Page 58 - 00 Volume 5 The Mine

Heavy machinery operators: (1)_____, Henry MacDonald, Joe Tohe, Clyde Lewis, Joe Slee, Reg Crampton and

Bob Ralph.
worked as an underground mine for about hole the size of a 3-bedroom house.
twenty years at the turn of the century. To avoid The contractors who work the mine for the Mines
further strain on the already overworked Department employ dredging because it is the easiest
underground mining industry, it was decided to and most economical way of getting rid of most of the
work Kimihia as an opencast. soft overburden.
First it was necessary to drain the lake and As well as millions of cubic yards of silt,
remove from 80 to 190 feet of pumiceous silt and excavations of the overburden has yielded numerous
fireclay overburden. So far the mine has yielded swamp kauri and rimu logs, as well as a beautifully
900,000 tons of coal. At the present rate of preserved Maori paddle. The presence of that relic is
mining the remaining 1.75 million tons should last evidence that the Waikato must have once left its old
another 20 years. course to form Lake Kimihia.
In two years a stopbank, one and a quarter miles long, The fireclay which forms the remainder of the
was built to mark the outer fringes of the workable overburden is stripped by a giant 5-cubic yard
deposits. It rises 13 feet above normal lake level, and excavator and loaded into motor scrapers which cart it
its crest, 31 feet wide, serves as a roadway for away for use in reclaiming the lake. The excavator
vehicles used in stripping the lake bed. Other can load a 25-ton capacity scraper in 1.5 minutes.

stopbanks divide the enclosed area into ponds. The Coal Uncovered
The Dredge’s Task The seam of coal exposed by these dredging
The pumiceous silt which forms the top layers of and stripping operations varies in thickness from 25 to
the lake bed is removed in two 30 foot slices by the 29 feet. It is broken up by blasting and loaded on to a
cutter-suction dredge. After the first slice has been short conveyor belt which takes it to the main conveyor
excavated and pumped ashore through a floating belt which in turn delivers it to the screens. There it is
pipeline, the water level is lowered by 30 feet and graded and crushed to "nut" size before being loaded
the process repeated. The dredge, which was into railway wagons. Kimihia "nuts" are used in light
prefabricated in Thames, is about 90 feet long and 28 industrial plants and the slack is sent to the Meremere
feet wide. power station.
It works 15 hours a day and removes 300 cubic Recently, hydraulic conditions set up by dredging
yards of material per hour - sufficient material to fill a caused two breaks in the main stop bank. This did not