Geochemical diversity of minerals of the pyrochlore group

Abstract

A systematic and rational nomenclature of minerals of the pyrochlore group are developed based on the results obtained by processing 671 chemical analyses of pyrochlore-group minerals from carbonatite complexes, alkali rocks, and their pegmatites, granite pegmatites, and alkali and albitized granites. The proportions of Nb, Ta, and Ti are typomorphic of pyrochlore from these four types of geological environments. The paper lists pervasive characteristics of the distribution of Na and Ca, REE, Th and U, Sr and Ba, K and Cs, Pb, Sn, Sb, and Bi in the minerals. Based on the occurrence of compositions with elevated concentrations of typomorphic elements at site B in the structure of the minerals, pyrochlore subspecies are recognized: pyrochlore, Ta-pyrochlore, Ta,Ti-pyrochlore, Zr-pyrochlore, Nb-betafite, Ta-betafite, Ti-betafite, Ti-microlite, Nb,Ti-microlite, Nb-microlite, and microlite, as well as 60 geochemically significant varieties with the predominance of certain cations at site A (REE-pyrochlore, U-pyrochlore, etc.). Aspects of a rational systematics of minerals of complicated isomorphic series are discussed.