The Metallurgy of Dredging: The gold-saving appliances of a dredge consist respectively of screens, tables, and sluices. The essential duty of the screen is to classify the material prior to concentration, it also serves to disintegrate or break up the material passing over or through it, so that particles of gold may not be carried off … Read more
The only minerals of any importance which are found in alluvial deposits are gold and other precious metals, tinstone, and those gems which by reason of their hardness and power of resisting chemical changes are preserved in their original state even after being scoured by water for long periods. It is now generally conceded that … Read more
In calculating the horse-power consumed by suction and by bucket dredges, figures have been taken from the various official reports on the mining industry in New Zealand, dates and pages in each instance being given. The calculations are made in theoretical horsepower, and for easy references are given in tabular form. The difference in the … Read more
These machines consist essentially of a floating structure, supplied with a powerful pump of centrifugal type, raising sand and water through a suction pipe. Characteristic types of suction dredges are the Ball and the Welman. The Welman patent pump is in many respects similar to a centrifugal pump; the runner, however, is differently constructed, the … Read more
The bucket dredge may be described as a continuous dipper dredge, the material being raised by a revolving chain of dippers or buckets, which scoop or dig into the deposit. The principle and system of raising material in these machines are almost identical with those of harbour dredges. The favourite type of bucket dredge is … Read more
The type of a Dredge is defined according to the Nature of the Work they do. Under this heading bucket dredges may be classed as: River dredges; paddock dredges. The river dredge is designed to work with some depth of water underneath it, and is not called upon to cut its own flotation. It is, therefore, not … Read more
Small electric dredges are great where water power is available within reasonable distance, electricity may be generated and transmitted by cable to the dredge, proving an economical substitute for steam, especially in localities where fuel is dear. The small space, too, occupied by the plant, and the ease with which it is handled, make electricity … Read more
The first steam dredge of the bucket type was launched on the Clutha in 1881. Such dredges differ from current-wheelers only in being provided with engine and boiler in place of the undershot wheel. The use of steam machinery, of course, increases the initial cost, adds to the working and maintenance expenses, and necessitates the … Read more
In the Current-wheel Dredge, the mechanism on these dredges is driven by an under-shot water-wheel, placed at one or at both sides of the scow and rotated by the current. Such dredges work with most safety and regularity in about a 3-knot current. An instance of a machine of this kind is the Mannherikia dredge, … Read more
Dredge Hull Among dredging hands, the “ hull ”—namely, “ port ” and “ starboard ” pontoons tied together—is usually termed the “ pontoon ” or “ pontoons.” The ordinary hull consists of two long, narrow pontoons, joined together for about a third of their length by a third small one, equal in width to … Read more