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Southdown |
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Western Australia, WA, Australia |
| Main commodities:
Fe
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Southdown magnetite deposit is located some 90 km NE of the Southern Ocean port of Albany within the Albany-Fraser Orogen, of south-western Western Australia.
The Albany-Fraser province is situated along the southern and southwestern margin of the Yilgarn Craton and consists mainly of highly deformed orthogneiss and less abundant paragneiss, mafic and felsic granulites, granitoids, metagabbros and widespread metasedimentary rocks. It also includes the 1300 Ma Fraser Complex which is a thrust stack of mainly gabbroic rocks metamorphosed to granulite facies. The orthogneisses are a product of Mesoproterozoic orogenic reactivation of Late Archaean, Palaeo- and Mesoproterozoic granitic rocks. Most of the granitoids are Proterozoic in age, and were accompanied by metamorphism and deformation representing at least two events, longitudinally dividing the province into two parts, the:
i). Biranup Complex (or supersuite) in the north-west, intruded at around 1700 to 1600 Ma, mostly composed of heterogeneous orthogneiss. This complex outcrops over an area of 9600 sq. km., trending in a NE direction with dimensions of around 400x100 km, and
ii). Nornalup Complex (or supersuite) in the south-east, which appears to include granites intruded at two ages, approximately 1300 and 1190 Ma. It is dominated by heterogeneous ortho- and paragneisses.
The Southdown deposit is hosted by the Biranup Complex which consists of quartzo-feldspathic gneisses, mainly derived from older granitoid precursors, interlayered with lesser metasedimentary rocks and metagabbro. The sequence has been intensely deformed with all primary layering having been transposed and the rocks recrystallised to produce granoblastic textures. SHRIMP dating of gneisses has returned ages of from 1634±26 Ma (biotite-hornblende granodiorite gneiss) to 1695±16 Ma (hornblende syenogranite gneiss).
Drilling indicates that the deposit comprises a gently east-plunging, overturned, tightly folded synform that is offset by both northwest and northeast trending faults. The core of the synform is complexly folded and occupied by intensely metamorphosed quartz-magnetite-clinopyroxene gneiss and garnet-biotite gneiss, including an infolded narrow, irregular band of quartz-sulphide gneiss. The vertical depth to the synform keel is approximately 300 m in the western end of the deposit and increases to >400 m the eastern portion of the deposit. The thickness of the magnetite mineralisation ranges from 70 to 100 m averaging 85 m. Detailed magnetic surveys indicate that the deposit extends over a strike length of approximately 12 km. The 2006 resource below relates to the eastern half of the mineralised system alone, while the 2012 resource also includes the western 6 km that had previously not been tested.
The country rock flanking the synform is composed of quartz-biotite gneiss, which grades inwards to a narrow band of feldspar-pyroxene gneiss, before another band of quartz-biotite gneiss and the core of quartz-magnetite gneiss described above.
Resources at the end of 2006 (Grange Resources, 2007) were:
- Indicated Resource: 347.2 Mt @ 38.1 wt% Fe, to produce a concentrate of 69.1% Fe, 1.9% SiO2, 1.4% Al2O3, 0.37% TiO2, 0.44% S, 0.05% Na2O, 0.09% K2O, 0.002% P, 0.23% MgO, 0.17% CaO, 0.035% Mn, 0.022% V, -2.8% LOI.
- Inferred Resource: 110.8 Mt @ 33.1 wt% Fe, to produce a concentrate of 68.9% Fe, 2.3% SiO2, 1.4% Al2O3, 0.41% TiO2, 0.58% S, 0.05% Na2O, 0.09% K2O, 0.002% P, 0.25% MgO, 0.20% CaO, 0.035% Mn, 0.023% V, -2.5% LOI.
- Total Resource: 458.0 Mt @ 36.9 wt% Fe, to produce a concentrate of 69.1% Fe, 2.0% SiO2, 1.4% Al2O3, 0.38% TiO2, 0.47% S, 0.05% Na2O, 0.09% K2O, 0.002% P, 0.24% MgO, 0.18% CaO, 0.035% Mn, 0.022% V, -2.7% LOI.
Resources at February 2012 (Grange Resources, 2012) were:
Measured - 423.0 Mt @ 37.6% Fe;
Indicated - 87.4 Mt @ 38.4% Fe;
Inferred - 710.6 Mt @ 31.5% Fe;
Total resources - 1221.0 Mt @ 34.1% Fe.
The plan in 2006 envisaged an annual mining rate of approximately 17 Mt of ore @ 36.6% Fe per annum, with a stripping ratio of approximately 2.6:1 to produce 6.5 Mt of 69% Fe concentrate. The nature of the ore allows for primary separation at a coarse particle size of 0.2 mm. This concentrate is to be piped as a slurry 100 km to Albany for dewatering and export to a pellet plant in Malaysia.
The most recent source geological information used to prepare this decription was dated: 2006.
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.
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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