Deposits - Yilgarn Craton, W.A.
Greenstone belts within the Yilgarn craton host banded iron formations that have produced significant exploitable hematite and magnetite deposits, predominantly in the older western half of the craton. These greenstone belts are composed of basaltic, komatiitic-basalt and felsic volcanic, volcaniclastic and sedimentary rocks, and include the ~3 Ga Koolyanobbing and Marda-Diemals greenstone belts in the Youanmi Terrane in the south (e.g., the Koolyanobbing, Mt Jackson and Windarling hematite deposits which individually had resources of 50 to 200 Mt @ >60% Fe), and in the Murchison Terrane to the northwest, (the Mid-west district) where the widespread, 2.95 to 3.05 Ga, Windanning Formation contains significant deposits, although other greenstone sequences dated at ~2.80 Ga and ~2.75 Ga also contain banded iron formations. The Murchison Terrane contains deposits such as Karara (2.4 Gt @ 34.1% Fe magnetite, with satellite DSO hematite deposits each of 10 to 15 Mt @ 61% Fe lump and fines ore), Extension Hill (~3.0 Ga BIF, with 1.7 Gt @ 35.1 wt.% DTR magnetic fraction; and satellite DSO hematite reources of ~20 Mt @ 59.5% Fe); Weld Range (2.7 to 2.6 Ga BIF, with 156 Mt @ 58% hematite ore). The Jack Hills deposit (total magnetite resource of 3.89 Gt @ 29.5% Fe and a lesser tonnage of currently mined DSO hematite) is hosted within the Eoarchaean to Palaeoarchaean (>3.2 to 4.0 Ga) Narryer Gneiss Terrane which comprises granulite facies metasedimentay rocks with lesser mafic/ultramafic rocks and banded iron formation.
The Albany-Fraser orogen forms the southeastern margin of the Southwest Terrane of the Yilgarn craton. It contains late Archaean, Palaeo- and Mesoproterozoic granitoid, volcanic and sedimentary rocks that have been reactivated to form 1700 to 1600 and 1300 to 1190 Ma complexes of highly deformed orthogneiss with lesser structurally interleaved paragneiss, mafic and felsic granulites, granitoids, metagabbros and widespread metasedimentary rocks. These rocks host folded, "conformable", quartz-magnetite-clinopyroxene gneiss mineralisation (e.g., Southdown with 1.22 Gt @ 34.1% Fe, upgradable to low impurity 69% Fe concentrate/pellets).
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Late Neoarchaean to Earliest Palaeoproterozoic Hamersley Group Iron Formations - Southern Pilbara Craton/Capricorn Orogen, W.A.
These are the single most important source of iron ore exploited in Australia. They are located on the southern margin of the Pilbara craton of Western Australia, within the 2.77 to near 2.35 Ga volcanic and sedimentary rock sequence of the Mount Bruce Supergroup. This sequence unconformably onlaps pre-2.80 Ga granitoids and greenstones of the Archaean Pilbara core exposed in the north, and is unconformably overlain by the up to 12 km thick Wyloo Group sediments that constitute the remainder of the Hamersley province sequence, continuing to near 1.80 Ga. The Mount Bruce Supergroup commences with the lowermost Fortescue Group (clastic sediments and 2.77 Ga mafic volcanism, followed by extensive sandstones and conglomerates and thick mafic sills, unconformably overlain by volcanic and sedimentary rocks, more mafic sills and a thick, uppermost, 2.69 to 2.63 Ga, organic and sulphide rich fine clastic sedimentary rock, associated mafic volcanic rocks and sills increasing southwards). The Fortescue Group is conformably overlain by the 2500 m thick Hamersley Group, the main hosts to iron ore deposits, characterised by around 1000 m of laterally extensive banded iron formation representing three major episodes.
The basal, ~200 m thick Marra Mamba (2.60 Ga) and ~600 m thick medial Brockman Iron Formations are separated by ~750 m of carbonate, shale and minor chert of the Wittenoom, Mount Sylvia and Mount McRea Shale Formations (2.60 to 2.48 Ga). This passive sequence is followed after the Brockman Iron Formation by the third phase of iron formation deposition (the ~600 m thick Weeli Wolli Iron Formation) which was accompanied by intense 2.45 Ga bimodal volcanism and mafic sills (which locally account for up to 80% of the sequence), overlain by up to 800 m of felsic volcanics of the Woongarra Formation and the uppermost ~450 m thick Boolgeeda Iron Formation. Thickness variations in the Hamersley Group are only minor. The Boolgeeda Iron Formation, the uppermost unit of the Hamersley Group passes conformably upwards into the 3000 to 5000 m thick Turee Creek Group, the youngest unit of the Mount Bruce Supergroup. The Turee Creek Group is basically a coarsening upwards clastic sequence in a choked basin - marking a major change from the starved basin of the Hamersley Group.
