Introduction
Bulahdelah Mountain lies on the eastern side of Bulahdelah township which is located on the Pacific Highway, in the Mid North Coast Region of NSW, about 230km north of Sydney. The mountain is located at latitude – 32.416667, longitude 152.216667.
Bulahdelah Mountain is a volcanic extrusion, also known as Alum Mountain, after a rare alunite deposit was discovered there in the late 1800s and subsequently mined until 1952.
Geological overview
In 1917, this alunite deposit was reported as one of only three known deposits in Australia and the largest deposit in the world.
There are three units in the Early Permian Alum Mountain Volcanics at Bulahdelah Mountain: Sams Road Rhyolite Member, which consists of ignimbrite, lava flows, tuff and breccia that has been variably altered by hydrothermal fluids; the Markwell Coal Measures, layers of high grade coal interbedded with carbonaceous shale, fine grained sandstone and conglomerate; and Burdekins Gap Basalt, an olivine basalt that varies from slightly weathered and strong, to the (more common) highly weathered and plastic clay.
Bulahdelah Mountain is an outcrop of steeply dipping upper Carboniferous volcanic rock, dominantly thick flows of basalt with smaller occurrences of rhyolite and trachybasalt. Interbedded sediments occur, and include thin coal beds which are of some geological interest. The mountain was created by the different rates of erosion of the volcanic units. A zone of intense hydrothermal alteration (mineral formation due to the inflow of heated meteoric waters) resulted in the deposition of the minerals quartz and alunite which are physically resistant. The high concentrations of quartz and alunite formed a topographic high, which was later named Alum Mountain.
Indigenous context
This mountain is significant to the local Worimi Aboriginal people who call it Boolah Dillah, meaning ‘the Great Rock’. It was a centre of social gatherings for indigenous groups, including the trading of practical materials.
The top of the mountain was considered a Men’s Place. Of geological interest is the trading of obsidian and alunite. The obsidian would have yielded very sharp flakes suitable for cleaning skins, cutting meat and other applications. Fragments of alunite were provided to tribal elders. These are thought to be used to help heal cuts and wounds by spreading sulphur from the oxidized surface of the rock. There was also a women’s ‘healing stream’ in the area possibly linked to childbirth.
The Karuah Local Aboriginal Land Council, representing the Worimi people, support the placement of the Bulahdelah rock in the National Rock Garden.
Modern history
The region of Bulahdelah Mountain (locally called Alum Mountain) became a centre for timber cutting from the 1850s, based around a community which was established at the present site of the town of Bulahdelah on the Myall River. In 1876, after bushfires burnt across Alum Mountain, a mill worker (John Cassidy) walked onto a burnt-out stump hole which displayed a brilliantly contrasting white powder in the ground. Government geologists were called in and confirmed the presence of unusually large quantities of alunite an aluminium potassium sulphate mineral, previously known as a valuable mineral in Italy and Hungary.
The Australian Alum Company commenced extraction on Alum Mountain in 1878 and in 1890 works were established at Bulahdelah for the production of alum and aluminium sulphate. Local consumption in Australia for alum was too small so the company exported the material to Runcorn near Manchester, England, where it was processed for use in the textile industry. In 1917, this alunite deposit was reported as one of only three known deposits in Australia and the largest deposit above ground in the world. Extraction continued on and off until 1952, having extracted over 73000 tonnes of ore.
The Dungog Chronicle, November 1924, records ‘A great quantity has been exported to Liverpool, England—generally as ballast for wool ships—where it is first put through dehydrating furnaces, then treated with weak sulphuric acid in lead lined vats heated to boiling point, and run off into crystallizing tanks. The crystal alum is finally washed and refined.’
Alunite varies in colour from white to yellow grey. The mineral is a hydrated aluminium potassium sulphate and occurs as veins and replacement masses in trachyte, rhyolite, and similar potassium-rich volcanic rocks. It is formed by the action of sulphuric acid bearing solutions on rocks during the oxidation and leaching of metal sulphide deposits. A scientific paper on the hydrothermal alteration at Alum Mountain by Ross Jenkins and John Nethery was published in 1992 entitled The development of Early Permian sequences and hydrothermal alteration in the Myall Syncline, central eastern New South Wales.
