The Rare Earth Elements in Apatites and Calcites from Iron Ore Deposits of Angara-Ilim Type (the Siberian Platform)

Alexander G. Polozov Institute of Geochemistry SB RAS, P.O.Box 4019 Irkutsk, 664033, Russia

The modern reviews of problem on rare earth elements (REE) behavior in hydrothermal and metasomatic processes have shown, that the primary data are being accumulated at present for diverse natural and experimental systems. The summarizing of this material is a goal of further researches.

Ce and Eu anomalies are mainly considered when analyzing the REE normalized pattern. In the most general case, anomalous behavior of these elements is determined by redox condition of solutions and availability of REE-bearing minerals. The variations of such parameters, as Eu/Eu* and Ce/Ce* are of interest when analyzing REE behavior in metasomatic and hydrothermal processes.

The present contribution considers the study of REE in the apatites and calcites from iron ore deposits of Angara-Ilim type. These deposits are generated as a result of at least three mineragenesis stages characterized by the own formations of magmatic, metasomatic and hydrothermal rocks, including various genetic and commercial ores.

Three types of apatites are distinguished on diagram (Fig.1). The first apatite type characterizes the primary magnetite-apatite ore, the second one illustrates the recristallization process of these ores, and the third one characterizes the apatite of the latest process. During the recristallization process the redox potential of solutions increases. The decrease of this potential of solution occurs under the formation of apatite on the latest stage.

Calcite from the examined calcite-magnetite assemblages are placed in the field of hydrothermal calcite. Two tendencies of Eu and Ce variations are distinguish on Eu/Eu* - Ce/Ce* diagram (Fig. 2). The first one is the simultaneous reduction of these parameters in recristallized calcite-magnetite assemblages with sulfides (Fig. 2,A). The second tendency consist in increase of Ce/Ce* at reduction Eu/Eu* in recristallized calcite-magnetite assemblages with sulfates (Fig. 2,B). It is interpreted as the effect of fluid restoration at the deficiency or at the presence of REE-bearing minerals.

The work was supported by the Russian Foundation for Basic Research, grant 94-05-17362-à.

Fig.1. REE composition of apatites from the iron ore deposits of Angara-Ilim types. Filled squares (1 on Fig.1,A,B) are the apatite from primary magnetite-apatite ores (2 on 1,A,B); empty squares are the recrystallized ones, and filled triangles (3) are the apatite from the latest formations.

Fig.2. Variations of Eu and Ce in Calcite-magnetite assemblages with sulfides (A) and sulfates (B) from the iron ore deposits. Filled squares are the earliest calcite-magnetite assemblages; empty squares are the recrystallized ones, and filled triangles are the latest calcite assemblages.