Annual General Conference AssemblĂŠe gĂŠnĂŠrale annuelle Edmonton, Alberta June 6-9, 2012 / 6 au 9 juin 2012
Gold Dredging in the Klondike and Number 4 Ken Johnson AECOM Abstract: The large scale mining era in the north that followed the Klondike Gold Rush pioneered techniques in northern planning, northern transportation, northern water resource development, northern mining, and the associated construction that is unique to the north because of the cold weather, permafrost, and isolation. Associated with the mining was the application of bucket dredges for mining placer gold. Dredge #4 is the largest vessel of its kind in North America for picking up gravel from a creek bed washing it with water to separate the gold and discarding waste rock at the discharge end. Floating on a pond of its owns creation the dredge lifted the gold bearing gravel by means of a chain of buckets. The buckets emptied into a hopper which fed into an inclined revolving circular screen (or trommel) where the gravel was washed by immense volumes of water. The fine material passed through the holes in the trommel into gold saving tables where it was sluiced and the gold was collected in a series of riffles and mats. Dredge #4 is 2/3 the size of a football field and 8 stories high. It has a displacement weight of over 3,000 tons (2,722 t), with a 16 cubic foot (.45 cubic metre) bucket capacity. Dredge #4 originally constructed in 1912 and was operational on the Klondike River in 1913; the dredge was completed reconstructed at a new operating site in 1941 using the original machinery and replacing all of the timber. The dredge is now a National Historic Site under the management of Parks Canada. 1.
The Gold Rush and the Introduction of Industrial Mining
George Carmack and two aboriginal companions, Skookum Jim and Dawson Charlie, made history on August 17, 1896, when they discovered gold on Bonanza Creek, a tributary of the Klondike River in the Yukon Territory. News of their discovery did not reach civilization until the following summer, but when it did it started the gold rush which spread across the continent. Men and women sold their shops and belongings to buy passages at Vancouver, Victoria, or Seattle on one of the coastal ships going north. From there they carried their supplies for 60 kilometres on their backs, climbing either the rugged White Pass or the Chilkoot Pass to the head of Bennett Lake. Once at Bennett Lake they constructed makeshift boats and rafts for a 800 kilometre trip to Dawson City. Before the 1898 winter freezeup more than 7,000 watercraft, carrying 30,000 gold seekers, were registered with the North West Mounted Police on the Klondike River system The so called gold rush was short lived and as much as it left a cultural legacy for the Yukon, it had limited influence on the long term gold mining of the Yukon. The reason for this is that the mining technology was crude and only effective for capturing the richest deposits of placer gold. More efficient technologies were needed to capture the deeper low grade deposits, the mining claims were too small for efficient operations and there was insufficient water for large scale mining. After the rush ended enterprising individuals began the process of removing the limitations. Machines, called gold dredges were brought in to undertake the large scale mining and the individual claims were consolidated to provide the working space for the dredges. GEN-1043-1
Figure 1: One of the original gold dredges operating in the Klondike circa 1900 Placer dredging, developed in New Zealand in the 1860's and refined in California by the late 1890's, was the most effective method of mining low grade placer gold deposits. The key was handling large volumes of gravel and sluicing out gold; a dredge could do the work of hundreds if not thousands of men. In September 1898, the first dredge in the Yukon began working the Yukon River. In 1905 large corporate interests had organized the land holdings covering much of the Klondike River valley and adjacent creeks. Large scale dredge operations began with a modest 0.21 cubic metres (7.5 cubic foot) dredge; dredge size was indicated by the size of the buckets scooping up the gravel, and a large bucket size meant a larger dredge. To support the operation of a dredge, a camp was required with a bunkhouse, several warehouses, a wood-fired electric power plant and a machine shop. A much larger and more sophisticated operation was soon to follow, and by 1910, construction of a 7500 kW (10,000 horsepower) hydroelectric plant, capable of operating year round, and the erection of the world’s largest dredge, with 0.45 cubic metre (16 cubic foot) buckets, was underway. Powering the dredge required electricity, which was provided by the development of hydro electric projects on the 12 Mile River, 40 kilometres north of Dawson City, and the North Klondike River, 30 kilometres east of Dawson City. Although the large dredge cost almost a half million dollars, its immediate financial success prompted an order of two more sister dredges in 1912. All of the machinery and wood structures used in the construction of the dredges were shipped unassembled from the south. The unassembled machinery and wood was shipped on a route that included ocean vessels, narrow gauge railways, and stern wheeler river boats. The operation of the dredges required the development transportation systems (land and river) capable of managing individual components that weighed as much as 20 tons. The transportation logistics for the equipment alone were immense with a 2500 kilometre transportation route from the Port of Vancouver to Dawson City. Once on site in the Klondike the equipment required complete assembly.
