FORMS OF OCCURRENCE OF RARE ALKALIES IN GRANITE

Abstract

Rare alkalies are assumed to occur in igneous rocks in three main forms: 1) as isomorphous impurities in rock-forming and accessory minerals, 2) as sorbed components (atomic and molecular dispersion), 3) as submicroscopic segregations of their own minerals. The first two are comparable to sparingly and readily mobile forms, i.e., leachable with weak solvents. We investigated readily mobile and sparingly soluble forms of these elements, as well as of Na and K, in weak solvents, in samples collected from alkalic basaltic rocks of the Tien Shan and from granites of the southern Pamirs. 20 to 40 percent of the alkalies in all igneous rocks occurs in a nonisomorphous form. These elements, being readily leachable by weak solvents, may be mobilized and involved in the hydrothermal process, and later accumulate under exogene and (or) endogene conditions, or are dispersed in the lithosphere and the hydrosphere. That is how leaching of both metasedimentary and igneous rocks could produce recent ground water relatively high in trace elements.