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Williams Opal Mine (Three Mile Hill Mine), Coolgardie, Coolgardie Shire, Western Australia, Australiai
Regional Level Types
Williams Opal Mine (Three Mile Hill Mine)Mine
CoolgardieCity
Coolgardie ShireShire
Western AustraliaState
AustraliaCountry

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Latitude & Longitude (WGS84): 30° 55' 2'' South , 121° 11' 35'' East
Latitude & Longitude (decimal): -30.91734,121.19329
GeoHash:G#: qdw0jgdm2
Locality type:Mine
Köppen climate type:BSh : Hot semi-arid (steppe) climate
Nearest Settlements:
PlacePopulationDistance
Coolgardie802 (2016)4.8km
Boulder5,178 (2017)32.2km
Kalgoorlie31,107 (2014)32.9km
Williamstown161 (2018)33.3km


Australia produces about 90% of the world's precious opal. However, in Western Australia, it is a very rare species. It has been found in only two locations in an area amounting to the size of western Europe.

Williams opal mine is located 4.8 kilometres north north-east of Coolgardie.

Precious black opal was mined at Williams Opal Mine in 1904, but abandoned shortly after due to the limited amount of opal available. All fell silent until the 1960's when an open-cut was developed over the old workings. Only a few blob-like concretions containing precious opal were recovered. The mine was worked again in 1989, extending the pit to 10-12 metres deep.

Opal is found in a 9 metre wide shear zone, within graphitic slate bands grading to thin feldspathic bands. The bands have silicified, and at one locality thin seams of precious opal have developed along cleavage and joint planes. The siliceous matrix is a relatively hard, black or dark grey, fine grained rock, and is jointed and foliated. A series of quartz veins have been intruded by this rock, and both are cut by a series of minute cracks up to 2.5mm thick filled with opal from precious to parts of no commercial value.

Most of the opal is in thin seams, and slivers were unfortunately mounted as jewellery rather than being retained as mineral specimens. The opal was black and grey, displaying red, orange, green and blue play of colours. The surrounding potch veins were wider and were glassy and bluish in colour. Mineral specimens from the location are very rare.

In 1989 the lease containing the Three Mile Hill opal mine was purchased by Peter Milic, an experienced opal prospector and miner who had previously worked at opal fields in South Australia, Lightning Ridge (NSW) and western Queensland. He began drilling and blasting at Three Mile Hill and immediately found small fragments of precious opal. According to Wattone (1992), at the end of September 1991 Milic recovered a magnificent piece of black opal weighing 16.5 kg, by following up small traces of opal in one area of the pit. Two days later another find of 2.5 kg and a third of 6 ounces was made. The large specimen was valued at AUD$5-6 million when appraised by valuer in Perth but no immediate buyer was found. The large piece was cut and taken to Adelaide, presumably to be sold. Some pieces from the 1991 find were apparently valued at AUD$5000-10000 per carat.

Regions containing this locality

Australian Plate (Australia Plate)Tectonic Plate
West Australian Element, Western Australia, AustraliaCraton
Yilgarn Craton, Western Australia, AustraliaCraton
Kambalda Nickel Metallogenic Province, Western Australia, AustraliaGeologic Province

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


3 valid minerals.

Rock Types Recorded

Note: this is a very new system on mindat.org and data is currently VERY limited. Please bear with us while we work towards adding this information!

Select Rock List Type

Alphabetical List Tree Diagram

Detailed Mineral List:

Graphite
Formula: C
Reference: Fetherston, J.M., Stocklmayer, S.M., Stocklmayer, V.C. (2013) Gemstones of Western Australia. Geological Survey of Western Australia, Mineral Resources Bulletin 25, 306 pages.
Opal
Formula: SiO2 · nH2O
Reference: Fetherston, J.M., Stocklmayer, S.M., Stocklmayer, V.C. (2013) Gemstones of Western Australia. Geological Survey of Western Australia, Mineral Resources Bulletin 25, 306 pages.
Opal var: Precious Opal
Formula: SiO2 · nH2O
Reference: Fetherston, J.M., Stocklmayer, S.M., Stocklmayer, V.C. (2013) Gemstones of Western Australia. Geological Survey of Western Australia, Mineral Resources Bulletin 25, 306 pages.
Quartz
Formula: SiO2
Reference: Fetherston, J.M., Stocklmayer, S.M., Stocklmayer, V.C. (2013) Gemstones of Western Australia. Geological Survey of Western Australia, Mineral Resources Bulletin 25, 306 pages, at p. 112.

List of minerals arranged by Strunz 10th Edition classification

Group 1 - Elements
Graphite1.CB.05aC
Group 4 - Oxides and Hydroxides
Opal4.DA.10SiO2 · nH2O
var: Precious Opal4.DA.10SiO2 · nH2O
Quartz4.DA.05SiO2

List of minerals arranged by Dana 8th Edition classification

Group 1 - NATIVE ELEMENTS AND ALLOYS
Semi-metals and non-metals
Graphite1.3.6.2C
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with [4] coordinated Si
Quartz75.1.3.1SiO2
Si Tetrahedral Frameworks - SiO2 with H2O and organics
Opal75.2.1.1SiO2 · nH2O
Unclassified Minerals, Mixtures, etc.
var: Precious Opal-SiO2 · nH2O

List of minerals for each chemical element

HHydrogen
H OpalSiO2 · nH2O
H Opal (var: Precious Opal)SiO2 · nH2O
CCarbon
C GraphiteC
OOxygen
O OpalSiO2 · nH2O
O Opal (var: Precious Opal)SiO2 · nH2O
O QuartzSiO2
SiSilicon
Si OpalSiO2 · nH2O
Si Opal (var: Precious Opal)SiO2 · nH2O
Si QuartzSiO2

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

Archean
2500 - 4000 Ma



ID: 803323
ultramafic and minor mafic rocks 74475

Age: Archean (2500 - 4000 Ma)

Description: Tremolite-chlorite-talc amphibolite, metapyroxenite, pyroxenite, peridotite, serpentinite, ultramafic schists, komatiite, high-Mg basalt; also chalcedony, silica, jasper, silcrete, silica cap rock on ultramafic rocks

Comments: igneous ultramafic intrusive; meta-igneous ultramafic volcanic; synthesis of multiple published descriptions

Lithology: Igneous ultramafic intrusive; meta-igneous ultramafic volcanic

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]

Neoarchean - Mesoarchean
2500 - 3200 Ma



ID: 3187518
Archean volcanic rocks

Age: Archean (2500 - 3200 Ma)

Comments: Yilgarn Craton

Lithology: Greenstone belt; mafic-ultramafic volcanic rocks

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

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Geological Survey of Western Australia (1994) Gemstones in Western Australia, 52 pages.
Fetherston, J.M., Stocklmayer, S.M., Stocklmayer, V.C. (2013) Gemstones of Western Australia. Geological Survey of Western Australia, Mineral Resources Bulletin 25, 306 pages, at p.112.
Fetherston, J.M., Stocklmayer, S.M., Stocklmayer, V.C. (2017) Gemstones of Western Australia, second edition. Geological Survey of Western Australia, Mineral Resources Bulletin 25, 356 pages.
Wattone, M. (1992) Way to the Gold II. Contraland Press, 126 pages.


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