Waihi Gold Mining Company Cyanide Tanks
Union Hill, Barry Rd, Waihi
List Entry Information
List Entry Status
List Entry Type
Historic Place Category 1
Private/No Public Access
15th February 1990
Date of Effect
15th February 1990
Pt Sec 356 Blk XVI OSD
The cyanide process for the extraction of gold from crushed ore made possible the economic operation of non-alluvial goldfields in New Zealand, and elsewhere e.g. Australia, United States, Mexico and South Africa. The world's first field trials of the process were held at Karangahake in 1889, and the patent was acquired by the New Zealand Government in 1897. So successful was the process that the Government, through the charging of a small royalty, had recovered its initial outlay by 1905. The process involves the mixing in the tanks of the finely-ground goldbearing ore in a solution of potassium cyanide. The suspension or slime was continually agitated by compressed air. It was then trickled over a bed of coarse metallic zinc on which the dissolved gold was precipitated, to be recovered by mechanical washing. In New Zealand and Australia the tanks were known generally as B & M tanks after their developers, Brown and McMiken, but elsewhere they are commonly referred to as Pachuca tanks.
Historical Significance or Value
These tanks are a spectacular physical reminder of the leading role played by New Zealand mining engineers in the development at the turn of the century of a new method of gold extraction from low grade ores. It enabled the Coromandel-Thames-Ohinemuri fields to be more fully exploited, and for a time, to figure as some of the highest producing gold mines in the world. The process was widely employed elsewhere in the world.
These cylindrical concrete tanks are the only examples of this type of construction and size in New Zealand.
These huge concrete cylinders which dominate the site of the former gold workings have a considerable landmark value.
Brown, C F
When he designed and built the first cyanide tanks to use the agitation process for the extraction of gold from low grade ores from cyanide solution, C.F. Brown was general manager of the Komata Gold Mines, Ohinemuri.
These six concrete cylinders are the largest cyanide tanks remaining in New Zealand. The cylinders are 16.7 metres (55ft) high and 3.66 metres (12ft) in diameter. Cyanide tanks elsewhere were smaller in size and variously made of wood, iron or steel.
Size and material of construction.
McAra, J. B., 1988
J B McAra, Gold Mining at Waihi 1878-1952, Waihi, 1988
L Barber, 1985, No Easy Riches : a History of Ohinemuri County, Paeroa and Waihi 1855-1935, Ohinemuri County Council and Richards Publishers
Porter, 1983 (2)
Frances Porter (ed.), Historic Buildings of New Zealand: North Island (2nd edn.), Auckland, 1983
This historic place was registered under the Historic Places Act 1980. This report includes the text from the original Building Classification Committee report considered by the NZHPT Board at the time of registration.
Please note that entry on the New Zealand Heritage List/Rarangi Korero identifies only the heritage values of the property concerned, and should not be construed as advice on the state of the property, or as a comment of its soundness or safety, including in regard to earthquake risk, safety in the event of fire, or insanitary conditions.