DREDGING FOR GOLD.
The many varying conditions under which gold is found is not the leastinteresting feature of the history of the yellow metal. In rock, sand,and sea it has been discovered, and even in the deposit of hot springsnow in activity. Large nuggets have been discovered in dry gravels,while prospectors have acquired much wealth by extracting gold fromriver beds, by the process known as panning--i. e., separating the dirtand mud from the metal by shaking the gold-bearing earth or gravel withwater in a pan.
While, however, many rivers have been thus exploited, explorers andscientists are agreed that there are still millions of dollars' worthof gold waiting to be unearthed from the bottom of rivers in differentparts of the world. In New Zealand and South America, for instance,convincing proof has been obtained that rich deposits of the preciousmetal still lie at the bottom of many of the rivers of those countries.The gold is usually found in the form of grains at some depth below thesurface, imbedded in mud and clay.
There are only two ways of recovering it--namely, either the river bedmust be dredged by floating dredgers, or the river must be divertedinto another channel while its bed is being stripped. The formermethod is the one generally adopted, dredgers having been used withconsiderable success on the Pacific Slope.
Attention has been attracted of late years to the possibilities ofrecovering gold from the rivers of Peru. For ages the gold-laden quartzof the land of the Incas--the people who covered the walls of theirtemples with plates of gold and used the precious metal to fashioncooking utensils--has been broken down by the denuding agencies offrost, rain, and snow, and carried into rivers, where it has remainedundiscovered, until recent explorations revealed an astonishing sourceof wealth.
Take the River Inambari and its tributaries, for instance. Anexamination of 30 miles of this river revealed the fact that itcontained gold to the average value of $1.75 per cubic yard, whichcould be extracted at a cost of 12 cents only. The result of thisexamination led to the formation of the Inambari Gold DredgingConcessions, Limited.
Sir Martin Conway some time ago explored upper Peru and the famousgold-producing valleys from which the Incas gained most of their greatstore of wealth. He came to the conclusion that in a certain area noless than $10,000,000 profit was to be made by extracting gold from therivers, and in order to begin obtaining this gold it was only necessaryto have a dredge on the spot. The same hour in which the dredge firstbegins to turn, gold will be won.
The dredges used up to the present have been almost exclusively of theendless-chain bucket or steam-shovel pattern. At one end of the boatis a powerful endless-chain bucket-dredge, which scrapes the gravelfrom the bottom and elevates it to a revolving screen in the boat. Thisin turn sifts out the bowlders, which are at once thrown to the bankof the river, while the fine material flows over tables covered withcocoanut matting, which acts like fine riffles, catching the gold inthe interstices. The matting is periodically lifted up and thoroughlyrinsed off, the rinsings are panned for gold, and the matting returnedfor another charge.
In the case of the Inambari Gold Dredging Company, a modern steeldredger has been made, which it is confidently estimated will work farquicker and in a much more effective and inexpensive manner than anyother dredger which has yet been used.