Analysis of the fractal clustering of ore deposits in the Spanish Iberian Pyrite Belt

Abstract

The Iberian Pyrite Belt (IPB) contains one of the greatest known concentrations of volcanic-hosted massive sulfides (VHMS) on Earth. Investigation of the spatial attributes of the mineralization using fractal methods, over a range of scales, and integrated within a GIS provides new information, of potential import to the exploration of VHMS deposits. At the mine-scale, stockworks, which act as feeders for hydrothermal fluids, show vein thickness distributions that are power-law ( D t ≈ 0.65 in one dimension) at length scales from about 10 −2 to 10 2 m. Box-counting of veins indicates a capacity dimension ( D c ) in the range of 1.60–1.65 in two dimensions, which is consistent with the vein thickness data. At larger scales, in the range 10 3 to 10 5 m, the distribution of mines and mineral prospects can be modelled as a fractal dust. When all the known mineral deposits and prospects are analyzed they have a capacity dimension D c ≈ 1.3. The VHMS deposits alone have a capacity dimension D c ≈ 0.9, indicating that they are clustered, with some indication that the ‘world-class’ deposits may be even more clustered. The different fractal analyses are integrated with information from geological and geophysical maps using a GIS. The distribution of prospects has been simulated using a simple multifractal model of the ore concentration and is constrained by known geological controls. Such a model has been implemented through the GIS.