South Australia, SA, Australia
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The Warramboo iron deposit is located on central Eyre Peninsula in South Australia, 28 kms southeast of the regional centre of Wudinna, 190 km north of Port Lincoln, 200 km WSW of Whyalla and 150 km to the NW of the proposed port at Cape Hardy on Spencers Gulf (#Location: 33° 14' 33"S, 135° 40' 10"E).
The deposit lies within the Coulta Domain of the Gawler Craton. The southern section of the Gawler Craton is composed of a series of generally north-south to NE-SW trending domains, from east to west, the:
Olympic Domain, covering York Peninsula and hosting the SA IOCG Province. It comprises an arcuate zone of Palaeoproterozoic sedimentary and felsic igneous rocks and
Mesoproterozoic granite, volcanics, quartz-rich sediments and conglomerates. The Olympic Domain is characterised by the development of regional iron oxide alteration (Ferris et al., 2002).
Spencer Domain largely corresponding to Spencers Gulf and the southeastern coastal margin of Eyre Peninsula, from Port Lincoln to Whyalla, where it hosts the the Middleback Range iron deposits. The domain comprises irregularly shaped intrusives of the 1850 Ma (U-Pb zircon dating Fanning, 1997) Donington Granitoid Suite, ranging in composition from gabbro-norite to highly evolved
leucogranite, with Inter-folded inliers of Palaeoproterozoic Hutchison Group metasediments. It is separated from the Cleve Domain to the NW by the Kalinjala Mylonite Zone (Ferris et al., 2002).
Cleve Domain, which occupies the south-eastern Eyre Peninsula, is dominated by basinal sediments of the Palaeoproterozoic Hutchison Group, unconformably
overlying Palaeoproterozoic Miltalie Gneiss and Archaean paragneiss and orthogneiss with a metamorphic age of ~2440 Ma. Syn-tectonic intermediate to felsic Moody Suite (~1700 Ma) rocks intrude the Hutchison Group metasediments. The Cleve Domain is separated from the Coulta Domain to the NW by a major northeast trending shear zone (Ferris et al., 2002).
Coulta Domain, which trends NE-SW and forms much of central Eyre Peninsula, varies from 40 to 60 km in width. This domain is dominated by Archaean metasedimentary and volcanic rocks of the Sleaford Complex, and high level, granitoid intrusives of the ~2517 Ma (U-Pb, Fanning, 1997) Dutton Suite, although a younger suite of gneisses dated at ~1900 to 1750 Ma, suggesting they unconformably overlie the older complex. The northern boundary of the complex with the Gawler Range Volcanic Domain, largely composed of ~1590 Ma felsic volcanic rocks, is inferred to be an east-west trending shear zone stitched by Hiltaba Suite (~1590 Ma) plutons. The western boundary with the Nuyts Domain is a faulted margin, juxtaposing rocks containing significantly younger intrusives (Ferris et al., 2002).
Nuyts Domain, representing much of western Eyre Peninsula to its SW coast with the Great Australian Bight of the Southern Ocean. The Domain comprises possible Palaeoproterozoic, ductile deformed metasediments and meta-igneous rocks into which extensive, variably magnetic, Palaeoproterozoic to Mesoproterozoic granitoids were emplaced. The domain is broadly delineated by a distinctive gravity low, reflecting its predominantly felsic igneous composition. A noticeable feature is the concentration of large Hiltaba Suite plutons around its structurally controlled northern and eastern margins (Ferris et al., 2002).
The Warramboo deposits are associated with a prominent arcuate-linear, east-west trending, complex magnetic anomaly with a length of ~50 km. Drilling at the Warramboo prospect has identified the source of this anomalous zone as a coarse-grained, granulite facies, metasedimentary magnetite-bearing gneiss that has been intensely folded. These rocks are all overlain by unconsolidated aeolian sands and calcrete.
