Walgidee Hills, Noonkanbah Station, Derby-West Kimberley Shire, Western Australia, Australiai

Regional Level Types
Walgidee Hills	Group of Hills
Noonkanbah Station	- not defined -
Derby-West Kimberley Shire	Shire
Western Australia	State
Australia	Country

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 contains 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 Australian 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. 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.

While the Walgidee Hills term covers all the sites under this section, it also refers to the largest deposit (Called Walgidee) at 2.5km in diameter, and immediately surrounding hills. Rare species on the collectors market are nearly always labelled Walgidee Hills, denoting the general area, often with no reference to which lamproite pipe the specimen comes from.

As far as diamonds are concerned this pipe could be the most significant on the field. It has a diameter of 2.5 kilometres. covering 490 Ha. Exploration work in the 1990's recovered 891 microdiamonds and 62 macrodiamonds. Further work by Graynic Metals Ltd around 2007, found a further 11 macrodiamonds of which 6 where colourless white, 4 brown and 1 yellow.

The site is a roughly circular body. It is olivine-rich rock with abundant altered olivine macrocrysts, and large crystals of leucite, diopside and potassic richterite.

Dykes and veins up to one metre wide of coarse-grained lamproite pegmatoids are near the centre of the body. These contain a large number crystals of a number of rare minerals such as priderite, wadeite, jeppeite, and shcherbakovite, and large plates of potassic richterite and perovskite, with crystals up to 1 mms across.

Localities in this Region

Other Regions, Features and Areas containing this locality

References