Application of fractal models to characterization and evaluation of vertical distribution of geochemical data in Zarshuran gold deposit, NW Iran

• Using fractal models to evaluate the continuity mineralization
• New Hurst exponent VBA programming was performed for evaluation of vertical distribution.
• Fractal models were utilized to predict the potential exploration targets at the surface.

Vertical distribution of geochemical data can provide useful information and appropriate criteria for recognition and classification of mineralized and non-mineralized zones. In this study, several fractal models including box-counting, power-law frequency and new Hurst exponent visual basic application (VBA) programming were applied to evaluate the continuity and irregularity of the Au mineralization, the characterization of the vertical distribution and identification of new exploration targets based on the 40 mineralized and non-mineralized boreholes in the Zarshuran gold deposit. The results of the box-counting method showed that the vertical distribution of the Au values in these boreholes exhibit self-similarity, with the values of box-dimension (Bd) ranging from 1.01 to 1.7. The Bd values indicated that all the boreholes have irregularities in the vertical distribution of the Au values. Power-law frequency results indicate that the vertical distribution of Au in the boreholes exhibit bi- and mono-fractal properties. The bi-fractal properties of the boreholes imply the multiple mineralization phases in the Zarshuran deposit. Fractal dimensions vary from 0.6 in the non- and weakly mineralized zones, to 3.4 in the mineralized zones. The large fractal dimensions of the mineralization showed more homogeneity within the mineralization. The Hurst exponent shows the homogeneous distribution of Au in the mineralized and non-mineralized boreholes. The values of the Hurst exponent range from 0.63 to 0.92, with R2 greater than 0.8, indicating good vertical distribution in the study area. The Au values for non-mineralized boreholes such as [A4] are greater than 0.5, which shows the homogeneous distribution of Au in the wall rocks. The interpolated maps of the Au mean grades, the coefficient of variation of the Au grades, Bd, dimension (D), Hurst exponents as independent variables, and the combination variable (‘H + Bd’) were utilized to predict the potential exploration targets at the surface. The results show that the zone of approximately the old arsenic mining (the main mine valley) and the Mal Darrassi Valley isthe main potential exploration targets in the Zarshuran mining district.