The Mount Bruce Supergroup is unconformably overlain by the ~2000 m thick Lower Wyloo Group, comprising basal conglomerate (containing Hamersley Group BIF clasts), finer clastics and 2209 Ma mafic volcanics, followed by dolomites to the west. A major unconformity separates the Lower and Upper Wyloo Groups. The latter was formed in an extensional basin and comprise up to 12 km of sedimentary rocks, and is overlain to the south by the poorly sorted clastics of the Ashburton Formation, which includes 1.84 to 1.83 Ga bimodal volcanics and was intruded by the 1.79 Ga Goolaloo Granite.
The southern half of the Hamersley Group was deformed by the north-south compressive, ~2.45 to 2.2 Ga Ophthalmia orogeny, that formed an east-west trending, northward-verging, fold and thrust belt, characterised by south-dipping thrust faults and asymmetric to overturned folds, which decrease in intensity to the north. A generation of NW trending folds were developed during the ~1.80 to 1.65 Ga Ashburton Orogeny, at the close of the Lower Wyloo Group, interacting with the Ophthalmia fold belt structures to form a series of domes and basins.
Hamersley Group iron ores are sub-divided into:
i). extensive flat lying martite-goethite ores, developed from both Marra Mamba and Brockman Iron Formations by deep supergene enrichment of precursor banded iron formations, mostly during the Mesozoic to Tertiary (e.g., Marandoo - 390 Mt @ 63% Fe; Brockman #2, #4, Nammuldi, Silvergrass - >1.2 Gt @ ~62% Fe; West Angelas - 515 Mt @ 61.8% Fe, Area C - 3.294 Gt @ 60.0% Fe, Nyidinghu - 1.756 Gt @ 58.2% Fe), Hope Downs - 1.35 Gt @ >61% Fe) and Roy Hill - 2.3 Gt @ 55.9% Fe). Ores developed from Marra Mamba Iron Formation, tend to have a higher proportion of ochreous goethite, which is more friable with a marked yellow colour, while those over the Brockman Iron Formation are generally brown and less friable;
ii). high grade hematite, mostly martite and microplaty hematite, but little goethite, predominantly developed within the Brockman Iron Formation within the main WNW-ESE trending Ophthalmia fold belt of the Hamersley Range. These ores commonly occur to much greater depths (to more than 400 m) and account for the largest high grade deposits of the province (e.g., Mount Whaleback - >3.5 Gt @ >60% Fe; Mount Tom Price - 900 Mt @ 64% Fe; and Channar - >290 Mt @ 63% Fe). Enrichment of the primary iron formation is interpreted to be predominantly hypogene, and to have taken place in three stages (Taylor et al., 2001, Hagerman et al., various and others). The first involved low to moderate temperature (110 to 280°C), highly saline, bicarbonate-saturated brines from the underlying sedimentary successions (e.g., Wittenoom dolomite and evaporites), transported via faults to the BIFs to migrated laterally in large folds, between shale aquitards. These fluids removed silica, leaving a thinned residue, enriched in iron oxides (mainly magnetite), carbonates (mainly siderite), magnesium silicates and apatite. This stage is evident at a number of deposits (e.g., Mount Tom Price and Paraburdoo) but not at others (e.g., Mount Whaleback) where subsequent pervasive oxidation of most rocks by succeeding stages removed all carbonates. Never the less, sections of the underlying shales adjacent to major faulting are greatly enriched in MgO and CaO and depleted in SiO2, due to significant amounts of fine- to medium-grained ferroan-dolomite and ankerite and cross-cutting chlorite and carbonate veins, consistent with this stage of alteration (Webb et al., 2004). The second stage involved deeply circulating, low temperature (<110°C), oxidised, Na-rich meteoric waters that interacted with evaporites, prior to their interaction with the BIF, to oxidise the mainly magnetite-siderite assemblage to hematite-ankerite, and then stripped all carbonate, leaving highly porous and permeable iron ore bands composed of martite-microplaty hematite-apatite, interbedded with magnesium-rich shale bands. A third, purely supergene stage, most likely in the Mesozoic to Tertiary, coincident with the formation of the martite-goethite ores described above, converted magnesium silicates to a kaolinitic residue, greatly thinning the shale bands, destroyed apatite, and leached calcium and phosphorus from the ore. This three stage process produced a highly porous hematite ore with a characteristic microplaty texture, interbedded with kaolinitic shale containing significant aluminium and titanium, which retained their relative proportions throughout the upgrading process. The main alteration and veining events associated with stages 1 and 2 in this region of the Hamersley Basin, most likely correspond to the collisional (D2) and extensional collapse (D3) phases of the Palaeoproterozoic ~2.30 to 2.20 Ga Ophthalmian Orogeny (related to interaction between the Yilgarn and Pilbara cratons), with one or two later phases probably associated with the waning stages of the ~1.70 to 1.65 Ga Capricorn Orogeny (D4) and/or later Proterozoic events (Brown et al., 2004). The Marra Mamba martite-goethite ore sheet in the Chichester Range, north of the Ophthalmia fold belt, but associated with structures on the northern margin of the Hamersley Basin, overprints and is underlain by microplaty hematite mineralisation (e.g., Cloudbreak and Christmas Creek - 3.379 Gt @ 56.6% Fe);
