Gibson Laterite

Western Australia, WA, Australia

Main commodities: Au
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The Gibson lateritic gold deposit is located some 15 km south of Mount Gibson in the Retaliation greenstone belt of the southern Murchison Province of the Archaean Yilgarn Craton in Western Australia.

The Retaliation greenstone belt comprises an east facing sequence of tholeiitic basalt overlain by felsic volcanogenic rocks in faulted contact with mafic rocks to the east. All are cut by north-south faulting.

The area is topographically flat with an extensive regolith and lateritic blanket formed during the Mesozoic and Tertiary, and covered by the products of Quaternary erosion.   Lateritic remnants at Gibson are 2 to 3 m thick.   On higher ground weathered sparse bedrock (mafic and felsic schists) and saprolite are exposed.   The auriferous laterite covers an area of 4 x 0.5 km, dipping east below sand and colluvial sandy pisolitic gravel (cemented to hard pan) up to 4 m thick.

The profile comprises, from the top:
Pisolitic sand - yellow sand with hematite and maghemite pisolites increasing in size and abundance with depth,
Laterite unit - with a gradational upper boundary from pisolite sand to hard cap cemented pisolites and nodules which comprise angular iron stained rock with skins of limonite, goethite, carbonate or silica which are the same as the cementing agent,
Saprolite zone - 5 to 20 m thick mottled purple, buff and white clays with iron staining due to ferricrete cement from above, and oxidation of sulphidic veins within the original bedrock.

Gold increases from the base of the transported cover to a peak of around 4 g/t Au just above the base of the laterite unit and rapidly declines at the top of the saprolite.

Basement mineralisation appeared to be associated with a multitude of vertical shear zones with an oxide cap averaging 5 g/t Au and an underlying sulphide interval with 4 g/t Au (with associates Ag-Cu-Zn-Bi-Sb-As).

Reserve figures include:
    Gibson laterites - 5.3 Mt @ 1.6 g/t Au (0.75 g/t Au cut-off, initial mineaable reserve, 1986),
    Hornet & Midway North basement oxide and sulphide ore - 2.44 Mt @ 4.5 g/t Au.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1990.    
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:
Gee R D  1990 - Gibson Lateritic Gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 259-264

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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