The mined alunite was sent by an incline tramline to bins on the bank of the Myall River, transported by steam punts to Port Stephens, and from there, conveyed to Sydney by steamer, to be shipped in bulk overseas. Quarry sites and ruins of the mining and transport of alunite still remain on the mountain and can be seen via the trail which winds up the incline to the lookout at the top.
About the NRG specimen
An eastern bypass of Bulahdelah Township on the Pacific Highway was approved in July 2007 under a joint Commonwealth—New South Wales initiative worth $315 million, enabling the construction of 8.6 km of new four-lane divided highway around the base of Alum Mountain. The bypass was opened on 27 June 2013.
During the excavation for the bypass, a D9 Bulldozer encountered a large chunk of rock which the driver immediately observed as different from the usual material encountered in the balance of the road site. The rock specimen was identified as typical of the alunite veining within rhyolite which was mined on Alum Mountain. The Bulahdelah Historical Society took charge of the spectacular ore specimen.
This is the nine tonne rock which the Bulahdelah Historical Society donated to the National Rock Garden, to be placed in a secure facility open to the Australian public in perpetuity, with appropriate cultural, historic and scientific information to be available on smart phone/tablet apps, and on the NRG web site.
The Bulahdelah Historical Society and the local Chamber of Commerce wanted to have this unique mining history shared with the public as part of the NRG with a view to stimulating geotourism in their small rural community.
After funds were raised to cover the costs of the shipment from Bulahdelah to the ACT, the rocks were placed on a truck and moved to the NRG’s rock storage site in Canberra on 16 September 2015.
DID YOU KNOW?
The Roman army doctor Dioscorideas referred to the medical uses for alum (which is derived from alunite) in his five volume encyclopedia called ‘De Materia Medica’, where he writes about using alum to stop bleeding, as well as to aid skin ulcers, dandruff and eczema.
Bulahdelah and Districts Historical Society
The Bulahdelah and Districts Historical Society was formed in May 1982 to preserve the unique history of the Bulahdelah area. The Courthouse Museum which now houses the collection of artefacts is made up of the main court building as well as the old kitchen/ laundry as well as the cells and holding courtyard area. The Society boasts a fine garden surrounding the Courthouse complex.
The Society has a fine collection of historical photos most of which have been digitised covering the local timber industry, alunite mining and village infrastructure like bridges, roads and buildings. The Society also runs activities during the year with historical talks, display, and attendance at the local Bulahdelah Show plus film nights from time to time.
Acknowledgements
The NRG Steering Committee is very pleased to acknowledge the support of the National Cultural Heritage Account of the Ministry for the Arts in the Attorney-General’s Department which provided the NRG with a grant of $3,300 in June 2015 to cover the transportation costs and the preparation of the specimen for display. The NRG also thanks the Karuah LALC, representing the Worimi people, for supporting the placement of this rock in the NRG, and the Bulahdelah Historical Society and the local Chamber of Commerce for encouraging the NRG to apply for a grant to acquire the specimen.
It is planned that a formal public promotion of the placement of this rock at the NRG will be conducted in Canberra when it is moved to a final display position in 2022.
Want to know more?
Bulahdelah Historical Society: http://bulahdelahhistorical.org.au/
Alum Mountain: http://www.geomaps.com.au/scripts/alummountain.php
An interesting video discussion of the mine operations and the characteristics of the region presented by Historical Society President, Kevin Carter, is available at: https://www.manningrivertimes.com.au/story/6306661/our-history-our-memories-thelegacy-of-bulahdelah-and-alum-mountain/
About the mineral alunite: https://www.britannica.com/science/alunite
Heritage aspects: https://www.environment.nsw.gov.au/heritageapp/ViewHeritageItemDetails.aspx?ID=1650597
Ross Jenkins and John Nethery (1992). The development of Early Permian sequences and hydrothermal alteration in the Myall Syncline, central eastern New South Wales, Australian Journal of Earth Sciences, Vol 39: No 2, pp223-237. https://doi.org/10.1080/08120099208728016
Author
This information was compiled by Mike Smith, Chair of the NRG’s NSW Rock Selection Sub-Committee.
