548 hawkes. GEOCHEMICAL PROSPECTING FOR ORES [Ch. 30 



requirements, a method that can be applied either directly in the 

 field or in local field headquarters is desirable in that the prospector 

 can know immediately whether or not he is on the trail of a hidden 

 deposit and thus can plan his sample collecting more effectively. The 

 speed and economy of the test are more critical than accuracy, as in 

 most problems the contrast in metal content indicative of ore is in 

 excess of several hundred percent. 



To date the most successful methods have been spectrographic and 

 colorimetric analysis and spot tests. 



Spectrographic analysis. Spectrographic analysis has been used 

 most extensively in geochemical prospecting work in Russia and 

 Sweden. Physicists of the Central Geological and Prospecting In- 

 stitute of the Soviet Union have developed spectrographic equipment 

 suitable for use either in the laboratory or under field conditions (Rats- 

 baum, 1939) . The field instrument can be dismounted and transported 

 with its mobile power supply by truck or, if necessary, on pack animals. 

 Under ideal operating conditions it is claimed that close to 1,000 

 soil analyses per day can be made by one crew (A. P. Solovov, per- 

 sonal communication). However, Sergeev (1941, p. 45) states that 

 under normal working conditions 140 spectrograms on the stationary 

 model or 100 on the field model can be prepared per day by a three- 

 man crew, exclusive of time required for sample preparation. This 

 equipment has been most successful with analyses of soil material for 

 tin, tungsten, lead, nickel, arsenic, antimony, and molybdenum (Safro- 

 nov and Sergeev, 1936; Sergeev, 1941, pp. 30-40; Tikhomirov and 

 Miller, 1946) . Estimations are made by visual comparison with stand- 

 ard spectrograms. Maximum sensitivity is said to be 0.01 percent for 

 tin, lead, nickel, arsenic, and antimony, and 0.05 percent for tungsten. 



In Sweden, stationary spectrographic equipment capable of high 

 productivity was developed by S. Palmqvist and N. Brundin, of the 

 Swedish Prospecting Company, in 1936. This instrument was designed 

 for analysis of ashed plant material and with a four-man crew could 

 turn out 400 determinations per day. Most success was obtained with 

 tin and tungsten, though some work was also done with lead, zinc, 

 chromium, molybdenum, copper, and silver (Svenska Prospekterings 

 Aktiebolaget, 1939; Hedstrom and Nordstrom, 1945, pp. 6-9). 



The advantages of the spectrographic method for geochemical pros- 

 pecting are its speed and the fact that many elements can be deter- 

 mined in a sample with little more work than it takes to determine one. 

 The disadvantages are the initial cost of equipment, difficult portabil- 

 ity, need for skilled operator, and lack of sensitivity for some important 

 elements, notably zinc. 



