Wiluna District - Wiluna, Bulletin, Regent, Galaxy, Matilda, Williamson, Caledonian, Mt Wilkinson
Western Australia, WA, Australia
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The Wiluna gold mines are located just to the SE of the town of Wiluna near the northern extremity of the Archaean Norseman-Wiluna greenstone belt of the Yilgarn Craton, Western Australia. Wiluna is 500 km north of Kalgoorlie which is in the same greenstone belt, and 50 km SW of Jundee. In addition to the main Wiluna mine, other workings and operations in the district within a 20 km radius of Wiluna include Bulletin, Regent, Galaxy, Matilda, Caledonian, Williamson and Mt Wilkinson.
(#Location: Wiluna - 26° 37' 59"S, 120° 14' 22"E; Matilda - 26° 45' 6"S, 120° 12' 54"E).
The Wiluna mines exploited a group of individual lode hosted gold deposits within a series of very low grade metamorphosed (prehnite-pumpellyite facies) Neoarchaean mafic and ultramafic lava flows (the "Mine Sequence"). The lodes are controlled by the Wiluna strike-slip fold system - a north and north-east trending, west and east dipping set of dextral principal and subsidiary faults (with minor oblique reverse or oblique normal movement) and an overall maximum cumulative displacement of 1350 m. The mineralised lodes are located on dilational jogs, divergent bends and horsetail splays, with shoots plunging moderately to steeply south.
Fault hosted ore breccias, net veined breccias and brecciated veins are significant loci for gold and contain mainly quartz (chalcedony), carbonates, fuchsite, arsenopyrite, pyrite and/or stibnite.
The Bulletin deposit is 5 km SE of Wiluna and lies within the Happy Jack - Bulletin Fault Zone, a 50 m wide brittle-ductile NE trending structure. The resource is contained within 5 shoots/lenses, with 90% being in the main zone which has a strike length of 200 to 300 m, persists down plunge for 600 m and is 3 to 6 m wide in the upper sections increasing to 30 m in the high grade core at a depth of 300 m.
The Matilda deposits occur in association with multiple shear zones within the broader, NNW trending, semi-regional, Coles Find Shear Zone developed along the contact between a felsic and mafic volcanic sequences to the east and west respectively. Mineralisation is hosted within a sequence of Neoarchaean mafic volcanic and sedimentary rocks that may be a parallel folded and faulted repetition of the Wiluna sequence to the east. The main mineralised interval is distributed over a 2.5 km long interval that is 500 m wide in the north and up to 750 m wide to the south. Shear zones contain multiple, ENE plunging, en echelon lodes that are 2 to >10 m thick, carrying grades of 2 to 10 g/t Au.
These deposits are part of the greater Wiluna belt, a 45 km strike length of the Wiluna "Mine Sequence" which hosts the Galaxy, Wiluna, Bulletin, Golden Age, Regent and Williamson deposits, plus the Matilda deposits, 6.5 km to the SW of Regent, within a 10 km mineralised interval of the parallel Coles Find Shear Zone.
The Wiluna district lodes were discovered in 1901 and by 1990 had produced 68.5 tonnes of gold. The mine was closed in 2007 after producing >120 t of Au.
District resources in 1990 were: 37 tonnes of remaining contained Au in ore with a grade of 3.8 g/t Au.
Historic production to 1987 at the Wiluna mine itself was: 8.936 Mt @ 6.18 g/t Au for 55.254 t Au.
Wiluna tailings retreatment from 1983: 6 Mt @ 0.4 g/t Au
Reserves at the Wiluna Mine in 1987 were: 8.58 Mt @ 1.82 g/t Au for 15.623 t Au.
Probable reserve at Bulletin, 1998: 1.9 Mt @ 8.5 g/t Au + Inferred resource of: 0.6 Mt @ 7.3 g/t Au.
Total remaining measured + indicated + inferred resources in the district in 2015 were (Blackham Resources Ltd, December, 2015):
Matilda mine - 12.5 Mt @ 1.8 g/t Au;
Williamson mine - 6.3 Mt @ 1.7 g/t Au;
Regent - 3.9 Mt @ 2.2 g/t Au;
Galaxy - 0.6 Mt @ 2.9 g/t Au;
Golden Age (at Wiluna) - 0.6 Mt @ 6.7 g/t Au;
Bulletin South open pit - 2.6 Mt @ 3.4 g/t Au;
West Lode Calvert - 4.2 Mt @ 5.3 g/t Au;
Henry 5-Woodley-Bulletin Deeps - 2.9 Mt @ 5.6 g/t Au;
Burgundy-Calais - 1.6 Mt @ 6.0 g/t Au;
Happy Jack-Creek Shear - 2.9 Mt @ 5.4 g/t Au;
Other Wiluna Deposits - 2.8 Mt @ 4.1 g/t Au.
TOTAL Resource - 44 Mt @ 3.3 g/t Au containing 145 t of gold.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this summary was dated: 2015.
Record last updated: 28/12/2015
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Chanter S C, Ellu P, Erickson M E, Jones G F P, Mikucki E 1998 - Bulletin gold deposit: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 105-110|
Hagemann S G, Groves D I, Ridley J R, Vearncombe J R 1992 - The Archean lode Gold deposits at Wiluna, Western Australia: high-level brittle-style mineralization in a strike-slip regime: in Econ. Geol. v87 pp 1022-1053|
Hagemann S G, Luders V 2003 - P-T-X conditions of hydrothermal fluids and precipitation mechanism of stibnite-gold mineralization at the Wiluna lode-gold deposits, Western Australia: conventional and infrared microthermometric constraints : in Mineralium Deposita v38 pp 936-952|
McGoldrick P 1990 - Wiluna gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 309-312|
Morgan P J, El-Raghy S 1990 - Matilda gold deposits, Wiluna: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 313-318|
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