Waihi Dredging Plant
The water level in the lake appears to have been similar to present, as the masonry dam has lost only timber capping of a few centimeters.
Tailings from Waihi batteries were discharged directly into the Ohinemuri. Before the cyanide process was used, tailings from the Waihi and Karangahake batteries could still contain 60% of their bullion content.
Perhaps a dragline initially, and certainly a suction dredge (30 ton per hour) was used to lift the tailings from the river. A bank-side bucket-chain elevator removed the tailings from the dredge barge, depositing them in a holding tank built in the river bank in front of the processing plant. Neither the foundations of this elevator, nor the tank are visible at the site (though no excavation has been attempted).
The tailings were elevated (bucket-chain) from the holding tank into the plant where they were cleaned and sorted for size (possibly in the area at the eastern end of the present foundations).
Eventually four tube mills were used to grind the tailings to the required size. They were about 20 ft long, about four feet in diameter, horizontal tubes, supported with bearings at each end. At one end was a geared drive wheel (with allowance made for this in the concrete mount).
The mountings for these tube mills, and the base of a large elevator, and the steam engine mounts make up the bulk of the intact foundation remains presently visible at the site (see plan on photograps page). Of note is the inclusion in some of the concrete mounts of (presumably used) flint stones. This may help establish the construction sequence of these foundations. Flints can also be found loose in the soil near these foundations, and a deposit of flint fragments is visible in the grass. Note also that a piece of concrete has fallen from the elevator base, and lies on the ground beneath it.
From the tube mills the slurry was processed in six large vertical air agitation tanks (cyanide tanks) to the north of the main building. Some of their bases are visible in the earth.
There existed several other buildings on the site, including assay room, boiler house, and a residential house (Bill Lawrence recalls people living in the house into the 1950s). The early photos do not show a boiler stack, but a latter one shows a new building with large stack, and substantial extensions to the plant. I wonder if an early boiler house may have been behind the main building, and therefore not visible (though I would still have expected to see the stack). The plant would have required considerable power.
A brick floor, presently covered by soil, may be remains of this later boiler house. Considerable other foundations are covered by soil also (evidence found by probing); excavation would be required to expose and document these. Bricks can be found in the soil around the whole the site.
A bulldozer modified the site circa 1985. Many concrete foundations and mounts have been moved from their original locations, and accumulated in several heaps about the site.
Old photographs of the early plant show what could be a tailings flume, or perhaps water race flume. It is not apparent whether water power was used. The purpose of the flume is unclear.
There was visible evidence of an access roadway through the paddocks, heading back to Waihi (2002). The stone foundations of this roadway were found by several new owners of the new subdivision.
Sand was found during the construction of the modern (2003) house on this site. This appears to be too coarse to be tailings from this plant (which were ground to slimes), so may have been stockpiled sand (the raw materials for this plant, dredged from the river).