Wiluna Gold Mine is an active gold mine operated by Wiluna Mining Corporation (administrators appointed) near the town of Wiluna, north of Perth in Western Australia's Goldfields region. Wiluna is one of the Goldfields' great mining centres, with historical production plus current resources of more than .
Overview
The mine is located within and adjacent to the native title of the Ngaanyatjarra Aboriginal people.
, total gold resources were over : Underground: at Open pits: at Tailings re-treatment and stockpiles: at Satellite deposits: at
, total gold reserves were over : Underground: at Open pits: at Tailings retreatment: at
Following recent upgrades, the Wiluna processing plant can treat all styles of mineralisation, including refractory and non-refractory (free-milling) gold deposits. Processing infrastructure includes a sulphide flotation facility commissioned in 2021, tailings retreatment facility commissioned in 2023 (Wiltails), free-milling circuit, knelson gravity concentrator, and currently idle Biox facility.
Additional mining-related infrastructure includes numerous idle open pit mines, over of underground development and five declines on care and maintenance, of drilling data, tailings storage facilities, 300-person village, gas pipeline and power station, Goldfields Highway connection, and commercial airport services at the Wiluna airport.
Historically, the Wiluna area was extensively mined from the discovery of gold in 1896 until the end of World War II. One of the few historical buildings remaining from the earlier days of mining is the old Mine Managers Lodge, now in ruins. There is some old equipment on display at the visitors' car park, notably an old crusher and an old mill. Just before entering Wiluna from the south, a wooden building on the right-hand side of the highway is the old railway station's shed. The railway dam can still be seen but the tracks which once went all the way to Meekatharra have been removed.
Geology The Wiluna gold deposits are categorised as orogenic gold deposits, with broad similarities to many other gold deposits in Western Australia. The deposits are hosted within the Archaean Wiluna Greenstone Belt, a 2.7 billion year-old series of basalts, felsic rocks, lamprophyres, and sediments that have undergrone greenschist facies metamorphism and brittle and ductile deformation. Gold mineralisation is mainly contained within three sub-parallel dextral strike-slip shear zones, called the East, West and Adelaide-Moonlight shears, with a combined strike length exceeding . The shears dip nearly vertically, pinch and swell along strike and down-dip, and contain the best gold grades where they intersect favourable host rocks and rock unit boundaries. The larger high-grade shoots have been given individual names, such as the East Lode, West Lode, Moonlight, Essex, Happy Jack and Bulletin deposits. Minor high-grade, free-milling mineralisation is hosted within quartz reef deposits such as Golden Age and can be treated conventionally. However, most of the shear-hosted gold occurs within pyrite and arsenopyrite crystals, requiring a stage of oxidation such as roasting, bacterial oxidation or pressure oxidation to liberate the gold.
History of discovery and metallurgical innovation Gold was discovered at Wiluna on Saint Patrick’s Day in 1896 by prospectors George Woodley, James Wotton and Jimmy Lennon.
Three main phases of gold production followed over a period of more than 125 years, in which the mine grew to be one of the largest gold producers in Australia, and also produced significant by-product arsenic and antimony.
The mine's fortunes rose and ebbed over the decades as gold market conditions fluctuated and advances in mining and processing technologies allowed the vast gold deposits at depth to be treated economically.
In the early years, mining focussed on easily won gold from quartz reefs in the district and shallow oxidised deposits in the East and West Lodes, with gold ore treated conventionally by crushing in stamp batteries, amalgamation and cyanidation of tailings. Mining ceased about 1910 following depletion of the oxide resources, and difficulty in recovery of the refractory sulphide gold mineralisation at depth, despite trials with roasting.
In the 1920s, the resource was recognised as large and low grade (by the standards of the time) and refractory at depth, requiring a different treatment method and a high production rate. The colourful Western Australian goldfields and London personality Claude de Bernales floated the Wiluna Gold Corporation (WGC) to develop the major East and West Lodes, construct a treatment plant and other services. In the 1930s, a large mining operation was underway utilising a new metallurgical process of sulphide flotation followed by roasting of the concentrate before conventional cyanidation and gold recovery.
In the early 1980s, the advent of carbon-in-pulp (CIP) metallurgical processing and modern mining methods meant that large, low-grade oxide and "free-milling" (non-refractory) deposits could be mined economically again, leading to the re-evaluation of historical mining districts throughout the Western Australian goldfields. At Wiluna, CIP processing ushered in the economic re-treatment and environmental rehabilitation of legacy mine tailings, and the large-scale development of open pit mines on the amenable oxidised portions of the gold deposits.
In 1993, a Bacterial oxidation (Biox) processing plant was installed allowing the recovery of gold from deeper refractory sulphide ore that was mined by open pits and underground mining methods. The Biox process is a pretreatment process for refractory gold ores or concentrates, using naturally occurring bacteria to break down the sulphide ore and liberate the gold for subsequent cyanidation. Wiluna's Biox plant was only the second of its kind to be installed in Australia, following commercialisation of the technology a few years earlier in 1988. The Biox operation ran continuously from 1984 to 2007 under the ownership of some small and larger mining companies such as Wiluna Mines, Great Central Mines, Normandy Mining and Newmont, and again from 2008 to 2013 under the ownership of Apex Minerals.
