Latitude & Longitude (WGS84):	19° 13' 37'' South , 122° 16' 48'' East
Latitude & Longitude (decimal):	-19.22694,122.28000
GeoHash:	G#: qswfwecdf
Locality type:	Deposit
Köppen climate type:	BSh : Hot semi-arid (steppe) climate

MVT lead zinc deposit

The deposit is 40 kilometres east of the Nita Downs pastoral station homestead, and 140 kilometres south of Broome. Scrubby sparse woodland and sand-dune dominate at the western edge of the Great Sandy Desert.

It is considered at the time of writing the fourth largest undeveloped zinc deposit in the world, and equal largest undeveloped zinc deposit in Australia.

It is up to 140 Mt epigenetic deposit hosted in Lower Ordovician carbonate rocks of the Willara Sub-Basin, within the Canning Basin. The deposit is hosted by the west north-west to east south-east trending Admiral Bay Fault Zone, a structurally complex area, with four major zones.

First is an extensively altered and fractured algal bioherm association (carbonate rock in the form of an ancient reef consisting of fossilised algae, and possibly other ancient sea life). Secondly a lower lead rich zone in the upper Goldwyer Formation and Lower Leo Member of the Nita Formation. Thirdly a hydrothermal dolomite zone, extensively replacing the Leo Member. Lastly an upper zinc rich zone of the Cudalgarra Member of the Nita Formation, and lower Bongabinni Formation.

There are two forming events. Firstly hydrothermal activity related to extensional faults in the early Ordivician period, resulting in extensive alteration and fracturing of the Goldwyer Formation bioherm association. This event did not lead to the deposition of any base metals. Secondly a Late Silurian period of metal fluids being expelled from the Willara Sub-Basin, finding its way into the extensional faults. This interacted with evaporative sulphates and hydrocarbons leading to extensive base metal mineralisation.

Hematite, jasper, magnetite and siderite is not thought to be genetically related to the epigenetic Pb-Zn MVT.

Mineralisation is found discontinually along an 18 kilometre corridor, 0.3 kilometres wide, and covering a total of 4.5 square kilometres. Mineralisation was formed in shallow water limestones on a fault controlled palaeohigh. The zinc rich section is up to 20 metres thick, and lead rich section up to 15 metres thick. There is an Inferred resource of 72 Mt @ 3.1 Zn, 2.9 Pb and 18 g/t Ag, although these figures have changed from time to time, depending on the latest drilling campaign.

The deposit was discovered in 1981 during petroleum exploration. It is a Mississippi Valley Type (MVT) deposit containing zinc, lead, silver and barite. It was explored by CRA Exploration Pty Ltd 1986 to 1992, and Kagara Limited 2004 to 2009. Kagara went into voluntary administration in 2014, and the leases were purchased by the PLD Corporation, which has since changed its name to Metalcity, for 7 million (Australian $).

The host rocks are dolomite, shale, siltstone, algal bioherm limestone and breccia. Underlying the deposit is conglomerate, limestone, sandstone, shale of the Lower Ordivician. Overlying the deposit is evaporative mudstone, siltstone and shale of the Upper Ordivician to Silurian periods, 550 metres in total thick.

This last point is important, as the deposit has generated much shareholder interest, promoted by the companies. One company has already gone to the wall, and the mineralisation is deep. On the other hand, few companies in Western Australia have an undeveloped deposit the size of Admiral Bay in its portfolio. The nearest port is Hedland about 400 kilometres to the south. Ore would need to be trucked, which is feasible for a boutique mine, but not large scale operations.

Mineral List

19 valid minerals.

Rock Types Recorded

Regional Geology

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

Quaternary - Cenozoic 0 - 66 Ma ID: 758736

dunes 38496 Age: Cenozoic (0 - 66 Ma) Description: Dunes, sandplain with dunes and swales; may include numerous interdune claypans; may be locally gypsiferous Comments: regolith; synthesis of multiple published descriptions Lithology: Regolith 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). [5]

Cretaceous 66 - 145 Ma ID: 3185296

Mesozoic sedimentary rocks Age: Cretaceous (66 - 145 Ma) Comments: Canning Basin Lithology: Conglomerate,siltstone,shale,sandstone Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

References

External Links