Abstract
Neutron activation data on Cd, Hg, Tl and Bi in 45 samples of abundant magmatic, sedimentary and metamorphic rocks and rock composites (consisting of a total of more than 200 samples) are reported. American standard rocks are included. On the base of literature values and the data of the present publication one arrives at the following average abundances for magmatic rocks in the upper continental crust: 110 ppb Cd, 30 ppb Hg, 970 ppb Tl, 60 ppb Bi and for sedimentary rocks: 260 ppb Cd, 330 ppb Hg, 830 ppb Tl, 375 ppb Bi. Abundance ratios for sedimentary to magmatic rocks are: 12 for Hg, 6 for Bi and 2·4 for Cd; the relative accumulation of the three elements in the sedimentary environment is assumed to be due to the degassing of the earth (excess volatile elements). In a thermal gradient of regional metamorphism from sedimentary to lower amphibolite facies a decrease of Hg, Bi and Cd from sedimentary abundances down to the range of “magmatic” abundances has been observed.
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