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The dredges were the end beneficiary of a civil engineering works that included the White Pass and Yukon Railways (transportation of machinery and timber), the Yukon River sternwheelers (transportation of machinery and timber), the Klondike Mines Railway (transportation of machinery and timber), the Yukon Ditch (a 115 km series flumes, ditches, piping used to supply water for hydraulic mining), and the 12 Mile River and North Klondike hydro electric projects (used to provide power for dredges operating in the area). 2.
How Dredges Work
A gold dredge is essentially a giant gold pan mounted on a floating barge. One end of the dredge picks up the gravel from the creek bed, the middle section washes the gravel with water and separates out the gold, and the other end discards the waste rock and water. The digging ladder is a large triangular steel box hinged at the rear. Dredge buckets, connected to each other with large steel pins, are wrapped around the length of the digging ladder, much like a chain saw blade. The buckets on Dredge #4 weighed almost 2100 kg (4,600 lbs) each and lifted almost 800 kg (a ton) of gravel. The bucket line, equipped with 68 of these buckets, could dig 14 metres (45 feet) below water level. Every minute the ladder lifted as much gravel as three men could shovel in a whole day. Pivoting on the large spud anchoring the back, the dredge was winched from side to side cutting a great arc in the gravel face and leaving a pile of coarse tailings behind. On its way up the digging ladder the “bow decker” scraped the clay off the lips of the bucket ensuring every piece of gold went through the dredge. At the top the buckets emptied into a large dump box. Tumbling through the box, the gravel was washed into a large, sloping, rotating cylinder known as the “trommel”. The trommel, perforated through its length with holes from 6 mm (¼ inch) diameter at its upper end to slots 18 mm to 37 mm ( ¾ inches to 1 ½ inches) at the lower end, weighs 73 tonnes (80 tons) and is 15 metres (50 feet) long and 3 metres (10 feet) in diameter. Suspended in the trommel is a large pipeline spraying water up the slope to ensure the gravel was well washed and that all the lumps are broken up. Boulders and large stones rolled down the length of the trammel and onto a conveyor belt that carried them up the stacker, dropping them 37 metres (120 feet) behind the dredge. The sweeping action of the dredge operation marked the dredge’s passage with the deposit of tailings in a distinctive arc pattern. Gravel, sand, and gold were washed through the trommel perforations into a distributor box underneath and from there flowed onto the sluice tables. The sluice tables are long troughs with coconut matting and steel riffles on the bottom. A constant flow of water kept all the material moving down the sluices. The heavier gold, caught in the matting and riffles, stays behind. Three quarters of the gold was caught in the first 1.25 metres (4 feet) of coconut matting with another fifth concentrated in the small distributor. Waste gravel and water spilled over the stern into the dredge pond.
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Figure 2: Operating components of a gold dredge
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Figure 3: Exterior of rotating trommel in Dredge #4. 3.
Building Dredge # 4
Dredge No. 4 is two thirds the size of a football field and 8 stories high. It has a displacement weight of over 2700 tonnes (3,000 tons)). The dredge could dig 17 metres (48 feet) below water level, and 5 metres (17 feet) above water level using hydraulic monitors and washing the gravel banks down. The dredge has a pumping capacity of 19 cubic metres per minute (5000 USGPM). The cost of the dredge in 1912 was about $500,000 ($12 million today). Dredge #4 originally constructed in 1912, and was operational on the Klondike River in 1913. By the First World War a dozen dredges, including some of the largest in the world, churned through the valleys of the Klondike region. Dredge #4 was purchased from the Marion Steam Shovel Co. of Ohio. All the lumber for the dredges was precut in southern British Columbia and ready for assembly. Shipped from Vancouver, the dismantled dredges went over the coastal mountains from the ocean port of Skagway by the White Pass and Yukon Route Railway to Whitehorse at the head of navigation on the Yukon River. At Whitehorse the platforms and warehouses were choked with the thousands of tons of freight; some of the crates weighed over 20 tons. Stern wheeler boats relayed the material down the Yukon River through the summer of 1912.
