Pyrochlore and whole rock chemistry of carbonatites and phoscorites at Sokli, finland

摘要

At Sokli (Northern Finland), niobium ores of highly complex compositions are associated with weathered carbonatites and related rocks. An extensive geochemical study of a suite of whole rock samples has been undertaken, coupled with a petrographical and mineral chemical study of the principal Nb-bearing phase, pyrochlore. Using the pyrochlore mineral chemistry from fresh rock samples as a petrogenetic indicator, it is possible to describe the magmatic evolution of the complex in terms of the differentiation of carbonated melts (Ca-Mg-Si-Fe-P rich), of which the calcite carbonatites represent relatively early cumulates, the dolomite carbonatites late residual liquids, while phoscorites form throughout this differentiation process.