KIRUNA-TYPE IRON OXIDE-APATITE DEPOSITS, BAFQ DISTRICT, CENTRAL IRAN: FLUID-AIDED GENESIS OF FLUORAPATITE-MONAZITE-XENOTIME ASSEMBLAGES

摘要

In the Bafq region, Central Iran, apatite from Kiruna-type iron oxide-apatite deposits is enriched in LREE (up to 2 wt.%), Na, Si, and Cl (up to 15% of the halogen component), but altered apatite is strongly depleted in these elements. Monazite and xenotime inclusions with low Th and U and associated with a distinct pervasive porosity are found in the altered areas of the apatite and are a direct product of fluid-aided coupled dissolution-reprecipitation processes. Monazite-xenotime thermometry indicates that these inclusions formed below 400-300 degrees C, which agrees well with available fluid inclusion data. Comparison of these iron oxide-apatite deposits with other Kiruna-type iron oxide-apatite deposits suggests that they formed from highly differentiated volcanic magmas which interacted with both magmatic and externally derived fluids shortly after crystallization and during cooling. The concentrations of Sr, Mn, and Y in the apatites ranges from 40-824 ppm, 10-440 ppm, and 66-3700 ppm, respectively, which strongly supports a granitoid source for genesis of the iron ores. An extensive Na-Ca metasomatic alteration zone, with magnetite-apatite mineralization, existence of magmatic bodies grading to breccias, and fluid inclusion data all point to the involvement of both magmatic and hydrothermal processes in the ore formation.