Groote Eylandt

Northern Territory, NT, Australia

Main commodities: Mn
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The Groote Eylandt manganese deposit is located on the island of Groote Eylandt in the Gulf of Carpentaria, Northern Territory, Australia, some 50 km from the coast of Arnhem Land and 650 km ESE of Darwin.

Groote Eylandt lies on the eastern margin of the Proterozoic McArthur Basin.   The ore deposit is developed within flat lying Cretaceous rocks deposited unconformably on a basement of Palaeoproterozoic crystalline rocks and Mesoproterozoic quartzites.   The Cretaceous rocks may exceed 100m in thickness and comprise early to middle Cretaceous Mullaman Formation sediments deposited in two small local basins.

The northern basin contains un-fossiliferous quartz sandstones derived from the basement quartzites, overlain by a shallow marine glauconitic claystone, the top of which bears the primary pisolitic and oolitic manganese ores, and which are followed by the secondary ores, concretionary manganese and weathering products of variable age.

The southern basin sequence is dominated by sandy siltstone which is calcareous in part and contains manganese carbonate oolites at a deeper stratigraphic level and minor manganese oxide cemented sandstones near surface.

The orebody comprises mainly primary pisoliths and ooliths which occur as an almost continuous layer some 22 km long, 6 km wide and up to 9 m, but averaging 3 m thick within the sandy layers of the Mullaman Formation.   The manganese varies from massive oxides, through a mixture of oxides and kaolinitic clays and quartz sands to disseminated oxides in a sandy clay matrix.

The major ores are found either at a shallow depth or exposed in a series of WNW trending, joint controlled, partly infilled depressions between elongate inliers of basement quartzite, or they lie directly on broad terraces cut into the basement quartzite, or to the west as an almost continuous sheet that dips gently at 3° W

The ore minerals are chielfy pyrolusite and cryptomelane with minor manganite.

To 1990 some 48 Mt of ore had been mined with 152 Mt @ +40% Mn remaining in situ.

For detail see 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:
Bolton B R, Berents H W, Frakes L A  1990 - Groote Eylandt Manganese deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v2 PP 1575-1579
Bolton B R, Frakes L A, Cook J N,  1988 - Petrography and origin of inversely graded manganese pisolite from Groote Eylandt, Australia: in    Ore Geology Reviews   v4 pp 47-69
Dammer D, Chivas A R, McDougall I  1996 - Isotopic dating of supergene Manganese Oxides from the Groote Eylandt Deposit, Northern Territory, Australia: in    Econ. Geol.   v91 pp 386-401
McIntosh J L, Farag J S, Slee K J  1975 - Groote Eylandt manganese deposits: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 5 pp 815-821
Ostwald J  1981 - Evidence for a biogeochemical origin of the Groote Eylandt Manganese ores: in    Econ. Geol.   v76 pp 556-567
Ostwald J  1992 - Genesis and paragenesis of the tetravalent Manganese Oxides of the Australian continent: in    Econ. Geol.   v87 pp 1237-1252
Ostwald J,  1990 - The biogeochemical origin of the Groote Eylandt manganese oxide pisoliths and ooliths, northern Australia : in    Ore Geology Reviews   v5 pp 469-490
Ostwald J,  1988 - Mineralogy of the Groote Eylandt manganese oxides: A review: in    Ore Geology Reviews   v4 pp 3-45
Pracejus B, Bolton B R  1992 - Geochemistry of supergene Manganese Oxide deposits, Groote Eylandt, Australia: in    Econ. Geol.   v87 pp 1310-1335
Pracejus B, Bolton B R, Frakes L A and Abbott M  1990 - Rare-earth element geochemistry of supergene manganese deposits from Groote Eylandt, Northern Territory, Australia: in    Ore Geology Reviews   v5 pp 293-314
Pracejus B, Bolton B R, Frakes L A,   1988 - Nature and development of supergene manganese deposits, Groote Eylandt, Northern Territory, Australia: in    Ore Geology Reviews   v4 pp71-98

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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