Brooks on an |Accident to, and repair of, Dredge 21 at Yuba, California' in which the author outlines the extensive damage done to a bucket-line dredge when the digging face collapsed, and the subsequent $US 4.1 million repair programme.
MacVicar asks |Why use bucket-line dredges and what developments are involved in taking the alluvial mining industry into the 21st century'.
For gold and tin in difficult ground, the bucket-line dredge with integral treatment plant is the preferred choice.
A 10-ft [sup.3] bucket-line dredge will weigh about 1,200 mt and treat about 200,000 m [sup.3]/month while a similar sized cutter-suction machine will treat about 600,000 m [sup.3]/month.
(ADL) is the inheritor of the original Lobnitz design of bucket-line dredge. Today, ADL is consultanting in placer mining and designs and supplies a wide range of dredges and treatment plants for the recovery of alluvial gold, diamonds, tin and other heavy minerals.
IHC Holland has been building bucket-line dredges since the end of the 19th century and, in 1979, built the world's largest bucket-line dredge in combination with a Singapore shipyard for offshore tin mining in Indonesia.
As with bucket-line dredges, mooring is by spuds or mooring ropes.
Bucket-line dredges have onboard treatment plants but smaller suction type machines feed separate skid or pontoon-mounted plants.
For gold, tin and diamonds, treatment plants are similar to those installed on bucket-line dredges, consisting of a trommel to wash the product and usually three stages of jigging.