Mapping of district-scale potential targets using fractal models

The Pulang porphyry-Cu deposit is one of the most important copper deposits discovered in China in the last five years. In this deposit, the irregular distributions of high concentrations of metals are associated with four intrusive complexes and fault structures. In the present study, fractal models including box-counting dimension (Bd), power-law frequency and Hurst exponent are applied to characterize the vertical distributions of Cu values along boreholes in the deposit, and to delineate target areas in the Pulang copper district. The resulting box-counting model shows that the vertical distributions of Cu in both mineralized and nonmineralized boreholes exhibit self-similarity, with values of Bd ranging from 1.01 to 1.43, and mineralized boreholes have values of Bd higher than those of non-mineralized boreholes. The resulting power-law frequency model shows that the vertical distributions of Cu in mineralized boreholes are bifractal whereas they are monofractal in non-mineralized boreholes. The bifractal vertical distributions of Cu values are generally associated with multiple ore-forming stages/periods or complicated ore-forming functions of geological background. The Hurst exponents of Cu data from all continuously mineralized boreholes are >0.5, indicating that the Pulang porphyry-Cu deposit has good vertical continuity of mineralization, or that the development of orebodies was relatively stable in this geological setting. High Hurst exponents (>0.85) can be utilized to identify subsurface mineralized targets, whereas lower Hurst exponents (