iii). magnetite-rich ores, mostly within the Brockman Iron Formation, occurring as a laminated, metamorphosed oxide-facies iron formation in which the original chert or jasper bands have been recrystallised into distinguishable grains of quartz and the iron is present as thin layers of hematite, magnetite or martite (e.g., Cape Preston - 2.185 Gt @ 22.1% MagFe and 31.3% Total Fe). At Cape Preston/Balmoral, the main host Joffre Member of the Brockman iron formation, has a condensed thickness of 300 m, compared to the regional 360 m. This suggests removal of components of the unit, possibly by similar hypogene fluids that leached silica and produced a magnetite-rich assemblage from BIFs as the first stage in the production of microplaty hematite ore, as described above.
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Late Neoarchaean to Palaeoproterozoic Iron Formations - Gawler Craton, S.A.
The Middleback Range iron ore deposits are the home of the Australian iron and steel industry, located 25 to 40 km to the west of the steel furnaces of the port of Whyalla on the east coast of Eyre Peninsular. They lie within an ~60 km long, north-south trending, series of discontinuous strike ridges of BIF reflected by a strong magnetic signature, and are situated in the central-eastern Gawler Craton. This pronounced ridge magnetic anomaly reflects a magnetite-rich BIF beneath an upper supergene hematite modified zone that averages 90 m in thickness. Hematite deposits include Iron Knob, Iron Monarch, Iron Prince, Iron Princess, Iron Baron, Iron Queen, Cavalier, Iron Chieftain, Iron Duke and Iron Duchess. These deposits lie within a broad region of high magnetic intensity that reflect the ~3.24 to 3.15 Ga Mesoarchaean units that are the basement to the 5000 m thick, late Neoarchaean to Palaeoproterozoic (~2.5 to ~1.73 Ga), Hutchison Group, which comprises a mixed sequence of chemical and clastic metasedimentary, volcanic and intrusive rocks that were variably deformed during the 1.73 to 1.69 Ga Kimban Orogeny. The Hutchison Group is interpreted to include a lower, ~2.5 Ga Middleback Group, comprising quartzite, dolomite, Lower Middleback Jaspilite, amphibolite, quartz-biotite-muscovite-sillimanite-garnet-tourmaline schist and Upper Middleback Jaspilite (Szpunar et al., 2011). These rocks have, until recently, been regarded as being ~1.8 Ga. They are now interpreted to be unconformably overlain by two younger sequences, the lower of which includes pelitic schist, quartzites, amphibolites and the 1.79 Ga Myola Volcanics rhyodacite, while the younger is composed of the 1.75 Ga McGregor Volcanics which are bimodal, acidic and lesser basaltic volcanic rocks and overlying metasiltstone, interbedded with iron-rich calc-silicate rocks (Szpunar et al., 2011). The Middleback Range deposits are hosted by the Lower Middleback Jaspilite of the Middleback Group which is found across the Gawler craton. The Lower Middleback Jaspilite is a carbonate facies iron formations of iron carbonate, silica and iron oxides which weathers to porous goethite-limonite rocks at surface. Sulphide facies and graphite are intercalated at depth. The unit becomes more siliceous and iron oxide rich higher in the sequence with prominent iron bearing silicates, including iron rich talc and cummingtonite-grunerite series amphiboles. The hematite mineralisation consists almost entirely of fine-grained, dense and generally massive hematite, locally overprinted by a later generation of hematite in the form of bands or veins of coarsely crystalline, specular hematite. The Iron Magnet deposit, which lies down-dip and lateral to the Iron Duke hematite deposit, represents a hypogene enriched magnetite BIF that has not undergone supergene modification, and is an example of the magnetite resources of the Middleback ranges. The magnetite mineralisation is hydrothermal in origin, with the bulk of the ore occurring as pervasive and selective replacement, locally to massive magnetite, accompanied by lesser magnetite breccia. Production + resources of hematite are >350 Mt @ ~60% Fe, with current magnetite resources of ~230 Mt @ ~39% Fe.
