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Razorback

South Australia, SA, Australia

Main commodities: Fe
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The Razorback iron deposit is located ~240 km NNE of Adelaide and 125 km ENE of Port Pirie in South Australia (#Location: 32° 57' 22"S, 139° 42' 55"E).

The magnetite-rich host rocks of the Razorback deposit belong to the Braemar Iron Formation, section of the basal sedimentary sequence of the Neoproterozoic Umberatana Group, located within the Nackarra Arc of the Adelaide Fold Belt. 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, while the Nackarra Arc forms a curvilinear structural arc that extends from east of Adelaide 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 Glaciation (750 to 700 Ma). The Braemar Iron Formation is thickest within the Baratta Trough, a fault bounded basin located in the Yunta-Olary region of the Nackarra Arc of South Australia. 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, also in South Australia. It has been suggested that the Braemar Iron Formation was the result of chemical precipitation during interglacial/postglacial periods. In the Baratta Trough, the base of the Umberatana Group (and Yudnanuta Subgroup) is occuppied by the Pualco Tillite, that unconformably overlies sedimentary rocks of the Burra Group and comprises glaciogenic feldspathic siltstones, sandstones and greywackes. The Pualco Tillite is transitionally overlain by the Benda Siltstone. The Benda Siltstone is in turn disconformably overlain by thin dolomites and siltstones of the Wilyerpa Formation and Warcowie Member. Ferruginous facies of both the Pualco Tillite and Benda Sandstone are informally referred to as the Braemar Iron Formation.

The Braemar Iron Formation occurs at the top of the main glacial sequence and comprises interbedded/interlaminated iron formations, bedded iron formations and tillitic iron formations. In the areas around the Razorback deposit, Braemar Iron Formation 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. Delamerian Orogeny low-pressure, intermediate- to high-temperature metamorphism produced mid-greenschist facies rocks in the Razorback deposit area.

The Razorback Ridge iron deposit is located on the ~42° north dipping limb of the Pualco Anticline. The Braemar Iron Formation at Razorback has been divided into seven sedimentary packages, annotated A to G, with a total thickness of between 480 to 780 m. Of these, members B, D and G are of economic interest, all of which outcrop at surface, with Unit B forming a prominent ridge.

Mineralisation at Razorback has good continuity along the ~3 km strike length and generally dips at between 40 and 45°. Unit B on average is ~70 m thick, while Unit D is ~30 m thick, with grades of between 24 and 27% Fe. Drilling indicates only minor faulting and minor weathering at surface. The latter has been further divided into three easily recognised subunits, B1, B2 and B3 which are marked by well defined lithological contacts. B1 is characterised by a bedded, magnetite-rich siltstone, with minor thin beds of dolomitic siltstone and fine sandstone, and is overlain by Unit B2, a tillitic/diamictitic ferruginous siltstone with varying dropstone content. This in turn is overlain by Unit B3, an interlaminated iron-rich siltstone, much like Unit B1, but with increased siltstone/sandstone interlaminations.

Unit D comprises a bedded ferruginous siltstone (D1) overlain by a ferruginous tillitic unit (D2), followed by an interlaminated iron formation (D3), while Unit G occurs as 0.30 to 1 m thick interbedded magnetite-rich siltstone and shale.

The bedded or laminated ore has a dense black to dark grey ultra-fine matrix of magnetite with infrequent grey to white dolomitic siltstone/sandstone interbeds or interlaminations. The magnetite is well bedded, forming laterally continuous beds, with the aforementioned siltstone/sandstone interbeds appearing every 5 to 20 cm, with thicknesses ranging from fine laminae to 5 cm. Siltstone/sandstone beds are lenticular and commonly discontinuous. Sedimentary structures are frequent throughout and are especially noticeable along magnetite/siltstone margins, including water-escape structures. Soft-sediment deformation is also obvious and is characterised by convolute laminations and slumped beds with low angle cross bedding.

The tillitic ore is a medium to dark grey ironstone formation, characterised by a massive unit, containing erratics ranging in diameter from 10 mm to 1 m in diameter within an ultra-fine matrix of magnetite. The lithic fragments are typically laminated sediments and granite. In general the clasts are sporadic and make up between 5 and 20% of the orebody with a variable sand component of <5% at the Razorback Ridge resource.

Inferred Resource in mid 2011 were stated at (Flis et al., 2011 and Royal Resources website, 2012):
    537.2 Mt @ 25.5% Fe, 41.4% SiO2, 6.7% Al2O3, 0.20% P, 4.8% LOI.
The project has an exploration target size of 4.8 to 8.0 Gt @ at grades of 18 to 45% Fe.

Mineral resources in January 2013 were stated at (Royal Resources ASX Release, January, 2013):
  Razorback deposit
    Indicated resource 980 Mt @ 21.6% Fe, 43.0% SiO
2, 7.0% Al2O3, 0.21% P,
    Inferred resource 520 Mt @ 19.6% Fe, 45.8% SiO
2, 7.4% Al2O3, 0.25% P,:
  Iron Peak
    Indicated resource 213 Mt @ 21.0% Fe, 45.0% SiO
2, 7.4% Al2O3, 0.18% P,
    Inferred resource 103 Mt @ 21.4% Fe, 44.6% SiO
2, 7.4% Al2O3, 0.18% P,
  For a combined resource of 1.8 Gt @ 21% Fe, including an indicated resources of 1.2 Gt @ 21.5% Fe.

Overall, the ore produces a low contaminant, high iron content (>67% Fe) magnetite concentrate at grind sizes of 45µm. Both magnetite (16%) and hematite (4%) are to be recovered. An overall strip ratio of 0.79:1 is anticipated (Royal Resources ASX Release, January, 2013).

Davis Tube Recoveries (DTR) grades are of hematite fines equivalent grade’ at 106 µm grind size, and DRI quality (>67% Fe) at the 45 µm grind size. DTR Weight Recoveries of 18.3 to 27.4% were observed for the interbedded (Unit B3) and bedded magnetite (Unit B1), producing 57.6 to 68.4% Fe concentrate grades. The tillitic unit (Unit B2), with iron grades down-graded in ore by the presence of magnetite-poor dropstones, has the lowest Weight Recovery of the three units, at 11 to 15.1%, but with similar concentrate grades to Units B1 and B3. Magnetic recovery weights are improved in this unit with the removal of dropstones through magnetic cobbing (dry, coarse magnetic separation) during beneficiation.

The deposit is close to both the existing heavy-duty Broken Hill-Port Pirie railway line and trunk electricity transmission lines, and to a number of regional centres of population, while being in semi-arid grazing land.

The most recent source geological information used to prepare this summary was dated: 2011.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
   Selected References:
Flis, M., England, G. and Thomas, T.,  2011 - Razorback Iron Ore Project - A New Iron District to Meet the Growing Demand of an Iron Hungry World: in   Proceedings, Iron Ore 2011 Conference, 11-13 July 2011, Perth, Western Australia, The Australasian Institute of Mining and Metallurgy, Melbourne,    pp. 615-623


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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