Abstract

Rare earth elements in apatites in different ore types show characteristic patterns which are related to different modes of formation of the ores. Most of the apatite-bearing iron ores are associated with alkaline magmas with LREE/HREE fractionation varying from moderate to steep. Iron-apatite deposits of Bafq-Saghand district (Central Iran) have a high concentration of REE (ΣREE = 1000-18500 ppm), and show a strong LREE/HREE ratio with a pronounced negative Eu anomaly. Eu depletion indicates that magmas have undergone near-surface feldspar crystal fractionation. These REE patterns are different from sedimentary apatites (phosphorites) which have a low REE contents and Ce negative anomalies. The REE patterns of apatites, iron-apatite ores, greenstone host rocks and magnetite ores in each iron-apatite deposits of Central Iran are similar and only have different REE contents. This similarity indicates a genetic relation for these rocks. All of iron-apatite deposits of central Iran have similar REE patterns too, which in turn show a genetic relation for all of these deposits. The REE patterns of apatites from iron ores in Central Iran are comparable to the REE patterns of apatites in Kiruna-type iron ores in elsewhere of the world. This similarity indicates a similar origin and processes in their genesis. The REE patterns of apatites in different deposits of Central Iran iron ores and Kirunatype iron ores show an affinity to alkaline to sub-alkaline magmas and rifting environment. The alkaline host rocks of Central Iran iron ores are clearly related to an extensional setting where rifting was important (SSE – NNW fault lines). A probable source for this large scale ore forming processes is relatively low partial melting of mantlic rocks. The ores have originated by magmatic differentiation as a late phase in the volcanic cycle forming sub-surface injections or surface flows. These ores have formed during magmatism as immiscible liquids (silicate and Fe-P-rich magmatic liquids) which separated from strongly differentiated magmas aided by a large volatile and alkali elements content. Within the iron-apatite deposits of central Iran the Esfordi, Gazestan, Zarigan and Lakeh-Siah deposits are the best areas for REE mineralization (ΣREE = 0.78 – 1.85 %). According to the spatial distribution of iron-apatite deposits in this region and REE content of these deposits, it can be expected significant resources of REE are being in Bafq-Saghand region.