One gold dredge was on Bear Creek, Hogatzu River, and the other on the Ungalik River, and the platinum dredge was in the Goodnews Bay district. In September 1969, two gold dredges and me platinum dredge were operating in Alaska. Its earlier version is shown in figure 1. The last gold dredge of the more than 60 operating in California in the 1930’s was shut down on October 1, 1968. Some gold dredging operations were resumed after the war, but most remained closed because of the widening gap between mining costs and the fixed price of gold. The dredging industry continued to produce war-needed scheelite in Montana, platinum in Alaska, and columbium in Idaho. Long stackers for gravel disposal made it possible to dredge relatively deep placers and to work against high banks not possible with a headline system.Īfter a very successful and profitable period of mining from 1895 to 1942, cost gold-placer operations in the United States were closed down by Government Order L-208 issued during World War II. The California dredge produced more yardage and operated more efficiently considering all types of formations. In California stackers combined with sluices were found more practical. Often long sluices were used to dispose of the waste. They used headlines instead of spuds because of the easier digging and because there were no high banks ahead to hinder their use. The New Zealand dredges, which were lighter in construction, were designed primarily to excavate softer formations.
Gold mining dredge plus#
It had short tail sluices and relatively long stackers to dispose of oversize gravel, usually plus 5/8 inch. The California-type dredge, because of the need to dig in gravel containing large boulders and in cemented, clayey, or tightly compacted formations, was strongly built and was equipped with spuds, heavy vertical movable piles, to hold the dredge firmly in place. Not versatile enough to operate under the varied and often rugged dredging conditions in California, it was soon discarded and a variation called the California type was developed after the Montana design. The first gold dredge to operate in California was a New Zealand type at Oroville in 1898. To it was added a washing and treating system similar to that used in New Zealand. The dredge design incorporated the bucket-line equipment already found successful in the Eastern United States. The first successful dredging operation in the United States started at Bannock, Mont., in 1895. Their adaptation to placer mining began in New Zealand in 1882 when gold-saving equipment was added behind the excavators. Over time their design and efficiency improved. The first floating bucket-line dredges were developed in Europe during the 16th century to excavate harbors. The bibliography in this report was prepared primarily as a source of references for placer exploration and dredging. Two of the more current papers that cover foreign gold dredging are McFarland’s paper on dredging in the Yukon, Canada, and O’Neill’s paper on dredging in Colombia and Bolivia, South America. Peele’ s Mining Engineers’ Handbook is another general reference of considerable value. Charles Janin’s “Gold Dredging in the United States” is an excellent general reference although written 50 years ago. There are no current publications that describe modern design and operation of dredges. The risk involved can be reduced by a thorough exploration program balanced with a sound engineering study. Like any mineral deposit, a placer deposit should be evaluated on the basis of the most practical and efficient system suited to it. It provides data concerning current application and identification of the natural and unchangeable environmental conditions to be considered in selecting a system. It brings together the old and proven dredging concepts with newer and more current techniques integrating these ideas with actual cost experience standardized to 1967. This report is focused on placer mining by dredging. Emphasis was given to large deposits which would permit the economies of large-scale production methods. Two gold dredges and one platinum dredge were still operating in Alaska.īecause of the increasing national requirements for gold the Bureau of Mines in 1966 initiated a Heavy Metals study to investigate and appraise potential gold-bearing deposits that might contribute to domestic gold production. Gold dredging in the adjacent States had already ceased because of increasing operating costs, decreasing placer values, and the fixed price of gold. The last gold dredge in California stopped operating in October 1968.
At present dredge mining in this country is at a low level.
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