DREDGING ETHICS.

Otago Witness, Issue 2455, 3 April 1901, Page 19

DREDGING ETHICS.

(Bt Our Wakatiptt Cobrespoxdent.) Although dredging for gold can in no sense of the term be described as mining work, it partakes of all the joys and fears, to say nothing of the vices, the whiles, and the snares of other gold-mining enterprises. Be^ng a form of gold-getting by itself, and different from all all other ways adopted for that purpose, it has developed features of its own that have to be met and dealt with by methods specially suited to the circumstances. Among its new phases there are difficulties that hinder the healthy progress of dredging in no small degree, winch to overcomo have baffled all attempts, seriously interfering with success, and in not a few instances causing most lamentable failures. The chief trouble that has met the dredger 1 has cropped up in connection ■with what is described as DRY LAND DREDGING. Dry land dredging at the present moment is, to say the least of it, out of fashion, being regarded with anything but favour. Two reasons mainly account for this state of affairs. One is that much of the dry ground had been previously worked by other method", more re Jiable for cleaning up the gold tban any dredge could do. A mistake was also made by expecting too much from new "up-to-date " dredges, which had nothing but a fineeounding phrase to recommend them, lhe second mam reason is that the burface soiloften stiff clay and tussocks —interfered with the saving of the gold. The surface soil or clay mixed with the gold-beanr.g wash aud water in the proco=3 of dredging makes a puddle as thick as the proverbial pea soup, carrying off a large proportion of the gold, without affording it even a chance of being saved. In the case of stiff clay it is still worse. Besides converting the water into a puddle too thick for allowing the finer gold to be saved, the clay breaks up into lumps, which, rolling down the tables, annex the coarser specks already lodged there and carry them off. To all this must be added the mischief caused by the tussocks. Discharged into the revolving rcreen by the buckets with the stones and gold-bearing wash, the tussocks are beaten into balls of tenacious fibre, which with every revolution of the screen are actually rolling in gold, involving and retaining a goodly portion of it in its meshes, and are discharged with the gold on the tailings heap. All this is plain fact, well known to every dredging man, and proof of it is furnished every day. There is not a dry land dredge in places where there is surface soil carrying tussocks but that loses as much gold as it saves, and so giievous is the trouble that it affects injuriously dry land dredging as an investment. Th.p extent to which this state of affairs reacts upon dredging is nothing short of serious, for it does not require a high-degree divination to ccc that river dredging is a definite quantity, while the area of dry land dredging ground is practically unlimited. The fact is .that in not a great many years dredging in Otago will be almost entirely confined to dry land. Fortunately, past experience in dry land dredging goes to proye that the disfavour under which the pursuit labours at present is not owing to the poverty of the ground in gold but is clearly traceable to defects in the methods of treating it. It is true many attempts have been made and numerous suggestions have been projected with the view of Overcoming the difficulties—so far without success;— but it does therefore not follow that no such means exist and that it will never be discovered. Some day some lucky genius will Siit upon a plan that will meet all requirements and dispose of both clay and tussock effectually. In the February number of the ' jNew Zealand Mines Record" Mr Postlethwaite, late .of Dunedin, gives a description of the Marigold Company's dredge, California. TSe dredge is worked by electricity, the available mower, amounting to 90 horse-power, distributed as follows:—Bucket belt, 50 horse•power; pump. 30 horse-power; winches, 10 fiorse-power. From the statement that the holes in the revolving screen are three-eighths of an inch in diameter it may be assumed that the dredge has to deal with medium and fine gJold. There are two pumps, one of which delivers 2000 gal per minute in the screen alone, the other pays water into the distributing box and various save-all grizzlier. This eugimeus

quantity of water passes over tables having an area of 300 square feet, and is far beyond what is used in Otago. It is true that the California dredge is estimated to treat 150 cubic feet of wash per hour, which is also in excess of what is done in Otago, except perhaps in a few instances. Taking the delivery of the second pump, which is not given in the report, also at 2000 gallons per minute thi3 would give 4000 gal to wash 2^ cubic yards per minute. Looked at in the light of these figures, the quantity of water used appears to be abnormal, not to say excessive. But the conditions under which tho dredge works not being given, nothing definite can be said on the subject, and otherwise these figures? convey only a hazy notion of why so large a quantity of water is used. On the other hand, it requires no special demonstration to show that the reason the clay soil produces so thick a puddle as to carry off the gold is because not enough water is UEed to reduce it to a consistency to make it give up the gold and leave it behind. It is Btill far too common an occurrence in Otago that the quantity of water used in proportion to the bulk of wash and clay treated is very much a matter of prejudice, custom, and sometimes even superstition. The quantity of water should be proportioned more to the extent of the surface area of the tables than any other condition, provided that enough water be used in every case to wash clean all stones and gravel passed through the gold-saving apparatus. In the opinion of a great number of practical men, the disfavour with which dry land dredging is now regarded is traceable in part to the adoption of defective ways and means of treating the wash which carries the gold. The average surface area of the tables is far too small to allow of a good head of water being used. Though the subject is of sufficient importance to receive extended and careful attention, enough has been said for the present to point out a way which, if followed and improved upon, will free dry land dredging from some of the odium from which it suffers, and suffers injustly.