Tui Mine, Te Aroha, Matamata-Piako District, Waikato Region, New Zealandi

Regional Level Types
Tui Mine	Mine
Te Aroha	- not defined -
Matamata-Piako District	District
Waikato Region	Region
New Zealand	Country

The Tui Mine is an abandoned mine site on the western flanks of Mt Te Aroha.

The mine produced a range of base metals, including copper, lead and zinc from 1966 to 1973, when it was abandoned by Norpac Mining Co. The site is located within the catchments of the Tui and Tunakohoia Streams, both of which flow into the Waihou River at the base of Mt Te Aroha.

The site consists of a number of mine adits, waste rock and ore dumps and stockpiles and deposited tailings from the ore processing. There are various water discharges from the site including adit drainage, natural catchment drainage and contaminated under drainage (low pH, high dissolved metals concentrations) from waste rock and tailings.

The mine closed in 1973, with Norpac Mining Co. going bankrupt in 1975. Abandoned mine sites like these are sometimes a treasure trove for mineral collectors, as Tui Mine proved, with fossickers uncovering a range of secondary lead, zinc, and copper specimens, often miniature to thumbnail in size, occasionally bigger.

The mine site was leaching heavy metals into nearby streams, and the tailings dam was under threat of collapse, which would have flooded parts of Te Aroha with water saturated with heavy metals. From 2011 to 2016, the New Zealand government undertook major remediation work costing around NZ$22 million. Since 1991, new mining ventures must lodge with the government a bond to at least partly cover the cost of this type of situation, however for the period the mine was open 1967-1973, no such law was in place.

The access road to the mine is closed and gated. A walk trail from Te Aroha passes nearby to the mine site, and it can be accessed from this for those keen and/or fit. The substantial rehabilitation of the site, means new specimens are unlikely from the location.

The deposit was discovered by Clement Augustus Cornes in 1884. The initial period of mining was between this date and 1902, and was singularly unsuccessful. Difficult access, a lack of capital, and the refractory nature of the ore all thwarted efforts. The mine was originally called the Champion, however went through several short lived name changes, several owners, with a number of named neighbouring leases.

The first company was the Thames Lead and Silver Company which intended to provide flux to the Te Aroha Gold and Silver Company, however the ore's high zinc content made it unsuitable. (Hart, 2016) provides a blow by blow description of mining during this period.

In the Norpac mining period, 100 tonnes per day of zinc, lead, and copper ore was being produced at 17% Zn, 7% Pb, 0.6% Cu, 1.3 oz Ag, with the Champion lode producing in addition 1.0 oz Au per tonne. The mine in this period produced a total of 13 159 tonnes of zinc concentrate, 7755 tonnes of Cu-Pb concentrate, 3040 kg of silver, and 69 kg of gold from 163 000 tonnes of ore.

The deposit contains two lodes called Champion and Ruakaka. The first trends north-east, and the second east-west, and diverge at depth. They are located along normal faults, consisting of quartz cemented wall rock breccia, within which is a younger brecciated zone cemented with quartz and sulphides. There are three generations of chalcopyrite, and two generations of pyrite formed by fault movement and brecciation episodes. Ore increases in richness where the lodes dip steepest.

The wall rock is massive andesite, where unaltered containing labradorite, augite, and hypersthene. This is overlain by a 3 metre zone tentatively called a tuff, then overlain by an 8 metre ignimbrite zone containing fragments of argillite, volcanic rocks, pumice, and much clays. This is overlain by a quartz andesite, then a quartz bearing volcanic breccia both strongly altered to chlorite, adularia, clay, and carbonates.

Alteration is strongest nearest the lodes, and envelopes them with magnetite altered to pyrite; pyroxenes to chlorite and minor calcite and epidote; plagioclase to adularia, calcite and epidote; adularia to sericite; and lastly the addition of secondary quartz.

There are at least three distal alteration zones occupying areas much jointed. The veins in these areas contain milky quartz, with occasional comb quartz in cavities. In places the quartz contains adularia, epidote, wairakite, and rare prehnite, with calcite in the vein centres.

The lodes occupy shear zones with strongly brecciated rocks, with quartz cemented fault breccia 1-5 metres wide, with the younger mineralised breccia within this, containing angular fragments of wall rock, white quartz, cemented with sulphides and finer grained clear quartz. The ore within this is unevenly distributed, and tends to decrease with depth. In order of abundance is yellow sphalerite, galena, chalcopyrite, pyrite, tetrahedrite, pale yellow marcasite, and trace cinnabar.

Pyrite is widely disseminated in the altered wall rock, while the other sulphides are confined to the lodes. The sulphides are disseminated in the cement, or found as veinlets. Bright red cinnabar encrusts some quartz lined cavities, and otherwise as druses. Kaolinite fills some cavities. The No. 3 level of the Ruakaka lode shows galena partly oxidised to cerussite, while the upper levels of the deposits show minor supergene covellite replacing replacing sphalerite and chalcopyrite.

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References