DEVELOPMENT OF DREDGING IN AMERICA.

Otago Witness, Issue 2664, 5 April 1905, Page 24

DEVELOPMENT OF DREDGING IN AMERICA.

The S-an Francisco correspondent of the Melbourne Age writes — Dredge mining has attained a development in California and some of the other Western. St»te3 reached nowhere el=e. There are districts in Australia in which American dredging methods mi^ht be introduced with pront. The dredge 0 .~ie not confined to the rivers. They plough thiough dry country,, taking along with them their own body of water, and swallow a 50ft slice off the top of a.n acre in a month, leaving behind a mountain of barren debris, on. which not even weed will grow. Vineyards and orchards have been destroyed for the sake of the gold in the earth, the immediate profit of the busiress being very high. The dredge stands in a pool of water, fed by a pipe- from pome eonrce, which may be a. few yaids or 100 miles away, and it dredges up the ground m front, carries it up into its '• fo' castle " by means of an endles chain of buckets, puddles the dirt in a stream of water, which is poured in upon it from the supply pipe, and after separating the gold it casts out the rock and mud in its wake. The buckets or scoops on the end'ess chain attack the earth, against which thr dredge is anchored, and each in turn bites in, taking up soil, gravel, or rocks. Porno of the latter are as large as a man's body. The contents of the scoops are dumped into ai rapidly revolving cylinder, fed with 5000 gal of water a minute. The gold is separated by the i:«?e of quicksilver and cocoanut matting, the fibres of which catch ar.d hold fast the finest oarticl-'^ of the yellow metsl.

A dredging machine costs about £20,000. It is 3J2 irr.mense contrivance, from 100 ft to 265ffc long, with a crane running- up to ?. height of from 50ft to 100 ft. Run by a, foTce of eight men, a dredge in a day of three eight-hour shifts, can do the work of 5000 men and carts. The expense of handling the earth has been, reduced to as low as lid per cubic yard, and it i:ever goeg above S\d. Ground thai would not satisfy a Chinese, working under the old placer methods, or what are known in Australia as alluvial methods, now pays handsome profits by means of the dredges. One diedge will work over an. acre in a month, and take out £4000 in gold. In the neighbourhood of Oroville, California, there pro 35 dredges, each of which has paid for itself in a single season's work. Mo-st of ihe Califoxnipu dredges are working in districts made famous years ago by placer milling, and generally near streams, but in Idaho, Montana, and Colorado, they a,re ploughing through valleys hundreds of miles from any watercourse Vast wealth is being taken. from soil which the placer mining permitted to go to waste. The transformation of orchards, vineyards, a?id gardens into waste, is the saddest feature of the industry. Some mineTs have bought up choice residenca districts, and are converting pretty gardens into heaps of rubble. The miners are often willing to pay £600 an acre, well knowing that they can take £4000 in gold out of its soil, and tii<ur offers almost always have induced owners to sell out. The devastation wrought by the machines, however, has at length aroused a'arrn, and a movement has been started, requiring ihe mining companies to ros*ore I'b.e soil. This could be clone, it is said, at a slight expense. Two from New Zealand were the first to introduce dredge mining into xhis country. The machine they* got from New Zealand baa been duplicated many times, but with innumerable new features, added by American ingenuity, until now it represents the best results of engineering skill. Before a dredge is put on to the ground, much prospecting is do-na •with a keystone drill. A core of earth is forced up to the surface and carefully analysed.