The Warramboo iron deposits, in central Eyre Peninsula, ~150 km to the west of the Middleback Ranges, are most likely of the same age as the Middleback Group. These deposits, which are up to 300 m thick, have a indicated + inferred resource of 2.6 Gt @ 16% Fe, 53% SiO2, 13% Al2O3, 0.08% P, and have undergone high grade metamorphism to produce a coarsely crystalline magnetite-quartz ore with 1.5 mm average crystal size. This ore, although low grade, can be easily disaggregated to a very coarse grind size (106 to 125 µm) and subjected to dry magnetic separation, to produce a premium high grade iron concentrate product, transported to the coast by slurry pipeline, and sold as sinter feed magnetite fines (Iron Road Ltd, 2013).
Extensive pre-1.75 Ga iron formations in the Mount Woods Inlier of the north-eastern Gawler craton may be either Middleback Group equivalents, or part of a Palaeoproterozoic sequence. The host succession has been metamorphosed to amphibolite to granulite facies, and overprinted by regional, early Mesoproterozoic IOCG-style alteration. Small high grade DSO mines include the specular hematite Peculiar Knob, with resources of 32.5 Mt @ 63.2% Fe and the Cairn Hill magnetite-copper-gold deposit with 11.4 Mt @ 49.5% Fe, 0.4% Cu, 0.1g/t Au. Some early Mesoproterozoic (1.60 to 1.57 Ga) IOCG deposits in the craton, are to produce by-product magnetite concentrates, e.g., Hillside on Yorke Pensinsular, with resources of 226 Mt @ 0.7% Cu, 0.18 g/t Au, 14.1% Fe. Other, large IOCG-related magnetite accumulations are known along the eastern margin of the craton, mostly at depths too great to be economic, e.g., Acropolis containing ~500 Mt @ ~60% Fe.
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Late Palaeoproterozoic Kimberley Basin - Northern W.A.
The Kimberley Basin occurs as a preserved 400 x 400 km block composed of a >10 000 m thick sequence of shelf sandstones and siltstones, with minor dolomite. This sequence incorporates a ~600 to 1300 m thick basaltic unit (the Carson Volcanics, near the middle of the sequence), an ~3000 m thick sill to locally extrusive tholeiitic dolerite, granophyre and lesser gabbro (towards the top of the succession), and a late, ~900 m thick sill of quartz feldspar granite porphyry (mainly in the ore deposit area). The host Yampi Member was deposited between 1880 and 1760 Ma, and comprises a well bedded white, hematite bearing (in matrix) and hematite sandstone (in grains) with minor arkose and numerous thin phyllite and an impersistent basal conglomerate. This unit disconformably overlies a widespread siltstone unit, which is, in turn, separated from the underlying Carson volcanics by ~500 m of sandstone. The deposit is found on the SW margin of the basin, where it overlaps the pre-existing NW-SE trending King Leopold Mobile Belt that remained active through the deposition of the basin. The orebodies, at Yampi Sound, Koolan Island, Cockatoo Island and Irvine Island occur as a clump of contiguous deposits on the western margin of the preserved basin. They are restricted to hematite-rich basal conglomeratic sections of the Yampi Member, which grades into hard friable hematite with irregular and impersistent intercalations of hematite sand and hematite conglomerate. The hematite is present as both or either interstitial or clast material. Much of the ore is porous and appears to have undergone de-silicification which has enhanced the iron grade. In places, the siliceous cobbles of the conglomerates have been replaced by hematite. The host sediments have been folded into overturned synclines and anticlines. The Main Ore Body on Koolan Island was 2000 m long, up to 30 m thick and was mined from a height of 180 m to sea level, and has been drilled to 190 m below sea level with un-diminished grades of 66 to 67% Fe. Estimated total production + current resources of the group of deposits are of the order of 150 Mt @ ~64% Fe.
