120 



depth of water, each mineral site and each t.vi>e of sediment or bedrock exerts 

 an influence on the prospecting method, the undersea mineral hunter must 

 have a variety of instruments and techniques at his command. After careful 

 thought for each locality, he selects the equipment which can be most effectively 

 employed at the least cost. 



Small amounts of potentially valuable minerals such as phosphorite, rutile, 

 cassiterite, ilmenite, zircon — even platinum and gold — can be found undersea in 

 many places. But the objective of undersea mining is to recover products which 

 must be sold at prices controlled by world demand. Thus, the prosi>ector is more 

 likely to be the representative of a mining company interested in developing 

 imdersea wealth than a curious scientist whose product is a technical paper. 

 He is concerned with finding mineral deposits of sufficient size and concentra- 

 tion to be of economic significance. To this moment (as far as the author knows) 

 there has never been a profitable mining operation in an oceanic offshore area. 

 This inhibits mining companies who are otherwise interested in exploring the 

 sea floor. 



Methods of exploration will be discussed presently, but these must be selected 

 in accordance with the geological situation and the probable mining conditions. 

 Ideas about what minerals to look for and where to look for them are important 

 because sound concepts of economics, geology, and engineering can greatly 

 reduce the areas in which it is worthwhile for a prospector to search. Obvious- 

 ly, it would be a hopeless task to look for all minerals everywhere beneath the 

 sea. The undersea prospector must have logical reasons why valuable minerals 

 may be present and some feasible method in mind for recovering them. 



There are several general classes of possible ore deposits: (1) placer de- 

 posits, (2) chemical precipitates, and (3) vein or bedded deposits. Each of these 

 poses an entirely different prospecting problem. The interest to date has mainly 

 been in the first two categories where the geological method has been generally 

 to examine the sea bottom offshore near known placers onshore, or to sample 

 deeper waters with a simple chain dredge in areas where nodules have been found 

 by scientific investigators. 



There are several water-depth zones, each of which is prospected in a different 

 fashion and with a special point of view less than 8 meters ; 8 to 50 meters ; 50 to 

 500 meters and the continental slope and deep ocean basins. The depth segregation 

 derives from the following circumstances. Less than eight meters on an open 

 coast includes the surf zone — an area of breaking waves with turbulent water and 

 longshore currents — in which prospecting is very difficult. This area of oceanic 

 violence is from 100 to 1,000 meters wide and, except on very calm days, is danger- 

 ous for all ships and dredges. 



The depth zone between 8 and 50 meters is the most conveniently mineable 

 at this stage of development of our new industry. However, no existing production 

 mining dredge reaches to a depth greater than 50 meters, even in calm water. 

 This is a critical depth for placer type operations because deeper digging in 

 rough water will require major machinery developments. The depths from fifty 

 to 500 meters comprise all the remaining areas of the continental shelves and 

 the upper reaches of the continental slope — which includes most of the likely 

 phosphorite deposits. These surface nodule deposits can probably be skimmed by 

 fairly simple machinery with comparatively little development — although this 

 has not yet been done. Beyond the 500 meter depth are the slope and basin de- 

 posits — mostly very fine grained sediment with some nodular precipitates. 



Most mining companies considering these depth zones, and the minerals likely 

 to be available, will decide to concentrate on the depths between eight and fifty 

 meters. The very shallow, violent surf zone (on exposed coasts) and the deep 

 ocean basins probably will continue to be expensive to prospect and mine. 



COST — ^A FACTOR 



Of course, it is generally acknowledged that with today's technology it is 

 possible to invent a system or a machine that will perform nearly any task, but 

 usually not at an acceptable cost if the product produced must compete in the 

 world market. This is a compelling reason to search areas which could be mined 

 soon with minimal development. 



If the prospector is going to search for placer deposits — heavy mineral grains 

 in sands and gravels — he begins by considering the geological evidence that is 

 conveniently available. Obviously one of the first places to look beneath the sea 

 is adjacent to onshore areas where successful placer mining has been done. 

 This may be offshore of a beach or river where valuable minerals were mined 



