Munni Munni Complex

Western Australia, WA, Australia

Main commodities: PGE PGM Pt Pd Au Cu Ni
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The Munni Munni Complex is a PGE bearing Archaean (2850 Ma) layered mafic-ultramafic complex within the Pilbara Craton, 45 km south of Karratha in north-wetern Western Australia.

The complex intrudes older granites generally dated between 3500 and 2800 Ma and is unconformably overlain by the late Archaean to Palaeoproterozoic Mount Bruce Supergroup of the Hamersley Basin.

The Munni Munni Complex covers an area of 225 sq. km (9x25 km) and is at least 5.5 km thick.   It is composed of a lower, 1850 m thick ultramafic series overlain by a >3630 m gabbroic series.

The ultramafic series is layered, dipping at 20 to 40° S and comprises a sequence of cyclically layered olivine cumulates and clinopyroxene cumulates.   Orthopyroxene and chromite are only significant in the upper 100 m of this series, the Websterite Zone.   Rock types include dunite, lherzolite, olivine websterite, clinopyroxenite and websterite, with porphyritic websterite, bronzitite and lesser chromite websterite, norite and minor chromitite in the Websterite Zone.

The gabbroic zone includes a lower interval of inverted pigeonite bearing gabbros and gabbronorites and an upper zone of interlayered magnetite bearing anorthositic gabbros and gabbronorites, with granophyres at the top and a series of quartz monzonites and quartz syenites in the south-east of the complex.

The PGE mineralisation is hosted by the porphyritic websterite of the Websterite Zone and is associated with an interval of copper-nickel sulphide accumulation some 0 to 15 m below the sharp ultramafic-gabbro contact.   The PGE layer has been defined over a strike length of more than 7.5 km (in 1990) and to a depth of 600 m and remained open along strike and down dip.

The porphyritic websterite comprises 0 to 15% olivine, 10 to 30% porphyritic bronzite and 60 to 80% augite with 0 to 20% intercumulus plagioclase.   It contains 1 to 2% chalcopyrite and pyrrhotite with trace pentlandite.   The PGE layer is generally 2 to 5 m (averaging 2.5 m) thick, at the base of the 5 to 15 m thick Cu-Ni zone (found 0 to 15 m below the gabbro-ultramafic contact).   PGE grades in the central portion average 1.0 g/t Pt, 1.6 g/t Pd, 0.3 g/t Au, 0.3% Cu, 0.2% Ni.

The resource potential in 1990 was of the order of 20 to 30 Mt @ approx 2.9 g/t Pt+Pd+Au, 0.3% Cu, 0.2% Ni to a depth of 500 m, enclosing significant but smaller tonnages of 5 to 7 g/t PGE .

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:
Williams C R, Nisbet B W, Hoatson D M  1990 - Munni Munni Complex Platinum group mineralisation: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 145-150

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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