From 2016 to 2022, free-milling deposits in the region were mined and processed through the CIP plant under the ownership of Blackham Resources (renamed to Wiluna Mining Corporation in 2020). In the 18 months to 31 December 2021, Wiluna Mining Corporation invested in the redevelopment of Wiluna, with comminution and flotation facilities, knelson gravity concentrator, tailings retreatment facility, new tailings storage, camp and power upgrades, mine dewatering, of drilling, of underground development, and technical studies.
In December 2021, a new sulphide flotation plant was commissioned that allowed for the treatment of sulphide ore from underground and the sale of gold concentrates to offtake customers in Russia and elsewhere internationally, including Polymetal International, a world leader in refractory ore processing utilising modern Pressure oxidation (POX) techniques.
Three phases of history
First phase: 1896 to 1910 In 1896, gold was discovered in the region, which was then known as Lake Way, by three prospectors, George Woodley, James Wotton and Jimmy Lennon.Wiluna – Edge of the desert, author: Phil Heydon, publisher: Hesperian Press, published: 1996, page: IV. Retrieved 23 March 2003
On 29 December 1897, a nugget was found in Wiluna, then the largest found in the colony of Western Australia.Wiluna – Edge of the desert, author: Phil Heydon, publisher: Hesperian Press, published: 1996, page: 15. Retrieved 23 March 2003
The town prospered from the development of the mine until the First World War. Around 1910, however, the mine declined because the refractory ore at greater depths could not be treated. As a consequence, the town's population shrank to less than 150 people.
Second phase: 1924 to 1949 In 1924, Claude de Bernales floated the Wiluna Gold Corporation to undertake a drilling program and revive the Wiluna mine. De Bernales went to London in 1926 and raised £1 million to work the Wiluna mines. A later issue of promissory notes for £300,000 was backed by the Western Australian State Government. The state government also built a railway line from Meekatharra for transport of supplies including fuel oil for power generation. When the mine reopened in 1931 it attracted a substantial workforce and stimulated community growth and within four years produced gold worth £3 million.John H Laurence, 'de Bernales Claudew Albo (1876-1963)’, Australian Dictionary of Biography, National Centre of Biography, Australian National University, https://adb.anu.edu.au/biography/de-bernales-claude-albo-5935 /text10117, published first in hardcopy 1981, accessed online 21 June 2018. By 1939, the town had grown to a population of 9,000 thanks to the employment the mine provided.
WGC employed an innovative metallurgical processing route where refractory gold ore was treated using sulphide flotation followed by roasting of the concentrate, conventional cyanidation and gold recovery.
Gold recovery at the flotation stage was initially around 80% as salty mine water was initially used in the grinding and flotation sections. A change to fresh water in 1936 increased the gold recovery in the flotation stage to 85-89%. Flotation concentrate was then dewatered in thickeners and filters, and passed into Edwards roasters and the calcine pulped with fresh water, lime and cyanide solution before grinding in a tube mill. Thickening and filtration then led to a Merrill-Crowe precipitation plant using zinc dust for precipitation of the gold. The cyanide residues were stored in shallow dams and allowed two years to weather before being leached and the gold solution being reintroduced into the main circuit.
An arsenic tri-oxide plant was also installed capturing arsenic fumes from the roasters, and was the largest producer of arsenic in the southern hemisphere.
Gold ore at the Moonlight deposit contained the antimony ore mineral, stibnite, which was notoriously difficult to roast and cyanide, and a pilot plant was built to investigate the smelting of Moonlight concentrates by sintering, blast furnace smelting with lead and lead concentrates, and refining to obtain the gold. Crushed Moonlight mine ore was railed a short distance to the Wiluna treatment plant and processed in the parallel grinding and flotation circuit producing a sulphide concentrate for further processing, and a separate antimony concentrate for sale. A Dwight-Lloyd sintering machine, blast furnace and refinery were installed and commenced operation in October 1936. The smelter treated Wiluna and Moonlight arsenical concentrates, and cyanide residues combined with pig lead and sintered lead concentrates using ore brought in from the Northampton lead mine (several hundred kilometres away near Geraldton in Western Australia).
The sintering plant was superseded by a smelter that was eventually able to process almost every ore type at Wiluna. The smelter produced a gold bearing lead bullion assaying 11 per cent antimony, one per cent arsenic and 0.5 per cent copper that presented unusual refining problems. A process was developed by the company consisting of five stages: hot drossing using sawdust arsenic refining by adding caustic antimonial slag copper refining by adding sawdust second stage of copper refining de-golding by adding zinc
The smelting process obtained about five per cent higher recovery than the roasting and cyanidation process.
In 1935 Wiluna became the second largest gold mine in Australia, behind only the Lake View and Star mine at Kalgoorlie-Boulder, and production peaked at of gold in 1938.