ARSENIC 



59 



copper of 1:50; of the resources of cobalt, 3 per- 

 cent are considered to be arsenical with an average 

 ratio of arsenic to cobalt of 2:1; and of the tin 

 resources, 10 percent are considered to be arsenical 

 with an average ratio of arsenic to tin of 10:1. 



Several factors stemming from the relation of 

 arsenic to primary metals are considered when cal- 

 culating the various arsenic-metal ratios. For ex- 

 ample, arsenic does not occur in placer deposits of 

 gold or tin or in gold deposits hosted by Precam- 

 brian conglomeratic sandstone. Gold placer deposits 

 can be disregarded for they are a relatively small 

 source of gold and the absence of arsenic from them 

 is of little account in the estimate, whereas tin 

 placer deposits are an important source of tin and 

 the absence of arsenic from them seriously affects 

 the estimate. Gold deposits in ancient conglomeratic 

 sandstone deposits are the most important source 

 of gold, and the absence of arsenic from them dras- 

 tically affects the estimate. The ratio of arsenic to 

 cobalt was weighted to favor arsenic in order to 

 account for the additional arsenic that is combined 

 with nickel, copper, and iron in native silver and 

 nickel-cobalt arsenide deposits. Lateritic deposits of 

 nickel and cobalt are disregarded as sources of 

 arsenic. Such deposits may have in part been de- 

 rived from primary deposits of native silver and 

 nickel-cobalt arsenides, but arsenic apparently es- 

 caped in the weathering process. 



The resource figures for arsenic shovsTi herein 

 were largely derived from data for gold, copper, and 

 other base metals published in other chapters of this 

 volume. Each of the continental areas is assumed to 

 contain sufficient resources of some of the more 

 important types of arsenic-bearing deposits so that 

 general estimates accurate within an order of mag- 

 nitude can be made. The hypothetical resources of 

 arsenic are estimated to be equal to the total of 

 identified resources of arsenic occurring with base 

 metals plus one-third the identified resources of 

 arsenic occurring with the gold. 



Arsenic is currently produced in about 25 coun- 

 tries. The types of arsenic-bearing deposits and the 

 countries in which they occur are shown in table 10. 



SPECULATIVE RESOURCES 



Arsenic deposits which may form by the mobiliza- 

 tion, concentration, and redeposition of arsenic in 

 favorable geologic environments could be an addi- 

 tional resource of arsenic. 



Most of the arsenic or arsenical deposits that have 

 been discussed here are types which were derived 

 from magmatic or magma-related sources ; a few, 

 however, were derived from adjoining host rocks. 



Table 10. — Types of arsenic deposits of the world 



Type of deposit 



Enargite-bearing copper- 

 zinc-lead deposits. 



Arsenical pyritic copper 

 deposits. 



Native silver and nickel- 

 cobalt arsenide-bear- 

 ing deposits. 



Arsenical gold deposits - 



Arsenic sulfide and 

 arsenic sulfide gold 

 deposits. 



Arsenical tin deposits 



Areas 



United States, Argentina, Chile, 

 Peru, Mexico, Republic of the 

 Philippines, Spain, Yugoslavia, 

 U.S.S.R. 



United States, Sv?eden, Federal 

 Republic of Germany, Japan, 

 France, U.S.S.R. 



Canada, Norvi^ay, German Demo- 

 cratic Republic, Czechoslovakia. 



.United States, Brazil, Canada, 

 Republic of South Africa, 

 Australia, U.S.S.R. 

 United States, People's Republic 

 of China. 



.United States, Bolivia, Australia, 

 Indonesia, Malaysia, Republic 

 of South Africa. 



Studies of ancient rock terranes show that certain 

 types of ore deposits are broadly related to certain 

 rocks, and studies of sulfur isotopes indicate that 

 metals in disseminated sulfide minerals in the sur- 

 rounding rocks were the likely source of metals con- 

 centrated in the ore deposits. The metals were mo- 

 bilized when sufficiently energized and then moved 

 by diffusion through the rock and accumulated in 

 favorable structures. 



Under local favorable conditions in areas where 

 the rock has a high arsenic content, arsenic or 

 arsenical deposits might be found. Geochemical 

 studies show that shale averages 5-15 ppm arsenic 

 and that sulfide-rich organic shale of marine origin 

 contains even greater amounts. Although organic- 

 rich shale is widespread and has formed in many 

 geologic periods, the number of ore deposits found 

 in it is few. The few that have been found may have 

 formed under exceptional circumstances in which 

 metals became highly concentrated in sea water. 

 Rather than investigate organic-rich shale units on 

 a broad basis, efforts should be concentrated on 

 areas that have been subjected either to extreme 

 structural deformation and (or) to metamorphism 

 or that have been intruded by large bodies of igne- 

 ous rock. In such areas, the metals may have been 

 mobilized and concentrated in favorable structural 

 settings. These areas are likely to be regional in 

 scope and to be recognizable from stratigraphic, 

 structural, and other geologic relationships. Such 

 areas include parts of depressed belts or geosyn- 

 clines, which are the locales of organic-rich marine 

 shale. Other such areas include ancient crystalline 

 terranes where graphitic schist, the metamorphic 

 equivalent of organic-rich shale, is present. 



The amount of arsenic in organic shale is esti- 

 mated to total about 10" tons; if as much as 0.01 

 percent of this arsenic is concentrated in minable 



