U, Th and K in Rocks from the Bosumtwi Crater (Ghana) and in the Ivory Coast Tektites ~1) L. RYBACH* and J. A. S. ADAMS ** U, Th and K have been determined in 20 Ivory Coast tektites by nondestructive gamma ray spectrometry. Five total rock samples from the Bosumtwi Crater have been analyzed by the same method (the Department of Geology and Geophysics, Massachusetts Institute of Technology, Cambridge, USA, and the Max-Planck-Institut fiir Kern- physik, Heidelberg, West Germany, kindly furnished the specimens). The U and Th abundances in the Ivory Coast tektites are shown, compared to other tektite groups, in Fig. 1. The Ivory Coast tektites are noteworthy in having an average of 1.9 ppm Th and a mean Th/U ratio of 2.6, both of which are significantly lower than values in any single specimen or group of tektites reported in the literature. The K contents have been checked by flame photometry and electron microprobe methods. The mean K content (1.45% K) is also signifi- cantly lower than values for other tektite groups. The mean K/U ratio, 1.32 × 104, is clearly ,~ terrestrial ,~ (cf. WASS~RBURG et al., 1964). The old (2 × 10~y~,rs) Precambrian rocks from the Bosumtwi Crater area show signs of intensive shock deformation which was studied in thin sections; in samples from the inner slope of the Crater quartz with cleavage planes, diaplectic quartzglass, plagioclase glass (partly recrystallized) and coesite aggregates have been found. ST/3F- FLER (1966) describes similar features in the Ries suevite. The mean U, Th and K concentrations of the Crater rocks are * Swiss Federal Institute of Technology, Zurich (Switzerland). ** Department of Geology, Rice University, Houston (USA). (I) Paper presented at the IUGG 14th General Assembly° IAVCEI Session, Sym- posium on Geochemical Problems (Ziirich, Sept, 1967), and accepted for publication by the Organizing Committee.