GIANTS ON THE GOLDFIELDS
By ALAN HASSELL ?
Copyright 7/7/93 all rights reserved
Dredging although not a new method of gold recovery in Australia actually became a payable method of gold recovery at the turn of the century. Dredging river beds for gold was originally attempted in varoius localities in California following the great gold rushes of 1849. Most efforts achieved poor results and the principle still in it's infancy was regarded a failure owing to poor returns and other problems.
Attempts to recover gold in New Zealand using dredges proved to be highly successful. It was also found that dredges could work the shallow alluvial workings where the depth of the alluvium was not over 40 feet in depth. During the early days of development of the dredge, numerous improvments were made to these so called MONSTERS until they became known as efficient gold winners.
One of the biggest drawbacks, in the early stages of development was the fact the tailings deposited astern of the dredge often blocked it in altogether. This was overcome with the introduction of elevators for stacking the tailings accoring to reports in the Australian Mining Standard of 17th March 1898. Having established when that particular article appeared, it is safe to say that dredging had only been introduced into Australia several years earlier.
Reinforcement of this is a mention in an old record in which the'Goldbank' dredge was operating in Glenmore, Otago, New Zealand in 1896, but dredging had not started in Australia. One of the pioneer's was a man named William Telford who gained his experience in N.Z. and bought a wealth of knowledge to Australia which he used to his benefit. The great advantage of dredging was the fact that it could be profitable in many rivers and alluvial flats where no other method of working it was applicable.
Owing to the enormous amounts of material being lifted and treated per day, area's considered unpayable could and often did yield handsome profits by dredging. In one report regarding New Zealand it stated that ground containing less than 2 grains of gold per ton had made the shareholders a good dividend, even after lost time for shifting the dredge and repairing breakages. Dredges were capable of lifting and processing 40-60 tons of material per hour from a depth of between 35 and 40 feet would cost, launched around ?3,500 to ?5000.
It was estimated that it would cost two men working on each eight hour shift, a blacksmith and manager with knowledge of machinery a grand total of between œ35 to œ45 per week expenses at the time. The gigantic machine's dimensions were usually the hull 92 foot long, breadth, over all, 23 feet, Depth 5 feet, width of well, 5 feet, length of ladder, 62 feet from centre of punt to centre of lower tumbler. The depth dredged with the ladder at 45 degrees is 35 feet.
Overhead view showing trommel, screens and sluices top left corner
The hulls were built of separate pontoons braced together with timber baulks 16'' x 12'' then decked out with Kauri. Ann average dredge would have 40 buckets on a continuous belt, each having a capacity of 3 cubic feet which in effect meant that 120 cubic yards of material could be treated with every revolution of the buckets. Steam engines were used to provide power to the plant, drive the trommels and a ten inch centrifugal pump. The later being used to supply an ample supply of water for the trommel and sluice boxes that has a fall of between 18 inches to two foot in every 12 feet.
Sluice boxes were 3 foot six inches wide and 30 to 40 foot long. Cocoa matting was placed under the perforated plates in the sluice boxes to retain fine gold and black sands (tin). In operation the buckets would rotate below the water level digging a huge hole, filling the buckets in the process.
Material bought up by the buckets would be dumped into a hopper which emptied into a revolving drum, now known as a trommel, with holes varying from 3/8'' to 1/2'' in diameter. Stones and course shingle fall onto a semi circular iron shoot which delivers the material to the sluice boxes, where concentrates are caught. Waste material is then delivered to the elevator which can be raised or lowered and are capable of stacking tailings 20 to 30 foot high. At least 25-26 dredges operated in the Ovens Valley, Harrietville and Bright area's between 1906 and 1921.
Another report suggests that as many as 42 bucket dredges were actually working in Victoria. Eleven in Castlemaine. One of the most productive operators at the time was the Junction 1 & 2 dredging syndicates, operating in harrrietville, between 1906-1921 produced 33,868 ounces from 396 acres and paid a dividend of ?43,112.00. Total production of gold in the same area from 1900-1922 was 296,028 ounces from 3,231 acres and dividends of ?302,965 were paid.
During the period 1933-54 dredging operations produced 32,329 ounces of gold from only 260 acres paying ?53,750 in dividends. The production from reef operations for the same period was only 15,078 ounces of gold recovered from a crushing of 15,368 tons of ore. in 1932, a massive dredge, the largest ever built in Australia was constructed by Thompson & Company of Castlemaine and assembled on the site at Eldorado, Victoria. The 328 foot long dredge weighed 2,100 tons had 120 huge buckets and could be lowered to a depth of 90 feet.
It was powered by huge electric motors using power supplied by the State Electricity Company. It was capable of treating 200,000 tons of material per month, working day and night. During the 1960s an upsurge of Australian History resulted in the Eldorado Dredge being added to the National trust register and declared a historic building in 1976. This massive structure can still be seen today, rotting away in the historic township of Eldorado, Vicoria.
The Eldorado dredge was dwarfed when the Harrietville (Tronoh) Company's dredge started operations in the Ovens River Valley in 1942. The Tronoh was the largest ever built in the Southern Hemisphere, weighing over 5,000 tons and cost ?378,000 to build at the time. It ceased operations in May 1954 and in August of the same year, the Eldorado closed down having recovered 70,664 ounces of gold and 1356 tons of tin.
Little is known about the activities and subsequent fate of the Tronoh or for that matter any of the other massive dredges that once worked and recovered gold in Victoria. Many were sold off as scrap and disappeared forever. Apart from the Eldorado another one is situated outside Malden on the road to ravenswood.
Many years ago another dredge worked Newstead, the worked ground has been restored to it's original condition and no traces of dredging operations can be found in this area. Much of the land today is currently under pasture. In 1985 Planet Resources Group indicated a modern version of bucket dredges could produce 20,000 ounces of gold annually from 3 to 5 million cubic metres mined down to 20 metres. The plant would cost ?15.000,000 and employ 40 people. On 12/2/1987 Bright Council objected against the resumption of dredging on the grounds of noise, pollution and land restoration. So ends an era when monsters ruled the goldfields. Maybe one day, we might see their return, but I cant see it happening as long as we have conservationists. Ends story Happy Hunting. ?
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