Abstract
Abstract. Airborne geophysical anomaly separation using conventional statistics and the fractal/multifractal concentration-area (C-A) method has been applied to the Tark and Avanligh 1:50 000 sheets in NW Iran. The geophysical survey that resulted in the airborne geophysical data was conducted for uranium exploration in both areas. Selected anomalies were further investigated by using surface radiometric data. Firstly, threshold values to define anomalies were determined and compared by means of conventional statistical methods. Several relatively large anomalies were identified with uranium (U) equal to 1.7 eppm and 1.9 eppm in the Tark and Avanligh areas, respectively; locally these U anomalies have magnitudes exceeding 3.5 eppm in both areas. Log-log plots obtained for the C-A method indicate existence of two separate stages of U enrichment, with a major event being the cause of U concentration values above 6.1 and 3.4 eppm in the Tark and Avanligh areas, respectively. These higher intensity anomalies are located in the northwestern part of the Tark and in the southern part of the Avanligh sheets. In both areas, the C-A anomalies were further investigated using ground radiometric data and XRF analysis revealing higher than 150 and 280 ppm U concentration values in the two areas, respectively. Correlation between the anomalies and geological units show that the anomalies are associated with limestone and sandstone units.
Highlights
Airborne geophysical data especially gamma ray spectrometry are utilized to identify uranium targets (Raghuwanshi, 1992)
Study on Tark and Avanligh 1:50 000 sheets reveal the potential use of the C-A method for geophysical airborne anomaly separation as an appropriate tool for geophysical and mineral exploration
The advantages of this method are in its simplicity and easy computational implementation, as well as the possibility to compute a numerical value of the anomalous threshold; which is the most fundamental criteria for cross examination of information with numerical data from different sources, generally used in airborne radiometric data
Summary
Airborne geophysical data especially gamma ray spectrometry are utilized to identify uranium targets (Raghuwanshi, 1992). Concentration-area (C-A) fractal method was used in order to explain the geophysical airborne data, including U (eppm) from the Tark and Avanligh 1:50 000 sheets, NW Iran. To demonstrate and prove that data distribution has a multifractal nature, an extensive computation is required (Halsey et al, 1986; Evertz and Mandelbrot, 1992) This method has several constrains especially when the boundary effects on irregular geometrical data sets are involved (Agterberg et al, 1996; Goncalves, 2001; Cheng, 2007; Xie et al, 2010). Bolviken et al (1992), Turcotte (1997), Goncalves (2001), Gettings (2005), Li and Cheng (2006) and Afzal et al (2010) This theory improves the development of an alternative interpretation validation and useful methods to be applied to geophysical distributions analysis. Detected parameters of these data include U235, Th232 and K40
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