Fractal nature of the distribution of stockworks (feeder zones) and mineralizations of the Iberian Pyrite Belt: Application to mineral exploration

The Iberian Pyrite Belt (IPB) lies in the south-western part of the Iberian Peninsula and contains the greatest concentration of VHMS deposits in the world. The IPB has been estimated to hold a minimum resource of >1.700 Mt of massive pyrite, complex and stockwork type mineralization that includes deposits of giant world class status.

The geometry of the stockworks (feeder zones) has been studied at different scales from field outcrops to the mining district. Block-size and fracture-length (F₁ ≈ 1.64) in two-dimensions, and vein thickness distribution (D_t ≈ 0.65) in one-dimension all have a power-law scaling. Capacity dimension obtained by box-counting from different stockworks is always consistent (D_c in the range of 1.60-1.65). The relationships between the measured fractal dimensions strongly support the fractal nature of stockworks. Fractal models suggest that F₁ ≈ D_c ≈ D_t+1, which agrees with the measured values. These observations have been made at length scales from a few 10s mm to about 10¹ m and may be extrapolated to about 10² m, based on qualitative assessment of available exposures.

At larger scales (in the range of 10¹ to 10² km), an analysis of the distribution of the mines and occurrences has been performed in a GIS. The results show that the economic VHMS deposits suggest a clustered (localized) distribution (D_c ≈ 0.6). Based on the available geology and the airborne geophysical (gravity and magnetic) survey from the whole IPB, a Probability Density Function (PDF) algorithm using a Kernel function has been applied to generate areas which would be expected to contain some undiscovered deposits. The results of the simulations show a very consistent D_c ≈ 0.6, which agrees with the underlying fractal characteristics of the deposits. This type of analysis can be utilized as a new tool for the mineral exploration of the IPB.