Walgidee Hills lamproite, Noonkanbah Station, Derby-West Kimberley Shire, Western Australia, Australia
|Latitude & Longitude (WGS84):||18° 18' South , 124° 51' East|
|Latitude & Longitude (decimal):||-18.30000,124.85000|
|Köppen climate type:||BSh : Hot semi-arid (steppe) climate|
While the Argyle Mine in the east Kimberley produces many rough diamond specimens for collectors but little else, the west Kimberley field produces a suite of rare species highly sought after by collectors. Specimens are always labelled Walgidee Hills, and it appears many come from surplus stock from research projects.
Located 100 kilometres east of Derby, the region contains over 100 lamproite pipes, over a 7 500 square kilometre area. This includes swarms of pipes at Ellendale, as well as Calwynyardah and Noonkanbah further south. They are either leucite or olivine rich. Diamonds do occur in these but have not been available to collectors. About 60% of the pipes contain diamonds, the olivine rich pipes the most.
Western Australia holds the world's oldest rocks, but these lamproite pipes were formed 'yesterday' as far as Western Australian geology is concerned, Miocene 21-22 million years ago. When the Australian and Asian tectonic plates collided, it led to violent volcanic eruptions, forming large shallow craters. This was followed by further normal volcanic eruptions, which filled the craters with lava lakes, forming lamproite tuff. The olivine pipes weather more readily than the surrounding country rock forming shallow pans.
The pipes form a wine glass shape, covering a diameter at the surface ranging from 100m to 1 kilometre. They cut through the Palaeozoic sediments of the Leonard Shelf, 500-1500m deep through the Devonian to Permian platform. The leucite rich lamproite pipes contain phlogopite, diopside or titanian potassium richterite as major mafic phases, grading to olivine rich lamproite which contain most of the diamonds. The leucite in the pipes is mainly pseudomorphed by mixtures of K-feldspar, zeolite, chalcedony, opaline silica or clay, with fine grained hematite as inclusions. Ilmenite is found in only a few of the pipes.
The first geologist to visit the area was R.A. Farquhason in 1920. University of Western Australiam geology professors, A. Wade and P.T. Prider studied the pipes in 1940. Diamonds were not encountered until exploration by the Ashton Joint Venture in the mid 1970's.
Walgidee Hills is the type locality for jeppeite, but as to which lamproite pipe, is not mentioned in the reference. It was discovered by geologist, J. Jeppe in 1969, while working for exploration company Stellar Minerals Ltd. Jeppe found crystals 2mm x 2mm in scree samples, and further crystals were found by hand sorting jig concentrates from 2 tonnes of lamproite and eluvial material. Subsequent investigation of the lamproite pipe found the species to be abundant but crystals sparse. In solid rock it is plentiful as black finely prismatic to acicular, fragile aggregates, closely associated with and overgrown on priderite
Mineral ListMineral list contains entries from the region specified including sub-localities
25 valid minerals. 4 (TL) - type locality of valid minerals. 1 erroneous literature entry.
Rock Types Recorded
Rock list contains entries from the region specified including sub-localities
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Entries shown in red are rocks recorded for this region.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Middle Triassic - Early Triassic|
237 - 252.17 Ma
Age: Triassic (237 - 252.17 Ma)
Stratigraphic Name: Blina Shale
Comments: argillaceous detrital sediment; sedimentary siliciclastic; synthesis of multiple published descriptions
Lithology: Argillaceous detrital sediment; sedimentary siliciclastic
Reference: Raymond, O.L., Liu, S., Gallagher, R., Zhang, W., Highet, L.M. Surface Geology of Australia 1:1 million scale dataset 2012 edition. Commonwealth of Australia (Geoscience Australia).