Karloning pegmatite (O'Neil's pegmatite; Koonkoobing Hill pegmatite), Mukinbudin, Mukinbudin Shire, Western Australia, Australiai

Regional Level Types
Karloning pegmatite (O'Neil's pegmatite; Koonkoobing Hill pegmatite)	Pegmatite
Mukinbudin	- not defined -
Mukinbudin Shire	Shire
Western Australia	State
Australia	Country

Also known as O'Neil's pegmatite, named after the owner of the farm, John O'Neil, the pegmatite is found on. Also known as Koonkoobing Hill feldspar pegmatite.
Located 48 kilometres north east of Mukinbudin at the end of Forest Avenue, which turns off the Mukinbudin-Wialki Road.

The farm owner started mining in 1975, producing 172 tonnes of feldspar. Snowstone Pty Ltd purchased the lease in 1976, they and later Anglo Australian Resources NL mined 6 560 tonnes of feldspar until 1988. Imdex Feldspar Pty Ltd then took over the lease reworking the mine dumps from 1992 to 1996, but could not find a market, and relinquished the lease. Brian Adams and Graeme Hepple then started reprocessing the dump material from 2001.

The pegmatite is large at 90 metres width and 1 500 metres long. As mining has only taken place on a small part of the pegmatite, it potentially holds more mineral surprises. The quarry at the pegmatite shows a white quartz core, albite zone, potassium feldspar zone, quartz-microcline zone, and a microcline-quartz-biotite wall zone.

The albite zone contains rare giant biotite crystals and rare earth minerals such as fergusonite (Y), xenotime (Y) and allanite, as well as magnetite crystals to 1mm and ilmenite.

The allanite forms black metamict masses with no crystal faces typical of the species in the region. Clusters of fergusonite (Y) crystals show three forms difficult to summarise in the space here- from most to least common- (1) elongated crystals with square cross sections forming sprays (2) intergrown masses with xenotime (3) multi-crystalline xenotime nodules with an elongated fergusonite crystal emerging from its centre. Xenotime is found as greyish red crystals 0.5 cm in diameter, or as rounded multi-intergrown crystals to 4 cm, or as intergrown subhedral masses to 5cm. Sometimes it is found associated with fergusonite in all three forms. Tests have showed the density of xenotime at the deposit can be as low as 4.13, when the species is normal 4.4 to 5.1 in density.

The writer could not access the quarry as it is an active mine. However material from the mullock piles have been used to construct embankments next to some nearby roads, and some of the species were able to be identified from examining these.

Other Regions, Features and Areas containing this locality

References