MERCURY 



411 



southern China through southern U.S.S.R. to the 

 Alpine belt of southern Europe (Bailey, 1959), have 

 correlated their distribution with a general Tertiary 

 belt of volcanoes referred to as the "belt of fire." 

 In the past 6 years, geologists have recognized the 

 relation of major tectonism and volcanism to mov- 

 ing crustal plates and have developed the revolu- 

 tionary "new global tectonics" (Heirtzler and 

 others, 1968; LePichon, 1968). Comparison of the 

 occurrence of mercury deposits with the new global 

 elements (fig. 48) shows that most deposits occur 

 on the continentward side of post-Jurassic subduc- 

 tion zones. Especially, they are localized where 

 oceanic crust and its accompanying trough deposits 

 are swept downward beneath the margins of blocks 

 of continental crust. This suggests that the mer- 

 cury originally contained in the marginal eugeo- 

 synclinal sediments, or perhaps even in oceanic 

 crustal material, has been distilled out of the 

 downward-plunging plate and emplaced at a higher, 

 cooler level along or above the subduction zone. 

 Additional search in the less explored parts of the 

 world lying close to such subduction zones, such as 

 in Indonesia, on Kamchatka, or in the Papua-Fiji 

 belt, should find entirely new mercury districts. 



In the main mercury belt of the United States, 

 which trends through the California Coast Ranges 

 and has yielded 85 percent of the U.S. production, 

 global tectonic relations also apply in a striking and 

 significant fashion. As shown in figure 49, virtually 

 all the productive deposits lie close to, and gen- 

 erally just below, the Coast Range thrust, which is 

 a major late Mesozoic subduction zone (Bailey and 

 others, 1970). This major structure provides an 

 unusually fine guide to where to look for more ore, 

 but through the past 100 years, the part of Cali- 

 fornia indicated to be most favorable has been so 

 well explored that the discovery of new mercury 

 deposits of significant size cannot be expected. 



The use of principles of global tectonics indicates 

 areas to be explored for new mercury deposits, and 

 new ones will probably be found along the favorable 

 belts. Considering the rate of discovery of the past 

 100 years, it seems likely that even with better 

 geologic guides and exploration techniques, the 

 amount of mercury discovered in new districts will 

 not equal the amount consumed. Most of the undis- 

 covered resources will come from new ore bodies to 

 be found in districts now being exploited. 



PROSPECTING TECHNIQUES 



The most widely used, and most successful, pros- 

 pecting technique has been simple panning of stream 

 sediments or slope debris. Most standard geophysical 



methods have been tried, but they do not seem to 

 be generally applicable to the search for mercury 

 deposits. In recent years, various geochemical ex- 

 ploration techniques have been used with some suc- 

 cess. Stream sediment sampling has been done by 

 Clark and others (1970a, b, c, and 1971), and soil 

 sampling has been widely used. Shacklette (1965) 

 has applied geobotanical methods, and McCarthy, 

 Vaughn, Learned, and Meuschke (1969) have shown 

 that determination of mercury vapor in soil or air 

 over deposits is useful for locating mercury or some 

 base-metal deposits. Recent refinements of methods 

 for measuring trace amounts of mercury have made 

 geochemical methods of prospecting more reliable 

 and useful (Barringer, 1966; Dinnin and Worthing, 

 1966 ; Hinkle and others, 1966 ; Vaughn, 1967 ; Man- 

 ning (1970), Plimmer and Klingebiel, 1971; Weiss- 

 berg, 1971). 



PROBLEMS FOR RESEARCH 



The immediate problems of mercury supply for 

 the United States are chiefly nongeologic. For many 

 years the domestic mercury-mining industry has 

 had difliculty competing with foreign producers who 

 have such rich ores and cheap labor that they can 

 undersell U.S. producers, thus closing down U.S. 

 mines. Intensive exploration might find a new rich 

 ore body in the United States, but the chances of 

 such a discovery are small. The problems of utiliz- 

 ing our lower grade ores are well known and need 

 no discussion here. However, in the past 5 years a 

 new problem has been introduced — that of the un- 

 desirable effects of mercury pollution — and much 

 research is needed to evaluate properly the degree 

 of mercury pollution brought about by industrializa- 

 tion and its effects. 



Both mercury liquid and vapor, as well as nearly 

 all compounds of mercury, are toxic; fortunate 

 exceptions are the most common ore minerals, the 

 mercuric sulfides. Mercury poisoning has been rec- 

 ognized for centuries and has been guarded against 

 by both mercury mining and utilizing industries. 

 Recently, it has become a concern, partly because 

 of public awareness regarding general environ- 

 mental deterioration, and partly because recent im- 

 provements in detection and measurement tech- 

 niques have for the first time allowed accurate 

 determination of low-level mercury contamination. 

 In addition, the increased use of mercurial germi- 

 cides and the more numerous chlorine-caustic soda 

 plants discharging mercurial waste into lakes and 

 rivers have led to identified cases of mercury poison- 

 ing of birds, fishes, and humans (Goldwater, 1971; 

 Wallace and others, 1971). 



