Union Hill and the Waihi Battery
Union Hill is a remarkable heritage area which has a rich and colourful past.
Waihi - Union Hill - Waihi Battery:
The Ohinemuri district was formally declared a gold field on 3 March 1875. Up to 900 diggers made their way over the district, initially pegging claims around Karangahake Mountain where gold had been discovered by John Thorp and party in 1868. Unfortunately the scarcity of alluvial gold proved a major disappointment. Some promising quartz reefs were discovered in the Waitekauri Valley, and at Owharoa. The Waihi area was also prospected during 1876, without any payable gold being found.
Life in the Waihi district, at this time was at this time very primitive access being mostly by bridle tracks or clay roads which often followed old bridle tracks. Supplies brought in by boat were obtained from Paeroa, Bowentown or Katikati carried by drays if there were roads, or otherwise by packhorses. The country was mostly covered in heavy bush, except for the Waihi Plains which were covered in fern and stunted Manuka scrub.
The peak of English investment coincided with the first recognition of Waihi as the outstanding gold mining enterprise in New Zealand.
There is little left of tis once great industrial site, but the remaining concrete buildings and foundations have a story to tell and the heritage value of this site is immense.
- Investment by large English companies allowed vast outlay for exploration, and mine development expensive machinery and to experiment with new technology.
- First claims probably staked out on Union Hill in 1884 or 1885 included the Union, Pride of Waihi, (later Rosemont) and Amaranth.
- 1885 first shaft sunk (Old No.1)
- First Waihi Gold Mining Company floated in London December 1887 and purchased the Union, Rosemont, Amaranth and smaller Trio, Nelson and Winner claims.
- Company commenced construction of a new battery at the base of Union Hill early 1888 completed 1889.
- Union Company of 1895 became subsidiary of Waihi Co by 1900.
- 1898 Waihi battery expanded from 69 to 90 stampers.
- 1895 -96 Waihi Battery was enlarged to 90 stamps making the Waihi mill the largest in NZ at the time.
- The base of Union Hill was the site of the Waihi Battery also known as the Waihi Mill, at one time the largest processing mill in New Zealand.
- Hill itself extensively mined by a succession of mining concerns.
- 1888 - First ore roasting kilns to be built on the Hauraki Goldfields.
- 1893 - Additional kilns constructed.
- Thirteen on site, ten in remarkable condition still exist. Victoria battery at Waikino only has five roasting kilns.
- 1894 February, Cassel's plant completed first successful use of cyanide at Waihi, demonstrating beyond question that Martha low- grade ore was suitable for treatment with excellent results from this method.
- Six air- agitation tanks( also known as B& M, cyanide, Pachuca, conical or tall tanks)
- The only air-agitation tanks still standing in NZ.
- 1909 two built - 1910 four built constructed of Ferro - concrete.
- The Smelt house and Refinery operated for the life of the Waihi Battery, and the Victoria Battery.
- Entire production of gold/silver precipitate of the WGM Company and latterly Martha Gold Mining Co, was treated and refined on the site, refined gold and silver being the end product.
- Virtually the entire bullion production of the Waihi district passed through this facility.
- The Old Union No. 1, and the New No.1 and Mascotte shafts are still open.
- The New No 1. Shaft retains rare winding engine - room remains.
- Numerous adits can be found on the hill.
- Amaranth adit being the most notable.
- Firewood for kilns and engines is conveyed from the bush by tramway.
- 1900 Tramway connects the Union mine with the Union battery.
- 1901The Waihi GMC takes over the Union - Waihi Company's properties including the Silverton Union battery, Moore Street.
- 1902 Mining stops on Union Hill
- 1902 Waihi stamp-mill altered from dry to wet-crushing, conversion completed January 1903.
- 1903 Shed over ore roasting kilns removed.
- 1907- Sawmill erected to deal with timber brought down the Mataura Tramway.
- 1911 Union mill closed down
- 1912 Waihi Strike
- 1913 Waihi Mill has closed
- The early tailing ponds on the site were literally scrap heaps of used machinery, rails, broken stamper blocks, heads and other discarded mill residues.