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Figure 4: Dredge #4 resting on Bonanza Creek On a site near the Dawson City townsite, almost 200 men and two steam shovels began preparing a large square pit 4.5 metres (15 feet) deep for the construction of the hull. The Klondike Mines Railway, its main line running just beside the construction pit, was busy hauling machinery and lumber from the Yukon River docks at Dawson to the site. By mid-August 1912 the hull framing was completed, and about 300 carpenters, pipefitters, and mechanics continued the work on the superstructure until cold weather stopped construction. Freeze-up on the Yukon River at the end of October, 1912 stopped a supply sternwheeler on route from Whitehorse carrying the last hundred tons of dredge machinery, at the Indian River, about 40 kilometres (25 miles) south of Dawson. In February, 1913 a winter road was cleared with a snow plough to provide access to the stranded sternwheeler. Twenty horses and several rigs began hauling the remaining machinery up to the dredge assembly site. By mid-March a small crew began to prepare the dredge for completion. As the weather warmed and the delayed equipment arrived more workers were hired. The machinery was installed, the superstructure painted, and by early May the huge dredge was ready to start to work. From its construction berth Dredge #4 started working east through land consolidated into one claim years before. As the dredge headed east it turned into the Bonanza Creek basin. The flats in this area had been a popular site for market gardens since the gold rush. As the dredging advanced 26 cabins were torn down or moved to make way for the dredge. Although some of the buildings belonged to long time residents, there was little protection for them because the Placer Mining Act gave the mining rights precedence over any surface rights. The land owners were paid the equivalent of the land clearing costs, assisted with moving their buildings, and paid for any vegetables ready for harvest.
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4.
Operations Surrounding Klondike Dredges
Five years of ground preparation is generally required before a dredge can mine the “paystreak” section of a gravel deposit. After prospecting with drills, the area with sufficient gold present is outlined as the ore body or “dredge limit”. Then the vegetation and any previous development must be cleared. Once exposed, the frozen muck begins to thaw and this is washed away to along the thawing to continue. One or two years before dredging, cold water points thaw the gravel to bedrock, and finally the dredge begins working the area. The large dredges usually ran for about 250 days each year. The digging usually started in late April or early May and continued 24 hours a day until heavy ice in the dredge pond blocked operations. A crew of about 10 men worked on Dredge #4. A "bullgang" on shore prepared for the dredge’s advance while on board men serviced equipment, guided the digging ladder, and kept the dredge clean. If there was a breakdown, it was an emergency because with a short season to mine it was critically important to make sure the dredge got as much gold as possible. The crews spent their time making sure nothing jammed and replacing worn equipment with a minimum of lost time. Two bow and two stern lines connected to “deadmen” on shore provided the anchoring system for controlling the movement of the dredge by an onboard winching system. The winching system allowed the dredge to move side to side from its anchoring point at the rear of the dredge, referred to as the "spud", and then ultimately advance to a new dredging position. Deadmen were large logs buried into the ground by the bullgang. The bullgang for Dredge #4 consisted of five men because the anchoring lines were so heavy. The bullgang also built dams to control the water levels in the dredge pond, and made sure that the power cable to the dredge was long enough.
Figure 5: Winching system for constant re positioning of gold dredge during operations. On board the dredge there was a hierarchy of positions, and the 10 man crew worked their way up through these positions with time. The lowest position was the bow decker, who was responsible for the front half of the dredge, the bowdecker scraped off the bucket lips, watched for damaged buckets and broken pins on the line, and kept the bow deck clean. He also pulled large roots and logs out of the buckets and cracked big rocks with a sledge to prevent jams in the dump box.
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The stern decker watched the course tailings conveyor or “tailings stacker” making sure it stayed clear of the tailing piles and didn’t bury the power cable. Especially important was making sure that nothing jammed the flow of gravel and rocks up the stacker. Most of the time the stern decker wasn’t that busy and had time to learn skills like cable splicing that were necessary for promotion to the position of oiler. The oiler had a very busy job because he looked after all the equipment on board, serviced the pumps, motors, tumblers and main drive. A strict routine of maintenance minimized the risk of breakdown as wearing parts were spotted before they failed. He also relieved the winchman for breaks and got to practice winching. The dredge master was responsible for the upkeep and output of the dredge. He planned the mining strategy for the creek, kept the dredge sheets noting crew hours and breakdowns, and ran the dredge during the day shift from the control room. Winchmen took over for the evening and night shifts, controlling all aspects of the dredge operation. During his shift the winchman ran the digging ladder, controlled the back and forth sweep of the dredge, and supervised the crew.
Figure 6: Control room or “winch room” on dredge #4; space heater is seen in the foreground Twice a week, and more often in especially rich ground, two men came out from the main camp and collected the gold from the dredge sluices. The dredge would shut down briefly while this clean-up crew rolled up the coconut mats at the very top of the sluices and took up any riffles showing gold below the mats. They gathered the mats and the dirt shoveled from the riffles into a large wooden clean-up box. New mats and the cleaned riffles went down and the dredge started up again. More thorough clean-ups of the whole dredge took place periodically. The clean-up crew washed out the mats, and using the small sluice box next to the wash box, they began concentrating the of roughly 70 kg (150 pounds) of sand and gold. By the time they finished there was about a half pail full of black sand (magnetite) and gold. This pail and the mat used in the sluice box were labeled with the dredge number and packed into the back of their truck. At the end of the day everything was hauled back to the gold room at the main camp for cleaning.
