Thallium distribution in intrusive rocks of the Pamirs and southern Tien Shan, Tajikistan

Based on the analysis of approximately 2000 samples, Tl concentrations were determined in intrusive rocks (predominantly granitoids) of the Pamirs and southern Tien Shan. The average Tl concentration equals 1 ppm, varying from 0.8 to 1 ppm in the granodiorites and from 1 to 1.3 ppm in the granites. The average Tl concentration of the leucogranites attains 1.4 ppm and, more rarely, 1.8 ppm. The rare-metal granitoids of the Pamirs bear 3.6 ppm Tl, and the analogous rocks in the southern Tien Shan contain as much as 8-9 ppm this element. The Late Paleozoic-Mesozoic alkaline basaltoids in the latter area contain 0.5-0.8 ppm Tl, and these values for the analogous rocks of Cenozoic age in the Pamirs are one order of magnitude higher: 5-8 ppm. The crustal clarke of Tl for the area is estimated at 0.7 ppm.