Zircon U-Pb geochronology of the country rock at Warramboo, the enveloping barren gneiss, indicates that sedimentary protoliths to the gneiss were deposited at ~2480 to 2470 Ma, with coeval igneous intrusions, regarded as being consistent with the Sleaford Complex basement rocks. Lane (2013) identified additional, substantially younger, zircon populations within the Warramboo magnetite gneiss, with ages of ~1900 to 1750 Ma, suggesting they unconformably overlie the Sleaford Complex basement. Monazite-based U-Pb geochronology data from Warramboo indicate these rocks were deformed and metamorphosed during the ~1735 to 1700 Ma Kimban Orogeny, suggesting the magnetite gneiss formed at the same time, through in situ concentration of Fe minerals during melting/migmatisation of an iron-rich pelite, and melt loss within the magnetite-bearing gneiss associated with high temperature metamorphism. During this process, the 'gangue' minerals are interpreted to have concentrated into migrating silicate melts, leaving the Fe-rich magnetite mineralisation as a residue. These younger gneisses are similar in age and lithology to the ferruginous, 1750 Ma, Price Metasediments, further south on the western margin of the Peninsula, west of Port Lincoln (Lane and Iron Road Ltd, 2013). These rocks would be of a similar age to the Wallaroo Group that is widespread in the Olympic Domain to the east.
The magnetite mineralisation is characterised by two main rock types. The first is a disseminated magnetite-gneiss and the other is a banded magnetite gneiss comprising layers of both disseminated and coarse-grained magnetite. In the oxidation profile, the magnetite has been altered to martite (hematite), maghemite (hematite and magnetite) and goethite. Petrological examination of drill chips and core shows the magnetite gneiss to be an irregularly layered, granulose metamorphic rock which may be called a microgneiss with an incipiently hornfelsic texture. This sequence is not a BIF, but an iron rich sediment clastic sedimentary rock (Lane et al., 2014).
The main deposit is composed of mineralisation that occurs as a number of structurally repeated, generally east-west striking, bands of 'higher grade' magnetite gneiss, that are 20 to >60 m thick, dipping south at <30 to near 90° over a width of 600 m and strike length of >3 km. To the north and south, the Warramboo magnetite gneiss package is bounded by barren Sleaford Gneisses composed of quartz, feldspar, garnet, sillimanite, cordierite and biotite rich metasediments and Quartz-feldspar-biotite±garnet meta-igneous rocks (Lane et al., 2014).
In more detail, over this strike interval, there are four main parallel, east-west striking bands, composed of two to the north (Dolphin and Boo-Loo) and two to the south (Murphy South and Rob Roy). The magnetic anomaly suggests that each of these pairs appears to represent limbs of a structures that close to the east.
The deposit comprises a large uniform and coarse-grained, orebody. Metallurgical testing and marketing studies indicate that a -106 µm (80% passing) product will be attractive to standard blast furnace sinter plant operations. Due to the coarseness of the concentrate, pelletising will be unnecessary. The concentrate is to be marketed as high quality sinter feed stock, suitable for blending with lower grade "earthy" Pilbara style fines. The attractive physical and chemical characteristics of the ore body, and its coarse grain size and simple liberation, is expected to allow efficient processing of the low head grades of the ore (Coffey Mining Ltd, 2014).
Ore reserves and mineral resources at February 2014 were (Coffey Mining Ltd for Iron Road Limited):
Ore reserves (using and 8% Fe cutoff):
Murphy South-Rob Roy
Proved reserve - 1871 Mt @ 15.6% Fe;
Probable reserve - 200 Mt @ 15.1% Fe;
TOTAL reserve - 2071 Mt @ 15.5% Fe.
Mineral resources (using and 8% Fe cutoff):
Murphy South-Rob Roy
Measured resource - 2222 Mt @ 15.69% Fe, 53.7% SiO2, 12.84% Al2O3, 0.08% P;
Indicated resource - 474 Mt @ 15.6% Fe, 53.7% SiO2, 12.8% Al2O3, 0.08% P;
Inferred resource - 667 Mt @ 16% Fe, 53% SiO2, 12% Al2O3, 0.08% P;
Inferred resource - 328 Mt @ 17% Fe, 52% SiO2, 12% Al2O3, 0.09% P;
TOTAL resource - 3.691 Gt @ 16% Fe, 53% SiO2, 13% Al2O3, 0.08% P - equivalent to 880 Mt @ 67% Fe (the concentrate grade)
Concentrate grade - 67% Fe, 3.3% SiO2, 1.9% Al2O3, 0.005% P.
The most recent source geological information used to prepare this summary was dated: 2014.
This description is a summary from published sources, the chief of which are listed below.
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