فهرست مطالب سمانه ضیاپور

Sheikh Habil area is located in 80km of Dehdasht city in southeast of Kohgiloyeh-Boyer Ahmad province, SW of Iran. Pabdeh Formation is located in the Zagros structural zone of Iran. The host rocks of the area are the Late Paleocene-Early Oligocene limestones, shales and marls. Calcite, fluorapatite, glauconite, quartz and clay minerals are the most observable minerals in these phosphorite rocks. The geochemical data show that the average contents of P2O5, U and ΣREE are 24.47%, 100ppm (with enrichment factor of 46.54) and 189.18 ppm, respectively. The (La/Yb)N is 0.62-0.54 and the (LREE/HREE)N is 0.62-0.72. The studied samples have negative Ce anomaly which indicates the existence of an anoxic environment during the Sheikh Habil phosphate deposition. These ratios show the relatively enrichment in HREEs with respect of LREEs. This data confirms that the Sheikh Habil phosphorites have high anomalies not only for P2O5 but also for U and HREEs. These data show that the other areas in Pabdeh Formation could be good targets for P2O5, U and REEs.

Two phosphorite deposits including Paghela and Gadok, within the Jiroud Formation (Upper Devonian) in the northeast of Firoozkuh in the Central Alborz geotectonic zone have been studied. Microscope studies show that fluorapatite is the main phosphate mineral and the main gangue minerals are calcite and quartz. The P2O5, Uranium and ∑REE contents in the Paghaleh phosphorite range between 35.5-41.2%, 4.8-6.4 and 623-803.2 ppm, and in the Gaduk phosphorite vary from 12.3 to 41.1%, 4.7 to 7.8 and 369.2 to 784.8 ppm, respectively. The REE patterns normalized to Post-Archean Australian shales in Firoozkuh phosphorites are characterized by convex patterns without specific Ce anomaly, which indicates anoxic conditions in the diagenesis environment of the phosphorite formation. Mineralogical and geochemical studies and the positive correlation of REEs with P2O5 and CaO show that the main host mineral of rare earth elements in the phosphorites of Firoozkuh is fluorapatite. Also, minor amount of zircon and trace amount of monazite inclusions in the apatite are other minerals that host rare earth elements in these phosphorites. The lack of uranium enrichment in Firoozkuh phosphorites is probably either due to the lack of favorable source rock with leachable uranium in the continent, or by the initial weak oxidant conditions during phosphatization, which prevented the conversion of U+6 dissolved in seawater to U+4, and uranium could not replace Ca within the apatite lattice.

The Dalir phosphate deposit is located 57 km southwest of Chalus city in Mazandaran province, the Central Alborz zone. This deposit is hosted by Soltanieh Formation, one of Iran's important hosts of sedimentary phosphates. The results of X-ray diffraction (XRD) analysis and optical and electron microscopy studies on the phosphate samples indicate that the main minerals include apatite, calcite, quartz, and dolomite accompanied by montmorillonite, pyrite, and barite in minor amounts; siderite, rutile, illite, and goethite in trace amounts. The concentration of P2O5, U, and REEs in the studied samples ranged from 5 to 16.1%, 1.9 to 5.5, and 45.9 to 136.9 ppm, respectively. The studied samples have negative Ce anomaly, indicating an anoxic environment during the Dalir phosphate deposition. Based on the factors controlling uranium concentration in phosphorites, the phosphate horizon of Soltanieh Formation does not have uranium enrichment potential due to warm to semi-warm humid paleoclimate with neutral to acidic pH of the seawater during the Dalir phosphate deposition in lower Cambrian. Finally, considering the results of the chemical analysis of phosphate samples of the Dalir deposit (lack of uranium enrichment) and also the factors controlling uranium concentration in phosphorites, it can be predicted that the other phosphate deposits of Soltanieh Formation probably not be uranium enriched.

The Chahgaz iron deposit (XIV Anomaly) is located in the Bafq mining district in the Central Iranian geostructural zone in Yazd province. The Chahgaz deposit is hosted by Early Cambrian subvolcanic and volcanic rocks that range compositionally from granite to diorite. The field gamma spectrometry, mineralogical and geochemical studies in this deposit indicate that the thorium mineralization is mainly associated with Na-Ca and Mg- alterations, and in minor amount with the magnetite ore. The mineralogical studies by optical and electron microscope (SEM and EPMA) indicate that the main thorium host mineral in the Chahgaz deposit is thorite associated with minor titanite, allanite and zircon. The average contents of Th and ΣREE in the Th-mineralization zone are 450 and 596 ppm, respectively. Thorite is paragenesis with albite, actinolite, tremolite and augite in the Na-Ca alteration zone, and with talc in the Mg- alteration zone. In the Th-bearing iron ore, thorite is paragenesis with magnetite, calcite and apatite mineral assemblage. The similarity in mantle-normalized REE patterns of host rocks and thorium mineralization zone suggests that Th-mineralization is related to Early Cambrian calc-alkaline magmatism in continental-margin arc setting. The occurrence of paragenetic magnetite with thorite and distinct negative Eu anomaly in the thorium mineralization zone can be inferred probably a reduced condition for thorium mineralizing fluids.