DREDGING THE MOLYNEUX.

Colonist, Volume VIII, Issue 772, 17 March 1865, Page 4

DREDGING THE MOLYNEUX.

(From the Otago Daily Times.)

That the bed of the Molyneux contains yet unworked treasures of gold 13 well and widely known. The means adopted to obtain these have been various. Hundreds of miners have anxiously watched the winter through on its banks, waiting the time when, from the hard-freezing of its mountain sources, the river should fall so low as to lay bare a portion of its bed. These hopes have proved fallacious, winters of such severity being apparently exceptional—thaws and rain floods more usually keeping the river full. Some again, in favorable positions, have formed wing-dams, and so exposed a little of the bed. Dredging up the grajvel occurred to many, and. although it was generally conceived that the rapidity of the current, and the nature of the bottom, would offer obstacles difficult, if not impossible, to overcome, yet several scoop dredges have been placed on the river ; ancl one of them has been worked with marked success—£7oo having, it is stated, been cleared in six weeks. The scoop dredge consists of a sorb of spoonbowl attached to a long handle, worked from a boat. The bowl is allowed to fall to the bottom ; it is then forced into the gravel or silt by one or more men pulling at the end of the boat, and is subsequently lifted, filled with riyer deposit, into the boat by means of a winch. This is necessarily a slow and laborious process, and is available only in comparatively shallow water. It is now proposed, by Mr. William Ward to employ a modification of the ordinary harbor dredge, with its endless chain of buckets, but in place of steam to use as the motive power the current of the river; in reality to make the river dredge and sluice its own deposit. The idea, though no doubt original as far as Mr. Ward is concerned, is not altogether new. Those of our readers who have been on the Ehine, the Moselle, or Inn, will probably call to mind the fiour mill moored in the middle of the stream and worked by the current of the river acting on a broad wheel. In some parts of the Ehine dredging of the river bottom is also effected in this manner.

Mr. Ward's apparatus consists of two oblong pontoons or boxes, thirty-feet in length, connected at one end, an open space being left between them for raising and lowering the large arm or beam round which the endless chain of buckets revolves.

A wheel on each side supported on a frame work at the fore part of the vessel, revolves by the action of the current on the floats, furnishing the moving power to the chain of buckets, each of which, as it scrapes the bottom, scoops up a certain portion of the gravel or silt, and deposits it into a hopper or tray with a perforated bottom, on which a stream of water constantly plays. This hopper inclines a little at one end, and has a movement from side to side communicated to it from the main shaft of the wheels. By this means the larger masses of gravel are discharged from it into a sluice box near the fore part of the boat, whence they pass overboardj while the smaller, with the particles

of gold andiron, sand, fall through the holes and pass over another sluice box running the length of the pontoons. There are two of these boxes in order that there may be no interruption of the work during the time of clearing oufc one box. Pumps worked by the same power raise a constant supply of water, which is discharged into an elevated cistern, and is thence distributed over the hopper containing the auriferous gravel. The arm over which the chain of buckets turns, and which conveys them to the bottom is thirty-six feet in length, so that considerable depths can be reached. It appears that the current of the Molyneux is more than sufficient to work this machine, a three or four knot current being even more than is needed. The highest engineering authority in such matters has reported favorably of the apparatus, considering it quite equal to the work to be undertaken. It is intended to moor the vessel in a moderate current, where the bottom has good indications of being auriferous, and where no large boulders are likely to be met with, veering from side to side by means of ropes attached to the banks. A very small number of men alone are required for the working, the greater part of the operations being accomplished by the machinery and water. It is estimated that from two to three hundred tons can easily be raised and passed through the sluice boxes in twentyfour hours and as two pennyweights to the ton is a low average for Molyneux gravel or silt dredged from selected ground, the returns will probably soon yield a handsome profit on the enterprize. Mr. Ward's model is at present in the Exhibition, and from its simplicity a very little explanation from the inventor causes it to be readily understood.