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Neoproterozoic Deposits in S.A., N.S.W., Queensland, N.T. and Tasmania,
Significant Neoproterozoic deposits and provinces include:
The magnetite-rich Braemar Iron Formation, within the basal sedimentary sequence of the Umberatana Group, located along the Nackarra Arc of the Adelaide Fold Belt, in South Australia and immediately adjacent far western NSW. The north-south oriented Adelaide Fold Belt represents a complex system of successive intracratonic rifting and subsequent basin formation associated with the prelude to the break-up of Rodinia. It persists from Kangaroo Island in the south, to the northernmost Flinders Ranges to the north. The ~400 km long Nackarra Arc forms a curvilinear structural arc that extends from northeast of Adelaide in the south, to Broken Hill (NSW) in the east, forming the southeastern limit of the Adelaide Fold Belt, immediately inboard of the Tasman Line that marks the margin of the Australian segment of Rodinia following breakup of the supercontinent. The sedimentation of the diamictite-dominant Umberatana Group coincides with Sturtian (Rapitan) Glaciation (750 to 700 Ma). The Braemar Iron Formation is thickest within the fault bounded Baratta Trough in the Yunta-Olary region of the Nackarra Arc of S.A. It is also evident in the Hawsons Knob area, south-west of Broken Hill in New South Wales and is stratigraphically equivalent to the Holowilena Ironstone of the Central Flinders Ranges, in S.A. It has been suggested that the Braemar Iron Formation was the result of chemical precipitation during interglacial/postglacial periods. The base of the Umberatana Group is occupied by the Pualco Tillite, that unconformably overlies sedimentary rocks of the Neoproterozoic Burra Group and comprises glaciogenic feldspathic siltstones, sandstones and greywackes. The Pualco Tillite is transitionally overlain by the Benda Siltstone, which is, in turn, disconformably overlain by thin dolomites and siltstone members. Ferruginous facies of both the Pualco Tillite and Benda Sandstone form the Braemar Iron Formation, that occurs at the top of the main glacial sequence and comprises interbedded/interlaminated, bedded and tillitic iron-rich sediments (ironstones). The ironstones occur as prominent outcrops and are interbedded with diamictites, dolostones, sandstone, siltstone and manganiferous siltstone which are regionally mappable with aeromagnetic data. Regional deformation, folding and faulting occurred during the Delamerian Orogeny (~514 to 500 Ma) resulting in open to tight folded patterns with a north-easterly orientation, and low-pressure, intermediate- to high-temperature metamorphism resulting in mid-greenschist facies rocks. The magnetite-dominant ironstone studied at Hawsons in NSW contains abundant blocky 25 to 150 µm subhedral to euhedral magnetite grains. The magnetite is generally inclusion free, and dispersed to weakly-banded within a simple quartz-biotite+chlorite silicate matrix of similar grain size. The texture is granoblastic to weakly lepidoblastic, with biotite (dominant) and/or regressive chlorite forming an irregular schistosity and few other minerals. The ore is soft and easily broken to separate into clean magnetite and silicate fractions that may be subjected to magnetic separation. There are a string of deposits distributed over a >250 km strike length, close to established towns, the Broken Hill to Port Pirie railway line and power lines. Deposits include Hawsons in NSW (1.4 Gt @ 15.5% magnetite DTR with a concentrate grade of 69.9% Fe); Razorback in SA (537.2 Mt @ 25.5% Fe, with an exploration target size of 4.8 to 8.0 Gt @ 18 to 45% Fe% magnetite DTR); Mutaroo Project (Muster Dam inferred resource 1.5 Gt @ 15.2% magnetite DTR with a concentrate grade of 69.8% Fe, and an Exploration Target of 2.4 to 4.0 Gt @ 15 to 18% magnetite DTR); Maldorky (indicated resource 156.7 Mt @ 29.3% Fe).
Ironstone beds within the South Nicholson Basin in NW Queensland and eastern Northern Territory outcrop around the rims of structural basins containing a 50 to 180 m sequence of Neoproterozoic siltstone, shale, sandstone and ironstone, dipping inwards at 15 to 30°. The mineralisation occurs in a number of beds that vary from 1 to 20 m in thickness of primary sideritic ironstone, composed of oolites of siderite, hematite and chamosite, with quartz grains, set in a matrix of siderite, hematite, minor quartz and carbon. Oxidation persists to depths of 10 to 30 m, producing a secondary hematite mineralogy with some limonite and quartz, which commonly retains an oolitic texture. Resources in the Constance Range district, ~180 km NW of Mount Isa, contain inferred resources at a number of sites within the basin of between 100 and 300 Mt @ 45 to 58% Fe.