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At the gold room the worker dumped the material into a gold pan and gradually worked it down. A magnet removed the black sand and panning removed surplus sand. Eventually the gold pans were dried in the oven and set on the floor by the back door until they cooled off. Then the gold was screened into pieces of about the same size to ease the final cleaning. Buckshot and iron pyrite (fool’s gold) were picked out and the fine sand was gradually blown out. Finally, the superintendent weighed the gold, credited the gold to the dredge, and put the gold in a five pound baking powder tin. Several times a month the gold was melted into gold bars utilizing a furnace. The gold bricks, usually a dozen at each melt, weighed 300 to 450 ounces each. 5.
Rebuilding Dredge #4
The high cost of maintaining an aging Dredge #4 limited the corporate profits, and in a ten year period through the 1930's the vessel made only $16,000 profit. In June 1939 the hull sprang a leak and in three minutes the dredge sank to the bottom of its pond. Although soon refloated the company knew the gold reserves in the area of Hunker Creek, 14 kilometres up the Klondike River from Dawson City, were almost exhausted, and therefore the dredge had to be moved. Engineers began planning a reconstruction of the dredge on Bonanza Creek for 1940.
Figure 7: Dredge #4 operating in the 1950's Over the 30 year life of old Dredge #4, there had been no significant improvements in dredge technology, and new dredges worked generally the same way as old dredges. The only problems with #4 were its disintegrating wooden hull and the lack of ground left to dredge in its current location in the Klondike Rive valley, and therefore the rebuilding plan included relocation and reuse of most of the equipment on the new dredge. In late August 1940, old Dredge #4 was shut down, and a crew began dismantling the dredge, salvaging much of the superstructure, and using the dredge winches to lift off the pumps, motors, trommel and other heavy gear. At the end of September a bulldozer dragged off the last pieces of machinery to the main camp. The old wooden hull was abandoned in its tailings where it finished working.
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Through the spring of 1940, the site for the new dredge was also being prepared. The road up Bonanza Creek, was improved and allowed the heavy pieces of machinery and huge new timbers to be hauled in. Bulldozers prepared a construction yard and dredge pit about three kilometers up Bonanza Creek from the Klondike River. A crew moved in a camp mess house and set up tents for the 70 workers, and built a temporary office and workshop. Power and telephone lines reached the camp and by mid-June construction material arrived at the site. The construction yard was a well-ordered space with all the timbers for the construction of the new hull laid out beside the road in the order of construction. Carpenters chamfered the edges of the big beams by hand, and a crew of painters primed each timber. The larger timber frames making up the hull were preassembled in the yard. Fitting work was complex and everything was measured and re-measured. In August 1940, a large 20 ton derrick began lifting the completed frames onto the prepared hull foundation and the scow began to take shape. At the end of October the crew pumped the pit full of water, the new hull floated, and work stopped for the winter. In the spring of 1941 work resumed on the superstructure with all of the reconditioned machinery arriving at the dredge from the main camp. In spite of the shortages of skilled labour as a result th of World War Two, by September 18 work was largely completed and it started digging. The design changes to Dredge #4 were the lengthening of the digging ladder and the tailings stacker, which were improvements which allowed the dredge to dig deeper down to the bedrock on Bonanza Creek. 6.
The Legacy of Dredge 4
Dredge #4 operated until 1959 with the termination of operations a result of gold production that could not keep up with the operating costs. The dredge sat in the final pond for more than 30 years before work began in 1991 to recondition it for a tourist attraction. During the summers of 1991 and 1992 the dredge was excavated, refloated and relocated by the Canadian military to its current position on higher ground to protect it from seasonal flooding. This significant historic resource and local tourism attraction is at the mid-point of a multi-year restoration project. The goal of the project is to repair and stabilize the front end of the dredge around the digging ladder by replacing rotting components with new wood. This project is part of a long-term project designed to stabilize the whole structure, an important cultural resource and designated national historic site. Repairs to Dredge #4 will help to ensure that this important symbol of Canada's history of gold mining, and extraction is protected in the future. A total of 19 dredges have operated in the Klondike region over the period of 1900 to 1966, and Dredge #4 is the only remaining intact dredge. References Johnson, Kenneth. Personal Photographs of Dredge #4. 2008. Neufeld D., Habiluk, P. Make it Pay! Gold Dredge 4 Parks Canada Website. www.pc.gc.ca/lhn-nhs/yt/klondike/natcul/natcul-dn4.aspx
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