Nb-Zr mineralization in the sallanlatvi carbonatites, Kola Peninsula, Russia

摘要

The Sallanlatvi complex is one of the least well studied alkaline-carbonatite intrusions in the Kola Alkaline Province. It has a simple concentric structure with, in order of intrusion, melteigite, ijolite and various carbonatites as the major components. Among the carbonatites, calcite, dolomite, magnesite-dolomite and siderite types can be distinguished according to field relationships, and modal and mineral composition. All types contain Nb-Zr mineralization but the calcite carbonatites are the major concentrators of these elements. The textural relationships and mineral chemistry of lueshite, pyrochlore, niobo-aeschynite-(Nd), ilmenite, baddeleyite, zircon and catapleiite indicate a complex history of primary crystallization and deuteric processes involving the Nb and Zr minerals. This is particularly true for pyrochlore which can be grouped into at least four varieties. The high Nb/Zr ratio and occurrence of lueshite as a major host for Nb in the Sallanlatvi carbonatites can be explained by te geochemical characteristics of the complex, in particular, by the high a(Na)/a(Ca) ratio during the early stages of carbonatite evolution.