Dredge No. 4 is a wooden-hulled bucketline sluice dredge that mined placer gold on the Yukon River from 1913 until 1959. It is now located along Bonanza Creek Road south of the Klondike Highway near Dawson City, Yukon, where it is preserved as one of the National Historic Sites of Canada. It is the largest wooden-hulled dredge in North America.
With its 72 large buckets, the dredge excavated gravel at the rate of 22 buckets per minute, processing of material per day. It was in use from late April or early May until late November each season, and sometimes throughout winter. During its operational lifetime, it captured nine tons of gold.
Background
About south of the dredge's current site, further into the Klondike Valley, is the Discovery Claim where gold was found in August 1896 by prospector George Carmack, his Tagish wife Kate, her brother Skookum Jim, and their nephew Dawson Charlie. This is considered the site where the Klondike Gold Rush began.
Integral to the operation of the dredge were the services available at Dawson City. There, financial services provided by the banks, administrative services provided by the Government of Canada, and the rail and steamship transportation network terminating at the city ensured that machinery needed for operation of the dredge would be readily supplied.
The Canadian Klondyke Mining Company built the Twelve Mile ditch in 1909, which would supply the water to operate hydraulic monitors on dredges. It also built dams and ditches to generate hydroelectricity, and by 1911 the North Fork Hydro Power Plant was operational about from the dredges it energized.
History
Designed by the Marion Steam Shovel Company, the bucketline sluice dredge was built on site at Claim 112 Below Discovery from mid 1912 until the onset of winter. The assembly site was near Ogilvie Bridge, named for William Ogilvie, near the current location of the bridge carrying the Klondike Highway to Dawson City. Construction was supervised by Howard Brenner, an engineer employed by the Marion Steam Shovel Company, who also supervised construction of Dredge No. 3 at the same time. A contract for the parts dated 13 March 1912 specified their shipment to the site in the summer of 1912, at a cost of $134,800 for each dredge, and the hull was built by the Canadian Klondike Mining Company.
The Canadian Klondyke Mining Company began operating the dredge in May 1913. After eleven years of operation, it had cut its way to the Boyle Concession, where it sank in 1924. By 1927, it had been refloated and worked its way to Hunker Creek, where it could produce up to of gold a day at claim 67 Below Discovery. It ceased operations in the area on 11 July 1940, and was rebuilt by the Yukon Consolidated Gold Corporation on Bonanza Creek, where it resumed operations on 11 September 1941. The wooden hull of the original dredge was discarded, left in the pond where it sank, but all other parts were salvaged for use in the reconstructed dredge. It worked its way downstream on one side of the valley, then back up the other side, until being decommissioned on 1 November 1959.
The immediate success of the dredge resulted in the Canadian Klondyke Mining Company ordering the construction of two more dredges the following year.
Operation
The electrically-powered machine required while digging, and more when moving its gangplank. With its installed hydraulic monitors, the eight-storey dredge would cut into gravel banks, washing down the released material for processing. The machine created a dredge pond by virtue of its operation, its size dependent on the valley in which it was operating, but sometimes reaching . It would rotate on two spuds, each and long.
The digging ladder enabled the dredge to dig a cut with an average arc of about . This wide arc was possible because of the use of two spuds. It could reach above water level and below it, with each of the 72 buckets capable of moving loads up to . Each bucket weighed , each flange , and each securing pin .