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Magellan, Cano, Pinzon, Drake

Western Australia, WA, Australia

Main commodities: Pb
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The Magellan and associated Cano, Pinzon and Drake lead carbonate deposits are located in the East Murchison Mineral Field, approximately 30 km north-west of Wiluna and 900 km northeast of Perth in Western Australia. The port of Esperance is 990 km by road and rail to the south (#Location 27° 14'S, 119° 57'E).

It is a sub-horizontal sheet of lead oxide mineralisation within 45 m of the surface, within the south-eastern corner of the Yerrida Basin, one of several Proterozoic basins separating and lapping onto the Pilbara and Yilgarn Archaean cratons to the north and south respectively. The Yerida Basin is part of the 2.2 to 1.8 Ga Capricorn Orogen and is the eastern basin of what was earlier mapperd as the larger Glengarry Basin. It comprises a sag basin succession of siliciclastics and evaporites and a volcano-sedimentary rift basin succession.

The generalised stratigraphic column for the Magellan region is as follows:

Archaean granite and greenstone which form the basement.
Unconformity
Yerrida Group
Juderina Formation, comprising the,
    Finlayson Member which is about 600 m thick and is composed of the a lower sequence of mature quartz sandstone and an upper sequence of siltstone and extensively silicified stromatolitic dolomite.
    Upper members of the Juderina Formation are locally missing;
Unconformity
Maraloou Formation, comprising 250 m of black carbonaceous shale.
Dolerite sills of the >700 m thick Killara Formation intrude the Maraloou Formation to the north of Magellan.
Unconformity
Earaheedy Group
Yelma Formation, which is preserved as an outlier forming a WNW trending, ~5 x 2.5 km mesa unconformably resting on Maraloou Formation, and represents a gentle syncline with a NW-trending axis. Other outliers of the same unit unconformably overlie either Finlayson Member or Maraloou Formation. Drill testing of these over an area of 200 sq. km indicates they have consistently elevated lead levels.

The Magellan deposit is hosted by carbonate and sandstone units of the Yelma Formation unconformably overlying Yerrida Group sediments. At Magellan the Yelma Formation comprises a basal sandstone unit, fining upward into a siltstone and claystone, which are in turn overlain by a quartz-clay (collapse) breccia that grades laterally into an unaltered stromatolitic dolomite, locally with vugs filled with crystalline quartz.

The fresh basal sandstone is a grey-green in colour, and is a 10 to 15 m thick, medium- to coarse-grained carbonaceous quartz wacke, containing minor interbeds of conglomerate and siltstone. Oxidation of the sandstone imparts a tan colour. The sandstone has a transitional upper contact to a tan siltstone in the top 2 to 4 m of the unit.

The quartz-clay breccia, which overlies the basal sandstone-siltstone unit, is up to 35 m thick and comprises fragments of silicified stromatolitic carbonate, chert, siltstone, vuggy euhedral crustiform quartz and colloform banded quartz. The breccia fragments range from 10 to 100 mm in diameter and are enclosed within a clay matrix. The upper 20 m of the quartz-clay breccia unit was intensely weathered during the Tertiary to form a silcrete layer.

The Yerrida Basin and the underlying Archaean basement are cut by a major NNW- and east-west trending fault systems transect the Yerrida Basin and the underlying Archaean basement. Bedding dips at a very shallow angle, rarely exceeding 5°.

The lead mineralisation occurs as a sub-horizontal sheet, hosted entirely within the YeIma Formation, composed of (in order of decreasing abundance) cerussite, anglesite, pyromorphite and coronadite (PbMn8016). Plattnerite (Pb02) has also been noted. Sulphide minerals are absent.

While cerussite is by far the dominant mineral, some vertical zoning is obvious, with an anglesite becoming the major component above the thickest parts of the deposit. The bulk of the lead oxide ore is hosted by the quartz-clay breccia unit, although the sandstones and claystones beneath this breccia also contain significant lead oxide mineralisation but only where weathering has occurred, indicating supergene enrichment and redistribution of the lead. Only low lead values are encountered in the upper, silcrete portion of the quartz-clay breccia unit.

Zinc grades are very low, with the Zn:Zn+Pb ratio being of the order of 1: 1000. Zinc is particularly strongly leached in the upper portion of the deposit and tends to increase gradually to several hundred ppm towards the base of oxidation. The Maraloou Formation carbonaceous shales contain up to 0.5% Zn immediately beneath the highest grade parts of the Magellan deposit.

The Magellan group of deposits are thought to represent the residue from extensive ancient sediment-hosted base metal mineralisation that has undergone prolonged weathering, dissolution, volume reduction and oxidation of the lead minerals. This residue was preserved when the climate changed to an arid environment before the heavier lead minerals were washed away.

The main Magellan deposit was discovered in 1991 with Cano identified in 2001 and Pinzon in 2004. The resources, as estimated at December 31, 2005, to a cut-off @ 2.5%Pb, are:

   Magellan - Measured + Indicated 13.9 Mt @ 6.0% Pb    + Inferred 3.3 Mt @ 5.0% Pb
   Cano - Measured + Indicated 2.7 Mt @ 5.6% Pb    + Inferred 0.1 Mt @ 4.4% Pb
   Pinzon - Measured + Indicated 4.8 Mt @ 5.3% Pb    + Inferred 1.5 Mt @ 4.2% Pb
   Drake - Inferred 2.3 Mt @ 4.4% Pb
   Total - Measured + Indicated 21.4 Mt @ 5.8% Pb    + Inferred 7.2 Mt @ 4.6% Pb

This resource is part of a much larger zone of lower grade mineralisation that at a 0.1% Pb cutoff comprises 210 Mt at 1.8% Pb.

The most recent source geological information used to prepare this summary 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.


  References & Additional Information
   Selected References:
McQuitty B M and Pascoe D J,  1998 - Magellan lead deposit: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne   Mono 22 pp 293-296


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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