- Mineral Resources 1970 - 80 scavenged 90 tons of cast iron and steel located in these ponds.
Ore Roasting Kilns:
- Ore was taking directly from the mine to the drying kilns where it was partially roasted.
- Quantity of firewood used ton for ton of ore.
- Why roast the ore?
- The drying would cause some oxidation of any sulphides in the ore and enhance the ability of the finely divided gold and silver to form an amalgam with the mercury when the crushed ore was mixed with it in the amalgamating pans.
o Main advantage was the greater ease with which the dry ore could be reduced to a very fine state in the stamp mortar- boxes.
- Built over a period of 1888-89 first four first built on the Hauraki goldfield
- By 1895 13 ore roasting kilns in use with an average capacity of 150 ton
- These brick lined ore roasting kilns and narrowest at the bottom like an inverted cone.
- Dried ore was drawn off from beneath the base of the kilns via a brick arch fitted with steel doors via shared access tunnels, into trucks, which were hoisted hydraulically to the crusher floor.
- The kilns worked on a continuous system by drawing off dried ore every three days.
- Kilns replenished by placing alternate layers of firewood and ore every 5 feet
- Range from 6.7 to 8m in diameter and 8 to 8.5 m in depth.
- Average capacity of kilns 150 tons each,
- 1902 Conversion from dry crushing to wet crushing, kilns redundant.
- 1903 Shed over kilns removed.
The Waihi Battery:
- Constructed in 1888, set up for dry crushing of ore the battery consisted of a cluster of buildings and other structures that were added to, modified or demolished and replaced over time.
- First building erected were a large mill house, engine/boiler house, sheds for drying kilns and rotary furnace, as well as blacksmiths and carpenters shop.
- Power was provided by wood-fired steam engines, later supplemented with water power generated from pelton wheels located in adjacent shaft.
- By May 1905 five Babcock & Wilcox boilers with automatic chain-gate stoker were installed in the power house
- Did not utilise stampers for crushing but used Globe rotary mills
- 1889, 30 head stamper battery installed, a further 30 stamps added 1890 or 1891, another 30 1884, total 90.
- Mining ceased Union Hill 1902 shortly after Union - Waihi properties has reverted to the Waihi Gold Mining Co. At this time the battery was also converted from dry to wet crushing.
- Waihi mill closed 1913, mainly due to reduced quantity of ore from the Martha mine and from then on ore was processed at the larger Victoria mill at Waikino.
Cyanide or Brown, or B &M (air-agitation) Tanks:
- Two built 1909 another four added 1910
- One local invention which became famous throughout the world was the B&M, agitator which made a great contribution to the successful treatment of ores by the cyanide process.
- These tanks consisted essentially of introduced compressed-air agitation of the pulverised ore in cyanide solution; this kept the pulp in circulation as nothing else could have done and at the same time provided supply of oxygen to assist in dissolving the gold and silver.
- Constructed of Ferro-concrete they are the largest surviving tanks of their kind in New Zealand.
- The six tanks are 16.7 m high and 2.7 m in diameter mounted on basal plinths.
- During 1889- 90 experiments were being carried out by the Cassel Cyanide Company into the extraction of gold by solution with potassium cyanide and precipitation with granulated zinc.
Extracts from Mine Statements for the Waihi Area 1881 - 1915
Gold Mining at Waihi 1878 1952 - J B McAra -Martha Press. 1988
The History of Gold Mining - J.H.M. Salmon- Government Printer .1963
A Survey of Historic Mining Sites in the Thames and Ohinemuri Areas of the Hauraki Goldfield - Neville A. Ritchie- DOC- Waikato Conservancy - 1990
Coromandel Gold- Phil Moore & Neville Ritchie- 1996
Conservation Plan for Union Hill, Waihi - Phillip R. Moore, Eric Lens, Ruth Ordish 2009.
Scavenging for Gold. J.P. Barbarich Managing Director, Mineral Resources (NZ) Ltd