Onedin prospect (Gordon Downs 1), Koongie Park Station, Halls Creek Shire, Western Australia, Australiai

Regional Level Types
Onedin prospect (Gordon Downs 1)	Prospect
Koongie Park Station	Station (farming)
Halls Creek Shire	Shire
Western Australia	State
Australia	Country

Carbonate-associated base metal mineralisation (sub-basin floor replacement VHMS deposit).

Note on the mineral list: Orth (2002) also mentions minor silver minerals.


Described as the second largest prospect in the Koongie Park area after the Sandiego prospect. A VHMS deposit showing zinc and minor lead and copper. There are two units at the Onedin prospect. The lower unit in the northern and western areas of the prospect is composed of tholeiitic basalt, turbidites,hemipelagic mudstone,chert and some ironstone with rhyolite bearing breccias. The upper unit is a diverse collection of a coarse grained sediment interbedded with turbidites, hemipelagic mudstone, volcaniclastic quartz bearing units with siliceous sandstone and mudstone, intruded by rhyolite, tholeiitic dolerite and late tholeiitic basalt dykes.

The footwall is a quartz bearing mudstone with chlorite-quartz-white mica. The host is a sequence of mudstone, sandstone, chert and ironstone with abundant Mg, Si and Ca in carbonate, talc, chlorite, quartz, and white mica. The hanging wall is quartz-albite, partially replaced by phyllosilicate minerals.

The sulphide is hosted by carbonate or chlorite schist, with zinc rich massive sulphide of sphalerite, pyrrhotite, chalcopyrite and pyrite, with minor galena and silver minerals, in two 10-60 metre thick carbonate lenses. Massive, vein and disseminated sulphides are hosted in chlorite schist between and above the lenses.

The carbonate (dolomite and ferroan dolomite) has caused an increase of Ph of the metal bearing fluid, thereby precipitating sulfide minerals. The carbonate alteration is complex with 13 different petrographic carbonate types forming 8 carbonate facies via diagenesis, hydrothermal alteration, mineralisation, deformation and metamorphism. The deposit was formed in a deep water environment with high levels of intrusion and extension. The local intrusions of rhyolitic sills resulted in lithification of the surrounding sediment and increasing the temperature, generating fluid circulation, and confining the fluid flow beneath a cap. The circulation in porous volcaniclastic sediment and the host sequence resulted in lower Na levels, and the precipitation of chlorite, quartz, muscovite, carbonate and talc. The carbonate was upgraded by alteration providing a trap to deposit the base metal sulfide minerals.

Other Regions, Features and Areas containing this locality

References