Similar deposits are recognised in the Neoproterozoic of the upper Macarthur Basin in northeastern NT, where large-tonnage oolitic, pisolitic and massive hematite occur in the Roper iron field e.g., Hodgson Downs and Sherwin Creek, (with 488 Mt @ 41.7% Fe, including 41.1 Mt @ 57.8% Fe) and Roper Bar (with 402 Mt @ 40.0% Fe including 32.1 Mt @ 56.8% Fe).
The Savage River deposits of northwestern Tasmania - which lie within the 90 km long by 10 km wide, SE-dipping, NE-SW trending, Neoproterozoic Arthur Metamorphic Complex, which stretches across the island from near Wynyard on Bass Straight, to south of the Pieman River mouth on the Southern Ocean. It is a thrust-related structural corridor of increased schistosity and metamorphism separating early- to mid-Neoproterozoic sedimentary rocks to the NW from a variety of lower Palaeozoic rocks to the SE. The dominant unit within the complex is the Whyte Schist, subdivided into an eastern sequence of quartz-mica rocks including thin micaceous quartzite beds, schist and phyllite, and the western sequence of amphibolite, chlorite and albite schist or quartz-muscovite schist. The degree of metamorphism ranges from upper greenschist to amphibolite facies. The southeastern contact is gradational with the younger sedimentary rocks, while the basal contact between more strongly metamorphosed rocks with undeformed older rocks to the NW is more abrupt, defined by thrusts. The magnetite deposits of the Savage River operation are the largest of a series of lenses that extend in a narrow belt over a strike length of 25 km, hosted within a strongly sheared and strike-faulted belt of mafic and ultramafic schist (amphibolite) and mylonite. This belt is around 500 m in width, strikes NNE-SSW and is enclosed within the Whyte Schist. The magnetite ore, which ranges from 40 to 150 m in width, is almost entirely enclosed within ultramafic rocks, mainly serpentinite and talc-carbonate schist. The Main Ore Zone has a known strike length of 4 km and can occur as two or more thinner lenses. Down dip continuity is indicated to depths of up to 600 m. The ore may be massive, layered with metamorphic foliation parallel segregations, or disseminated, and ranges from fine-grained to coarsely crystalline. The magnetite ores comprise three volumetrically important groups: pyritic, serpentinitic and talc-carbonate ores. Pyrite and serpentinite are ubiquitous. Talc, tremolite, actinolite, antigorite, chlorite, epidote, dolomite, quartz and apatite occur in varying amounts. Production + resources amount to ~400 Mt @ >50% Fe that is transported 90 km to Bass Straight by slurry pipeline to be pelletised and exported.
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Tertiary Channel Iron Deposits (CID) of the Hamersley Ranges - Pilbara Craton W.A.
The channel iron deposits (CID) mined in the Hamersley Province account for up to 40% of the total iron ore mined from the Hamersley Province of Western Australia. These deposits are of Miocene age and occupy meandering palaeochannels in a mature surface composed mainly of Archaean rocks containing iron formations. These palaeochannels are generally less than 1 km but can range to several kms in width and from 1 to more than 100 m thick. The Robe and Marillana/Yandi palaeochannels in the western and eastern Hamersley Province respectively contain the principal CID resources currently being mined. These two major CID channels extend over 100 to 150 km lengths, with the Robe system being up to 5 km wide. Other channel systems include the Solomon/Serenity, Rocklea, Caliwingina and West Pilbara channel deposits.
Known economic CID resources within the province exceed 12 Gt with grades of 56 to 58% Fe. The CIDs are dominated by goethitic granular facies, which are typically composed of ooids and lesser pisoids with hematite nuclei and goethite cortices, abundant goethitised wood/charcoal fragments and goethitic peloids, all cemented by goethite (Morris and Ramanaidou, 2007). The goethite was produced by chemically precipitated iron hydroxyoxides, derived from leaching of iron-rich soils in an organic environment. Common post depositional weathering produced secondary facies (Morris, 2007). In contrast, the often associated younger detrital ores, which are predominantly of Pliocene age, comprise colluvial/alluvial deposits of modified clasts of older proximal BIF mineralisation. These deposits are generally much more limited in total tonnage than the CID of BIF hosted hematite deposits.
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The most recent source geological information used to prepare this summary was dated: 2012.
This description is a summary from published sources, the chief of which are listed below.
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