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Ellendale |
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Western Australia, WA, Australia |
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Diamonds
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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 Ellendale diamond deposits are a cluster of 48 lamproitic intrusions located 125 km ESE of Derby within the WNW trending Lennard Shelf to the south of the Kimberley Block in northern Western Australia.
The Ellendale pipes cut Palaeozoic sediments of the Lennard Shelf which lap onto the King Leopold Mobile belt to the immediate north, separating then from the stable Kimberley Block further north. The pipes lie within the the North Australian craton which contains Archaean remnants overlain by Proterozoic platform cover that has been subjected to a Palaeoproterozoic thermal metamorphic event at 2200 to 1800 Ma followed by post tectonic 1800 to 1700 Ma granites which completed cratonisation. While there have been no further thermal events in the King Leopold Mobile Belt, it has been the locus of subsequent tectonic adjustments between the more stable blocks it separates during the Neoproterozoic and from the Palaeozoic to the Mesozoic. There has been both compression (thrusting within the mobile belt in the Ordovician and Devonian) and extension to form the Fitzroy Trough rift basin with shelf sedimentation (the Lennard Shelf) abutting the mobile belt to the south-west from the middle Palaeozoic to the late Cretaceous, followed by a continueing period of emergence.
The Ellendale pipes are Miocene (22 to 19 Ma) in age and cut through 500 to 1500 m of Devonian to Permian platform cover over a Precambrian basement similar to that in the King Leopold Mobile belt. More than 100 lamproite intrusions are known over a 7500 sq. km area surrounding the Ellendale swarm, 48 of which are in the NW trending 40 x 10 km Ellendate field and 43 that are aligned parallel to one of the major NW trending detachments faults in the Lennard Shelf parallel to the King Leopold Mobile Belt structures. Some 45 of the Ellendale intrusives are volcanic crater deposits, while 3 are sills. The lamproites are both leucite and olivine rich, with 60% being diamondiferous. Of these 71% are olivine rich, 36% are leucite lamproites, while the only pipes with significant grades are olivine rich.
Typically the pipes have a wine glass shape, with a diatreme stem, passing up into broad, shallow maar craters with diameters from 100 m to more than 1 km, representing surface areas of 2 to more than 100 ha. The maar craters contain early pyroclastics and epiclastics intruded and overlain by later magmatic lamproite forming lava lakes and domes in the central parts of the crater.
Ellendale diamonds are lustrous, of high clarity, mainly yellow, shiny surfaced, rounded dodecahedra.
The first of the pipes was discovered in 1976, but none have proved economic for large scale development. The main pipes as tested by 1990 had the following properties:
Ellendale 4 - 76 ha area, with 14 cpht in the higher grade tuff and 0.5 cpht in the lamproite.
Ellendale 7- 36 ha area, with 1 cpht in the higher grade tuff and much less in the lamproite.
Ellendale 9 - 46 ha area, with 5 cpht in the higher grade tuff and 5 cpht in the lamproite.
Ellendale 11 - 13 ha area, with 1 cpht in the higher grade tuff and much less in the lamproite.
Proposals were approved in 2003 for an initial smaller scale operation to exploit the top 3 m of two pipes (Ellendale 4 and 9) in the weathered and upgrade zone which yields grades of around 26 carats per hundred tonnes (cpht) and 10.3 cpht respectively from a 1.3 Mt resource. The second phase is to mine to a greater depth to extract a resource of 34 Mt @ 7.7 cpht, which is expected to convert into a reserve of 20 Mt @ 12 cpht (Kimberley Diamond Co. NL release, 2003).
Diamonds were mine from two pipes, Ellendale 9 from 2002 until 2015 and Ellendale 4 from 2005 two 2009 (Ahmat, 2012). Although of low grade (5 to 14 cpht), the Ellendale diamonds are characterised by a high proportion (60 to 90%) gem-quality stones, including white, brown and yellow diamonds. High value yellow diamonds were a signature of Ellendale with the mine producing nearly half of the world's annual supply of the stone. Total production from the Ellendale diamond deposits was more than 2 million carats (Boxer, Jaques and Rayner, 2017). In 2015, the lease holder at Ellendale was placed in voluntary administration, blamed on lower recovered grades and lower size distributions than expected along with significantly lower realised prices.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2003.
Record last updated: 3/9/2020
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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Hughes F E, Smith C B 1990 - Ellendale Diamond deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1115-1122
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McConochie D M and Smith C B 1989 - Iron-oxides as palaeotemperature indicators in Ellendale lamproite intrusions: in Kimberlites and related rocks, Volume 1, Their origin, Occurrence and emplacement Proc. 4th International Kimberlite Conference, Perth, WA, 1986 Geol. Soc. Aust, Spec. Publ. 14, Blackwell, Melbourne pp 520-527
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Smith C B and Lorenz V 1989 - Volcanology of the Ellendale lamproite pipes, Western Australia: in Kimberlites and related rocks, Volume 1, Their origin, Occurrence and emplacement Proc. 4th International Kimberlite Conference, Perth, WA, 1986 Geol. Soc. Aust, Spec. Publ. 14, Blackwell, Melbourne pp 505-519
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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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