Separation of geochemical anomalies of rare earth elements by concentration-area fractal model in Anomaly No. 5 of Saghand (Central Iran)

The studied area is situated in the Central Iran structural zone. Uranim, thorioum and REEs (Rare Earth Elements) mineralizations are hydrothermal type and metasomatic related to intrusive areas. Recognition of a geochemical anomaly from background is a basic problem in geochemical exploration. There are different kinds of methods that assist to delineate geochemical anomalies from background, ranged from the simple statistical methods to complex fractal ones. The fractal models are applicable in this branch (geochemistry) because of using all data and considering their special distributions and their new effective usage of surface geological and geochemical studies. In Saghand area, REEs show a high positive correlation with radioactive elements (uranium and thorium). Recognition of REEs’ geochemical anomalies from background was achieved using the concentration- area (C-A) fractal model by lithogeochemical data (91 samples) in the study area. (we have analyzed 15 elements and provided Ce, Y, Dy, Gd and La elements’ maps in this paper). In this method, the log-log plots of REEs were generated and their theresholds and mineralization populations were identified. The map of lithogeochemical anomalies were subsequently drawn and eventually the promising areas were identified. Furthermore, high intensive REEs geochemical anomalies were discriminated in western, NW, central, and southern parts of the study area. The REEs moderate anomalies are located in the metasomatic unitis associated with epidote and chlorite alterations in the central part of the study area. The southern anomalies of the region are located on the border where the basic dykes associated with the epidotic alterations are between metasomatic units and microdioritic ones. High intensive anomalies which are situated in the west of the studied area occurred within the metasomatic, porphyry microdioritic, and acidic volcanic rocks associated with the epidote alterations. The combinations of the geochemical and geological maps were found indicating that the radioactive element mineralization was of the metasomatite type and metasomatism was more than amphibolization and albitization. The primary rocks contain pyroclastic, diabase, porphyry dacite and gabbro has affected metasomatism and the main rock types created in the area include amphibole metasomatite, amphibole-albit metasomatite, albite metasomatite, amphibole-quartz- feldspar metasomatite, amphibole-feldspar-epidote metasomatite and amphibole-biotite-talc-chlorite-epidote metasomatite. The REEs appear as a complex with the radioactive elements in U and Th minerals (uraninite and davidite).