GEOCHRONOLOGICAL MODEL OF APATITE DEPOSITION BASED ON DATA FROM THE USSR

Abstract

The deposition of apatite in the past was preceded and promoted by numerous factors, chief among which were tectonic factors (endogenous conditions) and igneous and metamorphic factors. Thus, on tectonically stable structures, the development of commercial apatite deposits ended in the early Mesozoic, or more precisely, in the Early Triassic; in mobile belts it culminated in the early Paleozoic. In the Mesozoic and Cenozoic, exogenous ore deposition was vigorous on cratons. This represented mainly a beneficiation process that generated carbonatitic bodies whose weathered crusts contained apatite and apatite-francolite ores high, or moderately high, in P2O. These patterns of occurrence of apatite can be explained in terms of progressive evolution of the crust and associated tectonic processes in time, involving increasing rifting, more eruption of alkalic magma, and a decrease in metamorphism. The cratonic-stage magma that was most productive in terms of apatite generation was evolved during epiplatform activation by rifting, and led to deposition of alkaline ultramafic rock complexes containing carbonatite.